Pharmaceutical Microbiology: Glossary, Technical Words, Terms

GLOSSARY

AB Toxins. The structure and activity of many exotoxins are based on the AB model. In this model, the B portion of the toxin is responsible for toxin binding to a cell but does not directly harm it. The A portion enters the cell and disrupts its function.

Accessory Pigments. Photosynthetic pigments such as carotenoids and phycobiliproteins that aid chlorophyll in trapping light energy.

Acid Fast. Refers to bacteria like the mycobacteria that cannot be easily decolorized with acid alcohol after being stained with dyes such as basic fuchsin.

Acid-Fast Staining. A staining procedure that differentiates between bacteria based on their ability to retain a dye when washed with an acid alcohol solution.

Acidophile. A microorganism that has its growth optimum between about pH 0 and 5.5

Acquired Immune Deficiency Syndrome (AIDS). An infectious disease syndrome caused by the human immunodeficiency virus and is characterized by the loss of a normal immune response, followed by increased susceptibility to opportunistic infections and an increased risk of some cancers.

Acquired Immune Tolerance. The ability to produce antibodies against nonself antigens while “tolerating” (not producing antibodies against) self-antigens.

Acquired Immunity. Refers to the type of specific (adaptive) immunity that develops after ex-posure to a suitable antigen or is produced after antibodies are transferred from one individual to another.

Actinobacteria. A group of Gram-positive bacteria containing the actinomycetes and their high G + C relatives.

Actinomycete. An aerobic, Gram-positive bacterium that forms branching filaments (hyphae) and asexual spores.

Actinorhizae. Associations between actinomycetes and plant roots.

Activated Sludge. Solid matter or sediment composed of actively growing microorganisms that participate in the aerobic portion of a biological sewage treatment process. The microbes readily use dissolved organic substrates and transform them into additional microbial cells and carbon dioxide.

Active Immunization. The induction of active immunity by natural exposure to a pathogen or by vaccination.

Acute Infections. Virus infections with a fairly rapid onset that last for a relatively short time.

Acute Viral Gastroenteritis. An inflammation of the stomach and intestines, normally caused by Norwalk and Norwalklike viruses, other caliciviruses, rotaviruses, and astroviruses.

Adenine. A purine derivative, 6-aminopurine, found in nucleosides, nucleotides, coenzymes, and nucleic acids.

Adenosine Diphosphate (ADP). The nucleoside diphosphate usually formed upon the break-down of ATP when it provides enregy for work.

Adenosine 5′-triphosphate (ATP). The triphosphate of the nucleoside adenosine, which is a high energy molecule or has high phosphate group transfer potential and serves as the cell’s major form of energy currency.

Adhesin. A molecular component on the surface of a microorganism that is involved in adhesion to a substratum or cell. Adhesion to a specific host issue usually is a preliminary stage in pathogenesis, and adhesins are important virulence factors.

Adjuvant. Material added to an antigen to increase its immunogenicity. Common examples are alum, killed Bordetella pertussis, and an oil emulsion of the antigen, either alone (Freund’s incomplete adjuvant) or with killed mycobacteria (Freund’s complete adjuvant).

Aerobe. An organism that grows in the presence of atmospheric oxygen.

Aerobic Anoxygenic Photosynthesis. Photosynthetic process in which electron donors such as organic matter or sulfide, which do not result in oxygen evolution, are used under aerobic condi-tions.

Aerobic Respiration. A metabolic process in which molecules, often organic, are oxidized with oxygen as the final electron acceptor.

Aerotolerant Anaerobes. Microbes that grow equally well whether or not oxygen is present.

Aflatoxin. A polyketide secondary fungal metabolite that can cause cancer.

Agar. A complex sulfated polysaccharide, usually from red algae, that is used as a solidifying agent in the preparation of culture media.

Agglutinates. The visible aggregates or clumps formed by an agglutination reaction.

Agglutination Reaction. The formation of an insoluble immune complex by the cross-linking of cells or particles.

Airborne Transmission. The type of infectious organism transmission in which the pathogen is truly suspended in the air and travels over a meter or more from the source to the host.

Alkinetes. Specialized, nonmotile, dormant, thick-walled resting cells formed by some cyanobacteria.

Alga. A common term for a series of unrelated groups of photosynthetic eucaryotic micro-organisms lacking multicellular sex organs (except for the charophytes) and conducting vessels.

Algicide. An agent that kills algae.

Alkalophile. A microorganism that grows best at pHs from about 8.5 to 11.5.

Allergen. A substance capable of inducing allergy or specific susceptibility.

Alpha Hemolysis. A greenish zone of partial clearing around a bacteria colony growing on blood agar.

Alpha-proteobacteria. One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. This group contains most of the oligotrophic proteobacteria ; some have unusual metabolic modes such as methylotrophy, chemolithotrophy, and nitrogen fixing ability. Many have distinctive morphological features.

Alveolar Macrophage. A vigorously phagocytic macrophage located on the epithelial surface of the lung alveoli where it ingests inhaled particulate matter and microorganisms.

Amensalism. A relationship in which the product of one organism has a negative effect on another organism.

Ames Test. A test that uses a special Salmonella strain to test chemicals for mutagenicity and potential carcinogenicity.

Amino Acid Activation. The initial stage of protein synthesis in which amino acids are attached to transfer RNA molecules.

Aminoglycoside Antibiotics. A group of antibiotics synthesized by Streptomyces and Micromonospora, which contain a cyclohexane ring and amino sugars; all aminoglycoside antibi-otics bind to the small ribosomal subunit and inhibit protein synthesis.

Amphibolic Pathways. Metabolic pathways that function both catabolically and anabolically.

Amphitrichous. A cell with a single flagellum at each end.

Amphotericin B. An antibiotic from a strain of Streptomyces nodosus that is used to treat sys-temic fungal infections; it also is used topically to treat candidiasis.

Anaerobe. An organism that grows in the absence of free oxygen.

Anaerobic Digestion. The microbiological treatment of sewage wastes under anaerobic condi-tions to produce methane.

Anaerobic Respiration. An erergy-yielding process in which the electron transport chain ac-ceptor is an inorganic molecule other than oxygen.

Anammox Process. The coupled use of nitrite as an electron acceptor and ammonium ion as a donor under anaerobic conditions to yield nitrogen gas.

Anaphylaxis. An immediate (type I) hypersensitivity reaction following exposure of a sensi-tized individual to the appropriate antigen. Mediated by reagin antibodies, chiefly IgE.

Anthrax. An infectious disease of animals caused by ingesting Bacillus anthracis spores. Can also occur in humans and is sometimes called woolsorter’s disease.

Antibiotic. A microbial product or its derivative that kills susceptible microorganisms or inhib-its their growth.

Antimetabolite. A compound that blocks metabolic pathways function by competitively inhibit-ing a key enzyme’s use of a metabolite because it closely resembles the normal enzyme substrate.

Antimicrobial Agent. An agent that kills microorganisms or inhibits their growth.

Antisepsis. The prevention of infection or sepsis.

Antiseptic. Chemical agents applied to tissue to prevent infection by killing or inhibiting patho-gens.

Antitoxin. An antibody to a microbial toxin, usually a bacterial exotoxin, that combines specifi-cally with the toxin, in vivo and in vitro, neutralizing the toxin.

Apoptosis. Programmed cell death. The fragmentation of a cell into membrane-bound particles that are eliminated by phagocytosis. Apoptosis is a physiological suicide mechanism that pre-serves homeostasis and occurs during normal tissue turnover. It causes cell death in pathological circumstances, such as exposure to low concentrations of xenobiotics and infections by HIV and various other viruses.

Artificially Acquired Active Immunity. The type of immunity that results from immunizing an animal with a vaccine. The immunized animal now produces its own antibodies and activated lymphocytes.

Artificially Acquired Passive Immunity. The type of immunity that results from introducing into an animal antibodies that have been produced either in another animal or by in vitro methods. Immunity is only temporary.

Ascocarp. A multicellular structure in ascomycetes lined with specialized cells called asci in which nuclear fusion and meiosis produce ascospores. An ascocarp can be open or closed and may be referred to as a fruiting body.

Ascogenous Hypha. A specialized hypha that gives rise to one or more asci.

Ascomycetes. A division of fungi that form ascospores.

Ascus. A specialized cell, characteristic of the ascomycetes, in which two haploid nuclei fuse to produce a zygote, which immediately divides by meiosis ; at maturity an ascus will contain ascospores.

Aspergillosis. A fungal disease caused by species of Aspergillus.

Atomic Force Microscope. A type of scanning probe microscope that images a surface by mov-ing a sharp probe over the surface at a constant distance : a very small amount of force is exerted on the tip and probe movement is followed with a laser.

Attenuation. (1) A mechanism for the regulation of transcription of some bacterial operons by aminoacyl-tRNAs. (2) A procedure that reduces or abolishes the virulence of a pathogen without altering its immunogenicity.

Attenuator. A rho-independent termination site in the leader sequence that is involved in attenua-tion.

Autoclave. An apparatus for sterilizing objects by the use of steam under pressure. Its develop-ment tremendously stimulated the growth of microbiology.

Autogenous Infection. An infection that results from a patient’s own microbiota, regardless of whether the infecting organism became part of the patient’s microbiota subsequent to admission to a clinical care facility.

Autoimmune Disease. A disease produced by the immune system attacking self-antigens. Autoimmune disease results from the activation of self-reactive T and B cells that damage tissues after stimulation by genetic or environmental triggers.

Autoimmunity. Autoimmunity is a condition characterized by the presence of serum autoantibodies and self-reactive lymphocytes. It may be benign or pathogenic. Autoimmunity is a normal conse-quence of aging ; is readily inducible by infectious agents, organisms, or drugs ; and is potentially reversible in that it disappears when the offending “agent” is removed or eradicated.

Autotroph. An organism that uses CO₂ as its sole or principal source of carbon.

Auxotroph. A mutated prototroph that lacks the ability to synthesize an essential nutrient ; and, therefore, must obtain it or a precursor from its surroundings.

Axenic. Not contaminated by any foreign organisms ; the term is used in reference to pure micro-bial cultures or to germfree animals.

Bacillus. A rod-shaped bacterium.

Bacteremia. The presence of viable bacteria in the blood.

Bacteria. The domain that contains procaryotic cells with primarily diacyl glycerol diesters in their membranes and with bacterial rRNA. Bacteria also is a general term for organisms that are composed of procaryotic cells and are not multicellular.

Bacterial Artificial Chromosome (BAC). A cloning vector constructed from the E. coli F-factor plasmid that is used to clone foreign DNA fragments in E. coli.

Bacterial Vaginosis. Bacterial vaginosis is a sexually trasmitted disease caused by Gardnerella vaginalis, Mobiluncus spp., Mycoplasma hominis, and various anaerobic bacteria. Although a mild disease it is a risk factor for obstetric infections and pelvic inflammatory disease.

Bactericide. An agent that kills bacteria.

Bacteriochlorophyll. A modified chlorophyll that serves as the primary light-trapping pigment in purple and green photosynthetic bacteria.

Bacteriocin. A protein produced by a bacterial strain that kills other closely related strains.

Bacteriophage. A virus that uses bacteria as its host ; often called a phage.

Bacteriophage (phage) Typing. A technique in which strains of bacteria are identified based on their susceptibility to bacteriophages.

Bacteriostatic. Inhibiting the growth and reproduction of bacteria.

Bacteroid. A modified, often pleomorphic, bacterial cell within the root nodule cells of legumes; after transformation into a symbiosome it carries out nitrogen fixation.

Baeocytes. Small, spherical, reproductive cells produced by pleurocapsalean cyanobacteria through multiple fission.

Balanced Growth. Microbial growth in which all cellular constituents are synthesized at con-stant rates relative to eath other.

Balanitis. Inflammation of the glans penis usually associated with Candida fungi ; a sexually transmitted disease.

Barophilic or Barophile. Organisms that prefer or require high pressures for growth and repro-duction.

Barotolerant. Organisms that can grow and reproduce at high pressures but do not require them.

Basal Body. The cylindrical structure at the base of procaryotic and eucaryotic flagella that attaches them to the cell.

Batch Culture. A culture of microorganisms produced by inoculating a closed culture vessel containing a single batch of medium.

B-cell Antigen Receptor (BCR). A transmembrane immunoglobulin complex on the surface of a B cell that binds an antigen and stimulates the B cell. It is composed of a membrane-bound immunoglobulin, usually IgD or a modified IgM, complexed with another membrane protein (the Ig-α/Ig-β heterodimer).

Beta Hemolysis. A zone of complete clearing around a bacterial colony growing on blood agar. The zone does not change significantly in color.

β-Oxidation Pathway. The major pathway of fatty acid oxidation to produce NADH, FADH₂, and acetyl coenzyme A.

Beta-proteobacteria. One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Members of this subgroup are similar to the alpha-proteobacteria metabolically, but tend to use substances that diffuse from organic matter decomposition in anaerobic zones.

Binal Symmetry. The symmetry of some virus capsids (e.g., those of complex phages) that is a combination of icosahedral and helical symmetry.

Binary Fission. Asexual reproduction in which a cell or an organism separates into two cells.

Bioaugmentation. Addition of pregrown microbial cultures to an environment to perform a specific task.

Biochemical Oxygen Demand (BOD). The amount of oxygen used by organisms in water un-der certain standard conditions ; it provides an index of the amount of microbially oxidizable organic matter present.

Biodegradation. The breakdown of a complex chemical through biological processes that can result in minor loss of functional groups, fragmentation into larger constituents, or complete breakdown to carbon dioxide and minerals. Often the term refers to the undesired microbial-mediated destruction of materials such as paper, paint, and textiles.

Biofilms. Organized microbial systems consisting of layers of microbial cells associated with surfaces, often with complex structural and functional characteristics. Biofilms have physical/ chemical gradients that influence microbial metabolic processes. They can form on inanimate devices (catheters, medical prosthetic devices) and also cause fouling (e.g., of ships’ hulls, water pipes, cooling towers).

Biogeochemical Cycling. The oxidation and reduction of substances carried out by living organisms and/or abiotic processes that results in the cycling of elements within and between different parts of the ecosystem (the soil, aquatic environment, and atomshpere).

Bioinsecticide. A pathogen that is used to kill or disable unwanted insect pests. Bacteria, fungi, or viruses are used, either directly or after manipulation, to control insect populations.

Biologic Transmission. A type of vector-borne transmission in which a pathogen goes through some morphological or physiological change within the vector.

Bioluminescence. The production of light by living cells, often through the oxidation of mol-ecules by the enzyme luciferase.

Biopesticide. The use of a microorganism or another biological agent to control a specific pest.

Bioremediation. The use of biologically mediated processes to remove or degrade pollutants from specific environments. Bioremediation can be carried out by modification of the environ-ment to accelerate biological processes, either with or without the addition of specific microor-ganisms.

Biosensor. The coupling of a biological process with production of an electrical signal or light to detect the presence of particular substances.

Bioterrorism. The intentional or threatened use of viruses, bacteria, fungi, or toxins from living organisms to produce death or disease in humans, animals, and plants.

Biotransformation or Microbial Transformation. The use of living organisms to modify sub-stances that are not normally used for growth.

Black Peidra. A fungal infection caused by Piedraia hortae that forms hard black nodules on the hairs of the scalp.

Blastomycosis. A systemic fungal infection caused by Blastomyces dermatitidis and marked by suppurating tumors in the skin or by lesions in the lungs.

Botulism. A form of food poisoning caused by a neurotoxin (botulin) produced by Clostridium botulinum serotypes A-G; sometimes found in improperly canned or preserved food.

Bright-field Microscope. A microscope that illuminates the specimen directly with bright light and forms a dark image on a brighter background.

Broad-spectrum Drugs. Chemotherapeutic agents that are effective against many different kinds of pathogens.

Budding. A vegetative outgrowth of yeast and some bacteria as a means of asexual reproduction; the daughter cell is smaller than the parent.

Bulking Sludge. Sludges produced in sewage treatment that do not settle properly, usually due to the development of filamentous microorganisms.

Butanediol Fermentation. A type of fermentation most often found in the family Enterobacteriaceae in which 2, 3-butanediol is a major product; acetoin is an intermediate in the pathway and may be detected by the Voges-Proskauer test.

Candidiasis. An infection caused by Candida species of dimorphic fungi, commonly involving the skin.

Capsule. A layer of well-organized material, not easily washed off, lying outside the bacterial cell wall.

Carboxysomes. Polyhedral inclusion bodies that contain the CO₂ fixation enzyme ribulose 1, 5-bisphosphate carboxylase; found in cyanobacteria, nitrifying bacteria, and thiobacilli.

Carrier. An infected individual who is a potential source of infection for others and plays an important role in the epidemiology of a disease.

Caseous Lesion. A lesion resembling cheese or curd; cheesy. Most caseous lesions are caused by M. tuberculosis.

Casual Carrier. An individual who harbors an infectious organism for only a short period.

Cathelicidins. Antimicrobial peptides that are produced by skin cells and kill bacterial patho-gens. They destroy invaders by either punching holes in their membranes or solubilizing mem-branes through detergent-like action.

Cellulitis. A diffuse spreading infection of subcutaneous skin tissue caused by streptococci, staphylococci, or other organisms. The tissue is inflamed with edema, redness, pain, and inter-ference with function.

Cell Wall. The strong layer or structure that lies outside the plasma membrane; it supports and protects the membrane and gives the cell shape.

Cephalosporin. A group of β-lactam antibiotics derived from the fungus Cephalosporium, which share the 7-aminocephalosporanic acid nucleus.

Chancroid. A sexually transmitted disease caused by the Gram-negative bacterium Haemophilus ducreyi. Worldwide, chancroid is an important cofactor in the transmission of the AIDS virus. Also known as genital ulcer disease due to the painful circumscribed ulcers that form on the penis or entrance to the vagina.

Chemical Oxygen Demand (COD). The amount of chemical oxidation required to convert organic matter in water and waste water to CO₂.

Chemolithotropic Autotrophs. Microorganisms that oxidize reduced inorganic compounds to derive both energy and electrons; CO₂ is their carbon source. Also called chemolithoautotrophs.

Chemoorganotrophic Heterotrophs. Organisms that use organic compounds as sources of energy, hydrogen, electrons, and carbon for biosynthesis.

Chemostat. A continuous culture apparatus that feeds medium into the culture vessel at the same rate as medium containing microorganisms is removed; the medium in a chemostat contains one essential nutrient in a limiting quantity.

Chemotaxis. The pattern of microbial behaviour in which the microorganism moves toward chemical attractants and/or away from repellents.

Chemotherapeutic Agents. Compounds used in the treatment of disease that destroy pathogens or inhibit their growth at concentrations low enough to avoid doing undesirable damage to the host.

Chemotrophs. Organisms that obtain energy from the oxidation of chemical compounds.

Chickenpox (varicella). A highly contagious skin disease, usually affecting 2- to 7- year-old children; it is caused by the varicella-zoster virus, which is acquired by droplet inhalation into the respiratory system.

Chlamydiae. Members of the genus Chlamydia: gram-negative, coccoid cells that reproduce only within the cytoplasmic vesicles of host cells using a life cycle that alternates between el-ementary bodies and reticulate bodies.

Chlamydial Pneumonia. A penumonia caused by Chlamydia pneumoniae. Clinically, infec-tions are mild and 50% of adults have antibodies to the chlamydiae.

Cholera. An acute infectious enteritis, endemic and epidemic in Asia, which periodically spreads to the Middle East, Africa, Southern Europe, and South America; caused by Vibrio cholerae.

Choleragen. The cholera toxin; an extremely potent protein molecule elaborated by strains of Vibrio cholerae in the small intestine after ingestion of feces-contaminated water or food. It acts on epithelial cells to cause hypersecretion of chloride and bicarbonate and an outpouring of large quantities of fluid from the mucosal surface.

Chromoblastomycosis. A chronic fungal skin infection, producing wartlike nodules that may ulcerate. It is caused by the black molds Phialophora verrucosa or Fonsecaea pedrosoi.

Cilia. Threadlike appendages extending from the surface of some protozoa that beat rhythmi-cally to propel them; cilia are membrane-bound cylinders with a complex internal array of microtubules, usually in a 9 + 2 pattern.

Classical Complement Pathway. The antibody-dependent pathway of complement activation; it leads to the lysis of pathogens and stimulates phagocytosis and other host defenses.

Classification. The arrangement of organisms into groups based on mutual similarity or evolu-tionary relatedness.

Clone. A group of genetically identical cells or organisms derived by asexual reproduction from a single parent.

Coaggregation. The collection of a variety of bacteria on a surface such as a tooth surface because of cell-to-cell recognition of genetically distinct bacterial types. Many of these interac-tions appear to be mediated by a lectin on one bacterium that interacts with a complementary carbohydrate receptor on another bacterium.

Coagulase. An enzyme that induces blood clotting; it is characteristically produced by patho-genic staphylococci.

Coccidioidomycosis. A fungal disease caused by Coccidioides immitis that exists in dry, highly alkaline soils. Also known as valley fever, San Joaquin fever, or desert rheumatism.

Coccus. A roughly spherical bacterial cell.

Cold Sore. A lesion caused by the herpes simplex virus; usually occurs on the border of the lips or nares. Also known as a fever blister or herpes labialis.

Colicin. A plasmid-encoded protein that is produced by enteric bacteria and binds to specific receptors on the cell envelope of sensitive target bacteria, where it may cause lysis or attack specific intracellular sites such as ribosomes.

Coliform. A Gram-negative, non-sporing, facultative rod that ferments lactose with gas forma-tion within 48 hours at 35°C.

Colonization. The establishment of a site of microbial reproduction on an inanimate surface or organism without necessarily resulting in tissue invasion or damage.

Colony. An assemblage of microorganisms growing on a solid surface such as the surface of an agar culture medium; the assemblage often is directly visible, but also may be seen only micro-scopically.

Colony Forming Units (CFU). The number of microorganisms that form colonies when cul-tured using spread plates or pour plates, an indication of the number of viable microorganisms in a sample.

Colorless Sulphur Bacteria. A diverse group of non-photosynthetic proteobacteria that can oxidize reduced sulfur compounds such as hydrogen sulfide. Many are lithotrophs and derive energy from sulfur oxidation. Some are unicellular, whereas others are filamentous gliding bacteria.

Combinatorial Biology. Introduction of genes from one microorganism into another microor-ganism to synthesize a new product or a modified product, especially in relation to antibiotic synthesis.

Cometabolism. The modification of a compound not used for growth by a microorganism, which occurs in the presence of another organic material that serves as a carbon and energy source.

Commensal. Living on or within another organism without injuring or benefiting the other organism.

Common Vehicle Transmission. The transmission of a pathogen to a host by means of an inanimate medium or vehicle.

Communicable Disease. A disease associated with a pathogen that can be transmitted from one host to another.

Competent. A bacterial cell that can take up free DNA fragments and incorporate them into its genome during transformation.

Competition. An interaction between two organisms attempting to use the same resource (nutri-ents, space, etc.).

Competitive Exclusion Principle. Two competing organisms overlap in resource use, which leads to the exclusion of one of the organisms.

Complex Medium. Culture medium that contains some ingredients of unknown chemical com-position.

Complex Viruses. Viruses with capsids having a complex symmetry that is neither icosahedral nor helical.

Composting. The microbial processing of fresh organic matter under moist, aerobic conditions, resulting in the accumulation of a stable humified product, which is suitable for soil improve-ment and stimulation of plant growth.

Confocal Scanning Laser Microscope (CSLM). A light microscope in which monochromatic laser-derived light scans across the specimen at a specific level and illuminates one area at a time to form an image. Stray light from other parts of the specimen is blocked out to give an image with excellent contrast and resolution.

Congenital (neonatal) Herpes. A infection of a newbown caused by transmission of the herpesvirus during vaginal delivery.

Conjugation. The form of gene transfer and recombination in bacteria that requires direct cell-to-cell contact 2. A complex form of sexual reproduction commonly employed by protozoa.

Conjugative Plasmid. A plasmid that carries the genes for sex pili and can transfer copies of itself to other bacteria during conjugation.

Conoid. A hollow cone of spirally coiled filaments in the anterior tip of certain apicomplexan protozoa.

Constitutive Mutant. A strain that produces as inducible enzyme continually, regardless of need, because of a mutation in either the operator or regulator gene.

Constructed Wetlands. Intentional creation of marshland plant communities and their associated microorganisms for environmental restoration or to purify water by the removal of bacteria, or-ganic matter, and chemicals as the water passes through the aquatic plant communities.

Consumer. An organism that feeds directly on living or dead animals, by ingestion or by phagocytosis.

Contact Transmission. Transmission of the pathogen by contact of the source or reservoir of the pathogen with the host.

Continuous Culture System. A culture system with constant environmental conditions main-tained through continual provision of nutrients and removal of wastes.

Convalescent Carrier. An individual who has recovered from an infectious disease but contin-ues to harbor large numbers of the pathogen.

Cooperation. A positive but not obiligatory interaction between two different organisms. Also called protocooperation.

Cortex. The layer of a bacterial endospore that is thought to be particularly important in confer-ring heat resistance on the endospore.

Cryptococcosis. An infection caused by the basidiomycete. Cryptococcus neoformans, which may involve the skin, lungs, brain, or meninges.

Cryptosporidiosis. Infection with protozoa of the genus Cryptosporidium. The most common symptoms are prolonged diarrhea, weight loss, fever, and abdominal pain.

Cutaneous Diphtheria. A skin disease caused by Corynebacterium diphtheriae that infects wound or skin lesions, causing a slow-healing ulceration.

Cyanobacteria. A large group of bacteria that carry out oxygenic photosynthesis using a system like that present in photosynthetic eucaryotes.

Cyst. A general term used for a specialized microbial cell enclosed in a wall. Cysts are formed by protozoa and a few bacteria. They may be dormant, resistant structures formed in response to adverse conditions or reproductive cysts that are a normal stage in the life cycle.

Cytopathic Effect. The observable change that occurs in cells as a result of viral replication. Examples include ballooning, binding together, clustering, or ever death of the cultured cells.

Cytoplasmic Matrix. The protoplasm of a cell that lies within the plasma membrane and outside any other organelles. In bacteria it is the substance between the cell membrane and the nucleoid.

Cytotoxin. A toxin or antibody that has a specific toxic action upto cells; cytotoxins are named according to the cell for which they are specific (e.g., nephrotoxin).

Dane Particle. A 42 nm spherical particle that is one of three that are seen in hepatitis B virus infections. The Dane particle is the complete virion.

Dark-Field Microscopy. Microscopy in which the specimen is brightly illuminated while the background is dark.

Death Phase. The decrease in viable microorganisms that occurs after the completion of growth in a batch culture.

Decimal Reduction Time (D or D value). The time required to kill 90% of the microorganisms or spores in a sample at a specified temperature.

Decomposer. An organism that breaks down complex materials into simpler ones, including the release of simple inorganic products. Often a decomposer such as an insect or earthworm physi-cally reduces the size of substrate particles.

Defensin. Specific peptides produced by neutrophils that permeabilize the outer and inner mem-branes of certain microorganisms, thus killing them.

Defined Medium. Culture medium made with components of known composition.

Delta-proteobacteria. One of the five subgroups of proteobacteria. Chemoorganotrophic bac-teria that usually are either predators on other bacteria or anaerobes that generate sulfide from sulfate and sulfite.

Dendrogram. A treelike diagram that is used to graphically summarize mutual similarities and relationships between organisms.

Denitrification. The reduction of nitrate to gaseous products, primarily nitrogen gas, during anaerobic respiration.

Dental Plaque. A thin film on the surface of teeth consisting of bacteria embedded in a matrix of bacterial polysaccharides, salivary glycoproteins, and other substances.

Deoxyribonucleic Acid (DNA). The nucleic acid that constitutes the genetic material of all cellu-lar organisms. It is a polynucleotide composed of deoxyribonucleotides connected by phosphodiester bonds.

Dermatomycosis. A fungal infection of the skin; the term is a general term that comprises the various forms of tinea, and it is sometimes used to specifically refer to athelete’s foot (tinea pedis).

Desert Crust. A crust formed by microbial binding of sand grains in the surface zone of desert soil; crust formation primarily involves cyanobacteria.

Detergent. An organic molecule, other than a soap, that serves as a wetting agent and emulsifier; it is normally used as cleanser. But some may be used as antimicrobial agents.

Deuteromycetes. In some classification systems, the deuteromycetes or Fungi Imperfecti are a class of fungi. These organisms either lack a sexual stage or it has not yet been discovered.

Diauxic Growth. A biphasic growth pattern or response in which a microorganism, when exposed to two nutrients, initially uses one of them for growth and then alters its metabolism to make use of the second.

Differential Interference Contrast (DIC) Microscope. A light microscope that employs two beams of plane polarized light. The beams are combined after passing through the specimen and their interference is used to create the image.

Differential Media. Culture media that distinguish between groups of microorganisms based on differences in their growth and metabolic products.

Differential Staining Procedures. Staining procedures that divide bacteria into separate groups based on staining properties.

Diffusely Adhering E. coli (DAEC). DAEC strains of E. coli adhere over the entire surface of epithelial cells and usually cause diarrheal disease in immunologically naive and malnourished children.

Dikaryotic Stage. In fungi, having pairs of nuclei within cells or compartments. Each cell con-tains two separate haploid nuclei, one from each parent.

Dinoflagellate. An algal protist characterized by two flagella used in swimming in a spinning pattern. Many are bioluminescent and an important part of marine phytoplankton, some also are important marine pathogens.

Diphtheria. An acute, highly contagious childhood disease that generally affects the membranes of the throat and less frequently the nose. It is caused by Corynebacterium diphtheriae.

Dipicolinic Acid. A substance present at high concentrations in the bacterial endspore. It is thought to contribute to the endospore’s heat resistance.

Diplococcus. A pair of cocci.

Directed or Adaptive Mutation. A mutation that seems to be chosen so the organism can better adapt to its surroundings.

Disinfectant. An agent, usually chemical, that disinfects; normally, it is employed only with inani-mate objects.

Disinfection. The killing, inhibition, or removal of microorganisms that may cause disease. It usually refers to the treatment of inanimate objects with chemicals.

Disinfection By-products (DBPs). Chlorinated organic compounds such as trihalomethanes formed during chlorine use for water disinfection. Many are carcinogens.

Dissimilatory Nitrate Reduction. The process in which some bacteria use nitrate as the electron acceptor at the end of their electron transport chain to produce ATP. The nitrate is reduced to nitrite or nitrogen gas.

Dissimilatory Reduction. The use of a substance as an electron acceptor in energy generation. The acceptor (e.g., sulfate or nitrate) is reduced but not incorporated into organic matter during biosynthetic processes.

DNA Vaccine. A vaccine that contains DNA which encodes antigenic proteins. It is injected di-rectly into the muscle; the DNA is taken up by the muscle cells and encoded protein antigens are synthesized. This produces both humoral and cell-mediated responses.