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Glossary G-L
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gametangium (gam-ùe-tan_je-um; pl., gametangia)  A structure that contains gametes or in which gametes are formed.
(See page(s) 557)
gamma-proteobacteria  One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. This is the largest subgroup and is very diverse physiologically; many important genera are facultatively anaerobic chemoorganotrophs.
(See page(s) 498)
gas gangrene (gang_grøen)  A type of gangrene that arises from dirty, lacerated wounds infected by anaerobic bacteria, especially species of Clostridium. As the bacteria grow, they release toxins and ferment carbohydrates to produce carbon dioxide and hydrogen gas.
(See page(s) 915)
gastritis (gas-tri_tis)  Inflammation of the stomach.
(See page(s) 918)
gastroenteritis (gas_tro-en-ter-i_tis)  An acute inflammation of the lining of the stomach and intestines, characterized by anorexia, nausea, diarrhea, abdominal pain, and weakness. It has various causes including food poisoning due to such organisms as E. coli, S. aureus, Campylobacter (campylobacteriosis), and Salmonella species; consumption of irritating food or drink; or psychological factors such as anger, stress, and fear. Also called enterogastritis.
(See page(s) 929)
gas vacuole  A gas-filled vacuole found in cyanobacteria and some other aquatic bacteria that provides flotation. It is composed of gas vesicles, which are made of protein.
(See page(s) 51)
gene (jøen)  A DNA segment or sequence that codes for a polypeptide, rRNA, or tRNA.
(See page(s) 241)
gene gun  A device that uses high-pressure gas or another propellant to shoot a spray of DNA-coated microprojectiles into cells and transform them. Sometimes it is called a biolistic device.
(See page(s) 335)
generalized transduction  The transfer of any part of a bacterial genome when the DNA fragment is packaged within a phage capsid by mistake.
(See page(s) 308)
general recombination  Recombination involving a reciprocal exchange of a pair of homologous DNA sequences; it can occur any place on the chromosome.
(See page(s) 292)
generation time  The time required for a microbial population to double in number.
(See page(s) 115)
genetic engineering  The deliberate modification of an organism's genetic information by directly changing its nucleic acid genome.
(See page(s) 320)
genital herpes (her_pøez)  A sexually transmitted disease caused by the herpes simplex virus type 2.
(See page(s) 885)
genital ulcer disease  See chancroid.
(See page(s) 914)
genome (je_nøom)  The full set of genes present in a cell or virus; all the genetic material in an organism; a haploid set of genes in a cell.
(See page(s) 228)
genomics  The study of the molecular organization of genomes, their information content, and the gene products they encode.
(See page(s) 345)
genus (je_n@s)  A well-defined group of one or more species that is clearly separate from other genera.
(See page(s) 426)
geographic information system (GIS)  A data management system that organizes and displays digital map data from remote sensing and aids in the analysis of relationships between mapped features.
(See page(s) 850)
German measles  See rubella.
(See page(s) 875)
germicide (jer_mùõ-søõd)  An agent that kills pathogens and many nonpathogens but not necessarily bacterial endospores.
(See page(s) 138)
germination (jer²mùõ-na_shun)  The stage following bacterial endospore activation in which the endospore breaks its dormant state. Germination is followed by outgrowth.
(See page(s) 71)
Ghon complex (gon)  The initial focus of parenchymal infection in primary pulmonary tuberculosis.
(See page(s) 908)
giardiasis (je²ar-di_ah-sis)  A common intestinal disease caused by the parasitic protozoan Giardia lamblia.
(See page(s) 953)
gingivitis (jin-jùõ-vi_tis)  Inflammation of the gingival tissue.
(See page(s) 936)
gingivostomatitis (jin²jùõ-vo-sto²m@-ti_tis)  Inflammation of the gingiva and other oral mucous membranes.
(See page(s) 884)
gliding motility  A type of motility in which a microbial cell glides along when in contact with a solid surface.
(See page(s) 66, 482)
global regulatory systems  Regulatory systems that simultaneously affect many genes and pathways.
(See page(s) 281)
glomerulonephritis (glo-mer²u-lo-nùe-fri_tis)  An inflammatory disease of the renal glomeruli.
(See page(s) 905)
glucans  Polysaccharides composed of glucose units held together by glycosidic linkages. Some types of glucans have a(1_3) and a(1_6) linkages and bind bacterial cells together on teeth forming a plaque ecosystem.
(See page(s) 936)
gluconeogenesis (gloo_ko-ne_o-jen_e-sis)  The synthesis of glucose from noncarbohydrate precursors such as lactate and amino acids.
(See page(s) 209)
glycocalyx (gli_ko-kal_iks)  A network of polysaccharides extending from the surface of bacteria and other cells.
(See page(s) 61)
glycogen (gli_ko-jen)  A highly branched polysaccharide containing glucose, which is used to store carbon and energy.
(See page(s) 49, A-6)
glycolysis (gli-kol_ùõ-sis)  The anaerobic conversion of glucose to lactic acid by use of the Embden-Meyerhof pathway.
(See page(s) 176)
glycolytic pathway (gli_ko-lit_ik)  See Embden-Meyerhof pathway.
(See page(s) 176, A-13)
glyoxylate cycle (gli-ok_sùõ-lat)  A modified tricarboxylic acid cycle in which the decarboxylation reactions are bypassed by the enzymes isocitrate lyase and malate synthase; it is used to convert acetyl-CoA to succinate and other metabolites.
(See page(s) 216)
gnotobiotic (no_to-bi-ot_ik)  Animals that are germfree (microorganism free) or live in association with one or more known microorganisms.
(See page(s) 698)
Golgi apparatus (gol_je)  A membranous eucaryotic organelle composed of stacks of flattened sacs (cisternae), which is involved in packaging and modifying materials for secretion and many other processes.
(See page(s) 80)
gonococci (gon_o-kok_si)  Bacteria of the species Neisseria gonorrhoeae-the organism causing gonorrhea.
(See page(s) 915)
gonorrhea (gon_o-re_ah)  An acute infectious sexually transmitted disease of the mucous membranes of the genitourinary tract, eye, rectum, and throat. It is caused by Neisseria gonorrhoeae.
(See page(s) 915)
graft-versus-host disease  A disease that results when mature post-thymic T cells in donor grafts (e.g., bone marrow) recognize the host as foreign and attack it.
(See page(s) 773)
Gram stain  A differential staining procedure that divides bacteria into gram-positive and gram-negative groups based on their ability to retain crystal violet when decolorized with an organic solvent such as ethanol.
(See page(s) 28)
grana (gra_nah)  A stack of thylakoids in the chloroplast stroma.
(See page(s) 85)
granuloma (gran²u-lo_m@)  Term applied to nodular inflammatory lesions containing phagocytic cells.
(See page(s) 714)
greenhouse gases  Gases released from the earth's surface through chemical and biological processes that interact with the chemicals in the stratosphere to decrease the release of radiation from the earth. It is believed that this leads to global warming.
(See page(s) 689)
griseofulvin (gris²e-o-ful_vin)  An antibiotic from Penicillium griseofulvum given orally to treat chronic dermatophytic infections of skin and nails.
(See page(s) 820)
group translocation  A transport process in which a molecule is moved across a membrane by carrier proteins while being chemically altered at the same time.
(See page(s) 103)
growth  An increase in cellular constituents.
(See page(s) 113)
growth factors  Organic compounds that must be supplied in the diet for growth because they are essential cell components or precursors of such components and cannot be synthesized by the organism.
(See page(s) 99)
guanine (gwan_in)  A purine derivative, 2-amino-6-oxypurine, found in nucleosides, nucleotides, and nucleic acids.
(See page(s) 217)
Guillain-Barr syndrome (ge-yan_bar-ra_)  A relatively rare disease affecting the peripheral nervous system, especially the spinal nerves, but also the cranial nerves. The cause is unknown, but it most often occurs after an influenza infection or flu vaccination. Also called French Polio.
(See page(s) 874)
gumma (gum_ah)  A soft, gummy tumor occurring in tertiary syphilis.
(See page(s) 924)
gut-associated lymphoid tissue (GALT)  The defensive lymphoid tissue present in the intestines. See Peyer's patches.
(See page(s) 710)
H-2 complex  Term for the MHC in the mouse.
(See page(s) 745)
halobacteria or extreme halophiles  A group of archaea that have an absolute dependence on high NaCl concentrations for growth and will not survive at a concentration below about 1.5 M NaCl.
(See page(s) 461)
halophile (hal_o-føõl)  A microorganism that requires high levels of sodium chloride for growth.
(See page(s) 123)
Hansen's disease  See leprosy.
(See page(s) 916)
hantavirus pulmonary syndrome  The disease in humans caused by the pulmonary syndrome hantavirus. Deer mice shed the virus in their feces, humans inhale the virus and first develop ordinary flulike aches and pains. Within a few days the hantavirus causes lung damage and capillary leakage. After about a week the infected person enters a crisis phase and may die.
(See page(s) 877)
hapten (hap_ten)  A molecule not immunogenic by itself but that, when coupled to a macromolecular carrier, can elicit antibodies directed against itself.
(See page(s) 731)
harborage transmission  The mode of transmission in which an infectious organism does not undergo morphological or physiological changes within the vector.
(See page(s) 858)
hay fever  Allergic rhinitis; a type of atopic allergy involving the upper respiratory tract.
(See page(s) 768)
health (helth)  A state of optimal physical, mental, and social well-being, and not merely the absence of disease and infirmity.
(See page(s) 848)
healthy carrier  An individual who harbors a pathogen, but is not ill.
(See page(s) 854)
heat-shock proteins  Proteins produced when cells are exposed to high temperatures or other stressful conditions. They protect the cells from damage and often aid in the proper folding of proteins.
(See page(s) 273)
helical (hel_ùõ-kal)  In virology this refers to a virus with a helical capsid surrounding its nucleic acid.
(See page(s) 369)
helicases  Enzymes that use ATP energy to unwind DNA ahead of the replication fork.
(See page(s) 236)
hemadsorption (hem²ad-sorp_shun)  The adherence of red blood cells to the surface of something, such as another cell or a virus.
(See page(s) 832)
hemagglutination (hem²ah-gloo²tùõ-na_shun)  The agglutination of red blood cells by antibodies.
(See page(s) 756)
hemagglutinin (hem²ah-gloo_tùõ-nin)  The antibody responsible for a hemagglutination reaction.
(See page(s) 756)
hemoflagellate (he²mo-flaj_ùe-løøat)  A flagellated protozoan parasite that is found in the bloodstream.
(See page(s) 956)
hemolysin (he-mol_ùõ-sin)  A substance that causes hemolysis (the lysis of red blood cells). At least some hemolysins are enzymes that destroy the phospholipids in erythrocyte plasma membranes.
(See page(s) 797)
hemolysis (he-mol_ùõ-sis)  The disruption of red blood cells and release of their hemoglobin. There are several types of hemolysis when bacteria such as streptococci and staphylococci grow on blood agar. In a-hemolysis, a narrow greenish zone of incomplete hemolysis forms around the colony. A clear zone of complete hemolysis without any obvious color change is formed during b-hemolysis.
(See page(s) 531, 797)
hemolytic uremic syndrome  A kidney disease characterized by blood in the urine and often by kidney failure. It is caused by enterohemorrhagic strains of Escherichia coli O157:H7 that produce a Shiga-like toxin, which attacks the kidneys.
(See page(s) 932)
hemorrhagic fever  A fever usually caused by a specific virus that may lead to hemorrhage, shock, and sometimes death.
(See page(s) 877)
hepatitis (hep²ah-ti_tis)  Any infection that results in inflammation of the liver. Also refers to liver inflammation as such.
(See page(s) 889)
hepatitis A (formerly infectious hepatitis; hep²ah-ti_tis)  A type of hepatitis that is transmitted by fecal-oral contamination; it primarily affects children and young adults, especially in environments where there is poor sanitation and overcrowding. It is caused by the hepatitis A virus, a single-stranded RNA virus.
(See page(s) 892)
hepatitis B (formerly serum hepatitis; hep²ah-ti_tis)  This form of hepatitis is caused by a double-stranded DNA virus (HBV) formerly called the "Dane particle." The virus is transmitted by body fluids.
(See page(s) 889)
hepatitis C  About 90% of all cases of viral hepatitis can be traced to either HAV or HBV. The remaining 10% is believed to be caused by one and possibly several other types of viruses. At least one of these is hepatitis C (formerly non-A, non-B).
(See page(s) 890)
hepatitis D (formerly delta hepatitis)  The liver diseases caused by the hepatitis D virus in those individuals already infected with the hepatitis B virus.
(See page(s) 891)
hepatitis E (formerly enteric-transmitted NANB hepatitis)  The liver disease caused by the hepatitis E virus. Usually, a subclinical, acute infection results; however, there is a high mortality in women in their last trimester of pregnancy.
(See page(s) 892)
herd immunity  The resistance of a population to infection and spread of an infectious organism due to the immunity of a high percentage of the population.
(See page(s) 851)
herpes labialis  See cold sore.
(See page(s) 884)
herpetic keratitis (her-pet_ik ker²ah-ti_tis)  An inflammation of the cornea and conjunctiva of the eye resulting from a herpes simplex virus infection.
(See page(s) 884)
heterocysts  Specialized cells produced by cyanobacteria that are the sites of nitrogen fixation.
(See page(s) 473)
heteroduplex DNA  A double-stranded stretch of DNA formed by two slightly different strands that are not completely complementary.
(See page(s) 292)
heterogeneous nuclear RNA (hnRNA)  The RNA transcript of DNA made by RNA polymerase II; it is then processed to form mRNA.
(See page(s) 263)
heterolactic fermenters (het_er-o-lak_tik)  Microorganisms that ferment sugars to form lactate, and also other products such as ethanol and CO2.
(See page(s) 181)
heterotroph (het_er-o-trøof_)  An organism that uses reduced, preformed organic molecules as its principal carbon source.
(See page(s) 96)
heterotrophic nitrification  Nitrification carried out by chemoheterotrophic microorganisms.
(See page(s) 615)
hexon or hexamer  A capsomer composed of six protomers.
(See page(s) 370)
hexose monophosphate pathway (hek_søos mon_o-fos_føøat)  See pentose phosphate pathway.
(See page(s) 177)
Hfr strain  A bacterial strain that donates its genes with high frequency to a recipient cell during conjugation because the F factor is integrated into the bacterial chromosome.
(See page(s) 303)
high-energy molecule  A molecule whose hydrolysis under standard conditions makes available a large amount of free energy (the standard free energy change is more negative than about 27 kcal/mole); a high-energy molecule readily decomposes and transfers groups such as phosphate to acceptors.
(See page(s) 157)
high oxygen diffusion environment  A microbial environment in close contact with air and through which oxygen can move at a rapid rate (in comparison with the slow diffusion rate of oxygen through water).
(See page(s) 635)
histone (his_tøon)  A small basic protein with large amounts of lysine and arginine that is associated with eucaryotic DNA in chromatin.
(See page(s) 234)
histoplasmosis (his_to-plaz-mo_sis)  A systemic fungal infection caused by Histoplasma capsulatum var capsulatum.
(See page(s) 947)
hives (hùõvz)  An eruption of the skin.
(See page(s) 769)
holdfast  A structure produced by some bacteria and algae that attaches the cell to a solid object.
(See page(s) 491)
holoenzyme  A complete enzyme consisting of the apoenzyme plus a cofactor.
(See page(s) 161)
holozoic nutrition (hol_o-zo_ik)  In this type of nutrition, nutrients (such as bacteria) are acquired by phagocytosis and the subsequent formation of a food vacuole or phagosome.
(See page(s) 586)
homolactic fermenters (ho_mo-lak_tik)  Organisms that ferment sugars almost completely to lactic acid.
(See page(s) 181)
horizontal gene transfer  The process in which genes are transferred from one mature, independent organism to another.
(See page(s) 292)
hormogonia  Small motile fragments produced by fragmentation of filamentous cyanobacteria; used for asexual reproduction and dispersal.
(See page(s) 473)
host (høost)  The body of an organism that harbors another organism. It can be viewed as a microenvironment that shelters and supports the growth and multiplication of a parasitic organism.
(See page(s) 788)
host restriction  The degradation of foreign genetic material by nucleases after the genetic material enters a host cell.
(See page(s) 294)
human herpesvirus 6 (HHV-6, type A and B) (h@r_pøez)  HHV-6 was discovered in 1986 and was initially called the human B-lymphotropic virus. The virus was later shown to have a marked tropism for CD41 T cells and was renamed HHV-6. HHV-6 is genetically similar to cytomegalovirus. HHV-6 causes exanthem subitum (roseola infantum or sixth disease) in infants and has been suspected of involvement in many conditions, including opportunistic infections in immunocompromised patients, hepatitis, lymphoproliferative diseases, synergistic interactions with HIV, lymphadenitis, and chronic fatigue syndrome.
(See page(s) 887)
human immunodeficiency virus (HIV)  A lentivirus of the family Retroviridae that is associated with the onset of AIDS.
(See page(s) 878)
human leukocyte antigen complex (HLA)  An antigen on the surface of cells of human tissues and organs that is recognized by the immune system cells and therefore is important in graft rejection and regulation of the immune response. This is the same as MHC class II.
(See page(s) 745)
humoral (antibody-mediated) immunity (hu_mor-al)  The type of immunity that results from the presence of soluble antibodies in blood and lymph; also known as antibody-mediated immunity.
(See page(s) 729)
hybridoma (hi_brùõ-do_mah)  A fast-growing cell line produced by fusing a cancer cell (myeloma) to another cell, such as an antibody-producing cell.
(See page(s) 743)
hydrogenosome (hi-dro-jen_osom)  A microbodylike organelle that contains a unique electron transfer pathway in which hydrogenase transfers electrons to protons (which act as the terminal electron acceptors) and molecular hydrogen is formed.
(See page(s) 585)
hydrophilic (hi_dro-fil_ik)  A polar substance that has a strong affinity for water (or is readily soluble in water).
(See page(s) 46)
hydrophobic (hi²dro-fo_bik)  A nonpolar substance lacking affinity for water (or which is not readily soluble in water).
(See page(s) 46)
hyperendemic disease (hi²per-en-dem_ik)  A disease that has a gradual increase in occurrence beyond the endemic level, but not at the epidemic level, in a given population; also may refer to a disease that is equally endemic in all age groups.
(See page(s) 849)
hypermutation  A rapid production of multiple mutations in a gene or genes through the activation of special mutator genes. The process may be deliberately used to maximize the possibility of creating desirable mutants.
(See page(s) 246)
hypersensitivity (hi²per-sen_si-tiv²i-te)  A condition of increased immune sensitivity in which the body reacts to an antigen with an exaggerated immune response that usually harms the individual. Also termed an allergy.
(See page(s) 768)
hyperthermophile (hi²per-ther_mo-fùõl)  A bacterium that has its growth optimum between 80 degrees C and about 113 degrees C. Hyperthermophiles usually do not grow well below 55 degrees C.
(See page(s) 126, 626)
hypha (hi_fah; pl., hyphae)  The unit of structure of most fungi and some bacteria; a tubular filament.
(See page(s) 556)
hypoferremia (hi²po-fùe-re_me-ah)  Deficiency of iron in the blood.
(See page(s) 723)
hypotheca (hi-po-theca)  The smaller half of a diatom frustule.
(See page(s) 577)
hypothesis  A tentative assumption or educated guess developed to explain a set of observations.
(See page(s) 8)
hypoxic (hi pok_sik)  Having a low oxygen level.
(See page(s) 635)
icosahedral  In virology this term refers to a virus with an icosahedral capsid, which has the shape of a regular polyhedron having 20 equilateral triangular faces and 12 corners.
(See page(s) 369)
identification (i-den_tùõ-fùõ-ka_shun)  The process of determining that a particular isolate or organism belongs to a recognized taxon.
(See page(s) 422)
idiotype (id_e-o-tøõp_)  A set of one or more unique epitopes in the variable region of an immunoglobulin that distinguishes it from immunoglobulins produced by different plasma cells.
(See page(s) 734)
IgA  Immunoglobulin A; the class of immunoglobulins that is present in dimeric form in many body secretions (e.g., saliva, tears, and bronchial and intestinal secretions) and protects body surfaces. IgA also is present in serum.
(See page(s) 736)
IgD  Immunoglobulin D; the class of immunoglobulins found on the surface of many B lymphocytes; thought to serve as an antigen receptor in the stimulation of antibody synthesis.
(See page(s) 738)
IgE  Immunoglobulin E; the immunoglobulin class that binds to mast cells and basophils, and is responsible for type I or anaphylactic hypersensitivity reactions such as hay fever and asthma. IgE is also involved in resistance to helminth parasites.
(See page(s) 738)
IgG  Immunoglobulin G; the predominant immunoglobulin class in serum. Has functions such as neutralizing toxins, opsonizing bacteria, activating complement, and crossing the placenta to protect the fetus and neonate.
(See page(s) 736)
IgM  Immunoglobulin M; the class of serum antibody first produced during an infection. It is a large, pentameric molecule that is active in agglutinating pathogens and activating complement. The monomeric form is present on the surface of some B lymphocytes.
(See page(s) 736)
immobilization (im-mo_bil-i-za_shun)  The incorporation of a simple, soluble substance into the body of an organism, making it unavailable for use by other organisms.
(See page(s) 613)
immune complex (ùõ-møun_kom_pleks)  The product of an antigen-antibody reaction, which may also contain components of the complement system.
(See page(s) 756)
immune surveillance (ùõ-møun_sur-vøal_ans)  The still somewhat hypothetical process in which lymphocytes such as natural killer (NK) cells recognize and destroy tumor cells; other cells with abnormal surface antigens (e.g., virus-infected cells) also may be destroyed.
(See page(s) 760)
immune system  The defensive system in a host consisting of the nonspecific and specific immune responses. It is composed of widely distributed cells, tissues, and organs that recognize foreign substances and microorganisms and acts to neutralize or destroy them.
(See page(s) 705)
immunity (ùõ-mu_nùõ-te)  Refers to the overall general ability of a host to resist a particular disease; the condition of being immune.
(See page(s) 705)
immunoblotting  The electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets to demonstrate the presence of specific proteins through reaction with labeled antibodies.
(See page(s) 779)
immunodeficiency (im²u-no-dùe-fish_en-se; pl., immunodeficiencies)  The inability to produce a normal complement of antibodies or immunologically sensitized T cells in response to specific antigens.
(See page(s) 774)
immunodiffusion  A technique involving the diffusion of antigen and/or antibody within a semisolid gel to produce a precipitin reaction where they meet in proper proportions. Often both the antibody and antigen diffuse through the gel; sometimes an antigen diffuses through a gel containing antibody.
(See page(s) 779)
immunoelectrophoresis (ùõ-mu_no-e-lek_tro-fo-re_sis; pl., immunoelectrophoreses)  The electrophoretic separation of protein antigens followed by diffusion and precipitation in gels using antibodies against the separated proteins.
(See page(s) 781)
immunofluorescence (im_u-no-floo_o-res_ens)  A technique used to identify particular antigens microscopically in cells or tissues by the binding of a fluorescent antibody conjugate.
(See page(s) 781)
immunoglobulin (Ig; im_u-no-glob_u-lin)  See antibody.
(See page(s) 734)
immunology (im_u-nol_o-je)  The branch of science that deals with the immune system and attempts to understand the many phenomena that are responsible for both acquired and innate immunity. It also includes the use of antibody-antigen reactions in other laboratory work (serology and immunochemistry).
(See page(s) 705)
immunopathology (im_u-no-p@-thol_o-je)  The study of diseases or conditions resulting from immune reactions.
(See page(s) 790)
immunoprecipitation (im_u-no-pre-sip_i-ta_shun)  A reaction involving soluble antigens reacting with antibodies to form a large aggregate that precipitates out of solution.
(See page(s) 781)
immunotoxin (im_u-no-tok_sin)  A monoclonal antibody that has been attached to a specific toxin or toxic agent (antibody 1 toxin 5 immunotoxin) and can kill specific target cells.
(See page(s) 744)
impetigo (im_p@-ti_go)  This superficial cutaneous disease, most commonly seen in children, is characterized by crusty lesions, usually located on the face; the lesions typically have vesicles surrounded by a red border. It is the most frequently diagnosed skin infection caused by S. pyogenes (impetigo can also be caused by S. aureus).
(See page(s) 903)
inclusion bodies  Granules of organic or inorganic material lying in the cytoplasmic matrix of bacteria.
(See page(s) 49, 410)
inclusion conjunctivitis (in-klu_zhun kon-junk_tùõ-vi_tis)  An acute infectious disease that occurs throughout the world. It is caused by Chlamydia trachomatis that infects the eye and causes inflammation and the occurrence of large inclusion bodies.
(See page(s) 916)
incubation period  The period after pathogen entry into a host and before signs and symptoms appear.
(See page(s) 850)
incubatory carrier  An individual who is incubating a pathogen in large numbers but is not yet ill.
(See page(s) 854)
index case  The first disease case in an epidemic within a given population.
(See page(s) 849)
indicator organism  An organism whose presence indicates the condition of a substance or environment, for example, the potential presence of pathogens. Coliforms are used as indicators of fecal pollution.
(See page(s) 654)
inducer (in-døus_er)  A small molecule that stimulates the synthesis of an inducible enzyme.
(See page(s) 275)
inducible enzyme  An enzyme whose level rises in the presence of a small molecule that stimulates its synthesis.
(See page(s) 275)
industrial ecology  The study of the ecology of industrial societies with a major focus on material cycling, energy flow, and the ecological impacts of such societies.
(See page(s) 1022)
infantile paralysis (in_fan-til pah-ral_i-sis)  See poliomyelitis.
(See page(s) 892)
infection (in-fek_shun)  The invasion of a host by a microorganism with subsequent establishment and multiplication of the agent. An infection may or may not lead to overt disease.
(See page(s) 789)
infection thread  A tubular structure formed during the infection of a root by nitrogen-fixing bacteria. The bacteria enter the root by way of the infection thread and stimulate the formation of the root nodule.
(See page(s) 676)
infectious disease  Any change from a state of health in which part or all of the host's body cannot carry on its normal functions because of the presence of an infectious agent or its products.
(See page(s) 789)
infectious disease cycle (chain of infection)  The chain or cycle of events that describes how an infectious organism grows, reproduces, and is disseminated.
(See page(s) 852)
infectious dose 50 (ID50)  Refers to the dose or number of organisms that will infect 50% of an experimental group of hosts within a specified time period.
(See page(s) 368, 790)
infectious mononucleosis (mono; mon_o-nu_kle-o_sis)  An acute, self-limited infectious disease of the lymphatic system caused by the Epstein-Barr virus and characterized by fever, sore throat, lymph node and spleen swelling, and the proliferation of monocytes and abnormal lymphocytes.
(See page(s) 888)
infectivity (in_fek-tiv_i-te)  Infectiousness; the state or quality of being infectious or communicable.
(See page(s) 790)
inflammation (in_flah-ma_shun)  A localized protective response to tissue injury or destruction. Acute inflammation is characterized by pain, heat, swelling, and redness in the injured area.
(See page(s) 712)
influenza or flu (in_flu-en_zah)  An acute viral infection of the respiratory tract, occurring in isolated cases, epidemics, and pandemics. Influenza is caused by three strains of influenza virus, labeled types A, B, and C, based on the antigens of their protein coats.
(See page(s) 872)
ingoldian fungi  Aquatic hyphomycetes that often have a characteristic tetraradiate hyphal development form and which sporulate under water. Discovered by the British mycologist, C. T. Ingold, in the 1940s.
(See page(s) 641)
initial body  See reticulate body (RB).
(See page(s) 477)
innate or natural immunity  See nonspecific resistance.
(See page(s) 705)
insertion sequence (in-ser_shun se_kwens)  A simple transposon that contains genes only for those enzymes, such as the transposase, that are required for transposition.
(See page(s) 298)
integration  The incorporation of one DNA segment into a second DNA molecule to form a new hybrid DNA. Integration occurs during such processes as genetic recombination, episome incorporation into host DNA, and prophage insertion into the bacterial chromosome.
(See page(s) 394)
integrins (in_t@-grin)  A large and broadly distributed family of a/b heterodimers. Integrins are cellular adhesion receptors that mediate cell-cell and cell-substratum interactions. Integrins usually recognize linear amino acid sequences on protein ligands.
(See page(s) 712)
inteins  Internal intervening sequences of precursor self-splicing proteins that separate exteins and are removed during formation of the final protein.
(See page(s) 275)
intercalating agents  Molecules that can be inserted between the stacked bases of a DNA double helix, thereby distorting the DNA and inducing insertion and deletion mutations.
(See page(s) 248)
interdigitating dendritic cell  Special dendritic cells in the lymph nodes that function as potent antigen-presenting cells and develop from Langerhans cells.
(See page(s) 710)
interferon (IFN; in²t@r-føer_on)  A glycoprotein that has nonspecific antiviral activity by stimulating cells to produce antiviral proteins, which inhibit the synthesis of viral RNA and proteins. Interferons also regulate the growth, differentiation, and/or function of a variety of immune system cells. Their production may be stimulated by virus infections, intracellular pathogens (chlamydiae and rickettsias), protozoan parasites, endotoxins, and other agents.
(See page(s) 721, 822)
interleukin (in²t@r-loo_kin)  A glycoprotein produced by macrophages and T cells that regulates growth and differentiation, particularly of lymphocytes. Interleukins promote cellular and humoral immune responses.
(See page(s) 720)
intermediate filaments (in²ter-me_de-it fil_ah-ments)  Small protein filaments, about 8 to 10 nm in diameter, in the cytoplasmic matrix of eucaryotic cells that are important in cell structure.
(See page(s) 79)
intermediate host (in²ter-me_de-it høost)  The host that serves as a temporary but essential environment for development of a parasite and completion of its life cycle.
(See page(s) 789)
interspecies hydrogen transfer  The linkage of hydrogen production from organic matter by anaerobic heterotrophic microorganisms to the use of hydrogen by other anaerobes in the reduction of carbon dioxide to methane. This avoids possible hydrogen toxicity.
(See page(s) 604)
intertriginous candidiasis  A skin infection caused by Candida species. Involves those areas of the body, usually opposed skin surfaces, that are warm and moist (axillae, groin, skin folds).
(See page(s) 950)
intoxication (in-tok²si-ka_shun)  A disease that results from the entrance of a specific toxin into the body of a host. The toxin can induce the disease in the absence of the toxin-producing organism.
(See page(s) 794)
intraepidermal lymphocytes  T cells found in the epidermis of the skin that express the gd T-cell receptor.
(See page(s) 710)
intranuclear inclusion body (in²trah-nu_kel-ar)  A structure found within cells infected with the cytomegalovirus.
(See page(s) 885)
intrinsic factors  Food-related factors such as moisture, pH, and available nutrients that influence microbial growth.
(See page(s) 964)
intron (in_tron)  A noncoding intervening sequence in a split or interrupted gene, which codes for RNA that is missing from the final RNA product.
(See page(s) 263)
invasiveness (in-va_siv-nes)  The ability of a microorganism to enter a host, grow and reproduce within the host, and spread throughout its body.
(See page(s) 790)
ionizing radiation  Radiation of very short wavelength or high energy that causes atoms to lose electrons or ionize.
(See page(s) 130, 144)
isotype (i_so-tøõp)  A variant form of an immunoglobulin (e.g., an immunoglobulin class, subclass, or type) that occurs in every normal individual of a particular species. Usually the characteristic antigenic determinant is in the constant region of H and L chains.
(See page(s) 734)
Jaccard coefficient (SJ)  An association coefficient used in numerical taxonomy; it is the proportion of characters that match, excluding those that both organisms lack.
(See page(s) 427)
J chain  A polypeptide present in polymeric IgM and IgA that links the subunits together.
(See page(s) 736)
jock itch  See tinea cruris.
(See page(s) 944)
kelp (kelp)  A common name for any of the larger members of the order Laminariales of the brown algae.
(See page(s) 578)
keratinocyte  Cell found in skin-associated lymphoid tissue; secretes cytokines that may induce an inflammatory response.
(See page(s) 709)
keratitis (ker_ah-ti_tis)  Inflammation of the cornea of the eye.
(See page(s) 953)
kinetoplast (ki-ne_to-plast)  A special structure in the mitochondrion of kinetoplastid protozoa. It contains the mitochondrial DNA.
(See page(s) 588)
Kirby-Bauer method  A disk diffusion test to determine the susceptibility of a microorganism to chemotherapeutic agents.
(See page(s) 809)
Koch's postulates (koks pos_tu-løats)  A set of rules for proving that a microorganism causes a particular disease.
(See page(s) 7)
Koplik's spots (kop_liks)  Lesions of the oral cavity caused by the measles (rubeola) virus that are characterized by a bluish white speck in the center of each.
(See page(s) 874)
Korean hemorrhagic fever  An acute infection caused by a virus that produces varying degrees of hemorrhage, shock, and sometimes death. Krebs cycle See tricarboxylic acid (TCA)cycle.
(See page(s) 183, 877)
lactic acid fermentation (lak_tik)  A fermentation that produces lactic acid as the sole or primary product.
(See page(s) 179, A-19)
lager  Pertaining to the process of aging beers to allow flavor development.
(See page(s) 983)
lag phase  A period following the introduction of microorganisms into fresh culture medium when there is no increase in cell numbers or mass during batch culture.
(See page(s) 113)
laminarin (lam_i-na_rin)  One of the principal storage products of the golden-brown algae; a polymer of glucose.
(See page(s) 578)
Lancefield system (group; lans_feld)  One of the serologically distinguishable groups (as group A, group B) into which streptococci can be divided.
(See page(s) 532, 784)
land farming  The addition of waste material, such as a hydrocarbon waste, to the soil surface so that it will be degraded. The soil may be moistened or mixed to stimulate the desired degradation process.
(See page(s) 1011)
Langerhans cell  Cell found in the skin that internalizes antigen and moves in the lymph to lymph nodes where it differentiates into a dendritic cell.
(See page(s) 709)
late mRNA  Messenger RNA produced later in a virus infection, which codes for proteins needed in capsid construction and virus release.
(See page(s) 387)
latent period (la_tent)  The initial phase in the one-step growth experiment in which no phages are released.
(See page(s) 383)
latent virus infections  Virus infections in which the virus quits reproducing and remains dormant for a period before becoming active again.
(See page(s) 410)
leader sequence  A nontranslated sequence at the 5_ end of mRNA that lies between the operator and the initiation codon; it aids in the initiation and regulation of transcription.
(See page(s) 244, 261)
lectin complement pathway (lek_tin)  The lectin pathway for complement activation is triggered by the binding of a serum lectin (mannan-binding lectin; MBL) to mannose-containing proteins or to carbohydrates on viruses or bacteria.
(See page(s) 716)
legionellosis (le_j@-nel-o_sis)  See Legionnaires' disease.
(See page(s) 901)
Legionnaires' disease (legionellosis)  A pulmonary form of legionellosis, resulting from infection with Legionella pneumophila.
(See page(s) 901)
leishmanias (løesh_ma_ne-ùas)  Zooflagellates, members of the genus Leishmania, that cause the disease leishmaniasis.
(See page(s) 956)
leishmaniasis (løesh_mah-ni_ah-sis)  The disease caused by the protozoa called leishmanias.
(See page(s) 956)
lepromatous (progressive) leprosy (lep-ro_mah-tus lep_ro-se)  A relentless, progressive form of leprosy in which large numbers of Mycobacterium leprae develop in skin cells, killing the skin cells and resulting in the loss of features. Disfiguring nodules form all over the body.
(See page(s) 916)
leprosy (lep_ro-se) or Hansen's disease  A severe disfiguring skin disease caused by Mycobacterium leprae.
(See page(s) 916)
lethal dose 50 (LD50)  Refers to the dose or number of organisms that will kill 50% of an experimental group of hosts within a specified time period.
(See page(s) 368, 790)
leukemia (loo-ke_me-ah)  A progressive, malignant disease of blood-forming organs, marked by distorted proliferation and development of leukocytes and their precursors in the blood and bone marrow. Certain leukemias are caused by viruses (HTLV-1, HTLV-2).
(See page(s) 887)
leukocidin (loo_ko-si_din)  A microbial toxin that can damage or kill leukocytes.
(See page(s) 797)
leukocyte (loo_ko-søõt)  Any colorless white blood cell. Can be classified into granular and agranular lymphocytes.
(See page(s) 705)
lichen (li_ken)  An organism composed of a fungus and either green algae or cyanobacteria in a symbiotic association.
(See page(s) 598)
Liebig's law of the minimum (le_bigz)  Living organisms and populations will grow until lack of a resource begins to limit further growth.
(See page(s) 131)
lipopolysaccharide (lip_o-pol_e-sak_ah-røõd)  A molecule containing both lipid and polysaccharide, which is important in the outer membrane of the gram-negative cell wall.
(See page(s) 58)
liposome (lip_o-som)  A spherical particle formed by a lipid bilayer enclosing an aqueous solution. It may be used to administer chemotherapeutic agents or in diagnostic testing.
(See page(s) 782)
listeriosis (lis-ter_e-o_sis)  A sporadic disease of animals and humans, particularly those who are immunocompromised or pregnant, caused by the bacterium Listeria monocytogenes.
(See page(s) 931)
lithotroph (lith_o-trøof)  An organism that uses reduced inorganic compounds as its electron source.
(See page(s) 97)
log phase  See exponential phase.
(See page(s) 114)
lophotrichous (lo-fot_rùõ-kus)  A cell with a cluster of flagella at one or both ends.
(See page(s) 63)
low oxygen diffusion environment  An aquatic environment in which microorganisms are surrounded by deep water layers that limit oxygen diffusion to the cell surface. In contrast, microorganisms in thin water films have good oxygen transfer from air to the cell surface.
(See page(s) 635)
LPS-binding protein  A special plasma protein that binds bacterial lipopolysaccharides and then attaches to receptors on monocytes, macrophages, and other cells. This triggers the release of IL-1 and other cytokines that stimulate the development of fever and additional endotoxin effects.
(See page(s) 801)
Lyme disease (LD, Lyme borreliosis; løõm)  A tick-borne disease caused by the spirochete Borrella burgdorferi.
(See page(s) 910)
lymph node  A small secondary lymphoid organ that contains lymphocytes, macrophages, and dendritic cells. It serves as a site for (1) filtration and removal of foreign antigens and (2) the activation and proliferation of lymphocytes.
(See page(s) 709)
lymphocyte (lim_fo-søõt)  A nonphagocytic, mononuclear leukocyte (white blood cell) that is an immunologically competent cell, or its precursor. Lymphocytes are present in the blood, lymph, and lymphoid tissues. See B cell and T cell.
(See page(s) 705)
lymphogranuloma venereum (LGV; lim_fo-gran_u-lo_mah)  A sexually transmitted disease caused by Chlamydia trachomatis serotypes L1-L3, which affect the lymph organs in the genital area.
(See page(s) 917)
lymphokine (lim_fo-kin)  A biologically active glycoprotein (e.g., IL-1) secreted by activated lymphocytes, especially sensitized T cells. It acts as an intercellular mediator of the immune response and transmits growth, differentiation, and behavioral signals.
(See page(s) 720)
lysis (li_sis)  The rupture or physical disintegration of a cell.
(See page(s) 61)
lysogenic (li-so-jen_ik)  See lysogens.
(See page(s) 308, 390)
lysogens (li_so-jens)  Bacteria that are carrying a viral prophage and have the potential of producing bacteriophages under the proper conditions.
(See page(s) 308, 390)
lysogeny (li-soj_e-ne)  The state in which a phage genome remains within the bacterial host cell after infection and reproduces along with it rather than taking control of the host and destroying it.
(See page(s) 307, 390)
lysosome (li_so-søom)  A spherical membranous eucaryotic organelle that contains hydrolytic enzymes and is responsible for the intracellular digestion of substances.
(See page(s) 80)
lysozyme (li_søo-zøõm)  An enzyme that degrades peptidoglycan by hydrolyzing the b(1 _ 4) bond that joins N-acetylmuramic acid and N-acetylglucosamine.
(See page(s) 61, 710)
lytic cycle (lit_ik)  A virus life cycle that results in the lysis of the host cell.
(See page(s) 383)

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