Glossary for Microbiology 1
12D treatment: A sterilization process that would result in a decrease of the number of Clostridium botulinum endospores by 12 logarithmic cycles.
ABO blood group system: The classification of red blood cells based on the presence or absence of A and B carbohydrate antigens.
abscess: A localized accumulation of pus.
A-B toxin: Bacterial exotoxins consisting of two polypeptides.
acellular vaccine: A vaccine consisting of antigenic parts of cells.
acetyl group: An organic functional group derived from acetic acid.
acid: A substance that releases hydrogen ions (H+ ) when in solution; a proton donor.
acid-fast stain: A differential stain used to identify bacteria that are not decolorized by acid-alcohol.
acidic dye: A salt in which the color is in the negative ion; used for negative staining.
acidophile: A bacterium that grows below pH 4.
acquired immune deficiency: The inability, obtained during the life of an individual, to produce specific antibodies or T cells, due to drugs or disease.
activated macrophage: A macrophage that has increased phagocytic ability and other functions after exposure to mediators released by T cells after stimulation by antigens.
activated sludge system: A process used in secondary sewage treatment in which batches of sewage are held in highly aerated tanks; to ensure the presence of microbes efficient in degrading sewage, each batch is inoculated with portions of sludge from a precious batch.
activation energy: The minimum collision energy required for a chemical reaction to occur.
active site: A region on an enzyme that interacts with the substrate.
active transport: Net movement of a substance across a membrane against a concentration gradient; requires the cell to expend energy.
acute disease: A disease in which symptoms develop rapidly but last for only a short time.
acute-phase proteins: Serum proteins whose concentration changes by at least 25% during inflammation.
adaptive immunity: The ability, obtained during the life of the individual, to produce specific antibodies and T cells.
adenosarcoma: Cancer of glandular epithelial tissue.
adenosine diphosphate (ADP): The substance formed when ATP is hydrolyzed and energy is released.
adenosine triphosphate (ATP): Organic molecule that stores and releases chemical energy for use in body cells; an important intracellular energy source.
adherence: Attachment of a microbe or phagocyte to another cell's plasma membrane or other surface.
adhesin: A carbohydrate-specific binding protein that projects from prokaryotic cells; used for adherence, also called a ligand.
adjuvant: A substance added to a vaccine to increase its effectiveness.
aerial hyphae: Mycelial hyphae extending above the surface of where the mycelium is growing, where spores are produced. Also called reproductive hyphae.
aerobe: An organism requiring molecular oxygen (O2) for growth.
aerobic respiration: Respiration in which the final electron acceptor in the electron transport chain is molecular oxygen (O2).
aerotolerant anaerobe: An organism that does not use molecular oxygen (O2) but is not affected by its presence.
aflatoxin: A carcinogenic toxin produced by Aspergillus flavus.
agar: A complex polysaccharide derived from a marine alga and used as a solidifying agent in culture media.
agglutination: A joining together, or clumping of cells.
agranulocyte: A leukocyte without visible granules in the cytoplasm; includes monocytes and lymphocytes.
agranulocytosis: Destruction of granulocytic white blood cells.
alcohol: An organic molecule with the hydroxyl functional group, -OH.
alcohol fermentation: A catabolic process, beginning with glycolysis, that produces ethyl alcohol to reoxidize NADH.
aldehyde: An organic molecule with a terminal carbonyl functional group.
alga: A photosynthetic eukaryote; may be unicellular, filamentous, or multicellular but lack the tissues found in plants. Plural is algae.
algal bloom: An abundant growth of microscopic algae producing visible colonies in nature.
algin: A sodium salt of mannuronic acid (C6H8O6 ); found in brown algae.
allergen: An antigen that evokes a hypersensitivity response.
allergy: See hypersensitivity.
allograft: A tissue graft that is not from a genetically identical donor, i.e., not from self or an identical twin.
allosteric inhibition: The process in which an enzyme's activity is changed because of binding to the allosteric site.
allosteric site: The site on an enzyme at which a noncompetitive inhibitor binds.
allylamines: Antifungal agents that interfere with sterol synthesis.
amanitin: A polypeptide toxin produced by Amanita spp., inhibits RNA polymerase.
Ames test: A procedure using bacteria to identify potential carcinogens.
amination: The addition of an amino group.
amino acid: An organic acid containing an amino group and a carboxyl group.
aminoglycoside: An antibiotic consisting of amino sugars and an aminocyclitol ring, such as streptomycin.
amino group: An alkaline organic functional group, -NH2 .
ammonification: The release of ammonia from nitrogen-containing organic matter by the action of microorganisms.
amphibolic pathway: A pathway that is both anabolic and catabolic.
amphitrichous: Having tufts of flagella at both ends of a cell.
anabolism: All synthesis reactions in a living organism; the building of complex organic molecules from simpler ones.
anaerobe: An organism that does not require molecular oxygen (O2) for growth.
anaerobic respiration: Respiration in which the final electron acceptor in the electron transport chain is an inorganic molecule other than molecular oxygen (O2), such as a nitrate ion (NO3- ) or CO2.
anaerobic sludge digester: Anaerobic digestion used in secondary sewage treatment.
anal pore: A site in certain protozoa for elimination of waste.
analytical epidemiology: Comparison of a diseased group and a healthy group to determine the cause of the disease.
anamnestic response: See memory response.
anamorph: An ascomycete fungi that has lost the ability to reproduce sexually; the asexual stage of a fungus.
anaphylaxis: A hypersensitivity reaction involving IgE antibodies, mast cells, and basophils.
Animalia: The kingdom composed of multicellular eukaryotes lacking cell walls.
anion: An ion with a negative charge.
anoxygenic: Not producing molecular oxygen; typical of cyclic photophosphorylation.
antagonism: Active opposition; (1) When two drugs are less effective than either one alone. (2) Competition among microbes.
antibiotic: An antimicrobial agent, usually produced naturally by a bacterium or fungus.
antibody: A protein produced by the body in response to an antigen, and capable of combining specifically with that antigen.
antibody-dependent cell-mediated cytotoxicity (ADCC): The killing of antibody-coated cells by natural killer cells and leukocytes.
antibody titer: The amount of antibody in serum.
anticodon: The three nucleotides by which a tRNA recognizes an mRNA codon.
antigen: Any substance that causes antibody formation; also called immunogen.
antigen-antibody complex: The combination of an antigen with the antibody that is specific for it; the basis of immune protection and many diagnostic tests.
antigen-binding sites: A site on an antibody that binds to an antigenic determinant.
antigenic determinant: A specific region on the surface of an antigen against which antibodies are formed; also called epitope.
antigenic drift: A minor variation in the antigenic makeup of influenza viruses that occurs with time.
antigenic shift: A major genetic change in influenza viruses causing changes in H and N antigens.
antigenic variation: Changes in surface antigens that occur in a microbial population.
antigen-presenting cell (APC): A macrophage, dendritic cell, or B cell that engulfs an antigen and presents fragments to T cells.
antihuman immune serum globulin (anti-HISG): An antibody that reacts specifically with human antibodies.
antimetabolite: A competitive inhibitor.
antimicrobial drug: A chemical that destroys pathogens without damaging body tissues.
antimicrobial peptide: An antibiotic that is bactericidal and has a broad spectrum of activity; see bacteriocin.
antisense DNA: DNA that is complementary to the DNA encoding a protein; the antisense RNA transcript will hybridize with the mRNA encoding the protein and inhibit synthesis of the protein.
antisense strand (- strand): Viral RNA that cannot act as mRNA.
antisepsis: A chemical method for disinfection of the skin or mucous membranes; the chemical is called an antiseptic.
antiserum: A blood-derived fluid containing antibodies.
antitoxin: A specific antibody produced by the body in response to a bacterial exotoxin or its toxoid.
antiviral protein (AVP): A protein made in response to interferon that blocks viral multiplication.
apoenzyme: The protein portion of an enzyme, which requires activation by a coenzyme.
apoptosis: The natural programmed death of a cell; the residual fragments are disposed of by phagocytosis.
aquatic microbiology: The study of microorganisms and their activities in natural waters.
arbuscule: Fungal mycelia in plant root cells.
Archaea: Domain of prokaryotic cells lacking peptidoglycan; one of the three domains.
arthroconidia: An asexual fungal spore formed by fragmentation of a septate hypha. Also called arthrospore.
Arthus reaction: Inflammation and necrosis at the site of injection of foreign serum, due to immune complex formation.
artificially acquired active immunity: The production of antibodies by the body in response to a vaccination.
artificially acquired passive immunity: The transfer of humoral antibodies formed by one individual to a susceptible individual, accomplished by the injection of antiserum.
artificial selection: Choosing one organism from a population to grow because of its desirable traits.
ascospore: A sexual fungal spore produced in an ascus, formed by the ascomycetes.
ascus: A saclike structure containing ascospores; found in the ascomycetes.
asepsis: The absence of contamination by unwanted organisms.
aseptic packaging: Commercial food preservation by filling sterile containers with sterile food.
aseptic surgery: Techniques used in surgery to prevent microbial contamination of the patient.
aseptic techniques: Laboratory techniques used to minimize contamination.
asexual spore: A reproductive cell produced by mitosis and cell division (eukaryotes), or binary fission (actinomycetes).
atom: The smallest unit of matter that can enter into a chemical reaction.
atomic force microscopy: See scanned-probe microscopy.
atomic number: The number of protons in the nucleus of an atom.
atomic weight: The total number of protons and neutrons in the nucleus of an atom.
attenuated whole-agent vaccine: A vaccine containing live, attenuated (weakened) microorganisms.
autoclave: Equipment for sterilization by steam under pressure, usually operated at 15 psi and 121°C.
autograph: A tissue graft from one's self.
autoimmune disease: Damage to one's own organs due to action of the immune system.
autotroph: An organism that uses carbon dioxide (CO2) as its principal carbon source. See also chemoautotroph, photoautotroph.
auxotroph: A mutant microorganism with a nutritional requirement that is absent in the parent.
axial filament: The structure for motility found in spirochetes; also called endoflagellum.
azoles: Antifungal agents that interfere with sterol synthesis.
bacillus: (1) Any rod-shaped bacterium. (2) When written as a genus, refers to rod-shaped, endospore-forming, facultatively anaerobic, gram-positive bacteria. Plural is bacilli.
bacteremia: A condition in which there are bacteria in the blood.
bacteria: Domain of prokaryotic organisms, characterized by peptidoglycan cell walls; bacterium (singular) when referring to a single organism.
bacterial growth curve: A graph indicating the growth of a bacterial population over time.
bactericide: A substance capable of killing bacteria.
bacteriocin: An antimicrobial peptide produced by bacteria that kills other bacteria.
bacteriology: The scientific study of prokaryotes, including bacteria and archaea.
bacteriophage (phage): A virus that infects bacterial cells.
bacteriostasis: A treatment capable of inhibiting bacterial growth.
base: Any substance that, when dissolved in water, accepts hydrogen ions (H+ ) and/or releases hydroxide ions (OH- ). Also, most nitrogen containing organic compounds are bases.
base pairs: The arrangement of nitrogenous bases in nucleic acids, due to hydrogen bonding; in DNA, base pairs are A-T and G-C; in RNA, base pairs are A-U and G-C.
base substitution: The replacement of a single base in DNA by another base, causing a mutation; also called point mutation.
basic dye: A salt in which the color is in the positive ion; used for bacterial stains.
basidiospore: A sexual fungal spore produced in a basidium, characteristic of the basidiomycetes.
basidium: A pedestal that produces basidiospores; found in the basidiomycetes.
basophil: A granulocyte (leukocyte) that readily takes up basic dye and is not phagocytic; has receptors for IgE Fc regions.
batch production: An industrial process in which cells are grown for a period of time after which the product is collected.
B cell: A type of lymphocyte; differentiates into antibody-secreting plasma cells and memory cells.
BCG vaccine: A live, attenuated strain of Mycobacterium bovis used to provide immunity to tuberculosis.
beer: Alcoholic beverage produced by fermentation of starch.
benthic zone: The sediment at the bottom of a body of water.
Bergey's Manual: Bergey's Manual of Systematic Bacteriology, the standard taxonomic reference on bacteria; also refers to Bergey's Manual of Determinative Bacteriology, the standard laboratory identification reference on bacteria.
beta-lactam: Core structure of penicillins.
beta oxidation: The removal of two carbon units from a fatty acid to form acetyl CoA.
biguanide: A group of antimicrobial chemicals, including chlorhexidine, especially useful on skin and mucous membranes.
binary fission: Prokaryotic cell reproduction by division into two daughter cells.
binomial nomenclature: The system of having two names (genus and specific epithet) for each organism; also called scientific nomenclature.
bioaugmentation: The use of pollutant-acclimated microbes or genetically engineered microbes for bioremediation.
biochemical oxygen demand (BOD): A measure of the biologically degradable organic matter in water.
biocide: A substance capable of killing microorganisms.
bioconversion: Changes in organic matter brought about by the growth of microorganisms.
biofilm: A microbial community that usually forms as a slimy layer on a surface.
biogenesis: The theory that living cells arise only from preexisting cells.
biogeochemical cycle: The recycling of chemical elements by microorganisms for use by other organisms.
bioinformatics: The science of determining the function of genes through computer-assisted analysis.
biological transmission: The transmission of a pathogen from one host to another when the pathogen reproduces in the vector.
bioluminescence: The emission of light from the electron transport chain; requires the enzyme luciferase.
biomass: Organic matter produced by living organisms and measured by weight.
bioreactor: A fermentation vessel with controls for environmental conditions, e.g., temperature and pH.
bioremediation: The use of microbes to remove an environmental pollutant.
biotechnology: The industrial application of microorganisms, cells, or cell components to make a useful product.
biotype: See biovar.
biovar: A subgroup of a serovar based on biochemical or physiological properties; also called biotype.
bisphenol: A group of antimicrobial chemicals composed of two phenolic groups; includes triclosan.
blade: A flat leaflike structure of multicellular algae.
blastoconidium: An asexual fungal spore produced by budding from the parent cell.
blood-brain barrier: Cell membranes that allow some substances to pass from the blood to the brain but restrict others.
brightfield microscope: A microscope that uses visible light for illumination; the specimens are viewed against a white background.
broad-spectrum antibiotic: An antibiotic that is effective against a wide range of both gram-positive and gram-negative bacteria.
broth dilution test: A method of determining the minimal inhibitory concentration by using serial dilutions of an antimicrobial drug.
bubo: An enlarged lymph node caused by inflammation.
budding: (1) Asexual reproduction beginning as a protuberance from the parent cell that grows to become a daughter cell. (2) Release of an enveloped virus through the plasma membrane of an animal cell.
budding yeast: Following mitosis, a yeast cell that divides unevenly to produce a small cell (bud) from the parent cell.
buffer: A solution that resists changes in pH.
bulking: A condition arising when sludge floats rather than settles in secondary sewage treatment.
bullae: Large serum-filled vesicles in the skin. Singular is bulla.
burst size: The number of newly synthesized bacteriophage particles released from a single cell.
burst time: The time required from bacteriophage attachment to release.
Calvin-Benson cycle: The fixation of CO2 into reduced organic compounds; used by autotrophs.
capnophile: A microorganism that grows best at relatively high CO2 concentrations.
capsid: The protein coat of a virus that surrounds the nucleic acid.
capsomere: A protein subunit of a viral capsid.
capsule: An outer, viscous covering on some bacteria composed of a polysaccharide or polypeptide.
carbapenems: Antibiotics that contain a β-lactam antibiotic and cilastatin.
carbohydrate: An organic compound composed of carbon, hydrogen, and oxygen, with the hydrogen and oxygen present in a 2:1 ratio; carbohydrates include starches, sugars, and cellulose.
carbon cycle: The series of processes that converts CO2 to organic substances and back to CO2 in nature.
carbon fixation: The synthesis of sugars by using carbons from CO2 . See also Calvin-Benson cycle.
carbon skeleton: The chain or ring of carbon atoms in a molecule.
carboxyl group: An organic acid functional group, -COOH.
carboxysome: A prokaryotic inclusion containing ribulose 1,5-diphosphate carboxylase.
carcinogen: Any cancer-causing substance.
carrier: Organisms (usually refers to humans) that harbor pathogens and transmit them to others.
casein: Milk protein.
catabolism: All decomposition reactions in a living organism; the breakdown of complex organic compounds into simpler ones.
catabolite repression: Inhibition of the metabolism of alternate carbon sources by glucose.
catalase: An enzyme that catalyzes the breakdown of hydrogen peroxide to water and oxygen.
catalyst: A substance that increases the rate of a chemical reaction but is not altered itself.
cation: A positively charged ion.
CD (cluster of determination): Number assigned to an epitope on a single antigen, for example, CD4 protein, which is found on helper T cells.
cDNA (complementary DNA): DNA made in vitro from an mRNA template.
cell culture: Eukaryotic cells grown in culture media; also called tissue culture.
cell-mediated immunity: An immune response that involves T cells binding to antigens presented on antigen-presenting cells; T cells then differentiate into several types of effector T cells.
cell theory: All living organisms are composed of cells and arise from preexisting cells.
cellular respiration: See respiration.
cell wall: The outer covering of most bacterial, fungal, algal, and plant cells; in bacteria, it consists of peptidoglycan.
Centers for Disease Control and Prevention (CDC): A branch of the U.S. Public Health Service that serves a central source of epidemiological information.
central nervous system (CNS): The brain and the spinal cord. See also peripheral nervous system.
centriole: A structure consisting of nine microtubule triplets, found in eukaryotic cells.
centrosome: Region in a eukaryotic cell consisting of a pericentriolar area (protein fibers) and a pair of centrioles; involved in formation of the mitotic spindle.
cephalosporin: An antibiotic produced by the fungus Cephalosporium that inhibits the synthesis of gram-positive bacterial cell walls.
cercaria: A free-swimming larva of trematodes.
chancre: A hard sore, the center of which ulcerates.
chemical bond: An attractive force between atoms forming a molecule.
chemical element: A fundamental substance composed of atoms that have the same atomic number and behave the same way chemically.
chemical energy: The energy of a chemical reaction.
chemically defined medium: A culture medium in which the exact chemical composition is known.
chemical reaction: The process of making or breaking bonds between atoms.
chemiosmosis: A mechanism that uses a proton gradient across a cytoplasmic membrane to generate ATP.
chemistry: The science of the interactions between atoms and molecules.
chemoautotroph: An organism that uses an inorganic chemical as an energy source and CO2 as a carbon source.
chemoheterotroph: An organism that uses organic molecules as a source of carbon and energy.
chemokine: A cytokine that induces, by chemotaxis, the migration of leukocytes into infected areas.
chemotaxis: Movement in response to the presence of a chemical.
chemotherapy: Treatment of disease with chemical substances.
chemotroph: An organism that uses oxidation-reduction reactions as its primary energy source.
chimeric monoclonal antibody: A genetically engineered antibody made of human constant regions and mouse variable regions.
chlamydoconidium: An asexual fungal spore formed within a hypha.
chloramphenicol: A broad-spectrum bacteriostatic chemical.
chloroplast: The organelle that performs photosynthesis in photoautotrophic eukaryotes.
chlorosome: Plasma membrane folds in green sulfur bacteria containing bacteriochlorophylls.
chromatin: Threadlike, uncondensed DNA in an interphase eukaryotic cell.
chromatophore: An infolding in the plasma membrane where bacteriochlorophyll is located in photoautotrophic bacteria; also known as thylakoids.
chromosome: The structure that carries hereditary information, chromosomes contain genes.
chronic disease: An illness that develops slowly and is likely to continue or recur for long periods.
ciliary escalator: Ciliated mucosal cells of the lower respiratory tract that move inhaled particulates away from the lungs.
cilia: Relatively short cellular projections from some eukaryotic cells, composed of microtubules. Singular is cilium.
cistern: A flattened membranous sac in endoplasmic reticulum and the Golgi complex.
clade: A group of organisms that share a particular common ancestor; a branch on a cladogram.
cladogram: A dichotomous phylogenetic tree that branches repeatedly, suggesting the classification of organisms based on the time sequence in which evolutionary branches arose.
class: A taxonomic group between phylum and order.
clonal deletion: The elimination of B and T cells that react with self.
clonal selection: The development of clones of B and T cells against a specific antigen.
clone: A population of cells arising from a single parent cell.
clue cells: Sloughed-off vaginal cells covered with Gardnerella vaginalis.
coagulase: A bacterial enzyme that causes blood plasma to clot.
coccobacillus: A bacterium that is an oval rod. Plural: coccobacilli.
coccus: A spherical or ovoid bacterium. Plural: cocci.
codon: A sequence of three nucleotides in mRNA that specifies the insertion of an amino acid into a polypeptide.
coenocytic hypha: A fungal filament that is not divided into uninucleate cell-like units because it lacks septa.
coenzyme: A nonprotein substance that is associated with and that activates an enzyme.
coenzyme A (CoA): A coenzyme that functions in decarboxylation.
coenzyme Q: See ubiquinone.
cofactor: (1) The nonprotein component of an enzyme. (2) A microorganism or molecule that acts with others to synergistically enhance or cause disease.
coliforms: Aerobic or facultatively anaerobic, gram-negative, nonendospore-forming, rod-shaped bacteria that ferment lactose with acid and gas formation within 48 hours at 35°C.
collagenase: An enzyme that hydrolyzes collagen.
collision theory: The principle that chemical reactions occur because energy is gained as particles collide.
colony: A visible mass of microbial cells arising from one cell or from a group of the same microbes.
colony hybridization: The identification of a colony containing a desired gene by using a DNA probe that is complementary to that gene.
colony stimulating factor (CSF): A substance that induces certain cells to proliferate or differentiate.
commensalism: A symbiotic relationship in which two organisms live in association and one is benefitted while the other is neither benefitted nor harmed.
commercial sterilization: A process of treating canned goods aimed at destroying the endospores of Clostridium botulinum.
communicable disease: Any disease that can be spread from one host to another.
competence: The physiological state in which a recipient cell can take and incorporate a large piece of donor DNA.
competitive inhibitor: A chemical that competes with the normal substrate for the active site of an enzyme.
complement: A group of serum proteins involved in phagocytosis and lysis of bacteria.
complementary DNA (cDNA): DNA made in vitro from a mRNA template.
complement fixation: The process in which complement combines with an antigen-antibody complex.
complex medium: A culture medium in which the exact chemical composition is not known.
complex virus: A virus with a complicated structure, such as a bacteriophage.
composting: A method of solid waste disposal, usually plant material, by encouraging its decomposition by microbes.
compound: A substance composed of two or more different chemical elements.
compound light microscope (LM): An instrument with two sets of lenses that uses visible light as the source of illumination.
compromised host: A host whose resistance to infection is impaired.
condensation reaction: A chemical reaction in which a molecule of water is released. Also called dehydration synthesis.
condenser: A lens system located below the microscope stage that directs light rays through the specimen.
confocal microscopy: A light microscope that uses fluorescent stains and laser to make two- and three-dimensional images.
congenital: Refers to a condition existing at birth; may be inherited or acquired in uteri.
congenital immune deficiency: The inability, due to an individual's genotype, to produce specific antibodies or T cells.
conidiophore: An aerial hypha bearing conidiospores (conidium).
conidiospore: An asexual spore produced in a chain from a conidiophore. Also called conidium.
conidium: An asexual spore produced in a chain from a conidiophore. Also called conidiospore.
conjugated monoclonal antibody: See immunotoxin.
conjugated vaccine: A vaccine consisting of the desired antigen and other proteins.
conjugation: The transfer of genetic material from one cell to another involving cell-to-cell contact.
conjugative plasmid: A prokaryotic plasmid that carries genes for sex pili and for transfer of the plasmid to another cell.
constitutive enzyme: An enzyme that is produced continuously.
contact inhibition: The cessation of animal cell movement and division as a result of contact with other cells.
contact transmission: The spread of disease by direct or indirect contact or via droplets.
contagious disease: A disease that is easily spread from one person to another.
continuous cell line Animal cells that can be maintained through an indefinite number of generations in vitro.
continuous flow: An industrial fermentation in which cells are grown indefinitely with continual addition of nutrients and removal of waste and products.
corepressor: A molecule that binds to a repressor protein, enabling the repressor to bind to an operator.
cortex: The protective fungal covering of a lichen.
counterstain: A second stain applied to a smear, provides contrast to the primary stain.
covalent bond: A chemical bond in which the electrons of one atom are shared with another atom.
crisis: The phase of a fever characterized by vasodilation and sweating.
cristae: Foldings of the inner membrane of a mitochondrion. Singular is crista.
crossing over: The process by which a portion of one chromosome is exchanged with a portion of another chromosome.
culture: Microorganisms that grow and multiply in a container of culture medium.
culture medium: The nutrient material prepared for growth of microorganisms in a laboratory.
curd: The solid part of milk that separates from the liquid (whey) in the making of cheese, for example.
cutaneous mycosis: A fungal infection of the epidermis, nails, or hair.
cuticle: The outer covering of helminths.
cyanobacteria: Oxygen-producing photoautotrophic prokaryotes.
cyclic AMP (cAMP): A molecule derived from ATP, in which the phosphate group has a cyclic structure; acts as a cellular messenger.
cyclic photophosphorylation: The movement of an electron from chlorophyll through a series of electron acceptors and back to chlorophyll; anoxygenic; purple and green bacterial photophosphorylation.
cyst: (1) A sac with a distinct wall containing fluid or other material. (2) A protective capsule of some protozoa.
cysticercus: An encysted tapeworm larva.
cytochrome: A protein that functions as an electron carrier in cellular respiration and photosynthesis.
cytochrome oxidase: An enzyme that oxidizes cytochrome c.
cytokine: A small protein released from human cells that regulates the immune response; directly or indirectly may induce fever, pain, or T-cell proliferation.
cytolysis: The destruction of cells, resulting from damage to their cell membrane, that causes cellular contents to leak out.
cytopathic effect (CPE): A visible effect on a host cell, caused by a virus, that may result in host cell damage or death.
cytoplasm: In a prokaryotic cell, everything inside the plasma membrane; in a eukaryotic cell, everything inside the plasma membrane and external to the nucleus.
cytoplasmic streaming: The movement of cytoplasm in a eukaryotic cell.
cytoskeleton: Microfilaments, intermediate filaments, and microtubules that provide support and movement for eukaryotic cytoplasm.
cytosol: The fluid portion of cytoplasm.
cytostome: The mouthlike opening in some protozoa.
cytotoxic T (Tc) cells: A specialized T cell that destroys infected cells presenting antigens.
cytotoxic T lymphocyte (CTL): An activated Tc cell; kills cells presenting endogenous antigens.
cytotoxin: A bacterial toxin that kills host cells or alters their functions.
darkfield microscope: A microscope that has a device to scatter light from the illuminator so that the specimen appears white against a black background.
deamination: The removal of an amino group from an amino acid to form ammonia. See also ammonification.
death phase: The period of logarithmic decrease in a bacterial population. Also called logarithmic decline phase.
debridement: Surgical removal of necrotic tissue.
decarboxylation: The removal of CO2 from an amino acid.
decimal reduction time (DRT): The time (in minutes) required to kill 90% of a bacterial population at a given temperature. Also called D value.
decolorizing agent: A solution used in the process of removing a stain.
decomposition reaction: A chemical reaction in which bonds are broken to produce smaller parts from a large molecule.
deep-freezing: Preservation of bacterial cultures at -50°C to -95°C.
defensins: Small peptide antibiotics made by human cells.
definitive host: An organism that harbors the adult, sexually mature form of a parasite.
degeneracy: Redundancy of the genetic code; that is, most amino acids are encoded by several codons.
degerming: The removal of microorganisms in an area. Also called degermation.
degranulation: The release of contents of secretory granules from mast cells or basophils during anaphylaxis.
dehydration synthesis: See condensation reaction.
dehydrogenation: The loss of hydrogen atoms from a substrate.
delayed-type hypersensitivity: Cell-mediated hypersensitivity.
denaturation: A change in the molecular structure of a protein, usually making it nonfunctional.
dendritic cell: A type of antigen-presenting cell characterized by long fingerlike extensions; found in lymphatic tissue and skin.
denitrification: The reduction of nitrogen in nitrate to nitrite or nitrogen gas.
dental plaque: A combination of bacterial cells, dextran, and debris adhering to the teeth.
deoxyribonucleic acid (DNA): The nucleic acid of genetic material in all cells and some viruses.
deoxyribose: A five-carbon sugar contained in DNA nucleotides.
dermatomycosis: A fungal infection of the skin. Also known as tinea or ringworm.
dermatophyte: A fungus that causes a cutaneous mycosis.
dermis: The inner portion of the skin.
descriptive epidemiology: The collection and analysis of all data regarding the occurrence of a disease to determine its cause.
desensitization: The prevention of allergic inflammatory responses.
desiccation: The removal of water.
diapedesis: See emigration.
dichotomous key: An identification scheme based on successive paired questions; answering one question leads to another pair of questions, until an organism is identified.
differential interference contrast (DIC) microscope: An instrument that provides a three-dimensional, magnified image.
differential medium: A solid culture medium that makes it easier to distinguish colonies of the desired organism.
differential stain: A stain that distinguishes objects on the basis of reactions to the staining procedure.
differential white blood cell count: The number of each kind of leukocytes in a sample of 100 leukocytes.
diffusion: The net movement of molecules or ions from an area of higher concentration to an area of lower concentration.
dimorphism: The property of having two forms of growth.
dioecious: Referring to organisms in which organs of different sexes are located in different individuals.
diplobacilli: Rods that divide and remain attached in pairs. Singular: diplobacillus
diplococci: Cocci that divide and remain attached in pairs. Singular: diplococcus
diploid cell: A cell having two sets of chromosomes; diploid is the normal state of a eukaryotic cell.
diploid cell line: Eukaryotic cells grown in vitro.
direct agglutination test: The use of known antibodies to identify an unknown cell-bound antigen.
direct contact transmission: A method of spreading infection from one host to another through some kind of close association between the hosts.
direct FA test: A fluorescent-antibody test to detect the presence of an antigen.
direct microscopic count: Enumeration of cells by observation through a microscope.
disaccharide: A sugar consisting of two simple sugars, or monosaccharides.
disease: An abnormal state in which part or all of the body is not properly adjusted or is incapable of performing normal functions; any change from a state of health.
disinfection: Any treatment used on inanimate objects to kill or inhibit the growth of microorganisms; a chemical used is called a disinfectant.
disk-diffusion method: An agar-diffusion test to determine microbial susceptibility to chemotherapeutic agents; also called Kirby-Bauer test.
D-isomer: A stereoisomer.
dissimilation: A metabolic process in which nutrients are not assimilated but are excreted as ammonia, hydrogen sulfide, and so on.
dissimilation plasmid: A plasmid containing genes encoding production of enzymes that trigger the catabolism of certain unusual sugars and hydrocarbons.
dissociation: The separation of a compound into positive and negative ions in solution. See also ionization.
disulfide bond: A covalent bond that holds together two atoms of sulfur.
DNA base composition: The mole-percentage of guanine plus cytosine in an organism's DNA.
DNA chip: A silica wafer that holds DNA probes; used to recognize DNA in samples being tested.
DNA fingerprinting: Analysis of DNA by electrophoresis of restriction enzyme fragments of the DNA.
DNA gyrase: See topoisomerase.
DNA ligase: An enzyme that covalently bonds a carbon atom of one nucleotide with the phosphate of another nucleotide.
DNA polymerase: Enzyme that synthesizes DNA by copying a DNA template.
DNA probe: A short, labeled, single strand of DNA or RNA used to locate its complementary strand in a quantity of DNA.
DNA sequencing: A process by which the nucleotide sequence of DNA is determined.
domain: A taxonomic classification based on rRNA sequences; above the kingdom level.
donor cell: A cell that gives DNA to a recipient cell during genetic recombination.
droplet transmission: The transmission of infection by small liquid droplets carrying microorganisms.
DTaP vaccine: Diphtheria-Tetanus-Pertussis vaccine; a combined vaccine used to provide active immunity, containing diphtheria and tetanus toxoids and Bordetella pertussis cell fragments.
D value: See decimal reduction time.
dysentery: A disease characterized by frequent, watery stools containing blood and mucus.
echinocandins: Antifungal agents that interfere with cell wall synthesis.
eclipse period: The time during viral multiplication, when complete infective virions are not present.
ecology: The study of the interrelationships between organisms and their environment.
edema: An abnormal accumulation of interstitial fluid in body parts or tissues, causing swelling.
electron: A negatively charged particle in motion around the nucleus of an atom.
electron acceptor: An ion that picks up an electron that has been lost from another atom.
electron donor: An ion that gives up an electron to another atom.
electronic configuration: The arrangement of electrons in shells or energy levels in an atom.
electron microscope: A microscope that uses electrons instead of light to produce an image.
electron shell: A region of an atom where electrons orbit the nucleus, corresponding to an energy level.
electron transport chain: A series of compounds that transfer electrons from one compound to another, generating ATP by oxidative phosphorylation. Also called electron transport system.
electroporation: A technique by which DNA is inserted into a cell using an electrical current.
elementary body: The infectious form of chlamydiae.
ELISA (enzyme-linked immunosorbent assay): A group of serological tests that use enzyme reactions as indicators.
embryonic stem cell: A cell from an embryo that has the potential to become a wide variety of specialized cell types.
emerging infectious disease (EID): A new or changing disease that is increasing or has the potential to increase in incidence in the near future.
emigration: The process by which phagocytes move out of blood vessels. Also called diapedesis.
Embden-Meyerhof pathway: See glycolysis.
enanthem: Rash on mucous membranes. See also exanthem.
encephalitis: Infection of the brain.
encystment: Formation of a cyst.
endemic disease: A disease that is constantly present in a certain population.
endergonic reaction: A chemical reaction that requires energy.
endocarditis: Infection of the lining of the heart (endocardium).
endocytosis: The process by which material is moved into a eukaryotic cell.
endoflagellum: See axial filament.
endogenous: (1) Infection caused by an opportunistic pathogen from an individual's own normal microbiota. (2) Antigens, usually of viral origin and degraded into fragments, generated within a cell.
endolith: An organism that lives inside rock.
endoplasmic reticulum (ER): A membranous network in eukaryotic cells connecting the plasma membrane with the nuclear membrane.
endospore: A resting structure formed inside some bacteria.
endotoxic shock: See gram-negative sepsis.
endotoxin: Part of the outer portion of the cell wall (lipid A) of most gram-negative bacteria; released on destruction of the cell.
end-product inhibition: See feedback inhibition.
energy level: Potential energy of an electron in an atom. See also electron shell.
enrichment culture: A culture medium used for preliminary isolation that favors the growth of a particular microorganism.
enteric: The common name for a bacterium in the family Enterobacteriaceae.
enterotoxin: An exotoxin that causes gastroenteritis, such as those produced by Staphyococcus, Vibrio, and Escherichia.
Entner-Doudoroff pathway: An alternate pathway for the oxidation of glucose to pyruvic acid.
envelope: An outer covering surrounding the capsid of some viruses.
enzyme: A molecule that catalyzes biochemical reactions in a living organism, usually a protein. See also ribozyme.
enzyme-linked immunosorbent assay: See ELISA.
enzyme-substrate complex: A temporary union of an enzyme and its substrate.
eosinophil: A granulocyte whose granules take up the stain eosin.
epidemic disease: A disease acquired by many hosts in a given area in a short time.
epidemiology: The science that studies when and where diseases occur and how they are transmitted.
epidermis: The outer portion of the skin.
epitope: See antigenic determinant.
equilibrium: The point of even distribution.
equivalent treatments: Different methods that have the same effect on controlling microbial growth.
ergot: A toxin produced in sclerotia by the fungus Claviceps purpurea that causes ergotism.
E test: An agar diffusion test to determine antibiotic sensitivity using a plastic strip impregnated with varying concentrations of an antibiotic.
ethambutol: A synthetic antimicrobial agent that interferes with the synthesis of RNA.
ethanol: Ethyl alcohol, CH3CH2OH
etiology: The study of the cause of a disease.
eukarya: Members of the Domain Eukarya (animals, plants, fungi, and protists).
eukaryote: A cell having DNA inside a distinct membrane-enclosed nucleus.
eukaryotic species: A group of closely related organisms that can interbreed.
eutrophication: The addition of organic matter and subsequent removal of oxygen from a body of water.
exanthem: Skin rash. See also enanthem.
exchange reaction: A chemical reaction that has both synthesis and decomposition components.
exergonic reaction: A chemical reaction that releases energy.
exon: A region of a eukaryotic chromosome that is used to encode a protein.
exotoxin: A protein toxin released from living, mostly gram-positive bacterial cells.
experimental epidemiology: The study of a disease using controlled experiments.
exponential growth phase: See log phase.
extracellular polysaccharide (EPS): A glycocalyx, composed of sugars, that permits bacteria to attach to various surfaces.
extreme halophile: An organism that requires a high salt concentration for growth.
extreme thermophile: See hyperthermophile.
extremophile: A microorganism that lives in environmental extremes of temperature, acidity, alkalinity, salinity, or pressure.
extremozymes: Enzymes produced by extremophiles.
facilitated diffusion: The movement of a substance across a plasma membrane from an area of higher concentration to an area of lower concentration, mediated by transporter proteins.
facultative anaerobe: An organism that can grow with or without molecular oxygen (O2).
facultative halophile: An organism capable of growth in, but not requiring, 1 to 2% salt.
Flavin adenine dinucleotide (FAD): A coenzyme that functions in the removal and transfer of hydrogen ions (H+ ) and electrons from substrate molecules.
fatty acid methyl ester (FAME): A reaction product of fatty acids used to identify microbes by the presence of specific fatty acids.
family: A taxonomic group between order and genus.
feedback inhibition: Inhibition of an enzyme in a particular pathway by the accumulation of the end-product of the pathway; also called end-product inhibition.
fermentation: The enzymatic degradation of carbohydrates in which the final electron acceptor is an organic molecule; ATP is synthesized by substrate-level phosphorylation and O2 is not required.
fermentation test: Method used to determine whether a bacterium or yeast ferments a specific carbohydrate; usually performed in a peptone broth containing the carbohydrate, a pH indicator, and an inverted tube to trap gas.
fever: An abnormally high body temperature.
F factor (fertility factor): A plasmid found in the donor cell in bacterial conjugation.
fibrinolysin: A kinase produced by streptococci.
filtration: The passage of a liquid or gas through a screenlike material; a 0.45 μm filter removes most bacteria.
fimbria: An appendage on a bacterial cell used for attachment. Plural is fimbriae.
FISH (Fluorescent in situ hybridization): Use of rRNA probes to identify microbes without culturing.
fission yeast: Following mitosis, a yeast cell that divides evenly to produce two new cells.
fixed macrophage: A macrophage that is located in a certain organ or tissue (e.g., liver, lungs, spleen, lymph nodes); also called a histiocyte.
fixing: (1) In slide preparation, the process of attaching a specimen to a slide. (2) Regarding chemical elements, combining elements so that a critical element can enter the food chain. See also Calvin-Benson cycle; nitrogen fixation.
flaccid paralysis: Loss of muscle movement, loss of muscle tone.
flagellum: A thin appendage from the surface of a cell; used for cellular locomotion; composed of flagellin in prokaryotic cells, composed of nine pairs plus two central microtubules in eukaryotic cells. Plural is flagella.
flaming: The process of sterilizing an inoculating loop by holding it in an open flame.
flat sour spoilage: Thermophilic spoilage of canned goods not accompanied by gas production.
flatworm: An animal belonging to the phylum Platyhelminthes.
flavin adenine dinucleotide: See FAD.
flavin mononucleotide (FMN): A coenzyme that functions in the transfer of electrons in the electron transport chain.
flavoprotein: A protein containing the coenzyme flavin; functions as an electron carrier in electron transport chains.
flocculation: The removal of colloidal material during water purification by adding a chemical that causes colloidal particles to coalesce.
flow cytometry: A method of counting cells using a flow cytometer, which detects cells by the presence of a fluorescent tag on the cell surface.
fluid mosaic model: A description of the plasma membrane, which contains a fluid bilayer of phospholipid molecules in which protein molecules are floating.
fluke: A flatworm belonging to the class Trematoda.
fluorescence: The ability of a substance to give off light of one color when exposed to light of another color.
fluorescence-activated cell sorter (FACS): A modification of a flow cytometer that counts and sorts cells labeled with fluorescent antibodies.
fluorescence microscope: A microscope that uses an ultraviolet light source to illuminate specimens that will fluoresce.
fluorescent-antibody (FA) technique: A diagnostic tool using anti bodies labeled with fluorochromes and viewed through a fluorescence microscope. Also called immunofluorescence.
fluoroquinolone: A synthetic antibacterial agent that inhibits DNA synthesis.
FMN (flavin mononucleotide): A coenzyme that functions in the transfer of electrons in the electron transport chain.
focal infection: A systemic infection that began as an infection in one place.
folliculitis: An infection of hair follicles, often occurring as pimples.
fomite: A nonliving object that can spread infection.
forespore: A structure consisting of chromosome, cytoplasm, and endospore membrane inside a bacterial cell.
frameshift mutation: A mutation caused by the addition or deletion of one or more bases in DNA.
freeze-drying: See lyophilization.
FrA-ABS test: An indirect fluorescent-antibody test used to detect syphilis.
fulminating: A condition that develops quickly and rapidly increases in severity.
functional group: An arrangement of atoms in an organic molecule that is responsible for most of the chemical properties of that molecule.
fungus: An organism that belongs to the Kingdom Fungi; a eukaryotic absorptive chemoheterotroph. Plural is fungi.
furuncle: An infection of a hair follicle.
fusion: The merging of plasma membranes of two different cells, resulting in one cell containing cytoplasm from both original cells.
gamete: A male or female reproductive cell.
gametocyte: A male or female protozoan cell.
gamma globulin: See immune serum globulin.
gastroenteritis: Inflammation of the stomach and intestine.
gas vacuole: A prokaryotic inclusion for buoyancy compensation.
gel electrophoresis: The separation of substances (such as serum proteins or DNA) by their rate of movement through an electrical field.
gene: A segment of DNA (a sequence of nucleotides in DNA) encoding a functional product.
gene library: A collection of cloned DNA fragments created by inserting restriction enzyme fragments in a bacterium, yeast, or phage.
gene therapy: Treating a disease by replacing abnormal genes.
generalized transduction: The transfer of bacterial chromosome fragments from one cell to another by a bacteriophage.
generation time: The time required for a cell or population to double in number.
genetic code: The mRNA codons and the amino acids they encode.
genetic engineering: See recombinant DNA technology.
genetic recombination: The process of joining pieces of DNA from different sources.
genetics: The science of heredity and gene function.
genetic screening: Techniques for determining which genes are in a cell's genome.
genome: One complete copy of the genetic information in a cell.
genomics: The study of genes and their function.
genotype: The genetic makeup of an organism.
genus: The first name of the scientific name (binomial); the taxon between family and species. Plural is genera.
germicide: See biocide.
germination: The process of starting to grow from a spore or endospore.
germ theory of disease: The principle that microorganisms cause disease.
global warming: Retention of solar heat by gases in the atmosphere.
globulin: The class of proteins that includes antibodies. See also immunoglobulin.
glycocalyx: A gelatinous polymer surrounding a cell.
glycolysis: The main pathway for the oxidation of glucose to pyruvic acid; also called Embden-Meyerhof pathway.
Golgi complex: An organelle involved in the secretion of certain proteins.
graft-versus-host (GVH) disease: A condition that occurs when a transplanted tissue has an immune response to the tissue recipient.
gram-negative bacteria: Bacteria that lose the crystal violet color after decolorizing by alcohol; they stain red after treatment with safranin.
gram-negative sepsis: Septic shock caused by gram-negative endotoxins.
gram-positive bacteria: Bacteria that retain the crystal violet color after decolorizing by alcohol; they stain dark purple.
gram-positive sepsis: Septic shock caused by gram-positive bacteria.
Gram stain: A differential stain that classifies bacteria into two groups, gram-positive and gram-negative.
granulocyte: A leukocyte with visible granules in the cytoplasm; includes neutrophils, basophils, and eosinophils.
granzymes: Proteases that induce apoptosis.
green nonsulfur bacteria: Gram-negative, nonproteobacteria; anaerobic and phototrophic; use reduced organic compounds as electron donors for CO2 fixation.
green sulfur bacteria: Gram-negative, nonproteobacteria; strictly anaerobic and phototrophic; no growth in dark; use reduced sulfur compounds as electron donors for CO2 fixation.
griseofulvin: A fungistatic antibiotic; produced by Penicillium griseofulvum.
group translocation: In prokaryotes, active transport in which a substance is chemically altered during transport across the plasma membrane.
gumma: A rubbery mass of tissue characteristic of tertiary syphilis.
HAART (Highly Active Antiretroviral Therapy): A combination of drugs used to treat HIV infection.
halogen: One of the Group 7A elements: fluorine, chlorine, bromine, iodine, or astatine.
haploid cell: A eukaryotic cell or organism with only one of each type of chromosome.
hapten: A substance of low molecular weight that does not cause the formation of antibodies by itself, but does so when combined with a carrier molecule.
HACCP (Hazard Analysis and Critical Control Point): System of prevention of hazards, for food safety.
helminth: A parasitic roundworm or flatworm.
helper T (TH) cell: A specialized T cell that often interacts with an antigen and helps B cells produce antibodies to that antigen.
hemagglutination: The clumping of red blood cells.
hemoflagellate: A parasitic flagellate found in the circulatory system of its host.
hemolysin: An enzyme that lyses red blood cells.
herd immunity: The presence of immunity in most of a population.
hermaphroditic: Having both male and female reproductive capacities.
heterocyst: A large cell in certain cyanobacteria; the site of nitrogen fixation.
heterolactic: Describing an organism that produces lactic acid and other acids or alcohols as end-products of fermentation; e.g., Escherichia.
heterotroph: An organism that requires an organic carbon source; also called organotroph.
Hfr cell (High Frequency of Recombination Cell): A bacterial cell in which the F factor has become integrated into the chromosome.
HEPA (High-Efficiency Particulate Air) Filter: A screenlike material that removes particles larger than 0.3 μm from air.
HTST (High-Temperature Short-Time) Pasteurization: Pasteurizing at 72°C for 15 seconds.
histamine: A substance released by tissue cells that causes inflammation (vasodilation, capillary permeability, and smooth muscle contraction).
histocompatibility antigen: An antigen on the surface of human cells.
histone: A protein associated with DNA in eukaryotic chromosomes.
holdfast: The branched base of an algal stipe.
holoenzyme: An enzyme consisting of an apoenzyme and a cofactor.
homolactic: Describing an organism that produces only lactic acid from fermentation; e.g., Streptococcus.
horizontal gene transfer: Transfer of genes between two organisms in the same generation. See also vertical gene transfer.
host: An organism infected by a pathogen. See also definitive host; intermediate host.
host range: The spectrum of species, strains, or cell types that a pathogen can infect.
hot-air sterilization: Sterilization by the use of an oven at 170°C for approximately 2 hours.
H (hemagglutinin) spike: Antigenic projections from the outer lipid bilayer of Influenzavirus.
HLA (Human Leukocyte Antigen) Complex: Human cell surface antigens. See also MHC (major histocompatibility) complex.
humanized antibody: Monoclonal antibodies that are partly or fully human proteins.
humoral immunity: Immunity produced by antibodies dissolved in body fluids, mediated by B cells. Also called antibody-mediated immunity.
hyaluronidase: An enzyme secreted by certain bacteria that hydrolyzes hyaluronic acid and helps spread microorganisms from their initial site of infection.
hybridoma: A cell made by fusing an antibody producing B cell with a cancer cell.
hydrogen bond: A bond between a hydrogen atom covalently bonded to oxygen or nitrogen, and another covalently bonded oxygen or nitrogen atom.
hydrolysis: A decomposition reaction in which chemicals react with the H+ and OH- of a water molecule.
hydroxyl radical: A toxic form of oxygen ( ∙OH ) formed in cytoplasm by ionizing radiation and aerobic respiration.
hyperacute rejection: Very rapid rejection of transplanted tissue, usually in the case of tissue from nonhuman sources.
hyperbaric chamber: An apparatus to hold materials at pressures greater than 1 atmosphere.
hypersensitivity: An altered, enhanced immune reaction leading to pathological changes. Also called allergy.
hyperthermophile: An organism whose optimum growth temperature is at least 80°C. Also called extreme thermophile.
hypertonic solution: A solution that has a higher concentration of solutes than an isotonic solution. Also called hyperosmotic solution.
hypha: A long filament of cells in fungi or actinomycetes.
hypotonic solution: A solution that has a lower concentration of solutes than an isotonic solution. Also called hypoosmotic solution.
ID50: The number of microorganisms required to produce a demonstrable infection in 50% of the test host population.
idiophase: The period in the production curve of an industrial cell population in which secondary metabolites are produced; a period of stationary growth following the phase of rapid growth. See also trophophase.
IgA: The class of antibodies found in secretions.
IgD: The class of antibodies found on B cells.
IgE: The class of antibodies involved in hypersensitivities.
IgG: The most abundant class of antibodies in serum.
IgM: The first class of anti bodies to appear after exposure to an antigen.
imiquimod: A substance that improves the body's natural response to infection and disease.
immune complex: A circulating antigen-antibody aggregate capable of fixing complement.
immune deficiency: The absence of an adequate immune response; may be congenital or acquired.
immune serum globulin: The serum fraction containing immunoglobulins (antibodies). Also called gamma globulin.
immune surveillance: The body's immune response to cancer.
immunity: The body's defense against particular pathogenic microorganisms.
immunization: See vaccination.
immunodiffusion test: A test consisting of precipitation reactions carried out in an agar gel medium.
immunoelectrophoresis: The identification of proteins by electrophoretic separation, followed by serological testing.
immunofluorescence: See fluorescent-antibody technique.
immunogen: See antigen.
immunoglobulin (Ig): A protein (antibody) formed in response to an antigen which can react with that antigen. See also globulin.
immunology: The study of a host's defenses to a pathogen.
immunosuppression: Inhibition of the immune response.
immunotherapy: Making use of the immune system to attack tumor cells, either by enhancing the normal immune response or by using toxin-bearing specific antibodies. See also immunotoxin.
immunotoxin: An immunotherapeutic agent consisting of a poison bound to a monoclonal antibody.
inapparent infection: See subclinical infection.
incidence: The fraction of the population that contracts a disease during a particular period of time.
inclusion: Material held inside a cell, often consisting of reserve deposits.
inclusion body: A granule or viral particle in the cytoplasm or nucleus of some infected cells; important in the identification of viruses that cause infection.
incubation period: The time interval between the actual infection and first appearance of any signs or symptoms of disease.
indicator organism: A microorganism, such as a coliform, whose presence indicates conditions such as fecal contamination of food or water.
indirect agglutination test: An agglutination test using antigens attached to latex or other small particles. Also called passive agglutination test.
indirect contact transmission: The spread of pathogens by fomites (nonliving objects).
indirect FA test: A fluorescent-antibody test to detect the presence of specific antibodies.
inducer: A chemical or environmental stimulus that causes transcription of specific genes.
induction: The process that turns on the transcription of a gene.
infection: The growth of microorganisms in the body.
infectious disease: A disease in which pathogens invade a susceptible host and carry out at least part of their life cycle in the host.
inflammation: A host response to tissue damage characterized by redness, pain, heat, and swelling; and sometimes loss of function.
innate immunity: Host defenses that afford protection against any kind of pathogen. See also adaptive immunity.
innate resistance: The resistance of an individual to diseases that affect other species and other individuals of the same species.
inoculum: A culture medium in which microorganisms are implanted.
inorganic compound: A molecule or ionic compound that does not contain carbon.
insertion sequence (IS): The simplest kind of transposon.
integrase: An enzyme produced by HIV that allows the integration of HIV DNA into the host cell's DNA.
interferon (IFN): A specific group of cytokines; alpha-IFN and beta-IFN are antiviral proteins produced by certain animal cells in response to a viral infection, and gamma-IFN stimulates macrophage activity.
interleukin (IL): A chemical that causes T-cell proliferation. See also cytokine.
intermediate host: An organism that harbors the larval or asexual stage of a helminth or protozoan.
intoxication: A condition resulting from the ingestion of a microbially produced toxin.
intron: A region in a eukaryotic gene that does not code for a protein or mRNA.
invasin: A surface protein produced by Salmonella typhimurium and Escherichia coli that rearranges nearby actin filaments in the cytoskeleton of a host cell.
iodophor: A complex of iodine and a detergent.
ion: A negatively or positively charged atom or group of atoms.
ionic bond: A chemical bond formed when atoms gain or lose electrons in the outer energy levels.
ionization: The separation (dissociation) of a molecule into ions.
ionizing radiation: High-energy radiation with a wavelength less than l nm; causes ionization, such as X rays and gamma rays.
ischemia: Localized decreased blood flow.
isograft: A tissue graft from a genetically identical source (i.e., from an identical twin).
isomers: Molecules with the same chemical formula but different structures.
isoniazid (INH): A bacteriostatic agent used to treat tuberculosis.
isotonic solution: A solution in which, after immersion of a cell, osmotic pressure is equal across the cell's membrane. Also called isosmotic solution
isotope: A form of a chemical element in which the number of neutrons in the nucleus is different from the other forms of that element.
karyogamy: Fusion of the nuclei of two cells; occurs in the sexual stage of a fungal life cycle.
kelp: A multicellular brown alga.
keratin: A protein found in epidermis, hair, and nails.
ketolide: Semi-synthetic macrolide antibodies; effective against macrolide-resistant bacteria.
kinase: (1) An enzyme that removes a phosphate from ATP and attaches it to another molecule. (2) A bacterial enzyme that breaks down fibrin (blood clots).
kingdom: A taxonomic classification between domain and phylum.
kinin: A substance released from tissue cells that causes vasodilation.
Kirby-Bauer test: See disk-diffusion method.
Koch's postulates: Criteria used to determine the causative agent of infectious diseases.
koji: A microbial fermentation on rice; usually Aspergillus oryzae; used to produce amylase.
Krebs cycle: A pathway that converts two-carbon compounds to CO2, transferring electrons to NAD+ and other carriers. Also called Tricarboxylic acid (TCA) cycle or Citric acid cycle.
lactic acid fermentation: A catabolic process, beginning with glycolysis, that produces lactic acid to reoxidize NADH.
lagging strand: During DNA replication, the daughter strand that is synthesized discontinuously.
lag phase: The time interval in a bacterial growth curve during which there is no growth.
larva: The sexually immature stage of a helminth or arthropod.
latent disease: A disease characterized by a period of no symptoms when the pathogen is inactive.
latent infection: A condition in which a pathogen remains in the host for long periods without producing disease.
LD50 The lethal dose for 50% of the inoculated hosts within a given period.
leading strand: During DNA replication, the daughter strand that is synthesized continuously.
lectin: Carbohydrate-binding proteins on a cell.
lepromin test: A skin test to determine the presence of antibodies to Mycobacterium leprae, the cause of leprosy.
leukocidins: Substances produced by some bacteria that can destroy neutrophils and macrophages.
leukocyte: A white blood cell.
leukotriene: A substance produced by mast cells and basophils that causes increased permeability of blood vessels and helps phagocytes attach to pathogens.
L-form: Prokaryotic cells that lack a cell wall; can return to walled state.
lichen: A mutualistic relationship between a fungus and either an alga or a cyanobacterium.
ligand: See adhesin.
light-dependent reaction: The process by which light energy is used to convert ADP and phosphate into ATP. Also called the light reaction of photosynthesis. See also photophosphorylation.
light-independent reaction: The process by which electrons from NADPH and energy from ATP are used to reduce CO2 to sugar. Also called the dark reaction of photosynthesis. See also Calvin-Benson cycle.
light-repair enzyme: See photolyase.
limnetic zone: The surface zone of an inland body of water away from the shore.
limulus amoebocyte lysate (LAL) assay: A test to detect the presence of bacterial endotoxins.
lipase: An enzyme that breaks down triglycerides into their component glycerol and fatty acids.
lipid: A non-water soluble organic molecule, including triglycerides, phospholipids, and sterols.
lipid A: An endotoxin that is a component of the gram-negative outer membrane.
lipid inclusion: See inclusion.
lipopolysaccharide (LPS): A molecule consisting of a lipid and a polysaccharide, forming the outer membrane of gram-negative cell walls.
L-isomer: A stereoisomer.
lithotroph: See autotroph.
littoral zone: The region along the shore of the ocean or a large lake where there is considerable vegetation and where light penetrates to the bottom.
local infection: An infection in which pathogens are limited to a small area of the body.
localized anaphylaxis: An immediate hypersensitivity reaction that is restricted to a limited area of skin or mucous membrane; for example, hayfever, a skin rash, or asthma. See also systemic anaphylaxis.
logarithmic decline phase: See death phase.
log phase: The period of bacterial growth or logarithmic in crease in cell numbers; also called exponential growth phase.
lophotrichous: Having two or more flagella at one or both ends of a cell.
luciferase: An enzyme that accepts electrons from flavoproteins and emits a photon of light in bioluminescence.
lymphangitis: Inflammation of lymph vessels.
lymphocyte: A leukocyte involved in specific immune responses.
lyophilization: Freezing a substance and sublimating the ice in a vacuum; also called freeze-drying.
lysis: (1) Destruction of a cell by the rupture of the plasma membrane, resulting in a loss of cytoplasm. (2) In disease, a gradual period of decline.
lysogenic conversion: The acquisition of new properties by a host cell infected by a lysogenic phage.
lysogenic cycle: Stages in viral development that result in the incorporation of viral DNA into host DNA.
lysogeny: A state in which phage DNA is incorporated into the host cell without lysis.
lysosome: An organelle containing digestive enzymes.
lysozyme: An enzyme capable of hydrolyzing bacterial cell walls.
lytic cycle: A mechanism of phage multiplication that results in host cell lysis.
macrolide: An antibiotic that inhibits protein synthesis; for example, erythromycin.
macromolecule: A large biological molecule.
macrophage: A phagocytic cell; a mature monocyte.
macule: A flat, reddened skin lesion.
magnetosome: An iron oxide inclusion, produced by some gram-negative bacteria, that acts like a magnet.
major histocompatibility complex (MHC): The genes that code for histocompatibility antigens; also known as human leukocyte antigen (HLA) complex.
malolactic fermentation: The conversion of malic acid to lactic acid by lactic acid bacteria.
malt: Germinated barley grains containing maltose, glucose, and amylase.
malting: The germination of starchy grains resulting in glucose and maltose production.
margination: The process by which phagocytes stick to the lining of blood vessels.
mast cell: A type of cell found throughout the body that contains histamine and other substances that stimulate vasodilation.
matrix: Fluid in mitochondria.
maximum growth temperature: The highest temperature at which a species can grow.
m-cell (microfold cell): Intestinal cells that take up and transfer antigens to lymphocytes.
mechanical transmission: The process by which arthropods transmit infections by carrying pathogens on their feet and other body parts.
medulla: A lichen body consisting of algae (or cyanobacteria) and fungi.
meiosis: A eukaryotic cell replication process that results in haploid cells with half the chromosome number of the original cell.
membrane attack complex (MAC): Complement proteins C5-C9, which together make lesions in cell membranes that lead to cell death.
membrane filter: A screenlike material with pores small enough to retain microorganisms; a 0.45 μm filter retains most bacteria.
memory cells: A long-lived B cell or T cell responsible for the memory, or secondary, response.
memory response: A rapid rise in antibody titer following exposure to an antigen after the primary response to that antigen; also called anamestic response or secondary response.
meningitis: Inflammation of the meninges, the three membranes covering the brain and spinal cord.
merozoite: A trophozoite of Plasmodium found in red blood cells or liver cells.
mesophile: An organism that grows between about 10°C and 50°C; a moderate-temperature loving microbe.
mesosome: An irregular fold in the plasma membrane of a prokaryotic cell that is an artifact of preparation for microscopy.
messenger RNA (mRNA): The type of RNA molecule that directs the incorporation of amino acids into proteins.
metabolic pathway: A sequence of enzymatically catalyzed reactions occurring in a cell.
metabolism: The sum of all the chemical reactions that occur in a living cell.
metacercaria: The encysted stage of a fluke in its final intermediate host.
metachromatic granule: A granule that stores inorganic phosphate and stains red with certain blue dyes; characteristic of Corynebacterium diphtheriae. Collectively known as volutin.
methane: The hydrocarbon CH4 , a flammable gas formed by the microbial decomposition of organic matter. Also called natural gas.
methylate: Addition of a methyl group (-CH3 ) to a molecule; for example, methylated cytosine is protected from digestion by restriction enzymes.
microaerophile: An organism that grows best in an environment with less molecular oxygen (O2) than is normally found in air.
micrometer (μm): A unit of measurement equal to 10-6 m.
microorganism: A living organism too small to be seen with the naked eye; includes bacteria, fungi, protozoa, and microscopic algae; also includes viruses.
microtubule: A hollow tube made of the protein tubulin, the structural unit of eukaryotic flagella and centrioles.
microwave: Electromagnetic radiation with wavelength between 10-1 and 10-3 m.
minimal bactericidal concentration (MBC): The lowest concentration of chemotherapeutic agent that will kill test microorganisms.
minimal inhibitory concentration (MIC): The lowest concentration of a chemotherapeutic agent that will prevent growth of the test microorganisms.
minimum growth temperature: The lowest temperature at which a species will grow.
miracidium: The free-swimming, ciliated larva of a fluke that hatches from the egg.
missense mutation: A mutation that results in the substitution of an amino acid in a protein.
mitochondrion: An organelle containing Krebs cycle enzymes and the electron transport chain. Plural is mitochondria.
mitosis: A eukaryotic cell replication process in which the chromosomes are duplicated; usually followed by division of the cytoplasm of the cell.
mitosome: Eukaryotic organelle derived form degenerate mitochondria, found in Trichomonas and Giardia.
MMWR (Morbidity and Mortality Weekly Report): A CDC publication containing data on notifiable diseases and topics of special interest.
mole: An amount of a chemical equal to the atomic weights of all the atoms in a molecule of the chemical; 1 mole contains 6.023 x 1023 particles.
molecular biology: The science dealing with DNA and protein synthesis of living organisms.
molecular weight: The sum of the atomic weights of all atoms making up a molecule.
molecule: A combination of atoms forming a specific chemical compound.
monobactam: A synthetic antibiotic with a β-lactam ring that is monocyclic in structure, in contrast to the bicyclic β-lactam structure of the penicillins and cephalosporins.
monoclonal antibody (Mab): A specific antibody produced in vitro by a clone of B cells hybridized with cancerous cells.
monocyte: A leukocyte that is the precursor of a macrophage.
monoecious: Having both male and female reproductive capacities.
monomers: Small molecules that join together to form polymers.
mononuclear phagocytic system: A system of fixed macrophages located in the spleen, liver, lymph nodes, and red bone marrow.
monosaccharide: A simple sugar consisting of 3 to 7 carbon atoms, with the empirical formula CH2O.
monotrichous: Having a single flagellum.
morbidity: (1) The incidence of a specific disease. (2) The condition of being diseased.
morbidity rate: The number of people affected by a disease in a given period of time in relation to the total population.
mordant: A substance added to a staining solution to make it stain more intensely.
mortality: The number of deaths from a specific notifiable disease.
mortality rate: The number of deaths resulting from a disease in a given period of time in relation to the total population.
most probable number (MPN) method: A statistical determination of the number of coliforrns per 100 mL of water or 100 g of food.
motility: The ability of an organism to move by itself.
M protein: A heat-resistant and acid-resistant protein of streptococcal cell walls and fibrils.
mucous membranes: Membranes that line body openings, including the intestinal tract, open to the exterior; also called mucosa.
mutagen: An agent in the environment that brings about mutations.
mutation: Any change in the nitrogenous base sequence of DNA.
mutation rate: The probability that a gene will mutate each time a cell divides.
mutualism: A type of symbiosis in which both organisms, or populations are benefitted.
mycelium: A mass of long filaments of cells that branch and intertwine, typically found in molds.
mycolic acid: Long-chained, branched fatty acids characteristic of members of the genus Mycobacterium.
mycology: The scientific study of fungi.
mycorrhiza: A fungus growing in symbiosis with plant roots.
mycosis: A fungal infection.
mycotoxin: A toxin produced by a fungus.
NAD+: A coenzyme that functions in the removal and transfer of hydrogen ion (H+) and electrons from substrate molecules.
NADP+: A coenzyme that functions in the removal and transfer of hydrogen ion (H+) and electrons from substrate molecules.
nanobacteria: Bacteria well below the generally accepted lower limit diameter (about 0.2 μm) for bacteria.
nanometer (nm): A unit of measurement equal to 10-9 m, or 10-3 μm.
natural killer (NK) cell: A lymphoid cell that destroys tumor cells and virus-infected cells.
naturally acquired active immunity: Antibody production in response to an infectious disease.
naturally acquired passive immunity: The natural transfer of humoral antibodies, for example, transplacental transfer.
natural penicillins: Penicillin molecules made by molds of the genus Penicillium; penicillins G and V are examples. See also semisynthetic penicillins.
necrosis: Tissue death.
negative (indirect) selection: The process of identifying mutations by selecting cells that do not grow using replica plating.
negative staining: A procedure that results in colorless bacteria against a stained background.
neurotoxin: An exotoxin that interferes with normal nerve impulse conduction.
neutralization: An antigen-antibody reaction that inactivates a bacterial exotoxin or virus.
neutron: An uncharged particle in the nucleus of an atom.
neutrophil: A highly phagocytic granulocyte. Also called polymorphonuclear leukocyte (PMN), or polymorph.
nicotinamide adenine dinucleotide: See NAD+.
nicotinamide adenine dinucleotide phosphate: See NADP+ .
nitrification: The oxidation of nitrogen in ammonia to produce nitrate.
nitrogen cycle: The series of processes that converts nitrogen (N2) to organic substances and back to nitrogen in nature.
nitrogen fixation: The conversion of nitrogen (N2) into ammonia.
nitrosamine: A carcinogen formed by the combination of nitrite and amino acids.
nomenclature: The system of naming things.
noncommunicable disease: A disease that is not transmitted from one person to another.
noncompetitive inhibitor: An inhibitory chemical that does not compete with the substrate for an enzyme's active site. See also allosteric inhibition; competitive inhibitor.
noncyclic photophosphorylation: The movement of an electron from chlorophyll to NAD+; plant and cyanobacterial photophosphorylation.
nonionizing radiation: Short-wavelength radiation that does not cause ionization, such as ultraviolet (UV) radiation.
non-nucleoside reverse transcriptase inhibitor: A drug that binds with and inhibits the action of the HIV reverse transcriptase enzyme.
nonsense codon: A codon that does not encode any amino acid.
nonsense mutation: A base substitution in DNA that results in a nonsense codon.
normal microbiota: The microorganisms that colonize a host without causing disease; also called normal flora.
nosocomial infection: An infection that develops during the course of a hospital stay and was not present at the time the patient was admitted.
notifiable disease: A disease that physicians must report to the U.S. Public Health Service; also called reportable disease.
n (neuraminidase) spikes: Antigenic projections from the outer lipid bilayer of Influenzavirus.
nuclear envelope: The double membrane that separates the nucleus from the cytoplasm in a eukaryotic cell.
nuclear pore: An opening in the nuclear envelope through which materials enter and exit the nucleus.
nucleic acid: A macromolecule consisting of nucleotides, such as DNA and RNA.
nucleic acid hybridization: The process of combining single complementary strands of DNA.
nucleic acid vaccine: A vaccine made up of DNA, usually in the form of a plasmid; also called DNA vaccine.
nucleoid: The region in a bacterial cell containing the chromosome.
nucleolus: An area in a eukaryotic nucleus where rRNA is synthesized. Plural is nucleoli.
nucleoside: A compound consisting of a purine or pyrimidine base and a pentose sugar.
nucleoside analog: A chemical that is structurally similar to the normal nucleosides in nucleic acids but with altered base-pairing properties.
nucleoside reverse transcriptase inhibitor: A nucleoside analog anti-retroviral drug.
nucleotide: A compound consisting of a purine or pyrimidine base, a five-carbon sugar, and a phosphate.
nucleotide excision repair (NER) The repair of DNA involving removal of defective nucleotides and replacement with functional ones.
nucleus: (1) The part of an atom consisting of the protons and neutrons. (2) The part of a eukaryotic cell that contains the genetic material.
numerical identification: Bacterial identification schemes in which test values are assigned a number.
nutrient agar: Nutrient broth containing agar.
nutrient broth: A complex medium made of beef extract and peptone.
objective lenses: In a compound light microscope, the lenses closest to the specimen.
obligate aerobe: An organism that requires molecular oxygen (O2) to live.
obligate anaerobe: An organism that does not use molecular oxygen (O2) and is killed in the presence of O2.
obligate halophile: An organism that requires high osmotic pressures, such as high concentrations of NaCl.
ocular lens: In a compound light microscope, the lens closest to the viewer; also called the eyepiece.
oligodynamic action: The ability of small amounts of a heavy metal compound to exert antimicrobial activity.
oligosaccharide: A carbohydrate consisting of 2 to 20 monosaccharides, joined through dehydration synthesis.
oncogene: A gene that can bring about malignant transformation.
oncogenic virus: A virus that is capable of producing tumors; also called oncovirus.
oocyst: An encysted apicomplexan zygote in which cell division occurs to form the next infectious stage.
Opa: A bacterial outer membrane protein; cells with Opa form opaque colonies.
operator: The region of DNA adjacent to structural genes that controls their transcription.
operon: The operator and promoter sites and structural genes they control.
opportunistic pathogen: A microorganism that does not ordinarily cause a disease, but can become pathogenic under certain circumstances.
opsonization: The enhancement of phagocytosis by coating microorganisms with certain serum proteins (opsonins); also called immune adherence.
optimum growth temperature: The temperature at which a species grows best.
order: A taxonomic classification between class and family.
organelle: A membrane-enclosed structure within eukaryotic cells.
organic compound: A molecule that contains carbon and hydrogen.
organic growth factor: An essential organic compound that an organism is unable to synthesize.
osmosis: The net movement of solvent molecules across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
osmotic lysis: Rupture of the plasma membrane resulting from movement of water into the cell.
osmotic pressure: The force with which a solvent moves from a solution of lower solute concentration to a solution of higher solute concentration.
oxidation: The removal of electrons from a molecule.
oxidation pond: A method of secondary sewage treatment by microbial activity in a shallow standing pond of water.
oxidation-reduction: A coupled reaction in which one substance is oxidized and one is reduced; also called a redox reaction.
oxidative phosphorylation: The synthesis of ATP coupled with electron transport.
oxygenic: Producing oxygen, as in plant and cyanobacterial photosynthesis.
ozone: O3 .
PABA (para-aminobenzoic acid): a precursor for folic acid synthesis.
pandemic disease: An epidemic that occurs worldwide.
papule: Small, solid elevation of the skin.
parasite: An organism that derives nutrients from a living host.
parasitism: A symbiotic relationship in which one organism (the parasite) exploits another (the host) without providing any benefit in return.
parasitology: The scientific study of parasitic protozoa and worms.
parenteral route: A portal of entry for pathogens by deposition directly into tissues beneath the skin and mucous membranes.
pasteurization: The process of mild heating to kill particular spoilage microorganisms or pathogens.
pathogen: A disease-causing organism.
pathogenesis: The manner in which a disease develops.
pathogenicity: The ability of a microorganism to cause disease by overcoming the defenses of a host.
pathology: The scientific study of disease.
pellicle: (1) The flexible covering of some protozoa. (2) Scum on the surface of a liquid medium.
penicillins: A group of antibiotics produced either by Penicillium (natural penicillins) or by adding side chains to the β-lactam ring (semisynthetic penicillins).
pentose phosphate pathway: A metabolic pathway that can occur simultaneously with glycolysis to produce pentoses and NADH without ATP production; also called hexose monophosphate shunt.
peptide bond: A bond joining the amino group of one amino acid to the carboxyl group of a second amino acid, with the loss of a water molecule.
peptidoglycan: The structural molecule of bacterial cell walls consisting of the molecules N-acetylglucosamine, N-acetylmuramic acid, tetrapeptide side chain, and peptide side chain.
perforin: Protein that makes a pore in a tar get cell membrane, released by cytotoxic T cells.
pericarditis: Inflammation of the pericardium, the sac around the heart.
period of convalescence: The recovery period, when the body returns to its predisease state.
peripheral nervous system (PNS): The nerves that connect the outlying parts of the body with the central nervous system.
periplasm: The region of a gram-negative cell wall between the outer membrane and the cytoplasmic membrane.
peritrichous: Having flagella distributed over the entire cell.
peroxidase: An enzyme that breaks down hydrogen peroxide.
peroxide anion: An oxygen anion, consisting of two atoms of oxygen and a -2 charge (O22- ).
peroxisome: Organelle that oxidizes amino acids, fatty acids, and alcohol.
peroxygen: A class of oxidizing-type sterilizing disinfectants.
persistent viral infection: A disease process that occurs gradually over a long period.
pH: The symbol for the negative logarithm of hydrogen ion (H+ ) concentration; a measure of the relative acidity or alkalinity of a solution. pH = -log [H+ ]
phage: See bacteriophage.
phage conversion: Genetic change in the host cell resulting from infection by a bacteriophage.
phage typing: A method of identifying bacteria using specific strains of bacteriophages.
phagocyte: A cell capable of engulfing and digesting particles that are harmful to the body.
phagocytosis: The ingestion of solids by eukaryotic cells; cell eating.
phagolysosome: A digestive vacuole.
phagosome: A food vacuole of a phagocyte; also called a phagocytic vesicle.
phalloidin: A peptide toxin produced by Amanita phalloides, which affects plasma membrane function.
phase-contrast microscope: A compound light microscope that allows examination of structures inside cells through the use of a special condenser.
phenol: An aromatic alcohol, also called carbolic acid, or hydroxybenzene.
phenolic: A synthetic derivative of phenol used as a disinfectant.
phenotype: The external manifestations of an organism's genotype, or genetic makeup.
phosphate group: A portion of a phosphoric acid molecule attached to some other molecule.
phospholipid: A complex lipid composed of glycerol, two fatty acids, and a phosphate group.
phosphorous cycle: The various solubility stages of phosphorus in the environment.
phosphorylation: The addition of a phosphate group to an organic molecule.
photoautotroph: An organism that uses light as its energy source, and carbon dioxide (CO2 ) as its carbon source.
photoheterotroph: An organism that uses light as its energy source and an organic carbon source.
photolyase: An enzyme that splits thymine dimers in the presence of visible light.
photophosphorylation: The production of ATP in a series of redox reactions; electrons from chlorophyll initiate the reactions.
photosynthesis: The conversion of light energy from the sun into chemical energy; the light-fueled synthesis of carbohydrate from carbon dioxide (CO2 ).
phototaxis: Movement in response to the presence of light.
phototroph: An organism that uses light at its primary energy source.
phylogeny: The evolutionary history of a group of organisms; phylogenetic relationships are evolutionary relationships.
phylum: A taxonomic classification between kingdom and class.
phytoplankton: Free-floating photoautotrophs.
pilus: An appendage on a bacterial cell used for the transfer of genetic material during conjugation. Plural is pili.
pinocytosis: The engulfing of fluid by infolding of the plasma membrane in eukaryotes; cell drinking.
plankton: Free-floating aquatic organisms.
plantae: The kingdom composed of multicellular eukaryotes with cellulose cell walls.
plaque: A clearing in a bacterial lawn resulting from lysis by phages. See also dental plaque.
plaque-forming units (pfu): Visible viral plaques counted.
plasma: The liquid portion of blood in which the formed elements are suspended.
plasma cell: A cell that an activated B cell differentiates into, and then produces specific antibodies.
plasma membrane: The selectively permeable membrane enclosing the cytoplasm of a cell; the outer layer in animal cells, internal to the cell wall in other organisms. Also called cell membrane, or cytoplasmic membrane.
plasmid: A small circular DNA molecule that replicates independently of the chromosome.
plasmodium: (1) A multinucleated mass of protoplasm, as in plasmodial slime molds. (2) The genus that is the causative agent of malaria.
plasmogamy: Fusion of the cytoplasm of two cells; occurs in the sexual stage of a fungal life cycle.
plasmolysis: Loss of water from a cell in a hypertonic environment.
plate count: A method of determining the number of bacteria in a sample by counting the number of colony-forming units on a solid culture medium.
pleomorphic: Having many shapes, characteristic of certain bacteria.
pluripotent: A cell that can differentiate into a many different types of tissue cells.
pneumonia: Inflammation of the lungs.
point mutation: See base substitution.
polar molecule: A molecule with an unequal distribution of charges.
polyene antibiotic: An antimicrobial agent that alters sterols in eukaryotic plasma membranes and contains more than four carbon atoms and at least two double bonds.
polymer: A molecule consisting of a sequence of similar molecules, or monomers.
polymerase chain reaction (PCR): A technique using DNA polymerase to make multiple copies of a DNA template in vitro. See also cDNA.
polymorphonuclear leukocyte (PMN): See neutrophil.
polypeptide: (1) A chain of amino acids. (2) A group of antibiotics.
polysaccharide: A carbohydrate consisting of many monosaccharides (20 or more), joined through dehydration synthesis. See also oligosaccharide.
porins: A type of protein in the outer membrane of gram-negative cell walls that permits the passage of small molecules.
portal of entry: The avenue by which a pathogen gains access to the body.
portal of exit: The route by which a pathogen leaves the body.
positive (direct) selection: A procedure for picking out mutant cells by growing them.
pour plate method: A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify.
precipitation reaction: A reaction between soluble antigens and multivalent antibodies to form visible aggregates.
precipitin ring test: A precipitation test performed in a capillary tube.
predisposing factor: Anything that makes the body more susceptible to a disease or alters the course of a disease.
prevalence: The fraction of a population having a specific disease at a given time.
primary cell line: Human tissue cells that grow for only a few generations in vitro.
primary infection: An acute infection that causes the initial illness.
primary metabolite: A product of an industrial cell population produced during the time of rapid logarithmic growth. See also secondary metabolite.
primary producer: An autotrophic organism, either chemotroph or phototroph, that converts carbon dioxide into organic compounds.
primary response: Antibody production in response to the first contact with an antigen. See also memory response.
primary sewage treatment: The removal of solids from sewage by allowing them to settle out and be held temporarily in tanks or ponds.
prion: An infectious agent consisting of a self-replicating protein, with no detectable nucleic acids.
privileged site (tissue): An area of the body (or a tissue) that does not elicit an immune response.
probiotics: Microbes inoculated into a host to occupy a niche and prevent growth of pathogens.
prodromal period: The time following the incubation period when the first symptoms of illness appear.
profundal zone: The deeper water under the limnetic zone in an inland body of water.
proglottid: A body segment of a tapeworm containing both male and female organs.
prokaryote: A cell whose genetic material is not enclosed in a nuclear envelope, such as bacteria.
prokaryotic species: A population of cells that share certain rRNA sequences; in conventional biochemical testing, it is a population of cells with similar characteristic.
promoter: The starting site on a DNA strand for transcription of RNA by RNA polymerase.
prophage: Phage DNA inserted into the host cell's DNA.
prophylactic: Anything used to prevent disease.
prostaglandin: A hormone-like substance that is released by damaged cells, and intensifies inflammation.
prostheca: A stalk or bud protruding from a prokaryotic cell.
protease: An enzyme that digests protein (proteolytic enzymes).
protein: A large molecule containing carbon, hydrogen, oxygen, nitrogen, and usually sulfur; many proteins contain helical structure and/or pleated sheets.
protein kinase: An enzyme that activates another protein by adding a phosphate from ATP.
proteobacteria: Gram-negative, chemoheterotrophic bacteria that possess a signature rRNA sequence.
proteomics: The science of determining all of the proteins expressed in a cell.
protist: Term used for unicellular and simple multicellular eukaryotes; usually protozoa and algae.
proton: A positively charged particle in the nucleus of an atom.
protoplast: A gram-positive bacterium or plant cell treated to remove the cell wall.
protoplast fusion: A method of joining two cells by first removing their cell walls; used in genetic engineering.
protozoan: Unicellular eukaryotic organisms; usually chemoheterotrophic. Plural is protozoa.
provirus: Viral DNA that is integrated into the host cell's DNA.
pseudohypha: A short chain of fungal cells that results from the lack of separation of daughter cells after budding.
pseudopod: An extension of a eukaryotic cell that aids in locomotion and feeding.
psychrophile: An organism that grows best at about 15°C and does not grow above 20°C; a cold-loving microbe.
psychrotroph: An organism that is capable of growth between about 0°C and 30°C.
purines: The class of nucleic acid bases that includes adenine and guanine.
purple nonsulfur bacteria: Alphaproteobacteria; strictly anaerobic and phototrophic; grows on yeast extract in the dark; uses reduced organic compounds as electron donors for CO2 fixation.
purple sulfur bacteria: Gammaproteobacteria; strictly anaerobic and phototrophic; uses reduced sulfur compounds as electron donors for CO2 fixation.
pus: An accumulation of dead phagocytes, dead bacterial cells, and fluid.
pustule: A small pus-filled elevation of skin.
pyocyanin: A blue-green pigment produced by Pseudomonas aeruginosa.
pyrimidines: The class of nucleic acid bases that includes uracil, thymine, and cytosine.
quaternary ammonium compound (quat): A cationic detergent with four organic groups attached to a central nitrogen atom; used as a disinfectant.
quinolone: An antibiotic whose mode of action is to inhibit DNA replication by interfering with the enzyme DNA gyrase.
quorum sensing: The ability of bacteria to communicate and coordinate behavior via signaling molecules.
R: Used to represent nonfunctional groups of a molecule. See also resistance factor.
random shotgun sequencing: A technique for determining the nucleotide sequence in an organism's genome.
rapid plasma reagin (RPR) test: A serological test for syphilis.
r-determinant: A group of genes for antibiotic resistance carried on R factors.
receptor: An attachment for a pathogen on a host cell.
recipient cell: A cell that receives DNA from a donor cell during genetic recombination.
recombinant DNA (rDNA): A DNA molecule produced by combining DNA from two different sources.
recombinant DNA (rDNA) technology: Manufacturing and manipulating genetic material in vitro; also called genetic engineering.
recombinant vaccine: A vaccine made by recombinant DNA techniques.
redia: A trematode larval stage that reproduces asexually to produce cercariae.
redox reaction: See oxidation-reduction.
red tide: A bloom of planktonic dinoflagellates.
reducing medium: A culture medium containing ingredients that will remove dissolved oxygen from the medium to allow the growth of anaerobes.
reduction: The addition of electrons to a molecule.
refractive index: The relative velocity with which light passes through a substance.
regulatory T (TR) cells: Lymphocytes that appear to suppress other T cells.
relative risk: A comparison of the risk of disease in two groups.
rennin: An enzyme that forms curds as part of any dairy fermentation product; originally from calves' stomachs, now produced by molds and bacteria.
replica plating: A method of inoculating a number of solid minimal culture media from an original plate to produce the same pattern of colonies on each plate.
replication fork: The point where DNA strands separate and new strands will be synthesized.
repression: The process by which a repressor protein can stop the synthesis of a protein.
repressor: A protein that binds to the operator site to prevent transcription.
reservoir of infection: A continual source of infection.
resistance: The ability to ward off diseases through innate and adaptive immunity.
resistance ® factor: A bacterial plasmid carrying genes that determine resistance to antibiotics.
resistance transfer factor (RTF): A group of genes for replication and conjugation on the R factor.
resolution: The ability to distinguish fine detail with a magnifying instrument; also called resolving power.
respiration: A series of redox reactions in a membrane that generates ATP, the final electron acceptor is usually an inorganic molecule.
restriction enzyme: An enzyme that cuts double-stranded DNA at specific sites between nucleotides.
reticulate body: The intracellular growing stage of chlamydiae.
retort: A device for commercially sterilizing canned food by using steam under pressure; operates on the same principle as an autoclave, but is much larger.
reverse genetics: Genetic analysis that begins with a piece of DNA and proceeds to find out what it does.
reverse transcriptase: An RNA-dependent DNA polymerase; an enzyme that synthesizes a complementary DNA from an RNA template.
reversible reaction: A chemical reaction in which the end-products can readily revert to the original molecules.
RFLP (Restriction fragment length polymorphism): A fragment resulting from restriction-enzyme digestion of DNA.
Rh factor: An antigen on red blood cells of rhesus monkeys and most humans; possession makes the cells Rh+.
rhizine: A rootlike hypha that anchors a fungus to a surface.
ribonucleic acid (RNA): The class of nucleic acids that comprises messenger RNA, ribosomal RNA, and transfer RNA.
ribose: A five-carbon sugar that is part of ribonucleotide molecules and RNA.
ribosomal RNA (rRNA): The type of RNA molecule that forms ribosomes.
rRNA sequencing: Determination of the order of nucleotide bases in ribosomal RNA.
ribosome: The site of protein synthesis in a cell, composed of RNA and protein.
ribozyme: An enzyme consisting of RNA that specifically acts on strands of RNA to remove introns and splice together the remaining exons.
rifamycin: An antibiotic that inhibits bacterial RNA synthesis.
ring stage: A young Plasmodium trophozoite that looks like a ring in a red blood cell.
RNAi (RNA interference): Cellular degradation of double-stranded RNA, along with single-stranded RNA having the same sequence.
RNA primer: A short strand of RNA used to start synthesis of the lagging strand of DNA, and to start the polymerase chain reaction.
root nodule: A tumor-like growth on the roots of certain plants containing symbiotic nitrogen-fixing bacteria.
rotating biological contactor: A method of secondary sewage treatment in which large disks are rotated while partially submerged in a sewage tank exposing sewage to microorganisms and aerobic conditions.
rough ER: Rough endoplasmic reticulum, which has ribosomes on its surface.
roundworm: An animal belonging to the phylum Nematoda.
S (Svedberg unit): Notes the relative rate of sedimentation during ultra-high-speed centrifugation.
salt: A substance that dissolves in water and dissociates into cations and anions, neither of which is H+ or OH-.
sanitization: The removal of microbes from eating utensils and food preparation areas.
saprophyte: An organism that obtains its nutrients from dead organic matter.
sarcina: (1) A group of eight bacteria that remain in a packet after dividing. (2) When written as a genus, refers to gram positive, anaerobic cocci. Plural is sarcinae.
saturation: The condition in which the active site on an enzyme is occupied by the substrate or product at all times.
saxitoxin: A neurotoxin produced by some dinoflagellates.
scanned probe microscopy: Microscopic technique used to obtain images of molecular shapes, to characterize chemical properties, and to determine temperature variations within a specimen.
scanning acoustic microscope (SAM): A microscope that uses high frequency ultrasound waves to penetrate surfaces.
scanning electron microscope (SEM): An electron microscope that provides three-dimensional views of the specimen magnified 1,000 to 10,000 x.
scanning tunneling microscopy: See scanned-probe microscopy.
schizogony: The process of multiple fission, in which one organism divides to produce many daughter cells.
scientific nomenclature: See binomial nomenclature.
sclerotia: The compact mass of hardened mycelia of the fungus Claviceps purpurea that fills infected rye flowers; produces the toxin ergot.
scolex: The head of a tapeworm, containing suckers and possibly hooks.
secondary infection: An infection caused by an opportunistic microbe after a primary infection has weakened the host's defenses.
secondary metabolite: A product of an industrial cell population produced after the microorganism has largely completed its period of rapid growth and is in a stationary phase of the growth cycle. See also primary metabolite.
secondary response: See memory response.
secondary sewage treatment: Biological degradation of the organic matter in wastewater following primary treatment.
secretory vesicle: A membrane-enclosed sac produced by the cell's endoplasmic reticulum; transports synthesized material into the cytoplasm.
selective medium: A culture medium designed to suppress the growth of unwanted microorganisms and encourage the growth of desired ones.
selective permeability: The property of a plasma membrane to allow certain molecules and ions to move through the membrane while restricting others.
selective toxicity: The property of some antimicrobial agents to be toxic for a microorganism and nontoxic for the host.
self-tolerance: The ability of an organism to recognize and not make antibodies against self.
semiconservative replication: The process of DNA replication in which each double-stranded DNA molecule contains one original strand and one new strand.
semisynthetic penicillins: Modifications of natural penicillins by introducing different side chains that extend the spectrum of antimicrobial activity and avoid microbial resistance.
sense codon: A codon that codes for an amino acid.
sense strand (+ strand): Viral RNA that can act as mRNA.
sentinel animal: An organism in which changes can be measured to assess the extent of environmental contamination and its implication for human health.
sepsis: The presence of a toxin or pathogenic organism in blood and tissue.
septa: A cross-wall in a fungal hypha.
septate hypha: A hypha consisting of uninucleate cell-like units.
septicemia: The proliferation of pathogens in the blood, accompanied by fever; sometimes causes organ damage.
septic shock: A sudden drop in blood pressure induced by bacterial toxins.
serial dilution: The process of diluting a sample several times.
seroconversion: A change in a person's response to an antigen in a serological test.
serological testing: Techniques for identifying a microorganism based on its reaction with antibodies.
serology: The branch of immunology that studies blood serum and antigen-antibody reactions in vitro.
serotype: See serovar.
serovar: A variation within a species; also called serotype.
serum: The liquid remaining after blood plasma is clotted; contains antibodies (immunoglobulins).
severe sepsis: Decreased blood pressure and dysfunction of at least one organ.
sexual dimorphism: The distinctly different appearance of adult male and female organisms.
sexual spore: A spore formed by sexual reproduction.
Shiga toxin: An exotoxin produced by Shigella dysenteriae and enterohemorrhagic E. coli.
shock: Any life-threatening loss of blood pressure. See also septic shock.
shuttle vector: A plasmid that can exist in several different species; used in genetic engineering.
siderophore: Bacterial iron-binding proteins.
sign: A change due to a disease that a person can observe and measure.
simple stain: A method of staining microorganisms with a single basic dye.
singlet oxygen: Highly reactive molecular oxygen.
siRNA (Short interfering RNA): An intermediate in the RNAi process in which the long double-stranded RNA has been cut up into short double-stranded RNA sections of about 21 nucleotides.
site-directed mutagenesis: Techniques used to modify a gene in a specific location to produce the desired polypeptide.
slide agglutination test: A method of identifying an antigen by combining it with a specific antibody on a slide.
slime layer: A glycocalyx that is unorganized and loosely attached to the cell wall.
sludge: Solid matter obtained from sewage.
smear: A thin film of material containing microorganisms, spread over the surface of a slide.
smooth ER: Endoplasmic reticulum without ribosomes.
solute: A substance dissolved in another substance.
solvent: A dissolving medium.
Southern blotting: A technique that uses DNA probes to detect the presence of specific DNA in restriction fragments separated by electrophoresis.
specialized transduction: The process of transferring a piece of cell DNA adjacent to a prophage to another cell.
species: The most specific level in the taxonomic hierarchy. See also bacterial species; eukaryotic species; viral species.
specific epithet: The second or species name in a scientific binomial. See also species.
spectrum of microbial activity: The range of distinctly different types of microorganisms affected by an antimicrobial drug; a wide range is referred to as a broad spectrum of activity.
spheroplast: A gram-negative bacterium treated to damage the cell wall, resulting in a spherical cell.
spicule: One of two external structures on the male roundworm used to guide sperm.
spike: A carbohydrate-protein complex that projects from the surface of certain viruses.
spiral: See spirillum and spirochete.
spirillum: (1) A helical or corkscrew-shaped bacterium. (2) When written as a genus, refers to aerobic, helical bacteria with clumps of polar flagella. Plural is spirilla.
spirochete: A corkscrew-shaped bacterium with axial filaments.
splicing: A process by which an RNA molecule cuts out introns and rejoins exons to produce a molecule of mRNA.
spontaneous generation: The idea that life could arise spontaneously from nonliving matter.
spontaneous mutation: A mutation that occurs without a mutagen.
sporadic disease: A disease that occurs occasionally in a population.
sporangiophore: An aerial hypha supporting a sporangium.
sporangiospore: An asexual fungal spore formed within a sporangium.
sporangium: A sac containing one or more spores.
spore: A reproductive structure formed by fungi and actinomycetes.
sporogenesis: See sporulation.
sporozoite: A trophozoite of Plasmodium found in mosquitoes, infective for humans.
sporulation: The process of spore and endospore formation; also called sporogenesis.
spread plate method: A plate count method in which inoculum is spread over the surface of a solid culture medium.
staining: Colorizing a sample with a dye to view through a microscope, or to visualize specific structures.
staphylococci: Cocci in a grape-like cluster or broad sheet. Singular is staphylococcus.
stationary phase: The period in a bacterial growth curve when the number of cells dividing equals the number dying, and the population size remains stationary.
stem cell: An undifferentiated cell that gives rise to a variety of specialized cells.
stereoisomers: Two molecules consisting of the same atoms, arranged in the same manner but differing in their relative positions; mirror images; also called D-isomer and L-isomer.
sterile: Free of microorganisms.
sterilization: The removal of all microorganisms, including endospores.
steroid: A specific group of lipids, including cholesterol and some hormones.
stipe: A stemlike supporting structure of multicellular algae and basidiomycetes.
storage vesicle: Organelles that form from the Golgi complex; contain proteins made in the rough ER and processed in the Golgi complex.
strain: Genetically different cells within a clone. See serovar.
streak plate method: A method of isolating a culture by spreading microorganisms over the surface of a solid culture medium.
streptobacilli: Rods that remain attached in chains after cell division. Singular is streptobacillus.
streptococci: (1) Cocci that remain attached in chains after cell division. (2) When written as a genus, refers to gram positive, catalase-negative bacteria. Singular is streptococcus.
streptogramin: Antibiotics that block protein synthesis at 70S ribosomes.
streptokinase: A blood-clot dissolving enzyme, produced by betahemolytic streptococci.
streptolysin: A hemolytic enzyme, produced by streptococci.
structural gene: A gene that determines the amino acid sequence of a protein.
subacute disease: A disease with symptoms that are intermediate between acute and chronic.
subclinical infection: An infection that does not cause a noticeable illness; also called inapparent infection.
subcutaneous mycosis: A fungal infection of tissue beneath the skin.
substrate: Any compound with which an enzyme reacts.
substrate-level phosphorylation: The synthesis of ATP by direct transfer of a high-energy phosphate group from an intermediate metabolic compound to ADP.
subunit vaccine: A vaccine consisting of an antigenic fragment.
sulfa drug: A bacteriostatic compound that interferes with folic acid synthesis by competitive inhibition.
sulfhydryl group: An organic functional group consisting of sulfur bound to hydrogen, -SH.
sulfur cycle: The various oxidation and reduction stages of sulfur in the environment, mostly due to the action of microorganisms.
sulfur granule: See inclusion.
superantigen: An antigen that activates many different T cells, thereby eliciting a large immune response.
superficial mycosis: A fungal infection localized in surface epidermal cells and along hair shafts.
superinfection: The growth of a pathogen that has developed resistance to an antimicrobial drug being used; the growth of an opportunistic pathogen.
superoxide dismutase (SOD): An enzyme that destroys superoxide free radicals.
superoxide free radical: A toxic form of oxygen (O2- ) formed during aerobic respiration.
surface-active agent: Any compound that decreases the tension between molecules lying on the surface of a liquid; also called surfactant.
susceptibility: The lack of resistance to a disease.
symbiosis: The living together of two different organisms or populations.
symptom: A change in body function that is felt by a patient as a result of a disease.
syncytium: A multinucleated giant cell resulting from certain viral infections.
syndrome: A specific group of signs or symptoms that accompany a disease.
synergism: (1) The effect of two microbes working together that is greater than the effect of either acting alone. (2) The principle whereby the effectiveness of two drugs used simultaneously is greater than that of either drug used alone.
synthesis reaction: A chemical reaction in which two or more molecules combine to form a new, larger molecule.
synthetic drug: A chemotherapeutic agent that is prepared from chemicals in a laboratory.
systematics: The science of organizing groups of organisms into a hierarchy.
systemic anaphylaxis: A hypersensitivity reaction causing vasodilation and resulting in shock; also called anaphylactic shock.
systemic (generalized) infection: An infection throughout the body.
systemic mycosis: A fungal infection in deep tissues.
tachyzoite: A rapidly growing trophozoite form of a protozoan.
T antigen: An antigen in the nucleus of a tumor cell.
tapeworm: A flatworm belonging to the class Cestoda.
target cell: An infected body cell to which defensive cells of the immune system bind.
taxa: Subdivisions used to classify organisms, e.g., domain, kingdom, phylum.
taxis: Movement in response to an environmental stimulus.
taxonomy: The science of the classification of organisms.
T cell: A type of lymphocyte, which develops from a stem cell processed in the thymus gland, that is responsible for cell-mediated immunity.
T-dependent antigen: An antigen that will stimulate the formation of antibodies only with the assistance of helper T cells. See also T-independent antigen.
teichoic acid: A polysaccharide found in gram-positive cell walls.
teleomorph: (1) The sexual stage in the life cycle of a fungus. (2) A fungus that produces both sexual and asexual spores.
temperature abuse: Improper food storage at a temperature that allows bacteria to grow.
terminator: The site on a DNA strand at which transcription ends.
tertiary sewage treatment: A method of waste treatment that follows conventional secondary sewage treatment; nonbiodegradable pollutants and mineral nutrients are removed, usually by chemical or physical means.
tetracycline: Broad-spectrum antibiotics that interfere with protein synthesis, produced by Streptomyces spp.
tetrad: A group of four cocci.
thallus: The entire vegetative structure or body of a fungus, lichen, or alga.
thermal death point (TDP): The temperature required to kill all the bacteria in a liquid culture in 10 minutes.
thermal death time (TDT): The length of time required to kill all bacteria in a liquid culture at a given temperature.
thermoduric: Heat resistant.
thermophile: An organism whose optimum growth temperature is between 50°C and 60°C; a heat loving microbe.
thermophilic anaerobic spoilage: Spoilage of canned foods due to the growth of thermophilic bacteria.
thylakoid: A chlorophyll-containing membrane in a chloroplast. A bacterial thylakoid is also known as a chromatophore.
tincture: A solution in aqueous alcohol.
T-independent antigen: An antigen that will stimulate the formation of antibodies without the assistance of helper T cells. See also T-dependent antigen.
tinea: Fungal infection of hair, skin, or nails.
Ti plasmid: An Agrobacterium plasmid carrying genes for tumor induction in plants.
titer: An estimate of the amount of antibodies or viruses in a solution; determined by serial dilution and expressed as the reciprocal of the dilution.
toll-like receptors (TLR): Transmembrane proteins of immune cells that recognize pathogens and activate an immune response directed against those pathogens.
topoisomerase: Enzyme that relaxes supercoiling of DNA ahead of replication fork; separates DNA circles at the end of DNA replication.
total magnification: The magnification of a microscopic specimen, determined by multiplying the ocular lens magnification by the objective lens magnification.
toxemia: The presence of toxins in the blood.
toxigenicity: The capacity of a microorganism to produce a toxin.
toxin: Any poisonous substance produced by a microorganism.
toxoid: An inactivated toxin.
trace element: A chemical element required in small amounts for growth.
transamination: The transfer of an amino group from an amino acid to another organic acid.
transcription: The process of synthesizing RNA from a DNA template.
transduction: The transfer of DNA from one cell to another by a bacteriophage. See also generalized transduction; specialized transduction.
transferrin: A human iron-binding protein that reduces iron available to a pathogen.
transfer RNA (tRNA): The type of RNA molecule that brings amino acids to the ribosomal site where they are incorporated into proteins.
transfer vesicle: Membrane-bound sacs that move proteins from the Golgi complex to specific areas in the cell.
transformation: (1) the process in which genes are transferred from one bacterium to another as "naked" DNA in solution. (2) The changing of a normal cell into a cancerous cell.
transient microbiota: The microorganisms that are present in an animal for a short time without causing a disease.
translation: The use of mRNA as a template in the synthesis of protein.
transmission electron microscope (TEM): An electron microscope that provides high magnifications (10,000 to 100,000 x) of thin sections of a specimen.
transport vesicle: Membrane-bound sacs that move proteins from the rough endoplasmic reticulum to the Golgi complex.
transporter protein: A carrier protein in the plasma membrane.
transposon: A small piece of DNA that can move from one DNA molecule to another.
trickling filter: A method of secondary sewage treatment in which sewage is sprayed out of rotating arms onto a bed of rocks or similar materials, exposing the sewage to highly aerobic conditions and microorganisms.
triglyceride: A simple lipid consisting of glycerol and three fatty acids.
triplex agent: A short segment of DNA that binds to a target area on a double strand of DNA blocking transcription.
trophophase: The period in the production curve of an industrial cell population in which the primary metabolites are formed; a period of rapid, logarithmic growth. See also idiophase.
trophozoite: The vegetative form of a protozoan.
tuberculin skin test: A skin test used to detect the presence of antibodies to Mycobacterium tuberculosis.
tumor necrosis factor (TNF): A polypeptide released by phagocytes in response to bacterial endotoxins; induces shock; also called cachectin.
tumor-specific transplantation antigen (TSTA): A viral antigen on the surface of a transformed cell.
turbidity: The cloudiness of a suspension.
turnover number: The number of substrate molecules acted on per enzyme molecule per second.
ubiquinone: A low-molecular weight, nonprotein carrier in an electron transport chain; also called coenzyme Q.
ultra-high-temperature (UHT) treatment: A method of treating food with high temperatures (140 to 150°C) for very short times to make the food sterile so that it can be stored at room temperature.
uncoating: The separation of viral nucleic acid from its protein coat.
undulating membrane: A highly modified flagellum on some protozoa.
use-dilution test: A method of determining the effectiveness of a disinfectant using serial dilutions.
vaccination: The process of conferring immunity by administering a vaccine; also called immunization.
vaccine: A preparation of killed, inactivated, or attenuated microorganisms or toxoids to induce artificially acquired active immunity.
vacuole: An intracellular inclusion that is surrounded by a plasma membrane in eukaryotic cells, or surrounded by a proteinaceous membrane in prokaryotic cells.
valence: The combining capacity of an atom or a molecule.
vancomycin: An antibiotic that inhibits cell wall synthesis.
variolation: An early method of vaccination using infected material from a patient.
vasodilation: Dilation or enlargement of blood vessels.
VDRL (Venereal Disease Research Laboratory) test: A rapid screening test to detect the presence of antibodies against Treponema pallidum.
vector: (1) A plasmid or virus used in genetic engineering to insert genes into a cell. (2) An arthropod that carries disease-causing organisms from one host to another.
vegetative: Referring to cells involved with obtaining nutrients, as opposed to reproduction.
vehicle transmission: The transmission of a pathogen by an inanimate reservoir.
vertical gene transfer: Transfer of genes from an organism or cell to its offspring.
vesicle: (1) A small serum-filled elevation of the skin. (2) Smooth oval bodies formed in plant roots by mycorrhizae. (3) Membrane-bound sacs found inside cells.
V factor: NAD+ or NADP+.
vibrio: (1) A curved or comma-shaped bacterium. (2) When written as a genus, a gram-negative, motile, facultatively anaerobic curved rod.
viral hemagglutination: The ability of certain viruses to cause the clumping of red blood cells in vitro.
viral hemagglutination inhibition test: A neutralization test in which antibodies against particular viruses prevent the viruses from clumping red blood cells in vitro.
viral species: A group of viruses sharing the same genetic information and ecological niche.
viremia: The presence of viruses in the blood.
virion: A complete, fully developed viral particle.
viroid: Infectious RNA.
virology: The scientific study of viruses.
virulence: The degree of pathogenicity of a microorganism.
virus: A submicroscopic, parasitic, filterable agent consisting of a nucleic acid surrounded by a protein coat.
volutin: Stored inorganic phosphate in a prokaryotic cell. See also metachromatic granule.
wandering macrophage: A macrophage that leaves the blood and migrates to infected tissue.
Western blotting: A technique that uses antibodies to detect the presence of specific proteins separated by electrophoresis.
whey: The fluid portion of milk that separates from curd.
xenobiotics: Synthetic chemicals that are not readily degraded by microorganisms.
xenodiagnosis: A method of diagnosis based on exposing a parasite-free normal host to the parasite and then examining the host for parasites.
xenotransplantation product: A tissue graft from another species; also called xenotransplant.
X factor: Substances from the heme fraction of blood hemoglobin.
yeast: Nonfilamentous, unicellular fungi.
yeast infection: Disease caused by growth of certain yeasts in a susceptible host.
zone of inhibition: The area of no bacterial growth around an antimicrobial agent in the disk-diffusion method.
zoonosis: A disease that occurs primarily in wild and domestic animals but can be transmitted to humans.
zoospore: An asexual algal spore; has two flagella.
zygospore: A sexual fungal spore characteristic of the zygomycetes.
zygote: A diploid cell produced by the fusion of two haploid gametes. Also called a fertilized egg.
(1) Tortora, Gerard J., Funke, Berdell R. and Case, Christine L., 2007, Microbiology: An Introduction, 9th Edition, Benjamin Cummings Publ.