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Microbiology, Fifth Edition
Microbiology, 5/e
Lansing M Prescott, Augustana College
Donald A Klein, Colorado State University
John P Harley, Eastern Kentucky University


Glossary A-F

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 797)
accessory pigments  Photosynthetic pigments such as carotenoids and phycobiliproteins that aid chlorophyll in trapping light energy.
(See 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 183)
acid dyes  Dyes that are anionic or have negatively charged groups such as carboxyls.
(See 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 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 28)
acidophile (as_id-o-føõl__)  A microorganism that has its growth optimum between about pH 0 and 5.5.
(See 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 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 878)
acquired immune tolerance  The ability to produce antibodies against nonself antigens while "tolerating" (not producing antibodies against) self-antigens.
(See 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 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 541)
actinomycete (ak²tùõ-no-mi_søet)  An aerobic, gram-positive bacterium that forms branching filaments (hyphae) and asexual spores.
(See 537)
actinorhizae  Associations between actinomycetes and plant roots.
(See 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 659)
activation energy  The energy required to bring reacting molecules together to reach the transition state in a chemical reaction.
(See 162)
active carrier  An individual who has an overt clinical case of a disease and who can transmit the infection to others.
(See 854)
active immunization  The induction of active immunity by natural exposure to a pathogen or by vaccination.
(See 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 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 101)
acute carrier  See casual carrier.
(See 854)
acute infections  Virus infections with a fairly rapid onset that last for a relatively short time.
(See 410)
acute viral gastroenteritis  An inflammation of the stomach and intestines, normally caused by Norwalk and Norwalklike viruses, other caliciviruses, rotaviruses, and astroviruses.
(See 891)
acyclovir (a-si_klo-vir)  A synthetic purine nucleoside derivative with antiviral activity against herpes simplex virus.
(See 821)
adenine (ad_e-nøen)  A purine derivative, 6-aminopurine, found in nucleosides, nucleotides, coenzymes, and nucleic acids.
(See 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 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 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 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 741)
adult T-cell leukemia  A type of white blood cell cancer caused by the HTLV-1 virus.
(See 887)
aerobe (a_er-øob)  An organism that grows in the presence of atmospheric oxygen.
(See 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 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 173)
aerotolerant anaerobes  Microorganisms that grow equally well whether or not oxygen is present.
(See 127)
aflatoxin (af²lah-tok_sin)  A polyketide secondary fungal metabolite that can cause cancer.
(See 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 105)
agglutinates  The visible aggregates or clumps formed by an agglutination reaction.
(See 775)
agglutination reaction (ah-gloo²tùõ-na_shun)  The formation of an insoluble immune complex by the cross-linking of cells or particles.
(See 756)
agglutinin (ah-gloo²tùõ-nin)  The antibody responsible for an agglutination reaction.
(See 756)
AIDS  See acquired immune deficiency syndrome.
(See 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 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 854)
akinetes  Specialized, nonmotile, dormant, thick-walled resting cells formed by some cyanobacteria.
(See 473)
alcoholic fermentation  A fermentation process that produces ethanol and CO2 from sugars.
(See 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 571)
algicide (al_jùõ-søõd)  An agent that kills algae.
(See 138)
algology (al-gol_o-je)  The scientific study of algae.
(See 571)
alkalophile  A microorganism that grows best at pHs from about 8.5 to 11.5.
(See 123)
allergen (al_er-jen)  A substance capable of inducing allergy or specific susceptibility.
(See 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 771)
allergy (al_er-je)  See hypersensitivity.
(See 768)
allograft (al_o-graft)  A transplant between genetically different individuals of the same species.
(See 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 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 734)
alpha hemolysis  A greenish zone of partial clearing around a bacterial colony growing on blood agar.
(See 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 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 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 711)
amantadine (ah-man_tah-den)  An antiviral compound used to prevent type A influenza infections.
(See 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 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 609)
American trypanosomiasis (Chagas' disease)  See trypanosomiasis.
(See 957)
Ames test  A test that uses a special Salmonella strain to test chemicals for mutagenicity and potential carcinogenicity.
(See 253)
amino acid activation  The initial stage of protein synthesis in which amino acids are attached to transfer RNA molecules.
(See 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 270)
aminoglycoside antibiotics (am_ùõ-no-gli_ko-søõd)  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 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 580)
amoeboid movement  Moving by means of cytoplasmic flow and the formation of pseudopodia (temporary cytoplasmic protrusions of the cytoplasm).
(See 590)
amphibolic pathways (am_fe-bol_ik)  Metabolic pathways that function both catabolically and anabolically.
(See 176)
amphitrichous (am-fit_rùe-kus)  A cell with a single flagellum at each end.
(See 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 820)
anabolism (ah-nab_o-lizm_)  The synthesis of complex molecules from simpler molecules with the input of energy.
(See 173)
anaerobe (an-a_er-øob)  An organism that grows in the absence of free oxygen.
(See 127)
anaerobic digestion (an_a-er-o_bik)  The microbiological treatment of sewage wastes under anaerobic conditions to produce methane.
(See 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 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 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 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 768)
anaplerotic reactions (an_ah-plùe-rot_ik)  Reactions that replenish depleted tricarboxylic acid cycle intermediates.
(See 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 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 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 894)
anoxic (@-nok_ sik)  Without oxygen present.
(See 635)
anoxygenic photosynthesis  Photosynthesis that does not oxidize water to produce oxygen; the form of photosynthesis characteristic of purple and green photosynthetic bacteria.
(See 199, 468)
antheridium (an_ther-id_e-um; pl., antheridia)  A male gamete-producing organ, which may be unicellular or multicellular.
(See 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 913)
antibiotic (an_tùõ-bi-ot_ik)  A microbial product or its derivative that kills susceptible microorganisms or inhibits their growth.
(See 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 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 723)
antibody-mediated immunity  See humoral immunity.
(See 729)
anticodon triplet  The base triplet on a tRNA that is complementary to the triplet codon on mRNA.
(See 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 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 734)
antigenic determinant site (epitope)  See epitope.
(See 731)
antigenic drift  A small change in the antigenic character of an organism that allows it to avoid attack by the immune system.
(See 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 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 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 812)
antimicrobial agent  An agent that kills microorganisms or inhibits their growth.
(See 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 283)
antisepsis (an²tùõ-sep_sis)  The prevention of infection or sepsis.
(See 138)
antiseptic (an²tùõ-sep_tik)  Chemical agents applied to tissue to prevent infection by killing or inhibiting pathogens.
(See 138)
antiserum (an_tùõ-se_rum)  Serum containing induced antibodies.
(See 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 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 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 591)
aplanospore (a_plan-o-spor)  A nonflagellated, nonmotile spore that is involved in asexual reproduction.
(See 573)
apoenzyme (ap_o-en_zøõm)  The protein part of an enzyme that also has a nonprotein component.
(See 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 750, 881)
aporepressor  An inactive form of the repressor protein, which becomes the active repressor when the corepressor binds to it.
(See 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 681)
arbuscules  Branched, treelike structures formed in cells of plant roots colonized by endotrophic mycorrhizal fungi.
(See 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 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 557)
arthrospore (ar_thro-spøor)  A spore resulting from the fragmentation of a hypha.
(See 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 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 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 561)
ascogenous hypha  A specialized hypha that gives rise to one or more asci.
(See 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 561)
ascomycetes (as²ko-mi-se_tøez)  A division of fungi that form ascospores.
(See 560)
ascospore (as_ko-spor)  A spore contained or produced in an ascus.
(See 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 561)
aseptic meningitis syndrome  See meningitis.
(See 902)
aspergillosis (as²per-jil-o_sis)  A fungal disease caused by species of Aspergillus.
(See 948)
assimilatory reduction  The reduction of an inorganic molecule to incorporate it into organic material. No energy is made available during this process.
(See 210, 211, 614)
associative nitrogen fixation  Nitrogen fixation by bacteria in the plant root zone (rhizosphere).
(See 675)
athlete's foot  See tinea pedis.
(See 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 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 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 281, 766)
attenuator  A rho-independent termination site in the leader sequence that is involved in attenuation.
(See 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 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 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 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 772)
autolysins (aw-tol_ùõ-sins)  Enzymes that partially digest peptidoglycan in growing bacteria so that the peptidoglycan can be enlarged.
(See 223)
autotroph (aw_to-trøof)  An organism that uses CO2 as its sole or principal source of carbon.
(See 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 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 66, 479)
bacillus (bah-sil_lus)  A rod-shaped bacterium.
(See 43)
bacteremia (bak_ter-e_me-ah)  The presence of viable bacteria in the blood.
(See 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 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 335)
bacterial (septic) meningitis  See meningitis.
(See 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 914)
bactericide (bak-tøer_ùõ-sid)  An agent that kills bacteria.
(See 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 199)
bacteriocin (bak-te_re-o-sin)  A protein produced by a bacterial strain that kills other closely related strains.
(See 297, 712, 972)
bacteriophage (bak-te_re-o-føaj_)  A virus that uses bacteria as its host; often called a phage.
(See 364, 382)
bacteriophage (phage) typing  A technique in which strains of bacteria are identified based on their susceptibility to a variety of bacteriophages.
(See 842)
bacteriostatic (bak-te_re-o-stat_ik)  Inhibiting the growth and reproduction of bacteria.
(See 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 676)
baeocytes  Small, spherical, reproductive cells produced by pleurocapsalean cyanobacteria through multiple fission.
(See 475)
balanced growth  Microbial growth in which all cellular constituents are synthesized at constant rates relative to each other.
(See 114)
balanitis (bal_ah-ni_tis)  Inflammation of the glans penis usually associated with Candida fungi; a sexually transmitted disease.
(See 950)
barophilic (bar_o-fil_ik) or barophile  Organisms that prefer or require high pressures for growth and reproduction.
(See 129, 644)
barotolerant  Organisms that can grow and reproduce at high pressures but do not require them.
(See 129, 624)
basal body  The cylindrical structure at the base of procaryotic and eucaryotic flagella that attaches them to the cell.
(See 64, 90)
base analogs  Molecules that resemble normal DNA nucleotides and can substitute for them during DNA replication, leading to mutations.
(See 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 27)
basidiocarp (bah-sid_e-o-karp_)  The fruiting body of a basidiomycete that contains the basidia.
(See 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 561)
basidiospore (bah-sid_e-o-spøor)  A spore born on the outside of a basidium following karyogamy and meiosis.
(See 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 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 707)
batch culture  A culture of microorganisms produced by inoculating a closed culture vessel containing a single batch of medium.
(See 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 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 751)
benthic (ben_thic)  Pertaining to the bottom of the sea or another body of water.
(See 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 532, 797)
b-oxidation pathway  The major pathway of fatty acid oxidation to produce NADH, FADH2, and acetyl coenzyme A.
(See 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 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 376)
binary fission  Asexual reproduction in which a cell or an organism separates into two cells.
(See 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 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 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 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 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 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 1018)
biologic transmission  A type of vector-borne transmission in which a pathogen goes through some morphological or physiological change within the vector.
(See 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 505)
biomagnification  The increase in concentration of a substance in higher-level consumer organisms.
(See 618)
biopesticide  The use of a microorganism or another biological agent to control a specific pest.
(See 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 1012)
biosensor  The coupling of a biological process with production of an electrical signal or light to detect the presence of particular substances.
(See 1017)
biosynthesis  See anabolism.
(See 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 863)
biotransformation or microbial transformation  The use of living organisms to modify substances that are not normally used for growth.
(See 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 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 946)
blastospore (blas_to-spøor)  A spore formed by budding from a hypha.
(See 557)
B lymphocyte  See B cell.
(See 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 929)
bright-field microscope  A microscope that illuminates the specimen directly with bright light and forms a dark image on a brighter background.
(See 19)
Bright's disease  See glomerulonephritis.
(See 905)
broad-spectrum drugs  Chemotherapeutic agents that are effective against many different kinds of pathogens.
(See 808)
bronchial-associated lymphoid tissue (BALT)  The type of defensive tissue found in the lungs. Part of the nonspecific immune system.
(See 710)
bronchial asthma  An example of an atopic allergy involving the lower respiratory tract.
(See 769)
bubo (bu_bo)  A tender, inflamed, enlarged lymph node that results from a variety of infections.
(See 911)
bubonic plague  See plague.
(See 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 490)
bulking sludge  Sludges produced in sewage treatment that do not settle properly, usually due to the development of filamentous microorganisms.
(See 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 708)
burst  See rise period.
(See 383)
burst size  The number of phages released by a host cell during the lytic life cycle.
(See 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 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 207, A-20)
cancer (kan_ser)  A malignant tumor that expands locally by invasion of surrounding tissues, and systemically by metastasis.
(See 411)
candidal vaginitis  Vaginitis caused by Candida species.
(See 950)
candidiasis (kan_dùõ-di_ah-sis)  An infection caused by Candida species of dimorphic fungi, commonly involving the skin.
(See 949)
capsid (kap_sid)  The protein coat or shell that surrounds a virion's nucleic acid.
(See 369)
capsomer (kap_so-mer)  The ring-shaped morphological unit of which icosahedral capsids are constructed.
(See 390)
capsule  A layer of well-organized material, not easily washed off, lying outside the bacterial cell wall.
(See 61)
carboxysomes  Polyhedral inclusion bodies that contain the CO2 fixation enzyme ribulose 1,5-bisphosphate carboxylase; found in cyanobacteria, nitrifying bacteria, and thiobacilli.
(See 51, 207)
caries (kar_e-øez)  Tooth decay.
(See 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 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 854)
caseous lesion (ka_se-us)  A lesion resembling cheese or curd; cheesy. Most caseous lesions are caused by M. tuberculosis.
(See 908)
casual carrier  An individual who harbors an infectious organism for only a short period.
(See 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 173)
catabolite repression (kah-tab_o-løõt)  Inhibition of the synthesis of several catabolic enzymes by a metabolite such as glucose.
(See 281)
catalyst (kat_ah-list)  A substance that accelerates a reaction without being permanently changed itself.
(See 161)
catalytic site  See active site.
(See 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 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 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 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 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 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 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 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 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 814)
chancre (shang_ker)  The primary lesion of syphilis, occurring at the site of entry of the infection.
(See 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 914)
chemical oxygen demand (COD)  The amount of chemical oxidation required to convert organic matter in water and wastewater to CO2.
(See 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 187)
chemoheterotroph (ke_mo-het_er-o-trøof_)  See chemoorganotrophic heterotrophs.
(See 98)
chemolithotroph (ke_mo-lith_o-trøof)  See chemolithotrophic autotrophs.
(See 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 98)
chemoorganotrophic heterotrophs  Organisms that use organic compounds as sources of energy, hydrogen, electrons, and carbon for biosynthesis.
(See 98)
chemoreceptors  Special protein receptors in the plasma membrane or periplasmic space that bind chemicals and trigger the appropriate chemotaxic response.
(See 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 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 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 806)
chemotrophs (ke_mo-trøofs)  Organisms that obtain energy from the oxidation of chemical compounds.
(See 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 871)
chimera (ki-me_rah)  A recombinant plasmid containing foreign DNA, which is used as a cloning vector in genetic engineering.
(See 334)
chiral (ki_ r@l)  Having handedness: consisting of one or another stereochemical form.
(See 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 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 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 914)
chlamydospore (klam_ùõ-do-spøor_)  An asexually produced, thick-walled resting spore formed by some fungi.
(See 557)
chloramphenicol (klo_ram-fen_ õ-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 817)
chlorophyll (klor_o-fil)  The green photosynthetic pigment that consists of a large tetrapyrrole ring with a magnesium atom in the center.
(See 196)
chloroplast (klo_ra-plast)  A eucaryotic plastid that contains chlorophyll and is the site of photosynthesis.
(See 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 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 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 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 945)
chromogen (kro_me-jen)  A colorless substrate that is acted on by an enzyme to produce a colored end product.
(See 779)
chromophore group (kro_mo-føor)  A chemical group with double bonds that absorbs visible light and gives a dye its color.
(See 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 86)
chronic carrier  An individual who harbors a pathogen for a long time.
(See 854)
chrysolaminarin  The polysaccharide storage product of the chrysophytes and diatoms.
(See 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 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 89)
citric acid cycle  See tricarboxylic acid (TCA) cycle.
(See 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 758)
classification  The arrangement of organisms into groups based on mutual similarity or evolutionary relatedness.
(See 422)
clone (kløon)  A group of genetically identical cells or organisms derived by asexual reproduction from a single parent.
(See 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 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 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 934)
coagulase (ko-ag_u-las)  An enzyme that induces blood clotting; it is characteristically produced by pathogenic staphylococci.
(See 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 946)
coccus (kok_us, pl. cocci, kok_si)  A roughly spherical bacterial cell.
(See 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 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 240)
coenocytic (se²no-sit_ik)  Refers to a multinucleate cell or hypha formed by repeated nuclear divisions not accompanied by cell divisions.
(See 113, 556)
coenzyme (ko-en_zøõm)  A loosely bound cofactor that often dissociates from the enzyme active site after product has been formed.
(See 161)
cofactor  The nonprotein component of an enzyme; it is required for catalytic activity.
(See 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 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 712)
coliform (ko_lùõ-form)  A gram-negative, nonsporing, facultative rod that ferments lactose with gas formation within 48 hours at 35°C.
(See 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 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 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 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 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 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 995)
comedo (kom_ùe-do; pl., comedones)  A plug of dried sebum in an excretory duct of the skin.
(See 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 1013)
commensal (kùo-men_sal)  Living on or within another organism without injuring or benefiting the other organism.
(See 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 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 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 851)
common vehicle transmission  The transmission of a pathogen to a host by means of an inanimate medium or vehicle.
(See 857)
communicable disease  A disease associated with a pathogen that can be transmitted from one host to another.
(See 854)
community  An assemblage of different types of organisms or a mixture of different microbial populations.
(See 596)
competent  A bacterial cell that can take up free DNA fragments and incorporate them into its genome during transformation.
(See 305)
competition  An interaction between two organisms attempting to use the same resource (nutrients, space, etc.).
(See 609)
competitive exclusion principle  Two competing organisms overlap in resource use, which leads to the exclusion of one of the organisms.
(See 609, 987)
complementary DNA (cDNA)  A DNA copy of an RNA molecule (e.g., a DNA copy of an mRNA).
(See 321)
complement system  A group of plasma proteins that plays a major role in an animal's defensive immune response.
(See 714, 758)
complex medium  Culture medium that contains some ingredients of unknown chemical composition.
(See 105)
complex viruses  Viruses with capsids having a complex symmetry that is neither icosahedral nor helical.
(See 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 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 704, 948)
concatemer  A long DNA molecule consisting of several genomes linked together in a row.
(See 387)
conditional mutations  Mutations that are expressed only under certain environmental conditions.
(See 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 36)
congenital (neonatal) herpes  An infection of a newborn caused by transmission of the herpesvirus during vaginal delivery.
(See 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 876)
congenital syphilis  Syphilis that is acquired in utero from the mother.
(See 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 537, 557)
conidium (ko-nid_e-um; pl., conidia)  See conidiospore.
(See 537)
conjugants (kon_joo-gants)  Complementary mating types that participate in a form of protozoan sexual reproduction called conjugation.
(See 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 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 294)
conjunctivitis of the newborn  See ophthalmia neonatorum.
(See 916)
conoid (ko_noid)  A hollow cone of spirally coiled filaments in the anterior tip of certain apicomplexan protozoa.
(See 591)
consortium  A physical association of two different organisms, usually beneficial to both organisms.
(See 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 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 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 662)
consumer  An organism that feeds directly on living or dead animals, by ingestion or by phagocytosis.
(See 622)
contact transmission  Transmission of the pathogen by contact of the source or reservoir of the pathogen with the host.
(See 856)
continuous culture system  A culture system with constant environmental conditions maintained through continual provision of nutrients and removal of wastes.
(See 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 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 854)
copiotrophic  Having a high nutrient level.
(See 638)
corepressor (ko_re-pre_sor)  A small molecule that inhibits the synthesis of a repressible enzyme.
(See 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 69)
coryza (kùo-ri_zah)  See common cold.
(See 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 335)
cristae (kris_te)  Infoldings of the inner mitochondrial membrane.
(See 83)
cross-feeding  See syntropism.
(See 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 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 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 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 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 734)
cutaneous anthrax (ku-ta_ne-us an_thraks)  A form of anthrax involving the skin.
(See 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 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 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 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 586)
cytochromes (si_to-krøoms)  Heme proteins that carry electrons, usually as members of electron transport chains.
(See 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 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 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 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 49, 76)
cytoproct (si_to-prokt)  Site on a protozoan where undigestible matter is expelled.
(See 592)
cytosine (si_to-søen)  A pyrimidine 2-oxy-4-aminopyrimidine found in nucleosides, nucleotides, and nucleic acids.
(See 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 79)
cytostome (si_to-støom)  A permanent site in the protozoan ciliate body through which food is ingested.
(See 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 748)
cytotoxic T lymphocyte (CTL)  The activated T cell that can attack and destroy virus-infected cells, tumor cells, and foreign cells.
(See 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 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 889)
dark-field microscopy  Microscopy in which the specimen is brightly illuminated while the background is dark.
(See 22)
dark reactivation  The excision and replacement of thymine dimers in DNA that occurs in the absence of light.
(See 130)
deamination (de-am_i-na_shun)  The removal of amino groups from amino acids.
(See 192)
death phase  The decrease in viable microorganisms that occurs after the completion of growth in a batch culture.
(See 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 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 622)
defensin (de-fens_sin)  Specific peptides produced by neutrophils that permeabilize the outer and inner membranes of certain microorganisms, thus killing them.
(See 720)
defined medium  Culture medium made with components of known composition.
(See 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 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 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 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 708)
dendrogram  A treelike diagram that is used to graphically summarize mutual similarities and relationships between organisms.
(See 427)
denitrification (de-ni_trùõ-fùõ-ka_sh@n)  The reduction of nitrate to gas products, primarily nitrogen gas, during anaerobic respiration.
(See 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 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 54, 230)
dermatophyte (der_mah-to-føõt_)  A fungus parasitic on the skin.
(See 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 943)
desensitization (de-sen_si-ti-za_shun)  To make a sensitized or hypersensitive individual insensitive or nonreactive to a sensitizing agent.
(See 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 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 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 564)
diatoms (di_ah-toms)  Algal protists with siliceous cell walls called frustules. They constitute a substantial subfraction of the phytoplankton.
(See 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 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 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 106)
differential staining procedures  Staining procedures that divide bacteria into separate groups based on staining properties.
(See 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 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 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 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 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 69)
diplococcus (dip_lo-kok_us)  A pair of cocci.
(See 43)
directed- or adaptive mutation  A mutation that seems to be chosen so the organism can better adapt to its surroundings.
(See 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 848)
disease syndrome (sin_drùom)  A set of signs and symptoms that are characteristic of the disease.
(See 850)
disinfectant (dis_in-fek_tant)  An agent, usually chemical, that disinfects; normally, it is employed only with inanimate objects.
(See 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 138)
disinfection by-products (DBPs)  Chlorinated organic compounds formed during chlorine use for water disinfection. Many are carcinogens.
(See 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 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 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 650)
DNA ligase  An enzyme that joins two DNA fragments together through the formation of a new phosphodiester bond.
(See 239)
DNA microarrays (DNA chips)  Solid supports that have DNA attached in highly organized arrays and are normally used to evaluate gene expression.
(See 354, 1018)
DNA polymerase (pol-im_er-øas)  An enzyme that synthesizes new DNA using a parental DNA strand as a template.
(See 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 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 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 780)
doubling time  See generation time.
(See 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 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 856)
D value  See decimal reduction time.
(See 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 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 877)
eclipse period (e-klips_)  The initial part of the latent period in which infected host bacteria do not contain any complete virions.
(See 383)
ecosystem (ek_o-sis_tem)  A self-regulating biological community and its associated physical and chemical environment.
(See 596)
ectomycorrhizal  Referring to a mutualistic association between fungi and plant roots in which the fungus surrounds the root tip with a sheath.
(See 681)
ectoparasite (ek_to-par_ah-søõt)  A parasite that lives on the surface of its host.
(See 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 585)
ectosymbiosis  A type of symbiosis in which one organism remains outside of the other organism.
(See 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 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 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 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 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 335)
elementary body  A small, dormant body that serves as the agent of transmission between host cells in the chlamydial life cycle.
(See 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 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 176, A-13)
encystation (en-sis-_ta_shen)  The formation of a cyst.
(See 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 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 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 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 80)
endogenote (en²do-je_nøot)  The recipient bacterial cell's own genetic material into which the donor DNA can integrate.
(See 294)
endogenous infection (en-doj_ùe-nus in-fek_shun)  An infection by a member of an individual's own normal body microbiota.
(See 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 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 681)
endoparasite (en²do-par_ah-søõt)  A parasite that lives inside the body of its host.
(See 789)
endophyte (en_do-fùõt)  A microorganism living within a plant, but not necessarily parasitic on it.
(See 679)
endoplasm (en_do-plazm)  The central portion of the cytoplasm in a protozoan.
(See 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 79)
endosome (en_do-søom)  A membranous vesicle formed by endocytosis.
(See 80)
endospore (en_do-spøor)  An extremely heat- and chemical-resistant, dormant, thick-walled spore that develops within bacteria.
(See 68)
endosymbiont (en²do-sim_be-ont)  An organism that lives within the body of another organism in a symbiotic association.
(See 596)
endosymbiosis (en_do-sim_bi-o_sis)  A type of symbiosis in which one organism is found within another organism.
(See 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 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 799)
end product inhibition  See feedback inhibition.
(See 169)
energy  The capacity to do work or cause particular changes.
(See 154)
enology  The science of wine making.
(See 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 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 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 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 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 932)
enterotoxin (en²ter-o-tok_sin)  A toxin specifically affecting the cells of the intestinal mucosa, causing vomiting and diarrhea.
(See 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 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 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 55, 369)
enzootic (en²zo-ot_ik)  The moderate prevalence of a disease in a given animal population.
(See 849)
enzyme (en_zøõm)  A protein catalyst with specificity for both the reaction catalyzed and its substrates.
(See 161)
enzyme-linked immunosorbent assay (ELISA)  A technique used for detecting and quantifying specific antibodies and antigens.
(See 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 707)
epidemic (ep²ùõ-dem_ik)  A disease that suddenly increases in occurrence above the normal level in a given population.
(See 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 909)
epidemiologist (ep²ùõ-de²me-ol_o-jist)  A person who specializes in epidemiology.
(See 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 848)
episome (ep_ùõ-søom)  A plasmid that can exist either independently of the host cell's chromosome or be integrated into it.
(See 294)
epitheca (ep²ùõ-the_kah)  The larger of two halves of a diatom frustule (shell).
(See 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 731)
epizootic (ep²ùõ-zo-ot_ik)  A sudden outbreak of a disease in an animal population.
(See 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 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 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 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 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 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 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 887)
erythromycin (ùe-rith²ro-mi_sin)  An intermediate spectrum macrolide antibiotic produced by Streptomyces erythreus.
(See 817)
eschar (es_kar)  A slough produced on the skin by a thermal burn, gangrene, or the anthrax bacillus.
(See 914)
Eucarya  The domain that contains organisms composed of eucaryotic cells with primarily glycerol fatty acyl diesters in their membranes and eucaryotic rRNA.
(See 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 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 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 553)
eumycotic mycetoma (mi²se-to_mah)  See maduromycosis.
(See 945)
eutrophic (u-trof_ik)  A nutrient-enriched environment.
(See 648)
eutrophication (u²tro-fùõ-ka_shun)  The enrichment of an aquatic environment with nutrients.
(See 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 433)
excystation (ek²sis-ta_shun)  The escape of one or more cells or organisms from a cyst.
(See 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 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 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 270)
exoenzymes (ek²so-en_zøõms)  Enzymes that are secreted by cells.
(See 55)
exogenote (eks²o-je_nøot)  The piece of donor DNA that enters a bacterial cell during gene exchange and recombination.
(See 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 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 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 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 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 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 275)
extracutaneous sporotrichosis (spo²ro-tri-ko_sis)  An infection by the fungus Sporothrix schenckii that spreads throughout the body.
(See 945)
extreme barophilic bacteria  Bacteria that require a high-pressure environment to function.
(See 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 624)
extremophiles  Microorganisms that grow under harsh or extreme environmental conditions such as very high temperatures or low pHs.
(See 121, 624)
extrinsic factor  An environmental factor such as temperature that influences microbial growth in food.
(See 964)
facilitated diffusion  Diffusion across the plasma membrane that is aided by a carrier.
(See 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 127)
facultative psychrophile (fak_ul-ta²tiv si_kro-føõl)  See psychrotroph.
(See 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 750)
fatty acid synthetase (sin_thùe-tøas)  The multienzyme complex that makes fatty acids; the product usually is palmitic acid.
(See 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 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 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 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 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 722)
fever blister  See cold sore.
(See 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 295)
fimbria (fim_bre-ah; pl., fimbriae)  A fine, hairlike protein appendage on some gram-negative bacteria that helps attach them to surfaces.
(See 62)
final host  The host on/in which a parasitic organism either attains sexual maturity or reproduces.
(See 789)
first law of thermodynamics  Energy can be neither created nor destroyed (even though it can be changed in form or redistributed).
(See 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 27)
flagellin (flaj_ùe-lin)  The protein used to construct the filament of a bacterial flagellum.
(See 64)
flagellum (flah-jel_um; pl., flagella)  A thin, threadlike appendage on many procaryotic and eucaryotic cells that is responsible for their motility.
(See 63, 89)
flat or plane warts  Small, smooth, slightly raised warts.
(See 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 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 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 25)
fluorescent light (floo²o-res_ent)  The light emitted by a substance when it is irradiated with light of a shorter wavelength.
(See 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 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 926, 973)
food chain  The flow of energy and matter in living organisms through a producer-consumer sequence (See also food web).
(See 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 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 926)
food web  A network of many interlinked food chains, encompassing primary producers, consumers, decomposers, and detritivores.
(See 584)
F1 particle  Particle on the inner mitochondrial membrane, which is the site of ATP synthesis by oxidative phosphorylation.
(See 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 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 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 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 156)
French polio  See Guillain-BarrĊ½ syndrome.
(See 874)
fruiting body  A specialized structure that holds sexually or asexually produced spores; found in fungi and in some bacteria.
(See 512, 565)
frustule (frus_tøul)  A silicified cell wall in the diatoms.
(See 577)
fungicide (fun_jùõ-søõd)  An agent that kills fungi.
(See 138)
fungistatic (fun_jùõ-stat_ik)  Inhibiting the growth and reproduction of fungi.
(See 138)
fungus (fung_gus; pl., fungi)  Achlorophyllous, heterotrophic, spore-bearing eucaryotes with absorptive nutrition; usually, they have a walled thallus.
(See 553)
F value  The time in minutes at a specific temperature (usually 250°F) needed to kill a population of cells or spores.
(See 140)