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Glossary A-F
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Pronunciation Guide
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.
(See page(s) 797)
accessory pigments  Photosynthetic pigments such as carotenoids and phycobiliproteins that aid chlorophyll in trapping light energy.
(See page(s) 196)
acetyl coenzyme A (acetyl-CoA)  A combination of acetic acid and coenzyme A that is energy rich; it is produced by many catabolic pathways and is the substrate for the tricarboxylic acid cycle, fatty acid biosynthesis, and other pathways.
(See page(s) 183)
acid dyes  Dyes that are anionic or have negatively charged groups such as carboxyls.
(See page(s) 27)
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.
(See page(s) 543)
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.
(See page(s) 28)
acidophile (as_id-o-føõl__)  A microorganism that has its growth optimum between about pH 0 and 5.5.
(See page(s) 123)
acquired enamel pellicle  A membranous layer on the tooth enamel surface formed by selectively adsorbing glycoproteins (mucins) from saliva. This pellicle confers a net negative charge to the tooth surface.
(See page(s) 934)
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.
(See page(s) 878)
acquired immune tolerance  The ability to produce antibodies against nonself antigens while "tolerating" (not producing antibodies against) self-antigens.
(See page(s) 758)
acquired immunity  Refers to the type of specific immunity that develops after exposure to a suitable antigen or is produced after antibodies are transferred from one individual to another.
(See page(s) 729)
actinobacteria (ak²tùõ-no-bak-tøer-e-ah)  A group of gram-positive bacteria containing the actinomycetes and their high G 1 C relatives.
(See page(s) 541)
actinomycete (ak²tùõ-no-mi_søet)  An aerobic, gram-positive bacterium that forms branching filaments (hyphae) and asexual spores.
(See page(s) 537)
actinorhizae  Associations between actinomycetes and plant roots.
(See page(s) 682)
activated sludge (sluj)  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.
(See page(s) 659)
activation energy  The energy required to bring reacting molecules together to reach the transition state in a chemical reaction.
(See page(s) 162)
active carrier  An individual who has an overt clinical case of a disease and who can transmit the infection to others.
(See page(s) 854)
active immunization  The induction of active immunity by natural exposure to a pathogen or by vaccination.
(See page(s) 764)
active site  The part of an enzyme that binds the substrate to form an enzyme-substrate complex and catalyze the reaction. Also called the catalytic site.
(See page(s) 162)
active transport  The transport of solute molecules across a membrane against an electrochemical gradient; it requires a carrier protein and the input of energy.
(See page(s) 101)
acute carrier  See casual carrier.
(See page(s) 854)
acute infections  Virus infections with a fairly rapid onset that last for a relatively short time.
(See page(s) 410)
acute viral gastroenteritis  An inflammation of the stomach and intestines, normally caused by Norwalk and Norwalklike viruses, other caliciviruses, rotaviruses, and astroviruses.
(See page(s) 891)
acyclovir (a-si_klo-vir)  A synthetic purine nucleoside derivative with antiviral activity against herpes simplex virus.
(See page(s) 821)
adenine (ad_e-nøen)  A purine derivative, 6-aminopurine, found in nucleosides, nucleotides, coenzymes, and nucleic acids.
(See page(s) 217)
adenosine diphosphate (ADP; ah-den_o-søen)  The nucleoside diphosphate usually formed upon the breakdown of ATP when it provides energy for work.
(See page(s) 155)
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.
(See page(s) 155)
adhesin (ad-he_zin)  A molecular component on the surface of a microorganism that is involved in adhesion to a substratum or cell. Adhesion to a specific host tissue usually is a preliminary stage in pathogenesis, and adhesins are important virulence factors.
(See page(s) 792)
adjuvant (aj_@-v@nt)  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).
(See page(s) 741)
adult T-cell leukemia  A type of white blood cell cancer caused by the HTLV-1 virus.
(See page(s) 887)
aerobe (a_er-øob)  An organism that grows in the presence of atmospheric oxygen.
(See page(s) 127)
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 conditions.
(See page(s) 614)
aerobic respiration (res²pùõ-ra_shun)  A metabolic process in which molecules, often organic, are oxidized with oxygen as the final electron acceptor. 154,
(See page(s) 173)
aerotolerant anaerobes  Microorganisms that grow equally well whether or not oxygen is present.
(See page(s) 127)
aflatoxin (af²lah-tok_sin)  A polyketide secondary fungal metabolite that can cause cancer.
(See page(s) 967)
agar (ahg_ar)  A complex sulfated polysaccharide, usually extracted from red algae, that is used as a solidifying agent in the preparation of culture media.
(See page(s) 105)
agglutinates  The visible aggregates or clumps formed by an agglutination reaction.
(See page(s) 775)
agglutination reaction (ah-gloo²tùõ-na_shun)  The formation of an insoluble immune complex by the cross-linking of cells or particles.
(See page(s) 756)
agglutinin (ah-gloo²tùõ-nin)  The antibody responsible for an agglutination reaction.
(See page(s) 756)
AIDS  See acquired immune deficiency syndrome.
(See page(s) 878)
AIDS-related complex (ARC)  A collection of symptoms such as lymphadenopathy (swollen lymph glands), fever, malaise, fatigue, loss of appetite, and weight loss. It results from an HIV infection and may progress to frank AIDS.
(See page(s) 879)
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.
(See page(s) 854)
akinetes  Specialized, nonmotile, dormant, thick-walled resting cells formed by some cyanobacteria.
(See page(s) 473)
alcoholic fermentation  A fermentation process that produces ethanol and CO2 from sugars.
(See page(s) 179)
alga (al_gah)  A common term for a series of unrelated groups of photosynthetic eucaryotic microorganisms lacking multicellular sex organs (except for the charophytes) and conducting vessels.
(See page(s) 571)
algicide (al_jùõ-søõd)  An agent that kills algae.
(See page(s) 138)
algology (al-gol_o-je)  The scientific study of algae.
(See page(s) 571)
alkalophile  A microorganism that grows best at pHs from about 8.5 to 11.5.
(See page(s) 123)
allergen (al_er-jen)  A substance capable of inducing allergy or specific susceptibility.
(See page(s) 768)
allergic contact dermatitis  An allergic reaction caused by haptens that combine with proteins in the skin to form the allergen that produces the immune response.
(See page(s) 771)
allergy (al_er-je)  See hypersensitivity.
(See page(s) 768)
allograft (al_o-graft)  A transplant between genetically different individuals of the same species.
(See page(s) 773)
allosteric enzyme (al_o-ster_ik)  An enzyme whose activity is altered by the binding of a small effector or modulator molecule at a regulatory site separate from the catalytic site; effector binding causes a conformational change in the enzyme and its catalytic site, which leads to enzyme activation or inhibition.
(See page(s) 165)
allotype  Allelic variants of antigenic determinant(s) found on antibody chains of some, but not all, members of a species, which are inherited as simple Mendelian traits.
(See page(s) 734)
alpha hemolysis  A greenish zone of partial clearing around a bacterial colony growing on blood agar.
(See page(s) 531, 797)
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.
(See page(s) 487)
alternative complement pathway  An antibody-independent pathway of complement activation that includes the C3-C9 components of the classical pathway and several other serum protein factors (e.g., factor B and properdin).
(See page(s) 716)
alveolar macrophage  A vigorously phagocytic macrophage located on the epithelial surface of the lung alveoli where it ingests inhaled particulate matter and microorganisms.
(See page(s) 711)
amantadine (ah-man_tah-den)  An antiviral compound used to prevent type A influenza infections.
(See page(s) 821)
amebiasis (amebic dysentery) (am²e-bi_ah-sis)  An infection with amoebae, often resulting in dysentery; usually it refers to an infection by Entamoeba histolytica.
(See page(s) 950)
amensalism (a-men_s@l-iz-@m)  A relationship in which the product of one organism has a negative effect on another organism.
(See page(s) 609)
American trypanosomiasis (Chagas' disease)  See trypanosomiasis.
(See page(s) 957)
Ames test  A test that uses a special Salmonella strain to test chemicals for mutagenicity and potential carcinogenicity.
(See page(s) 253)
amino acid activation  The initial stage of protein synthesis in which amino acids are attached to transfer RNA molecules.
(See page(s) 266)
aminoacyl or acceptor site (A site)  The site on the ribosome that contains an aminoacyl-tRNA at the beginning of the elongation cycle during protein synthesis; the growing peptide chain is transferred to the aminoacyl-tRNA and lengthens by an amino acid.
(See page(s) 270)
aminoglycoside antibiotics (am_ùõ-no-gli_ko-s õd)  A group of antibiotics synthesized by Streptomyces and Micromonospora, which contain a cyclohexane ring and amino sugars; all aminoglycoside antibiotics bind to the small ribosomal subunit and inhibit protein synthesis.
(See page(s) 816)
amnesic shellfish poisoning (am-ne_sik)  The disease arising in humans and animals that eat seafood such as mussels contaminated with domoic acid from diatoms. The disease produces short-term memory loss in its victims.
(See page(s) 580)
amoeboid movement  Moving by means of cytoplasmic flow and the formation of pseudopodia (temporary cytoplasmic protrusions of the cytoplasm).
(See page(s) 590)
amphibolic pathways (am_fe-bol_ik)  Metabolic pathways that function both catabolically and anabolically.
(See page(s) 176)
amphitrichous (am-fit_rùe-kus)  A cell with a single flagellum at each end.
(See page(s) 63)
amphotericin B (am_fo-ter_i-sin)  An antibiotic from a strain of Streptomyces nodosus that is used to treat systemic fungal infections; it also is used topically to treat candidiasis.
(See page(s) 820)
anabolism (ah-nab_o-lizm_)  The synthesis of complex molecules from simpler molecules with the input of energy.
(See page(s) 173)
anaerobe (an-a_er-øob)  An organism that grows in the absence of free oxygen.
(See page(s) 127)
anaerobic digestion (an_a-er-o_bik)  The microbiological treatment of sewage wastes under anaerobic conditions to produce methane.
(See page(s) 659)
anaerobic respiration (an_a-er-o_bik)  An energy-yielding process in which the electron transport chain acceptor is an inorganic molecule other than oxygen.
(See page(s) 173)
anammox process  The coupled use of nitrite as an oxidant and ammonium ion as a reductant under anaerobic conditions to yield nitrogen gas.
(See page(s) 616)
anamnestic response (an_am-nes_tik)  The recall, or the remembering, by the immune system of a prior response to a given antigen.
(See page(s) 729, 743)
anaphylaxis (an_ah-fùõ-lak_sis)  An immediate (type I) hypersensitivity reaction following exposure of a sensitized individual to the appropriate antigen. Mediated by reagin antibodies, chiefly IgE.
(See page(s) 768)
anaplerotic reactions (an_ah-plùe-rot_ik)  Reactions that replenish depleted tricarboxylic acid cycle intermediates.
(See page(s) 216)
anergy (an_@r-je)  A state of unresponsiveness to antigens. Absence of the ability to generate a sensitivity reaction to substances that are expected to be antigenic.
(See page(s) 758)
annotation  The process of determining the location of specific genes in a genome map after it has been produced by nucleic acid sequencing.
(See page(s) 347)
anogenital condylomata (venereal warts) (kon_dùõ-lo_ mah-tah)  Warts that are sexually transmitted and caused by types 6, 11, and 42 human papillomavirus. Usually occur around the cervix, vulva, perineum, anus, anal canal, urethra, or glans penis.
(See page(s) 894)
anoxic (@-nok_ sik)  Without oxygen present.
(See page(s) 635)
anoxygenic photosynthesis  Photosynthesis that does not oxidize water to produce oxygen; the form of photosynthesis characteristic of purple and green photosynthetic bacteria.
(See page(s) 199, 468)
antheridium (an_ther-id_e-um; pl., antheridia)  A male gamete-producing organ, which may be unicellular or multicellular.
(See page(s) 561, 574)
anthrax (an_thraks)  An infectious disease of animals caused by ingesting Bacillus anthracis spores. Can also occur in humans and is sometimes called woolsorter's disease.
(See page(s) 913)
antibiotic (an_tùõ-bi-ot_ik)  A microbial product or its derivative that kills susceptible microorganisms or inhibits their growth.
(See page(s) 806)
antibody (immunoglobulin) (an_tùõ-bod_e)  A glycoprotein produced in response to the introduction of an antigen; it has the ability to combine with the antigen that stimulated its production. Also known as an immunoglobulin (Ig).
(See page(s) 734)
antibody-dependent cell-mediated cytotoxicity (ADCC)  The killing of antibody-coated target cells by cells with Fc receptors that recognize the Fc region of the bound antibody. Most ADCC is mediated by NK cells that have the Fc receptor or CD16 on their surface.
(See page(s) 723)
antibody-mediated immunity  See humoral immunity.
(See page(s) 729)
anticodon triplet  The base triplet on a tRNA that is complementary to the triplet codon on mRNA.
(See page(s) 266)
antigen (an_tùõ-jen)  A foreign (nonself) substance (such as a protein, nucleoprotein, polysaccharide, or sometimes a glycolipid) to which lymphocytes respond; also known as an immunogen because it induces the immune response.
(See page(s) 731)
antigen-binding fragment (Fab)  "Fragment antigen binding." A monovalent antigen-binding fragment of an immunoglobulin molecule that consists of one light chain and part of one heavy chain, linked by interchain disulfide bonds.
(See page(s) 734)
antigenic determinant site (epitope)  See epitope.
(See page(s) 731)
antigenic drift  A small change in the antigenic character of an organism that allows it to avoid attack by the immune system.
(See page(s) 852)
antigenic shift  A major change in the antigenic character of an organism that alters it to an antigenic strain unrecognized by host immune mechanisms.
(See page(s) 852)
antigen-presenting cells  Antigen-presenting cells (APCs) are cells that take in protein antigens, process them, and present antigen fragments to B cells and T cells in conjunction with class II MHC molecules so that the cells are activated. Macrophages, B cells, dendritic cells, and Langerhans cells may act as APCs.
(See page(s) 745)
antimetabolite (an_tùõ-mùe-tab_o-løõt)  A compound that blocks metabolic pathway function by competitively inhibiting a key enzyme's use of a metabolite because it closely resembles the normal enzyme substrate.
(See page(s) 812)
antimicrobial agent  An agent that kills microorganisms or inhibits their growth.
(See page(s) 139)
antisense RNA  A single-stranded RNA with a base sequence complementary to a segment of another RNA molecule that can specifically bind to the target RNA and inhibit its activity.
(See page(s) 283)
antisepsis (an²tùõ-sep_sis)  The prevention of infection or sepsis.
(See page(s) 138)
antiseptic (an²tùõ-sep_tik)  Chemical agents applied to tissue to prevent infection by killing or inhibiting pathogens.
(See page(s) 138)
antiserum (an_tùõ-se_rum)  Serum containing induced antibodies.
(See page(s) 742)
antitoxin (an_tùõ-tok_sin)  An antibody to a microbial toxin, usually a bacterial exotoxin, that combines specifically with the toxin, in vivo and in vitro, neutralizing the toxin.
(See page(s) 756, 796)
apical complex (ap_ùõ-kal)  A set of organelles characteristic of members of the phylum Apicomplexa: polar rings, subpellicular microtubules, conoid, rhoptries, and micronemes.
(See page(s) 591)
apicomplexan (a_pùõ-kom-plek_san)  A sporozoan protist that lacks special locomotor organelles but has an apical complex and a spore-forming stage. It is either an intra- or extracellular parasite of animals; a member of the phylum Apicomplexa.
(See page(s) 591)
aplanospore (a_plan-o-spor)  A nonflagellated, nonmotile spore that is involved in asexual reproduction.
(See page(s) 573)
apoenzyme (ap_o-en_zøõm)  The protein part of an enzyme that also has a nonprotein component.
(See page(s) 161)
apoptosis (ap²o-to_sis)  Programmed cell death. The fragmentation of a cell into membrane-bound particles that are eliminated by phagocytosis. Apoptosis is a physiological suicide mechanism that preserves homeostasis and occurs during normal tissue turnover. It is responsible for cell death in pathological circumstances, such as exposure to low concentrations of xenobiotics and infections by HIV and various other viruses. Apoptotic cells display profound structural changes such as plasma membrane blebbing and nuclear collapse. DNA is cleaved into short oligonucleosomal length DNA fragments. Apoptosis usually occurs after the activation ofr calcium-dependent endogenous endonuclease.
(See page(s) 750, 881)
aporepressor  An inactive form of the repressor protein, which becomes the active repressor when the corepressor binds to it.
(See page(s) 276)
arbuscular mycorrhizal (AM) fungi  The mycorrhizal fungi in a symbiotic fungus-root association that penetrate the outer layer of the root, grow intracellularly, and form characteristic much-branched hyphal structures called arbuscules.
(See page(s) 681)
arbuscules  Branched, treelike structures formed in cells of plant roots colonized by endotrophic mycorrhizal fungi.
(See page(s) 681)
Archaea  The domain that contains procaryotes with isoprenoid glycerol diether or diglycerol tetraether lipids in their membranes and archaeal rRNA (among many differences).
(See page(s) 424, 451)
arthroconidium (ar_thro-ko-nid_e-um; pl., arthroconidia)  A thallic conidium released by the fragmentation or lysis of hypha. It is not notably larger than the parental hypha, and separation occurs at a septum.
(See page(s) 557)
arthrospore (ar_thro-spøor)  A spore resulting from the fragmentation of a hypha.
(See page(s) 557)
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.
(See page(s) 730)
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.
(See page(s) 731)
ascocarp (as_ko-karp)  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.
(See page(s) 561)
ascogenous hypha  A specialized hypha that gives rise to one or more asci.
(See page(s) 561)
ascogonium (as²ko-go_ne-um; pl., ascogonia)  The receiving (female) organ in ascomycetous fungi which, after fertilization, gives rise to ascogenous hyphae and later to asci and ascospores.
(See page(s) 561)
ascomycetes (as²ko-mi-se_tøez)  A division of fungi that form ascospores.
(See page(s) 560)
ascospore (as_ko-spor)  A spore contained or produced in an ascus.
(See page(s) 558)
ascus (as_kus)  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.
(See page(s) 561)
aseptic meningitis syndrome  See meningitis.
(See page(s) 902)
aspergillosis (as²per-jil-o_sis)  A fungal disease caused by species of Aspergillus.
(See page(s) 948)
assimilatory reduction  The reduction of an inorganic molecule to incorporate it into organic material. No energy is made available during this process.
(See page(s) 210, 211, 614)
associative nitrogen fixation  Nitrogen fixation by bacteria in the plant root zone (rhizosphere).
(See page(s) 675)
athlete's foot  See tinea pedis.
(See page(s) 944)
atomic force microscope  A type of scanning probe microscope that images a surface by moving 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.
(See page(s) 38)
ATP-binding cassette transporters (ABC transporters)  Membrane protein complexes that use ATP energy to move substances across membranes without modifying the compound being transported. They require an extracytoplasmic substrate-binding protein for proper function.
(See page(s) 101)
attenuation (ah-ten²u-a_shun)  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.
(See page(s) 281, 766)
attenuator  A rho-independent termination site in the leader sequence that is involved in attenuation.
(See page(s) 279)
autoclave (aw_to-kløav)  An apparatus for sterilizing objects by the use of steam under pressure. Its development tremendously stimulated the growth of microbiology.
(See page(s) 140)
autogenous infection (aw-toj_e-nus)  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.
(See page(s) 866)
autoimmune disease (aw²to-ùõ-møun_)  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.
(See page(s) 772)
autoimmunity (aw²to-ùõ-mun_ùõ-te)  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 consequence 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.
(See page(s) 772)
autolysins (aw-tol_ùõ-sins)  Enzymes that partially digest peptidoglycan in growing bacteria so that the peptidoglycan can be enlarged.
(See page(s) 223)
autotroph (aw_to-trøof)  An organism that uses CO2 as its sole or principal source of carbon.
(See page(s) 96)
auxotroph (awk_so-trøof)  A mutated prototroph that lacks the ability to synthesize an essential nutrient and therefore must obtain it or a precursor from its surroundings.
(See page(s) 245)
axial filament  The organ of motility in spirochetes. It is made of axial fibrils or periplasmic flagella that extend from each end of the protoplasmic cylinder and overlap in the middle of the cell. The outer sheath lies outside the axial filament.
(See page(s) 66, 479)
bacillus (bah-sil_lus)  A rod-shaped bacterium.
(See page(s) 43)
bacteremia (bak_ter-e_me-ah)  The presence of viable bacteria in the blood.
(See page(s) 793)
Bacteria (bak-te_re-@)  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.
(See page(s) 424)
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.
(See page(s) 335)
bacterial (septic) meningitis  See meningitis.
(See page(s) 902)
bacterial vaginosis (bak-te_re-@l vaj_ùõ-no_sis)  Bacterial vaginosis is a sexually transmitted 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.
(See page(s) 914)
bactericide (bak-tøer_ùõ-sid)  An agent that kills bacteria.
(See page(s) 138)
bacteriochlorophyll (bak-te_re-o-klo_ro-fil)  A modified chlorophyll that serves as the primary light-trapping pigment in purple and green photosynthetic bacteria.
(See page(s) 199)
bacteriocin (bak-te_re-o-sin)  A protein produced by a bacterial strain that kills other closely related strains.
(See page(s) 297, 712, 972)
bacteriophage (bak-te_re-o-føaj_)  A virus that uses bacteria as its host; often called a phage.
(See page(s) 364, 382)
bacteriophage (phage) typing  A technique in which strains of bacteria are identified based on their susceptibility to a variety of bacteriophages.
(See page(s) 842)
bacteriostatic (bak-te_re-o-stat_ik)  Inhibiting the growth and reproduction of bacteria.
(See page(s) 138)
bacteroid (bak_tùe-roid)  A modified, often pleomorphic, bacterial cell within the root nodule cells of legumes; after transformation into a symbiosome it carries out nitrogen fixation.
(See page(s) 676)
baeocytes  Small, spherical, reproductive cells produced by pleurocapsalean cyanobacteria through multiple fission.
(See page(s) 475)
balanced growth  Microbial growth in which all cellular constituents are synthesized at constant rates relative to each other.
(See page(s) 114)
balanitis (bal_ah-ni_tis)  Inflammation of the glans penis usually associated with Candida fungi; a sexually transmitted disease.
(See page(s) 950)
barophilic (bar_o-fil_ik) or barophile  Organisms that prefer or require high pressures for growth and reproduction.
(See page(s) 129, 644)
barotolerant  Organisms that can grow and reproduce at high pressures but do not require them.
(See page(s) 129, 624)
basal body  The cylindrical structure at the base of procaryotic and eucaryotic flagella that attaches them to the cell.
(See page(s) 64, 90)
base analogs  Molecules that resemble normal DNA nucleotides and can substitute for them during DNA replication, leading to mutations.
(See page(s) 246)
basic dyes  Dyes that are cationic, or have positively charged groups, and bind to negatively charged cell structures. Usually sold as chloride salts.
(See page(s) 27)
basidiocarp (bah-sid_e-o-karp_)  The fruiting body of a basidiomycete that contains the basidia.
(See page(s) 561)
basidiomycetes (bah-sid_e-o-mi-se_tøez)  A division of fungi in which the spores are born on club-shaped organs called basidia.
(See page(s) 561)
basidiospore (bah-sid_e-o-spøor)  A spore born on the outside of a basidium following karyogamy and meiosis.
(See page(s) 558)
basidium (bah-sid_e-um; pl., basidia)  A structure that bears on its surface a definite number of basidiospores (typically four) that are formed following karyogamy and meiosis. Basidia are found in the basidiomycetes and are usually club-shaped.
(See page(s) 561)
basophil (ba_so-fil)  A phagocytic leukocyte whose granules stain bluish-black with a basic dye. It has a segmented nucleus. The granules contain histamine and heparin.
(See page(s) 707)
batch culture  A culture of microorganisms produced by inoculating a closed culture vessel containing a single batch of medium.
(See page(s) 113)
B cell, also known as a B lymphocyte  A type of lymphocyte derived from bone marrow stem cells that matures into an immunologically competent cell under the influence of the bursa of Fabricius in the chicken and bone marrow in nonavian species. Following interaction with antigen, it becomes a plasma cell, which synthesizes and secretes antibody molecules involved in humoral immunity. 705,
(See page(s) 751)
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-a/Ig-b heterodimer).
(See page(s) 751)
benthic (ben_thic)  Pertaining to the bottom of the sea or another body of water.
(See page(s) 571)
beta hemolysis  A zone of complete clearing around a bacterial colony growing on blood agar. The zone does not change significantly in color.
(See page(s) 532, 797)
b-oxidation pathway  The major pathway of fatty acid oxidation to produce NADH, FADH2, and acetyl coenzyme A.
(See page(s) 192)
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.
(See page(s) 495)
binal symmetry  The symmetry of some virus capsids (e.g., those of complex phages) that is a combination of icosahedral and helical symmetry.
(See page(s) 376)
binary fission  Asexual reproduction in which a cell or an organism separates into two cells.
(See page(s) 490, 573, 586)
binomial system  The nomenclature system in which an organism is given two names; the first is the capitalized generic name, and the second is the uncapitalized specific epithet.
(See page(s) 426)
biochemical oxygen demand (BOD)  The amount of oxygen used by organisms in water under certain standard conditions; it provides an index of the amount of microbially oxidizable organic matter present.
(See page(s) 657)
biodegradation (bi_o-deg_rah-da_shun)  The breakdown of a complex chemical through biological processes that can result in minor loss of functional groups, fragmentation into larger constitutents, 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.
(See page(s) 1010)
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).
(See page(s) 620, 920)
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 atmosphere).
(See page(s) 611)
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.
(See page(s) 1018)
biologic transmission  A type of vector-borne transmission in which a pathogen goes through some morphological or physiological change within the vector.
(See page(s) 858)
bioluminescence (bi_o-loo_mùõ-nes_@ns)  The production of light by living cells, often through the oxidation of molecules by the enzyme luciferase.
(See page(s) 505)
biomagnification  The increase in concentration of a substance in higher-level consumer organisms.
(See page(s) 618)
biopesticide  The use of a microorganism or another biological agent to control a specific pest.
(See page(s) 1018)
bioremediation  The use of biologically mediated processes to remove or degrade pollutants from specific environments. Bioremediation can be carried out by modification of the environment to accelerate biological processes, either with or without the addition of specific microorganisms.
(See page(s) 1012)
biosensor  The coupling of a biological process with production of an electrical signal or light to detect the presence of particular substances.
(See page(s) 1017)
biosynthesis  See anabolism.
(See page(s) 173)
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.
(See page(s) 863)
biotransformation or microbial transformation  The use of living organisms to modify substances that are not normally used for growth.
(See page(s) 1009)
black peidra (pe-a_drah)  A fungal infection caused by Piedraia hortae that forms hard black nodules on the hairs of the scalp.
(See page(s) 943)
blastomycosis (blas²to-mi-ko_sis)  A systemic fungal infection caused by Blastomyces dermatitidis and marked by suppurating tumors in the skin or by lesions in the lungs.
(See page(s) 946)
blastospore (blas_to-spøor)  A spore formed by budding from a hypha.
(See page(s) 557)
B lymphocyte  See B cell.
(See page(s) 705, 751)
botulism (boch_oo-lizm)  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.
(See page(s) 929)
bright-field microscope  A microscope that illuminates the specimen directly with bright light and forms a dark image on a brighter background.
(See page(s) 19)
Bright's disease  See glomerulonephritis.
(See page(s) 905)
broad-spectrum drugs  Chemotherapeutic agents that are effective against many different kinds of pathogens.
(See page(s) 808)
bronchial-associated lymphoid tissue (BALT)  The type of defensive tissue found in the lungs. Part of the nonspecific immune system.
(See page(s) 710)
bronchial asthma  An example of an atopic allergy involving the lower respiratory tract.
(See page(s) 769)
bubo (bu_bo)  A tender, inflamed, enlarged lymph node that results from a variety of infections.
(See page(s) 911)
bubonic plague  See plague.
(See page(s) 911)
budding  A vegetative outgrowth of yeast and some bacteria as a means of asexual reproduction; the daughter cell is smaller than the parent.
(See page(s) 490)
bulking sludge  Sludges produced in sewage treatment that do not settle properly, usually due to the development of filamentous microorganisms.
(See page(s) 659)
bursa of Fabricius (b@r_s@ f@-bris_e-@s)  Found in birds; the blind saclike structure located on the posterior wall of the cloaca; it performs a thymuslike function. A primary lymphoid organ where B-cell maturation occurs. Bone marrow is the equivalent in mammals.
(See page(s) 708)
burst  See rise period.
(See page(s) 383)
burst size  The number of phages released by a host cell during the lytic life cycle.
(See page(s) 383)
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.
(See page(s) 181, A-18)
Calvin cycle  The main pathway for the fixation (or reduction and incorporation) of CO2 into organic material by photoautotrophs during photosynthesis; it also is found in chemolithoautotrophs.
(See page(s) 207, A-20)
cancer (kan_ser)  A malignant tumor that expands locally by invasion of surrounding tissues, and systemically by metastasis.
(See page(s) 411)
candidal vaginitis  Vaginitis caused by Candida species.
(See page(s) 950)
candidiasis (kan_dùõ-di_ah-sis)  An infection caused by Candida species of dimorphic fungi, commonly involving the skin.
(See page(s) 949)
capsid (kap_sid)  The protein coat or shell that surrounds a virion's nucleic acid.
(See page(s) 369)
capsomer (kap_so-mer)  The ring-shaped morphological unit of which icosahedral capsids are constructed.
(See page(s) 390)
capsule  A layer of well-organized material, not easily washed off, lying outside the bacterial cell wall.
(See page(s) 61)
carboxysomes  Polyhedral inclusion bodies that contain the CO2 fixation enzyme ribulose 1,5-bisphosphate carboxylase; found in cyanobacteria, nitrifying bacteria, and thiobacilli.
(See page(s) 51, 207)
caries (kar_e-øez)  Tooth decay.
(See page(s) 936)
carotenoids (kah-rot_e-noids)  Pigment molecules, usually yellowish in color, that are often used to aid chlorophyll in trapping light energy during photosynthesis.
(See page(s) 196)
carrier  An infected individual who is a potential source of infection for others and plays an important role in the epidemiology of a disease.
(See page(s) 854)
caseous lesion (ka_se-us)  A lesion resembling cheese or curd; cheesy. Most caseous lesions are caused by M. tuberculosis.
(See page(s) 908)
casual carrier  An individual who harbors an infectious organism for only a short period.
(See page(s) 854)
catabolism (kah-tab_o-lizm)  That part of metabolism in which larger, more complex molecules are broken down into smaller, simpler molecules with the release of energy.
(See page(s) 173)
catabolite repression (kah-tab_o-løõt)  Inhibition of the synthesis of several catabolic enzymes by a metabolite such as glucose.
(See page(s) 281)
catalyst (kat_ah-list)  A substance that accelerates a reaction without being permanently changed itself.
(See page(s) 161)
catalytic site  See active site.
(See page(s) 162)
catheter (kath_ ùe-ter)  A tubular surgical instrument for withdrawing fluids from a cavity of the body, especially one for introduction into the bladder through the urethra for the withdrawal of urine.
(See page(s) 827)
cat-scratch disease (CSD)  A loosely defined syndrome caused by either of the following gram-negative bacilli: Bartonella (Rochalimaea) henselae or Afipia felis. The typical case of CSD is self-limiting, with abatement of symptoms over a period of days to weeks.
(See page(s) 914)
CD95 pathway  The CD95 receptor is found on many nucleated eucaryotic cells. When the receptor is bound to a specific ligand (CD95L), the CD95-CD95L complex activates several cytoplasmic proteins that initiate a cellular suicide cascade leading to apoptosis.
(See page(s) 750)
cell cycle  The sequence of events in a cell's growth-division cycle between the end of one division and the end of the next. In eucaryotic cells, it is composed of the G1 period, the S period in which DNA and histones are synthesized, the G2 period, and the M period (mitosis).
(See page(s) 87, 285)
cell-mediated immunity  The type of immunity that results from T cells coming into close contact with foreign cells or infected cells to destroy them; it can be transferred to a nonimmune individual by the transfer of cells.
(See page(s) 729)
cellular slime molds  Slime molds with a vegetative phase consisting of amoeboid cells that aggregate to form a multicellular pseudoplasmodium; they belong to the division Acrasiomycota.
(See page(s) 565)
cellulitis (sel²u-li_tis)  A diffuse spreading infection of subcutaneous skin tissue caused by streptococci, staphylococci, or other organisms. The tissue is inflamed with edema, redness, pain, and interference with function.
(See page(s) 903)
cell wall  The strong layer or structure that lies outside the plasma membrane; it supports and protects the membrane and gives the cell shape.
(See page(s) 88)
cephalosporin (sef_ah-lo-spøor_in)  A group of b-lactam antibiotics derived from the fungus Cephalosporium, which share the 7-aminocephalosporanic acid nucleus.
(See page(s) 814)
chancre (shang_ker)  The primary lesion of syphilis, occurring at the site of entry of the infection.
(See page(s) 923)
chancroid (shang_kroid)  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.
(See page(s) 914)
chemical oxygen demand (COD)  The amount of chemical oxidation required to convert organic matter in water and wastewater to CO2.
(See page(s) 657)
chemiosmotic hypothesis (kem_e-o-os-mot_ik)  The hypothesis that a proton gradient and an electrochemical gradient are generated by electron transport and then used to drive ATP synthesis by oxidative phosphorylation.
(See page(s) 187)
chemoheterotroph (ke_mo-het_er-o-trøof_)  See chemoorganotrophic heterotrophs.
(See page(s) 98)
chemolithotroph (ke_mo-lith_o-trøof)  See chemolithotrophic autotrophs.
(See page(s) 98, 193)
chemolithotrophic autotrophs  Microorganisms that oxidize reduced inorganic compounds to derive both energy and electrons; CO2 is their carbon source. Also called chemolithoautotrophs.
(See page(s) 98)
chemoorganotrophic heterotrophs  Organisms that use organic compounds as sources of energy, hydrogen, electrons, and carbon for biosynthesis.
(See page(s) 98)
chemoreceptors  Special protein receptors in the plasma membrane or periplasmic space that bind chemicals and trigger the appropriate chemotaxic response.
(See page(s) 67)
chemostat (ke_mo-stat)  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.
(See page(s) 120)
chemotaxis (ke_mo-tak_sis)  The pattern of microbial behavior in which the microorganism moves toward chemical attractants and/or away from repellents.
(See page(s) 67)
chemotherapeutic agents (ke_mo-ther-ah-pu_tik)  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.
(See page(s) 806)
chemotrophs (ke_mo-trøofs)  Organisms that obtain energy from the oxidation of chemical compounds.
(See page(s) 97)
chickenpox (varicella; chik_en-poks)  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.
(See page(s) 871)
chimera (ki-me_rah)  A recombinant plasmid containing foreign DNA, which is used as a cloning vector in genetic engineering.
(See page(s) 334)
chiral (ki_ r@l)  Having handedness: consisting of one or another stereochemical form.
(See page(s) 1010)
chitin (ki_tin)  A tough, resistant, nitrogen-containing polysaccharide forming the walls of certain fungi, the exoskeleton of arthropods, and the epidermal cuticle of other surface structures of certain protists and animals.
(See page(s) 554)
chlamydiae (kl@-mid_e-e)  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 elementary bodies and reticulate bodies.
(See page(s) 477)
chlamydial pneumonia (kl@-mid_e-@l noo-mo_ ne-@)  A pneumonia caused by Chlamydia pneumoniae. Clinically, infections are mild and 50% of adults have antibodies to the chlamydiae.
(See page(s) 914)
chlamydospore (klam_ùõ-do-spøor_)  An asexually produced, thick-walled resting spore formed by some fungi.
(See page(s) 557)
chloramphenicol (klo_ram-fen_ùõ-kol)  A broad-spectrum antibiotic that is produced by Streptomyces venezuelae or synthetically; it binds to the large ribosomal subunit and inhibits the peptidyl transferase reaction.
(See page(s) 817)
chlorophyll (klor_o-fil)  The green photosynthetic pigment that consists of a large tetrapyrrole ring with a magnesium atom in the center.
(See page(s) 196)
chloroplast (klo_ra-plast)  A eucaryotic plastid that contains chlorophyll and is the site of photosynthesis.
(See page(s) 85)
cholera (kol_er-ah)  An acute infectious enteritis, endemic and epidemic in Asia, which periodically spreading to the Middle East, Africa, Southern Europe, and South America; caused by Vibrio cholerae.
(See page(s) 930)
choleragen (kol_er-ah-gen)  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.
(See page(s) 930)
chromatin (kro_mah-tin)  The DNA-containing portion of the eucaryotic nucleus; the DNA is almost always complexed with histones. It can be very condensed (heterochromatin) or more loosely organized and genetically active (euchromatin).
(See page(s) 86)
chromoblastomycosis (kro_mo-blas_to-mi-ko_sis)  A chronic fungal infection of the skin, producing wartlike nodules that may ulcerate. It is caused by the black molds Phialophora verrucosa or Fonsecaea pedrosoi.
(See page(s) 945)
chromogen (kro_me-jen)  A colorless substrate that is acted on by an enzyme to produce a colored end product.
(See page(s) 779)
chromophore group (kro_mo-føor)  A chemical group with double bonds that absorbs visible light and gives a dye its color.
(See page(s) 27)
chromosomes (kro_mo-somz)  The bodies that have most or all of the cell's DNA and contain most of its genetic information (mitochondria and chloroplasts also contain DNA and genes).
(See page(s) 86)
chronic carrier  An individual who harbors a pathogen for a long time.
(See page(s) 854)
chrysolaminarin  The polysaccharide storage product of the chrysophytes and diatoms.
(See page(s) 577)
chytrids  A group of chytridiomycetes, which are simple terrestrial and aquatic fungi that produce motile zoospores with single, posterior, whiplash flagella. Also considered protists.
(See page(s) 564, 641)
cilia (sil_e-ah)  Threadlike appendages extending from the surface of some protozoa that beat rhythmically to propel them; cilia are membrane-bound cylinders with a complex internal array of microtubules, usually in a 9 1 2 pattern.
(See page(s) 89)
citric acid cycle  See tricarboxylic acid (TCA) cycle.
(See page(s) 183, A-16)
classical complement pathway  The antibody-dependent pathway of complement activation; it leads to the lysis of pathogens and stimulates phagocytosis and other host defenses.
(See page(s) 758)
classification  The arrangement of organisms into groups based on mutual similarity or evolutionary relatedness.
(See page(s) 422)
clone (kløon)  A group of genetically identical cells or organisms derived by asexual reproduction from a single parent.
(See page(s) 228, 741)
clostridial myonecrosis (klo-strid_e-al mi²o-ne-kro_sis)  Death of individual muscle cells caused by clostridia. Also called gas gangrene.
(See page(s) 915)
cluster of differentiation molecules (CDs)  Functional cell surface proteins or receptors that can be measured in situ from peripheral blood, biopsy samples, or other body fluids. They can be used to identify leukocyte subpopulations. Some examples include interleukin-2 receptor (IL-2R), CD4, CD8, CD25, and intercellular adhesion molecule-1 (ICAM-1).
(See page(s) 733)
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 interactions appear to be mediated by a lectin on one bacterium that interacts with a complementary carbohydrate receptor on another bacterium.
(See page(s) 934)
coagulase (ko-ag_u-las)  An enzyme that induces blood clotting; it is characteristically produced by pathogenic staphylococci.
(See page(s) 529)
coccidioidomycosis (kok-sid²e-oi²do-mi-ko_sis)  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.
(See page(s) 946)
coccus (kok_us, pl. cocci, kok_si)  A roughly spherical bacterial cell.
(See page(s) 42)
code degeneracy  The genetic code is organized in such a way that often there is more than one codon for each amino acid.
(See page(s) 240)
codon (ko_don)  A sequence of three nucleotides in mRNA that directs the incorporation of an amino acid during protein synthesis or signals the start or stop of translation.
(See page(s) 240)
coenocytic (se²no-sit_ik)  Refers to a multinucleate cell or hypha formed by repeated nuclear divisions not accompanied by cell divisions.
(See page(s) 113, 556)
coenzyme (ko-en_zøõm)  A loosely bound cofactor that often dissociates from the enzyme active site after product has been formed.
(See page(s) 161)
cofactor  The nonprotein component of an enzyme; it is required for catalytic activity.
(See page(s) 161)
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.
(See page(s) 884)
colicin (kol_ùõ-sin)  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.
(See page(s) 712)
coliform (ko_lùõ-form)  A gram-negative, nonsporing, facultative rod that ferments lactose with gas formation within 48 hours at 35°C.
(See page(s) 654)
colonization (kol²@-nùõ-za_sh@n)  The establishment of a site of microbial reproduction on an inanimate surface or organism without necessarily resulting in tissue invasion or damage.
(See page(s) 792)
colony  A cluster or 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 microscopically.
(See page(s) 106)
colony forming units (CFU)  The number of microorganisms that can form colonies when cultured using spread plates or pour plates, an indication of the number of viable microorganisms in a sample.
(See page(s) 118)
Colorado tick fever  A disease that occurs in the mountainous regions of the western United States. It is caused by an RNA virus of the genus Coltivirus that is spread from ground squirrels, rabbits, and deer to humans by the tick, Dermacentor andersoni. Complications are rare.
(See page(s) 878)
colorless sulfur bacteria  A diverse group of nonphotosynthetic 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.
(See page(s) 496)
combinatorial biology  Introduction of genes from one microorganism into another microorganism to synthesize a new product or a modified product, especially in relation to antibiotic synthesis.
(See page(s) 995)
comedo (kom_ùe-do; pl., comedones)  A plug of dried sebum in an excretory duct of the skin.
(See page(s) 701)
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.
(See page(s) 1013)
commensal (kùo-men_sal)  Living on or within another organism without injuring or benefiting the other organism.
(See page(s) 606)
commensalism (kùo-men_sal-izm²)  A type of symbiosis in which one individual gains from the association and the other is neither harmed nor benefited.
(See page(s) 606)
common cold  An acute, self-limiting, and highly contagious virus infection of the upper respiratory tract that produces inflammation, profuse discharge, and other symptoms.
(See page(s) 884)
common-source epidemic  An epidemic that is characterized by a sharp rise to a peak and then a rapid, but not as pronounced, decline in the number of individuals infected; it usually involves a single contaminated source from which individuals are infected.
(See page(s) 851)
common vehicle transmission  The transmission of a pathogen to a host by means of an inanimate medium or vehicle.
(See page(s) 857)
communicable disease  A disease associated with a pathogen that can be transmitted from one host to another.
(See page(s) 854)
community  An assemblage of different types of organisms or a mixture of different microbial populations.
(See page(s) 596)
competent  A bacterial cell that can take up free DNA fragments and incorporate them into its genome during transformation.
(See page(s) 305)
competition  An interaction between two organisms attempting to use the same resource (nutrients, space, etc.).
(See page(s) 609)
competitive exclusion principle  Two competing organisms overlap in resource use, which leads to the exclusion of one of the organisms.
(See page(s) 609, 987)
complementary DNA (cDNA)  A DNA copy of an RNA molecule (e.g., a DNA copy of an mRNA).
(See page(s) 321)
complement system  A group of plasma proteins that plays a major role in an animal's defensive immune response.
(See page(s) 714, 758)
complex medium  Culture medium that contains some ingredients of unknown chemical composition.
(See page(s) 105)
complex viruses  Viruses with capsids having a complex symmetry that is neither icosahedral nor helical.
(See page(s) 369)
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 improvement and stimulation of plant growth.
(See page(s) 686)
compromised host  A host with lowered resistance to infection and disease for any of several reasons. The host may be seriously debilitated (due to malnutrition, cancer, diabetes, leukemia, or another infectious disease), traumatized (from surgery or injury), immunosuppressed, or have an altered microbiota due to prolonged use of antibiotics.
(See page(s) 704, 948)
concatemer  A long DNA molecule consisting of several genomes linked together in a row.
(See page(s) 387)
conditional mutations  Mutations that are expressed only under certain environmental conditions.
(See page(s) 245)
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 spot 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.
(See page(s) 36)
congenital (neonatal) herpes  An infection of a newborn caused by transmission of the herpesvirus during vaginal delivery.
(See page(s) 886)
congenital rubella syndrome  A wide array of congenital defects affecting the heart, eyes, and ears of a fetus during the first trimester of pregnancy, and caused by the rubella virus.
(See page(s) 876)
congenital syphilis  Syphilis that is acquired in utero from the mother.
(See page(s) 923)
conidiospore (ko-nid_e-o-spøor)  An asexual, thin-walled spore borne on hyphae and not contained within a sporangium; it may be produced singly or in chains.
(See page(s) 537, 557)
conidium (ko-nid_e-um; pl., conidia)  See conidiospore.
(See page(s) 537)
conjugants (kon_joo-gants)  Complementary mating types that participate in a form of protozoan sexual reproduction called conjugation.
(See page(s) 586)
conjugation (kon²ju-ga_shun)  1. 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.
(See page(s) 302, 586)
conjugative plasmid  A plasmid that carries the genes for sex pili and can transfer copies of itself to other bacteria during conjugation.
(See page(s) 294)
conjunctivitis of the newborn  See ophthalmia neonatorum.
(See page(s) 916)
conoid (ko_noid)  A hollow cone of spirally coiled filaments in the anterior tip of certain apicomplexan protozoa.
(See page(s) 591)
consortium  A physical association of two different organisms, usually beneficial to both organisms.
(See page(s) 596)
constant region (CL and CH)  The part of an antibody molecule that does not vary greatly in amino acid sequence among molecules of the same class, subclass, or type.
(See page(s) 734)
constitutive mutant  A strain that produces an inducible enzyme continually, regardless of need, because of a mutation in either the operator or regulator gene.
(See page(s) 276)
constructed wetlands  Intentional creation of marshland plant communities and their associated microorganisms for environmental restoration or to purify water by the removal of bacteria, organic matter, and chemicals as the water passes through the aquatic plant communities.
(See page(s) 662)
consumer  An organism that feeds directly on living or dead animals, by ingestion or by phagocytosis.
(See page(s) 622)
contact transmission  Transmission of the pathogen by contact of the source or reservoir of the pathogen with the host.
(See page(s) 856)
continuous culture system  A culture system with constant environmental conditions maintained through continual provision of nutrients and removal of wastes.
(See page(s) 120)
contractile vacuole (vak_u-øol)  In protists and some animals, a clear fluid-filled cell vacuole that takes up water from within the cell and then contracts, releasing it to the outside through a pore in a cyclical manner. Contractile vacuoles function primarily in osmoregulation and excretion.
(See page(s) 585)
convalescent carrier (kon_vah-les_ent)  An individual who has recovered from an infectious disease but continues to harbor large numbers of the pathogen.
(See page(s) 854)
copiotrophic  Having a high nutrient level.
(See page(s) 638)
corepressor (ko_re-pre_sor)  A small molecule that inhibits the synthesis of a repressible enzyme.
(See page(s) 276)
cortex (kor_teks)  The layer of a bacterial endospore that is thought to be particularly important in conferring heat resistance on the endospore.
(See page(s) 69)
coryza (kùo-ri_zah)  See common cold.
(See page(s) 884)
cosmid (koz_mid)  A plasmid vector with lambda phage cos sites that can be packaged in a phage capsid; it is useful for cloning large DNA fragments.
(See page(s) 335)
cristae (kris_te)  Infoldings of the inner mitochondrial membrane.
(See page(s) 83)
cross-feeding  See syntropism.
(See page(s) 604)
crossing-over  A process in which segments of two adjacent DNA strands are exchanged; breaks occur in both strands, and the exposed ends of each strand join to those of the opposite segment on the other strand.
(See page(s) 292)
cryptins  Peptides produced by Paneth cells in the intestines. Cryptins are toxic for some bacteria, although their mode of action is not known.
(See page(s) 711)
cryptococcosis (krip_to-kok-o_sis)  An infection caused by the basidiomycete, Cryptococcus neoformans, which may involve the skin, lungs, brain, or meninges.
(See page(s) 561, 947)
cryptosporidiosis (krip_to-spo-rid_e-o_sis)  Infection with protozoa of the genus Cryptosporidium. The most common symptoms are prolonged diarrhea, weight loss, fever, and abdominal pain.
(See page(s) 952)
crystallizable fragment (Fc)  The stem of the Y portion of an antibody molecule. Cells such as macrophages bind to the Fc region, and it also is involved in complement activation.
(See page(s) 734)
cutaneous anthrax (ku-ta_ne-us an_thraks)  A form of anthrax involving the skin.
(See page(s) 913)
cutaneous diphtheria (ku-ta_ne-us dif-the_re-ah)  A skin disease caused by Corynebacterium diphtheriae that infects wound or skin lesions, causing a slow-healing ulceration.
(See page(s) 901)
cyanobacteria (si_ah-no-bak-te_re-ah)  A large group of bacteria that carry out oxygenic photosynthesis using a system like that present in photosynthetic eucaryotes.
(See page(s) 471)
cyclic photophosphorylation (fo_to-fos_for-ùõ-la_shun)  The formation of ATP when light energy is used to move electrons cyclically through an electron transport chain during photosynthesis; only photosystem I participates.
(See page(s) 198)
cyst (sist)  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.
(See page(s) 586)
cytochromes (si_to-krøoms)  Heme proteins that carry electrons, usually as members of electron transport chains.
(See page(s) 159)
cytokine (si_to-køõn)  A general term for nonantibody proteins, released by a cell in response to inducing stimuli, which are mediators that influence other cells. Are produced by lymphocytes, monocytes, macrophages, and other cells.
(See page(s) 720)
cytomegalovirus inclusion disease (si_to-meg_ah-lo-vi_rus)  An infection caused by the cytomegalovirus and marked by nuclear inclusion bodies in enlarged infected cells.
(See page(s) 885)
cytopathic effect (si_to-path_ik)  The observable change that occurs in cells as a result of viral replication. Examples include ballooning, binding together, clustering, or even death of the cultured cells.
(See page(s) 364, 832)
cytoplasmic matrix (si_to-plaz_mik)  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.
(See page(s) 49, 76)
cytoproct (si_to-prokt)  Site on a protozoan where undigestible matter is expelled.
(See page(s) 592)
cytosine (si_to-søen)  A pyrimidine 2-oxy-4-aminopyrimidine found in nucleosides, nucleotides, and nucleic acids.
(See page(s) 217)
cytoskeleton (si_to-skel_ùe-ton)  A network of microfilaments, microtubules, intermediate filaments, and other components in the cytoplasm of eucaryotic cells that helps give them shape.
(See page(s) 79)
cytostome (si_to-støom)  A permanent site in the protozoan ciliate body through which food is ingested.
(See page(s) 586)
cytotoxic T (TC) cell (si_to-tok_sik)  A cell that is capable of recognizing virus-infected cells through the major histocompatability molecules and developing into an activated cell that destroys the infected cells.
(See page(s) 748)
cytotoxic T lymphocyte (CTL)  The activated T cell that can attack and destroy virus-infected cells, tumor cells, and foreign cells.
(See page(s) 748)
cytotoxin (si_to-tok_sin)  A toxin or antibody that has a specific toxic action upon cells; cytotoxins are named according to the cell for which they are specific (e.g., nephrotoxin).
(See page(s) 797)
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.
(See page(s) 889)
dark-field microscopy  Microscopy in which the specimen is brightly illuminated while the background is dark.
(See page(s) 22)
dark reactivation  The excision and replacement of thymine dimers in DNA that occurs in the absence of light.
(See page(s) 130)
deamination (de-am_i-na_shun)  The removal of amino groups from amino acids.
(See page(s) 192)
death phase  The decrease in viable microorganisms that occurs after the completion of growth in a batch culture.
(See page(s) 115)
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.
(See page(s) 140)
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 physically reduces the size of substrate particles.
(See page(s) 622)
defensin (de-fens_sin)  Specific peptides produced by neutrophils that permeabilize the outer and inner membranes of certain microorganisms, thus killing them.
(See page(s) 720)
defined medium  Culture medium made with components of known composition.
(See page(s) 105)
Delta agent  A defective RNA virus that is transmitted as an infectious agent, but cannot cause disease unless the individual is also infected with the hepatitis B virus. See hepatitis D.
(See page(s) 891)
delta-proteobacteria  One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Chemoorganotrophic bacteria that usually are either predators on other bacteria or anaerobes that generate sulfide from sulfate and sulfite.
(See page(s) 507)
denaturation (de-na_chur-a_shun)  A change in the shape of an enzyme that destroys its activity; the term is also applied to changes in nucleic-acid shape.
(See page(s) 163)
dendritic cell (den-drit_ ik)  An antigen-presenting cell that has long membrane extensions resembling the dendrites of neurons. These cells are found in the lymph nodes, spleen, and thymus (interdigitating dendritic cells); skin (Langerhans cells); and other tissues (interstitial dendritic cells). Express MHC class II and B7 costimulatory molecules and thus are efficient presenters of antigens to T-helper cells.
(See page(s) 708)
dendrogram  A treelike diagram that is used to graphically summarize mutual similarities and relationships between organisms.
(See page(s) 427)
denitrification (de-ni_trùõ-fùõ-ka_sh@n)  The reduction of nitrate to gas products, primarily nitrogen gas, during anaerobic respiration.
(See page(s) 190, 616)
dental plaque (plak)  A thin film on the surface of teeth consisting of bacteria embedded in a matrix of bacterial polysaccharides, salivary glycoproteins, and other substances.
(See page(s) 934)
deoxyribonucleic acid (DNA; de-ok_se-ri_bo-nu-kle_ik)  The nucleic acid that constitutes the genetic material of all cellular organisms. It is a polynucleotide composed of deoxyribonucleotides connected by phosphodiester bonds.
(See page(s) 54, 230)
dermatophyte (der_mah-to-føõt_)  A fungus parasitic on the skin.
(See page(s) 943)
dermatomycosis (der_ma-to-mi-ko_sis)  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 athlete's foot (tinea pedis).
(See page(s) 943)
desensitization (de-sen_si-ti-za_shun)  To make a sensitized or hypersensitive individual insensitive or nonreactive to a sensitizing agent.
(See page(s) 769)
desert crust  A crust formed by microbial binding of sand grains in the surface zone of desert soil; crust formation primarily involves cyanobacteria.
(See page(s) 673)
detergent (de-ter_jent)  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.
(See page(s) 148)
deuteromycetes (doo_t@r-o-mi-se_tøez)  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.
(See page(s) 564)
diatoms (di_ah-toms)  Algal protists with siliceous cell walls called frustules. They constitute a substantial subfraction of the phytoplankton.
(See page(s) 577)
diauxic growth (di-awk_sik)  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.
(See page(s) 281)
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 intereference is used to create the image.
(See page(s) 25)
differential media (dif_er-en_shal)  Culture media that distinguish between groups of microorganisms based on differences in their growth and metabolic products.
(See page(s) 106)
differential staining procedures  Staining procedures that divide bacteria into separate groups based on staining properties.
(See page(s) 28)
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.
(See page(s) 932)
dikaryotic stage (di-kar-e-ot_ik)  In fungi, having pairs of nuclei within cells or compartments. Each cell contains two separate haploid nuclei, one from each parent.
(See page(s) 557)
dinoflagellate (di_no-flaj_e-løat)  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.
(See page(s) 579)
diphtheria (dif-the_re-ah)  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.
(See page(s) 900)
dipicolinic acid  A substance present at high concentrations in the bacterial endospore. It is thought to contribute to the endospore's heat resistance.
(See page(s) 69)
diplococcus (dip_lo-kok_us)  A pair of cocci.
(See page(s) 43)
directed- or adaptive mutation  A mutation that seems to be chosen so the organism can better adapt to its surroundings.
(See page(s) 246)
disease (di-zez)  A deviation or interruption of the normal structure or function of any part of the body that is manifested by a characteristic set of symptoms and signs.
(See page(s) 848)
disease syndrome (sin_drùom)  A set of signs and symptoms that are characteristic of the disease.
(See page(s) 850)
disinfectant (dis_in-fek_tant)  An agent, usually chemical, that disinfects; normally, it is employed only with inanimate objects.
(See page(s) 138)
disinfection (dis_in-fek_shun)  The killing, inhibition, or removal of microorganisms that may cause disease. It usually refers to the treatment of inanimate objects with chemicals.
(See page(s) 138)
disinfection by-products (DBPs)  Chlorinated organic compounds formed during chlorine use for water disinfection. Many are carcinogens.
(See page(s) 653)
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.
(See page(s) 190)
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.
(See page(s) 614)
diurnal oxygen shifts (di-er_nal)  The changes in oxygen levels that occur in waters when algae produce and use oxygen on a cyclic basis during day and night.
(See page(s) 650)
DNA ligase  An enzyme that joins two DNA fragments together through the formation of a new phosphodiester bond.
(See page(s) 239)
DNA microarrays (DNA chips)  Solid supports that have DNA attached in highly organized arrays and are normally used to evaluate gene expression.
(See page(s) 354, 1018)
DNA polymerase (pol-im_er-øas)  An enzyme that synthesizes new DNA using a parental DNA strand as a template.
(See page(s) 236)
DNA vaccine  A vaccine that contains DNA which encodes antigenic proteins. It is injected directly 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.
(See page(s) 767)
domains (do-møan_)  1. Compact, self-folding, structurally independent regions of proteins (usually around 100-300 amino acids in length); large proteins may have two or more domains connected by less structured stretches of polypeptide. In the antibody molecule, they are the loops, along with about 25 amino acids on each side, that form compact, globular sections. 2. The primary taxonomic groups above the kingdom level; all living organisms may be placed in one of three domains.
(See page(s) 274, 424, 734)
double diffusion agar assay (Ouchterlony technique)  An immunodiffusion reaction in which both antibody and antigen diffuse through agar to form stable immune complexes, which can be observed visually.
(See page(s) 780)
doubling time  See generation time.
(See page(s) 115)
DPT (diphtheria-pertussis-tetanus) vaccine  A vaccine containing three antigens that is used to immunize people against diphtheria, pertussis or whooping cough, and tetanus.
(See page(s) 901)
droplet nuclei  Small particles (1 to 4 mm in diameter) that represent what is left from the evaporation of larger particles (10 mm or more in diameter) called droplets.
(See page(s) 856)
D value  See decimal reduction time.
(See page(s) 140)
early mRNA  Messenger RNA produced early in a virus infection that codes for proteins needed to take over the host cell and manufacture viral nucleic acids.
(See page(s) 385)
Ebola virus hemorrhagic fever (a_bo-l@)  An acute infection caused by a virus that produces varying degrees of hemorrhage, shock, and sometimes death.
(See page(s) 877)
eclipse period (e-klips_)  The initial part of the latent period in which infected host bacteria do not contain any complete virions.
(See page(s) 383)
ecosystem (ek_o-sis_tem)  A self-regulating biological community and its associated physical and chemical environment.
(See page(s) 596)
ectomycorrhizal  Referring to a mutualistic association between fungi and plant roots in which the fungus surrounds the root tip with a sheath.
(See page(s) 681)
ectoparasite (ek_to-par_ah-søõt)  A parasite that lives on the surface of its host.
(See page(s) 788)
ectoplasm (ek_to-plazm)  The outer stiffer portion or region of the cytoplasm in a protozoan, which may be differentiated in texture from the inner portion or endoplasm.
(See page(s) 585)
ectosymbiosis  A type of symbiosis in which one organism remains outside of the other organism.
(See page(s) 701)
effacing lesion (le_zh@n)  The type of lesion caused by enteropathogenic strains of E. coli (EPEC) when the bacteria attach to and destroy the brush border of intestinal epithelial cells. The term AE (attaching-effacing) E. coli is now used to designate true EPEC strains that are an important cause of diarrhea in children from developing countries and in traveler's diarrhea.
(See page(s) 932)
ehrlichiosis (ar-lik_e-o_sis)  A tick-borne (Dermacentor andersoni, Amblyomma americanum) rickettsial disease caused by Ehrlichia chaffeensis. Once inside leukocytes, a nonspecific illness develops that resembles Rocky Mountain spotted fever.
(See page(s) 909)
electron transport chain  A series of electron carriers that operate together to transfer electrons from donors such as NADH and FADH2 to acceptors such as oxygen.
(See page(s) 184)
electrophoresis (e-lek_tro-fo-re_sis)  A technique that separates substances through differences in their migration rate in an electrical field due to variations in the number and kinds of charged groups they have.
(See page(s) 327)
electroporation (e-lek_tro-p@-ra_sh@n)  The application of an electric field to create temporary pores in the plasma membrane in order to insert DNA into the cell and transform it.
(See page(s) 335)
elementary body  A small, dormant body that serves as the agent of transmission between host cells in the chlamydial life cycle.
(See page(s) 477)
elongation cycle  The cycle in protein synthesis that results in the addition of an amino acid to the growing end of a peptide chain.
(See page(s) 270)
Embden-Meyerhof pathway (em_den mi_er-hof)  A pathway that degrades glucose to pyruvate; the six-carbon stage converts glucose to fructose 1,6-bisphosphate, and the three-carbon stage produces ATP while changing glyceraldehyde 3-phosphate to pyruvate.
(See page(s) 176, A-13)
encystation (en-sis-_ta_shen)  The formation of a cyst.
(See page(s) 586)
endemic disease (en-dem_ik)  A disease that is commonly or constantly present in a population, usually at a relatively steady low frequency.
(See page(s) 849)
endemic (murine) typhus (mu_rin ti_fus)  A form of typhus fever caused by the rickettsia Rickettsia typhi that occurs sporadically in individuals who come into contact with rats and their fleas.
(See page(s) 909)
endergonic reaction (end²er-gon_ik)  A reaction that does not spontaneously go to completion as written; the standard free energy change is positive, and the equilibrium constant is less than one.
(See page(s) 156)
endocytosis (en²do-si-to_sis)  The process in which a cell takes up solutes or particles by enclosing them in vesicles pinched off from its plasma membrane.
(See page(s) 80)
endogenote (en²do-je_nøot)  The recipient bacterial cell's own genetic material into which the donor DNA can integrate.
(See page(s) 294)
endogenous infection (en-doj_ùe-nus in-fek_shun)  An infection by a member of an individual's own normal body microbiota.
(See page(s) 905)
endogenous pyrogen (en-doj_e-nus pi_ro-jen)  A substance such as the lymphokine interleukin-1, which is produced by host cells and induces a fever response in the host. It also is called simply a pyrogen.
(See page(s) 801)
endomycorrhizal  Referring to a mutualistic association of fungi and plant roots in which the fungus penetrates into the root cells and arbuscules and vesicles are formed.
(See page(s) 681)
endoparasite (en²do-par_ah-søõt)  A parasite that lives inside the body of its host.
(See page(s) 789)
endophyte (en_do-fùõt)  A microorganism living within a plant, but not necessarily parasitic on it.
(See page(s) 679)
endoplasm (en_do-plazm)  The central portion of the cytoplasm in a protozoan.
(See page(s) 585)
endoplasmic reticulum (en²do-plas_mik rùe-tik_u-lum)  A system of membranous tubules and flattened sacs (cisternae) in the cytoplasmic matrix of eucaryotic cells. Rough or granular endoplasmic reticulum (RER or GER) bears ribosomes on its surface; smooth or agranular endoplasmic reticulum (SER or AER) lacks them.
(See page(s) 79)
endosome (en_do-søom)  A membranous vesicle formed by endocytosis.
(See page(s) 80)
endospore (en_do-spøor)  An extremely heat- and chemical-resistant, dormant, thick-walled spore that develops within bacteria.
(See page(s) 68)
endosymbiont (en²do-sim_be-ont)  An organism that lives within the body of another organism in a symbiotic association.
(See page(s) 596)
endosymbiosis (en_do-sim_bi-o_sis)  A type of symbiosis in which one organism is found within another organism.
(See page(s) 701)
endosymbiotic theory or hypothesis  The theory that eucaryotic organelles such as mitochondria and chloroplasts arose when bacteria established an endosymbiotic relationship with the eucaryotic ancestor and then evolved into eucaryotic organelles.
(See page(s) 85, 424)
endotoxin (en²do-tox_sin)  The heat-stable lipopolysaccharide in the outer membrane of the cell wall of gram-negative bacteria that is released when the bacterium lyses, or sometimes during growth, and is toxic to the host.
(See page(s) 799)
end product inhibition  See feedback inhibition.
(See page(s) 169)
energy  The capacity to do work or cause particular changes.
(See page(s) 154)
enology  The science of wine making.
(See page(s) 982)
enteric bacteria (enterobacteria; en-ter_ik)  Members of the family Enterobacteriaceae (gram-negative, peritrichous or nonmotile, facultatively anaerobic, straight rods with simple nutritional requirements); also used for bacteria that live in the intestinal tract.
(See page(s) 505)
enterohemorrhagic E. coli (EHEC) (en_t@r-o-hem²@-raj_ik)  EHEC strains of E. coli (0157:H7) produce several cytotoxins that provoke fluid secretion in traveler's diarrhea; however, their mode of action is unknown.
(See page(s) 932)
enteroinvasive E. coli (EIEC) (en_t@r-o-in-va_siv)  EIEC strains of E. coli cause traveler's diarrhea by penetrating and binding to the intestinal epithelial cells. EIEC may also produce a cytotoxin and enterotoxin.
(See page(s) 932)
enteropathogenic E. coli (EPEC) (en_t@r-o-path-o-jen_ik)  EPEC strains of E. coli attach to the brush border of intestinal epithelial cells and cause a specific type of cell damage called effacing lesions that lead to traveler's diarrhea.
(See page(s) 932)
enterotoxigenic E. coli (ETEC) (en_t@r-o-tok²sùõ-jen_ik)  ETEC strains of E. coli produce two plasmid-encoded enterotoxins (which are responsible for traveler's diarrhea) and are distinguished by their heat stability: heat-stable enterotoxin (ST) and heat-labile enterotoxin (LT).
(See page(s) 932)
enterotoxin (en²ter-o-tok_sin)  A toxin specifically affecting the cells of the intestinal mucosa, causing vomiting and diarrhea.
(See page(s) 797, 927)
Entner-Doudoroff pathway  A pathway that converts glucose to pyruvate and glyceraldehyde 3-phosphate by producing 6-phosphogluconate and then dehydrating it.
(See page(s) 179, A-15)
entropy (en_tro-pe)  A measure of the randomness or disorder of a system; a measure of that part of the total energy in a system that is unavailable for useful work.
(See page(s) 156)
envelope (en_vùe-løop)  1. All the structures outside the plasma membrane in bacterial cells. 2. In virology it is an outer membranous layer that surrounds the nucleocapsid in some viruses.
(See page(s) 55, 369)
enzootic (en²zo-ot_ik)  The moderate prevalence of a disease in a given animal population.
(See page(s) 849)
enzyme (en_zøõm)  A protein catalyst with specificity for both the reaction catalyzed and its substrates.
(See page(s) 161)
enzyme-linked immunosorbent assay (ELISA)  A technique used for detecting and quantifying specific antibodies and antigens.
(See page(s) 778)
eosinophil (e² o-sin,_o-fil)  A polymorphonuclear leukocyte that has a two-lobed nucleus and cytoplasmic granules that stain yellow-red. A mobile phagocyte that is highly antiparasitic.
(See page(s) 707)
epidemic (ep²ùõ-dem_ik)  A disease that suddenly increases in occurrence above the normal level in a given population.
(See page(s) 849)
epidemic (louse-borne) typhus (ep²i-dem_ik ti_fus)  A disease caused by Rickettsia prowazekii that is transmitted from person to person by the body louse.
(See page(s) 909)
epidemiologist (ep²ùõ-de²me-ol_o-jist)  A person who specializes in epidemiology.
(See page(s) 849)
epidemiology (epi²-de²me-ol_o-je)  The study of the factors determining and influencing the frequency and distribution of disease, injury, and other health-related events and their causes in defined human populations.
(See page(s) 848)
episome (ep_ùõ-søom)  A plasmid that can exist either independently of the host cell's chromosome or be integrated into it.
(See page(s) 294)
epitheca (ep²ùõ-the_kah)  The larger of two halves of a diatom frustule (shell).
(See page(s) 577)
epitope (ep_i-tøop)  An area of the antigen molecule that stimulates the production of, and combines with, specific antibodies; also known as the antigenic determinant site.
(See page(s) 731)
epizootic (ep²ùõ-zo-ot_ik)  A sudden outbreak of a disease in an animal population.
(See page(s) 849)
epizootiology (ep²i-zo-ot²e-ol_o-je)  The field of science that deals with factors determining the frequency and distribution of a disease within an animal population.
(See page(s) 849)
epsilon-proteobacteria  One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Slender gram-negative rods, some of which are medically important (Campylobacter and Helicobacter).
(See page(s) 514)
equilibrium (e²kwùõ-lib_re-um)  The state of a system in which no net change is occurring and free energy is at a minimum; in a chemical reaction at equilibrium, the rates in the forward and reverse directions exactly balance each other out.
(See page(s) 156)
ergot (er_got)  The dried sclerotium of Claviceps purpurea. Also, an ascomycete that parasitizes rye and other higher plants causing the disease called ergotism.
(See page(s) 561)
ergotism (er_got-izm)  The disease or toxic condition caused by eating grain infected with ergot; it is often accompanied by gangrene, psychotic delusions, nervous spasms, abortion, and convulsions in humans and in animals.
(See page(s) 561, 967)
erysipelas (er²ùõ-sip_ùe-las)  An acute inflammation of the dermal layer of the skin, occurring primarily in infants and persons over 30 years of age with a history of streptococcal sore throat.
(See page(s) 903)
erythema infectiosum (er²@-the_-m@)  A disease in children caused by the parvovirus B19. This disease is common in children between 4 and 11 years of age and is sometimes called fifth disease, since it was the fifth of six erythematous rash diseases in children in an older classification.
(See page(s) 887)
erythromycin (ùe-rith²ro-mi_sin)  An intermediate spectrum macrolide antibiotic produced by Streptomyces erythreus.
(See page(s) 817)
eschar (es_kar)  A slough produced on the skin by a thermal burn, gangrene, or the anthrax bacillus.
(See page(s) 914)
Eucarya  The domain that contains organisms composed of eucaryotic cells with primarily glycerol fatty acyl diesters in their membranes and eucaryotic rRNA.
(See page(s) 424)
eucaryotic cells (u²kar-e-ot_ik)  Cells that have a membrane-delimited nucleus and differ in many other ways from procaryotic cells; protists, algae, fungi, plants, and animals are all eucaryotic.
(See page(s) 11, 91)
euglenoids (u-gle_noids)  A group of algae (the division Euglenophyta) or protozoa (order Euglenida) that normally have chloroplasts containing chlorophyll a and b. They usually have a stigma and one or two flagella emerging from an anterior gullet.
(See page(s) 576)
Eumycota (u²mi-ko_t@)  A division of fungi in some classification systems. These are the true fungi consisting of the Zygomycetes, Ascomycetes, Basidiomycetes, and Chytridiomycetes.
(See page(s) 553)
eumycotic mycetoma (mi²se-to_mah)  See maduromycosis.
(See page(s) 945)
eutrophic (u-trof_ik)  A nutrient-enriched environment.
(See page(s) 648)
eutrophication (u²tro-fùõ-ka_shun)  The enrichment of an aquatic environment with nutrients.
(See page(s) 648)
evolutionary distance  A quantitative indication of the number of positions that differ between two aligned macromolecules, and presumably a measure of evolutionary similarity between molecules and organisms.
(See page(s) 433)
excystation (ek²sis-ta_shun)  The escape of one or more cells or organisms from a cyst.
(See page(s) 586)
exergonic reaction (ek²ser-gon_ik)  A reaction that spontaneously goes to completion as written; the standard free energy change is negative, and the equilibrium constant is greater than one.
(See page(s) 156)
exfoliative toxin (eks-fo_le-a²tiv) or exfoliatin (eks-føo²le-a_tin)  An exotoxin produced by Staphylococcus aureus that causes the separation of epidermal layers and the loss of skin surface layers. It produces the symptoms of the scaled skin syndrome.
(See page(s) 922)
exit site (E site)  The location on a ribosome to which an empty tRNA moves from the P site before it finally leaves the ribosome during protein synthesis.
(See page(s) 270)
exoenzymes (ek²so-en_zøõms)  Enzymes that are secreted by cells.
(See page(s) 55)
exogenote (eks²o-je_nøot)  The piece of donor DNA that enters a bacterial cell during gene exchange and recombination.
(See page(s) 294)
exon (eks_on)  The region in a split or interrupted gene that codes for RNA which ends up in the final product (e.g., mRNA).
(See page(s) 263)
exotoxin (ek²so-tok_sin)  A heat-labile, toxic protein produced by a bacterium as a result of its normal metabolism or because of the acquisition of a plasmid or prophage that redirects its metabolism. It is usually released into the bacterium's surroundings.
(See page(s) 794)
exponential phase (eks²po-nen_shul)  The phase of the growth curve during which the microbial population is growing at a constant and maximum rate, dividing and doubling at regular intervals.
(See page(s) 114)
expressed sequence tag (EST)  A partial gene sequence unique to a gene that can be used to identify and position the gene during genomic analysis.
(See page(s) 354)
expression vector  A special cloning vector used to express recombinant genes in host cells; the recombinant gene is transcribed and its protein synthesized.
(See page(s) 336)
exteins  Polypeptide sequences of precursor self-splicing proteins that are joined together during formation of the final, functional protein. They are separated from one another by intein sequences, which they flank.
(See page(s) 275)
extracutaneous sporotrichosis (spo²ro-tri-ko_sis)  An infection by the fungus Sporothrix schenckii that spreads throughout the body.
(See page(s) 945)
extreme barophilic bacteria  Bacteria that require a high-pressure environment to function.
(See page(s) 624)
extreme environment  An environment in which physical factors such as temperature, pH, salinity, and pressure are outside of the normal range for growth of most microorganisms; these conditions allow unique organisms to survive and function.
(See page(s) 624)
extremophiles  Microorganisms that grow under harsh or extreme environmental conditions such as very high temperatures or low pHs.
(See page(s) 121, 624)
extrinsic factor  An environmental factor such as temperature that influences microbial growth in food.
(See page(s) 964)
facilitated diffusion  Diffusion across the plasma membrane that is aided by a carrier.
(See page(s) 100)
facultative anaerobes (fak_ul-ta²tiv an-a_er-øobs)  Microorganisms that do not require oxygen for growth, but do grow better in its presence.
(See page(s) 127)
facultative psychrophile (fak_ul-ta²tiv si_kro-føõl)  See psychrotroph.
(See page(s) 126)
fas gene  The gene that is active in target cells which are susceptible to killing by cells expressing the Fas ligand, a member of the TNF family of cytokines and cell surface molecules.
(See page(s) 750)
fatty acid synthetase (sin_thùe-tøas)  The multienzyme complex that makes fatty acids; the product usually is palmitic acid.
(See page(s) 218)
fecal coliform (fe_kal ko_lùõ-form)  Coliforms whose normal habitat is the intestinal tract and that can grow at 44.5°C.
(See page(s) 654)
fecal enterococci (fe_kal en²ter-o-kok_si)  Enterococci found in the intestine of humans and other warm-blooded animals. They are used as indicators of the fecal pollution of water.
(See page(s) 656)
feedback inhibition  A negative feedback mechanism in which a pathway end product inhibits the activity of an enzyme in the sequence leading to its formation; when the end product accumulates in excess, it inhibits its own synthesis.
(See page(s) 169)
fermentation (fer²men-ta_shun)  An energy-yielding process in which an energy substrate is oxidized without an exogenous electron acceptor. Usually organic molecules serve as both electron donors and acceptors.
(See page(s) 173, 1000)
fever  A complex physiological response to disease mediated by pyrogenic cytokines and characterized by a rise in core body temperature and activation of the immune system.
(See page(s) 722)
fever blister  See cold sore.
(See page(s) 884)
F factor  The fertility factor, a plasmid that carries the genes for bacterial conjugation and makes its E. coli host cell the gene donor during conjugation.
(See page(s) 295)
fimbria (fim_bre-ah; pl., fimbriae)  A fine, hairlike protein appendage on some gram-negative bacteria that helps attach them to surfaces.
(See page(s) 62)
final host  The host on/in which a parasitic organism either attains sexual maturity or reproduces.
(See page(s) 789)
first law of thermodynamics  Energy can be neither created nor destroyed (even though it can be changed in form or redistributed).
(See page(s) 155)
fixation (fik-sa_shun)  The process in which the internal and external structures of cells and organisms are preserved and fixed in position.
(See page(s) 27)
flagellin (flaj_ùe-lin)  The protein used to construct the filament of a bacterial flagellum.
(See page(s) 64)
flagellum (flah-jel_um; pl., flagella)  A thin, threadlike appendage on many procaryotic and eucaryotic cells that is responsible for their motility.
(See page(s) 63, 89)
flat or plane warts  Small, smooth, slightly raised warts.
(See page(s) 894)
flavin adenine dinucleotide (FAD; fla_vin ad_ùe-nøen)  An electron carrying cofactor often involved in energy production (for example, in the tricarboxylic acid cycle and the b-oxidation pathway).
(See page(s) 159)
fluid mosaic model  The currently accepted model of cell membranes in which the membrane is a lipid bilayer with integral proteins buried in the lipid, and peripheral proteins more loosely attached to the membrane surface.
(See page(s) 47)
fluorescence microscope  A microscope that exposes a specimen to light of a specific wavelength and then forms an image from the fluorescent light produced. Usually the specimen is stained with a fluorescent dye or fluorochrome.
(See page(s) 25)
fluorescent light (floo²o-res_ent)  The light emitted by a substance when it is irradiated with light of a shorter wavelength.
(See page(s) 25)
fomite (fo_møõt; pl., fomites)  An object that is not in itself harmful but is able to harbor and transmit pathogenic organisms. Also called fomes.
(See page(s) 792, 857)
food-borne infection  Gastrointestinal illness caused by ingestion of microorganisms, followed by their growth within the host. Symptoms arise from tissue invasion and/or toxin production.
(See page(s) 926, 973)
food chain  The flow of energy and matter in living organisms through a producer-consumer sequence (See also food web).
(See page(s) 584)
food intoxication  Food poisoning caused by microbial toxins produced in a food prior to consumption. The presence of living bacteria is not required.
(See page(s) 927, 975)
food poisoning  A general term usually referring to a gastrointestinal disease caused by the ingestion of food contaminated by pathogens or their toxins.
(See page(s) 926)
food web  A network of many interlinked food chains, encompassing primary producers, consumers, decomposers, and detritivores.
(See page(s) 584)
F1 particle  Particle on the inner mitochondrial membrane, which is the site of ATP synthesis by oxidative phosphorylation.
(See page(s) 83, 187)
F_ plasmid  An F plasmid that carries some bacterial genes and transmits them to recipient cells when the F_ cell carries out conjugation; the transfer of bacterial genes in this way is often called sexduction.
(See page(s) 305)
fragmentation (frag²men-ta_shun)  A type of asexual reproduction in which a thallus breaks into two or more parts, each of which forms a new thallus.
(See page(s) 573)
frameshift mutations  Mutations arising from the loss or gain of a base or DNA segment, leading to a change in the codon reading frame and thus a change in the amino acids incorporated into protein.
(See page(s) 251)
free energy change  The total energy change in a system that is available to do useful work as the system goes from its initial state to its final state at constant temperature and pressure.
(See page(s) 156)
French polio  See Guillain-BarrĊ½ syndrome.
(See page(s) 874)
fruiting body  A specialized structure that holds sexually or asexually produced spores; found in fungi and in some bacteria.
(See page(s) 512, 565)
frustule (frus_tøul)  A silicified cell wall in the diatoms.
(See page(s) 577)
fungicide (fun_jùõ-søõd)  An agent that kills fungi.
(See page(s) 138)
fungistatic (fun_jùõ-stat_ik)  Inhibiting the growth and reproduction of fungi.
(See page(s) 138)
fungus (fung_gus; pl., fungi)  Achlorophyllous, heterotrophic, spore-bearing eucaryotes with absorptive nutrition; usually, they have a walled thallus.
(See page(s) 553)
F value  The time in minutes at a specific temperature (usually 250°F) needed to kill a population of cells or spores.
(See page(s) 140)







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