(See related pages)
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| salmonellosis (sal²mo-nel-o_sis) | An infection with certain species of the genus Salmonella, usually caused by ingestion of food containing salmonellae or their products. Also known as Salmonella gastroenteritis or Salmonella food poisoning. (See page(s) 931) |
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| sanitization (san²ùõ-ti-za_shun) | Reduction of the microbial population on an inanimate object to levels judged safe by public health standards; usually, the object is cleaned. (See page(s) 138) |
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| saprophyte (sap_ro-fit) | An organism that takes up nonliving organic nutrients in dissolved form and usually grows on decomposing organic matter. (See page(s) 557) |
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| saprozoic nutrition (sap²ro-zo_ik) | Having the type of nutrition in which organic nutrients are taken up in dissolved form; normally refers to animals or animal-like organisms. (See page(s) 586) |
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| satellite phenomenon | See syntrophism. (See page(s) 604) |
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| scaffolding proteins | Special proteins that are used to aid procapsid construction during the assembly of a bacteriophage capsid and are removed after the completion of the procapsid. (See page(s) 388) |
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| scale (skøal) | A platelike organic structure found on the surface of some cells (chrysophytes). (See page(s) 577) |
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| scanning electron microscope (SEM) | An electron microscope that scans a beam of electrons over the surface of a specimen and forms an image of the surface from the electrons that are emitted by it. (See page(s) 34) |
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| scanning probe microscope | A microscope used to study surface features by moving a sharp probe over the object's surface (e.g., the scanning tunneling microscope). (See page(s) 38) |
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| scanning tunneling microscope | A type of scanning probe microscope used to image a surface by moving a fine probe over it at a constant height, which is maintained by keeping a constant electron flow (tunneling current) between the tip and surface. (See page(s) 38) |
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| scarlatina (skahr²la-te_nah) | See scarlet fever. (See page(s) 905) |
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| scarlet fever (scarlatina; skar_let) | A disease that results from infection with a strain of Streptococcus pyogenes that carries a lysogenic phage with the gene for erythrogenic (rash-inducing) toxin. The toxin causes shedding of the skin. This is a communicable disease spread by respiratory droplets. (See page(s) 905) |
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| schizogony (skùõ-zog_o-ne) | Multiple asexual fission. (See page(s) 591) |
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| secondary metabolites | Products of metabolism that are synthesized after growth has been completed. (See page(s) 1002) |
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| secondary treatment | The biological degradation of dissolved organic matter in the process of sewage treatment; the organic material is either mineralized or changed to settleable solids. (See page(s) 659) |
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| second law of thermodynamics | Physical and chemical processes proceed in such a way that the entropy of the universe (the system and its surroundings) increases to the maximum possible. (See page(s) 156) |
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| secretory IgA (sIgA) | The primary immunoglobulin of the secretory immune system. See IgA. (See page(s) 738) |
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| secretory vacuole | In protists and some animals, these organelles usually contain specific enzymes that perform various functions such as excystation. Their contents are released to the cell exterior during exocytosis. (See page(s) 585) |
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| segmented genome | A virus genome that is divided into several parts or fragments, each probably coding for the synthesis of a single polypeptide; segmented genomes are very common among the RNA viruses. (See page(s) 374) |
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| selectins (s@-lek_tins) | A family of cell adhesion molecules that are displayed on activated endothelial cells; examples include P-selectin and E-selectin. Selectins mediate leukocyte binding to the vascular endothelium. (See page(s) 712) |
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| selective media | Culture media that favor the growth of specific microorganisms; this may be accomplished by inhibiting the growth of undesired microorganisms. (See page(s) 105) |
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| selective toxicity | The ability of a chemotherapeutic agent to kill or inhibit a microbial pathogen while damaging the host as little as possible. (See page(s) 807) |
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| self-assembly | The spontaneous formation of a complex structure from its component molecules without the aid of special enzymes or factors. (See page(s) 65, 207) |
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| sepsis (sep_sis) | Systemic response to infection. This systemic response is manifested by two or more of the following conditions as a result of infection: temperature .38 or ,36°C; heart rate .90 beats per min; respiratory rate .20 breaths per min, or pCO2 ,32 mm Hg; leukocyte count .12,000 cells per ml3 or .10% immature (band) forms. Sepsis also has been defined as the presence of pathogens or their toxins in blood and other tissues. (See page(s) 933) |
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| septate (sep_tøat) | Divided by a septum or cross wall; also with more or less regular occurring cross walls. (See page(s) 556) |
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| septic shock (sep_tik) | Sepsis associated with severe hypotension despite adequate fluid resuscitation, along with the presence of perfusion abnormalities that may include, but are not limited to, lactic acidosis, oliguria, or an acute alteration in mental status. Gram-positive bacteria, fungi, and endotoxin-containing gram-negative bacteria can initiate the pathogenic cascade of sepsis leading to septic shock. (See page(s) 933) |
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| septicemia (sep²tùõ-se_me-ah) | A disease associated with the presence in the blood of pathogens or bacterial toxins. (See page(s) 514, 793) |
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| septic tank (sep_tik) | A tank used to process small quantities of domestic sewage. Solid material settles out and is partially degraded by anaerobic bacteria as sewage slowly flows through the tank. The outflow is further treated or dispersed in aerobic soil. (See page(s) 663) |
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| septum (sep_tum; pl., septa) | A partition or cross-wall that occurs between two cells in a bacterial (e.g., actinomycete) or fungal filament, or which partitions off fungal structures such as spores. Septa also divide parent cells into two daughter cells during bacterial binary fission. (See page(s) 286, 556) |
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| serology (se-rol_o-je) | The branch of immunology that is concerned with in vitro reactions involving one or more serum constituents (e.g., antibodies and complement). (See page(s) 774) |
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| serotyping | A technique or serological procedure that is used to differentiate between strains (serovars or serotypes) of microorganisms that have differences in the antigenic composition of a structure or product. (See page(s) 784) |
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| serum (se_rum; pl., serums or sera) | The clear, fluid portion of blood lacking both blood cells and fibrinogen. It is the fluid remaining after coagulation of plasma, the noncellular liquid faction of blood. (See page(s) 742) |
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| serum resistance | The type of resistance that occurs with bacteria such as Neisseria gonorrhoeae because the pathogen interferes with membrane attack complex formation during the complement cascade. (See page(s) 801) |
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| settling basin | A basin used during water purification to chemically precipitate out fine particles, microorganisms, and organic material by coagulation or flocculation. (See page(s) 652) |
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| sex pilus (pi_lus) | A thin protein appendage required for bacterial mating or conjugation. The cell with sex pili donates DNA to recipient cells. (See page(s) 63, 303) |
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| sheath (shøeth) | A hollow tubelike structure surrounding a chain of cells and present in several genera of bacteria. (See page(s) 496) |
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| shigellosis (shùõ_g@l-o_sis) | The diarrheal disease that arises from an infection with a member of the genus Shigella. Often called bacillary dysentery. (See page(s) 931) |
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| SHIME system (simulated human intestinal microbial ecosystem) | A set of connected chemostat-like reactors that provide a sequence of environments similar to the human digestive system. (See page(s) 987) |
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| Shine-Dalgarno sequence | A segment in the leader of procaryotic mRNA that binds to a special sequence on the 16S rRNA of the small ribosomal subunit. This helps properly orient the mRNA on the ribosome. (See page(s) 244) |
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| shingles (zoster; shing_g_lz) | A reactivated form of chickenpox caused by the varicella-zoster virus. (See page(s) 872) |
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| siderophore (sid_er-o-for²) | A small molecule that complexes with ferric iron and supplies it to a cell by aiding in its transport across the plasma membrane. (See page(s) 104) |
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| sigma factor | A protein that helps the RNA polymerase core enzyme recognize the promoter at the start of a gene. (See page(s) 262) |
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| sign | An objective change in a diseased body that can be directly observed (e.g., a fever or rash). (See page(s) 850) |
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| silage | Fermented plant material with increased palatability and nutritional value for animals, which can be stored for extended periods. (See page(s) 986) |
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| silent mutation | A mutation that does not result in a change in the organism's proteins or phenotype even though the DNA base sequence has been changed. (See page(s) 249) |
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| simple matching coefficient (SSM) | An association coefficient used in numerical taxonomy; the proportion of characters that match regardless of whether or not the attribute is present. (See page(s) 426) |
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| single radial immunodiffusion (RID) assay | An immunodiffusion technique that quantitates antigens by following their diffusion through a gel containing antibodies directed against the test antigens. (See page(s) 779) |
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| site-specific recombination | Recombination of nonhomologous genetic material with a chromosome at a specific site. (See page(s) 292) |
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| skin-associated lymphoid tissue (SALT) | The lymphoid tissue in the skin that forms a first-line defense as a part of nonspecific immunity. (See page(s) 709) |
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| slash-and-burn agriculture | The cutting down and burning of tropical vegetation to make mineral nutrients available for use by introduced agricultural crops. (See page(s) 672) |
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| S-layer | A regularly structured layer composed of protein or glycoprotein that lies on the surface of many bacteria. It may protect the bacterium and help give it shape and rigidity. (See page(s) 62) |
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| slime | The viscous extracellular glycoproteins or glycolipids produced by staphylococci and Pseudomonas aeruginosa bacteria that allows them to adhere to smooth surfaces such as prosthetic medical devices and catheters. More generally, the term often refers to an easily removed, diffuse, unorganized layer of extracellular material that surrounds a bacterial cell. (See page(s) 61, 919) |
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| slime layer | A layer of diffuse, unorganized, easily removed material lying outside the bacterial cell wall. (See page(s) 61) |
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| slime mold | A common term for members of the divisions Acrasiomycota and Myxomycota. (See page(s) 564) |
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| slow sand filter | A bed of sand through which water slowly flows; the gelatinous microbial layer on the sand grain surface removes waterborne microorganisms, particularly Giardia, by adhesion to the gel. This type of filter is used in some water purification plants. (See page(s) 653) |
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| slow virus disease | A progressive, pathological process caused by a transmissible agent (virus or prion) that remains clinically silent during a prolonged incubation period of months to years after which progressive clinical disease becomes apparent. (See page(s) 410, 893) |
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| sludge (sluj) | A general term for the precipitated solid matter produced during water and sewage treatment; solid particles composed of organic matter and microorganisms that are involved in aerobic sewage treatment (activated sludge). (See page(s) 658) |
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| smallpox (variola; smawl_poks) | Once a highly contagious, often fatal disease caused by a poxvirus. Its most noticeable symptom was the appearance of blisters and pustules on the skin. Vaccination has eradicated smallpox throughout the world. (See page(s) 876) |
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| snapping division | A distinctive type of binary fission resulting in an angular or a palisade arrangement of cells, which is characteristic of the genera Arthrobacter and Corynebacterium. (See page(s) 542) |
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| sorocarp | The fruiting structure of the Acrasiomycetes. (See page(s) 565) |
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| sorus | A type of fruiting structure composed of a mass of spores or sporangia. (See page(s) 565) |
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| SOS repair | A complex, inducible repair process that is used to repair DNA when extensive damage has occurred. (See page(s) 255) |
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| source | The location or object from which a pathogen is immediately transmitted to the host, either directly or through an intermediate agent. (See page(s) 854) |
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| Southern blotting technique | The procedure used to isolate and identify DNA fragments from a complex mixture. The isolated, denatured fragments are transferred from an agarose electrophoretic gel to a nitrocellulose filter and identified by hybridization with probes. (See page(s) 322) |
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| specialized transduction | See restricted transduction. (See page(s) 309) |
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| species (spe_shøez) | Species of higher organisms are groups of interbreeding or potentially interbreeding natural populations that are reproductively isolated. Bacterial species are collections of strains that have many stable properties in common and differ significantly from other groups of strains. (See page(s) 425) |
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| specific immune response (acquired or specific immunity) | See acquired immunity. (See page(s) 705) |
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| spermosphere | The region surrounding a germinating seed where released organic matter stimulates microbial growth. (See page(s) 974) |
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| spheroplast (sføer_o-plast) | A relatively spherical cell formed by the weakening or partial removal of the rigid cell wall component (e.g., by penicillin treatment of gram-negative bacteria). Spheroplasts are usually osmotically sensitive. (See page(s) 61) |
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| spike | See peplomer. (See page(s) 374) |
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| spirillum (spi-ril_um) | A rigid, spiral-shaped bacterium. (See page(s) 44) |
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| spirochete (spi_ro-køet) | A flexible, spiral-shaped bacterium with periplasmic flagella. (See page(s) 44, 479) |
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| spleen (spløen) | A secondary lymphoid organ where old erythrocytes are destroyed and blood-borne antigens are trapped and presented to lymphocytes. (See page(s) 708) |
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| split or interrupted gene | A structural gene with DNA sequences that code for the final RNA product (expressed sequences or exons) separated by regions coding for RNA absent from the mature RNA (intervening sequences or introns). (See page(s) 263) |
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| spongiform encephalopathies | Degenerative central nervous system diseases in which the brain has a spongy appearance; they appear due to prions. (See page(s) 893) |
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| spontaneous generation (spon-ta_ne-us) | The hypothesis that living organisms can arise from nonliving matter. (See page(s) 2) |
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| sporadic disease (spo-rad_ik) | A disease that occurs occasionally and at random intervals in a population. (See page(s) 849) |
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| sporangiospore (spo-ran_je-o-spøor) | A spore born within a sporangium. (See page(s) 539, 557) |
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| sporangium (spo-ran_je-um; pl., sporangia) | A saclike structure or cell, the contents of which are converted into an indefinite number of spores. It is borne on a special hypha called a sporangiophore. (See page(s) 68, 557) |
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| spore (spøor) | A differentiated, specialized form that can be used for dissemination, for survival of adverse conditions because of its heat and dessication resistance, and/or for reproduction. Spores are usually unicellular and may develop into vegetative organisms or gametes. They may be produced asexually or sexually and are of many types. (See page(s) 573) |
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| sporogenesis (spor_o-jen_ùe-sis) | See sporulation. (See page(s) 69) |
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| sporotrichosis (spo²ro-tri-ko_sis) | A subcutaneous fungal infection caused by the dimorphic fungus Sporothrix schenckii. (See page(s) 945) |
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| sporulation (spor²u-la_shun) | The process of spore formation. (See page(s) 69) |
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| spread plate | A petri dish of solid culture medium with isolated microbial colonies growing on its surface, which has been prepared by spreading a dilute microbial suspension evenly over the agar surface. (See page(s) 106) |
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| sputum (spu_tum) | The mucous secretion from the lungs, bronchi, and trachea that is ejected (expectorated) through the mouth. (See page(s) 829) |
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| stalk (stawk) | A nonliving bacterial appendage produced by the cell and extending from it. (See page(s) 490) |
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| standard free energy change | The free energy change of a reaction at 1 atmosphere pressure when all reactants and products are present in their standard states; usually the temperature is 25°C. (See page(s) 156) |
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| standard reduction potential | A measure of the tendency of a reductant to lose electrons in an oxidation-reduction (redox) reaction. The more negative the reduction potential of a compound, the better electron donor it is. (See page(s) 157) |
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| staphylococcal food poisoning (staf²i-lo-kok_al) | A type of food poisoning caused by ingestion of improperly stored or cooked food in which Staphylococcus aureus has grown. The bacteria produce exotoxins that accumulate in the food. (See page(s) 932) |
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| staphylococcal scalded skin syndrome (SSSS) | A disease caused by staphylococci that produce an exfoliative toxin. The skin becomes red (erythema) and sheets of epidermis may separate from the underlying tissue. (See page(s) 922) |
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| starter culture | An inoculum, consisting of a mixture of carefully selected microorganisms, used to start a commercial fermentation. (See page(s) 978) |
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| stationary phase (sta_shun-er²e) The phase | of microbial growth in a batch culture when population growth ceases and the growth curve levels off. (See page(s) 114) |
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| statistics (stah-tis_tiks) | The mathematics of the collection, organization, and interpretation of numerical data. (See page(s) 849) |
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| stem-nodulating rhizobia | Rhizobia (members of the genera Rhizobium, Bradyrhizobium, and Azorhizobium) that produce nitrogen-fixing structures above the soil surface on plant stems. These most often are observed in tropical plants and produced by Azorhizobium. (See page(s) 682) |
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| sterilization (ster²ùõ-lùõ-za_shun) | The process by which all living cells, viable spores, viruses, and viroids are either destroyed or removed from an object or habitat. (See page(s) 137) |
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| stigma (stig_mah) | A light-sensitive eyespot, which is found in some algae and photosynthetic protozoa; it is believed to be involved in phototaxis, at least in some cases. (See page(s) 575) |
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| stoneworts | A group of approximately 250 species of algae that have a complex growth pattern, with nodal regions from which whorls of branches arise; they are abundant in fresh to brackish waters. (See page(s) 576) |
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| strain | A population of organisms that descends from a single organism or pure culture isolate. (See page(s) 425) |
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| streak plate | A petri dish of solid culture medium with isolated microbial colonies growing on its surface, which has been prepared by spreading a microbial mixture over the agar surface, using an inoculating loop. (See page(s) 107) |
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| streptococcal pneumonia | An endogenous infection of the lungs caused by Streptococcus pneumoniae that occurs in predisposed individuals. (See page(s) 905) |
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| streptococcal sore throat (strep²to-kok_al) | One of the most common bacterial infections of humans. It is commonly referred to as "strep throat." The disease is spread by droplets of saliva or nasal secretions and is caused by Streptococcus spp. (particularly group A streptococci). (See page(s) 905) |
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| streptolysin-O (SLO) (strep-tol_ùõ-sin) | A specific hemolysin produced by Streptococcus pyogenes that is inactivated by oxygen (hence the "O" in its name). SLO causes beta-hemolysis of blood cells on agar plates incubated anaerobically. (See page(s) 797) |
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| streptolysin-S (SLS) | A product produced by Streptococcus pyogenes that is bound to the bacterial cell but may sometimes be released. SLS causes beta hemolysis on aerobically incubated blood-agar plates and can act as a leukocidin by killing leukocytes that phagocytose the bacterial cell to which it is bound. (See page(s) 797) |
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| streptomycin (strep_to-mi²sin) | A bactericidal aminoglycoside antibiotic produced by Streptomyces griseus. (See page(s) 816) |
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| strict anaerobes | See obligate anaerobes. (See page(s) 127) |
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| stroma (stro_mah) | The chloroplast matrix that is the location of the photosynthetic carbon dioxide fixation reactions. (See page(s) 85) |
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| stromatolite (stro²mah-to_løõt) | Dome-like microbial mat communities consisting of filamentous photosynthetic bacteria and occluded sediments (often calcareous or siliceous). They usually have a laminar structure. Many are fossilized, but some modern forms occur. (See page(s) 423) |
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| structural gene | A gene that codes for the synthesis of a polypeptide or polynucleotide with a nonregulatory function. (See page(s) 277) |
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| subacute sclerosing panencephalitis | Diffuse inflammation of the brain resulting from virus and prion infections. (See page(s) 874) |
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| subgingival plaque (sub-jin_jùõ-val) | The plaque that forms at the dentogingival margin and extends down into the gingival tissue. (See page(s) 936) |
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| substrate-level phosphorylation | The synthesis of ATP from ADP by phosphorylation coupled with the exergonic breakdown of a high-energy organic substrate molecule. (See page(s) 177) |
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| subsurface biosphere | The region below the plant root zone where microbial populations can grow and function. (See page(s) 691) |
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| sulfate reduction (sul_føat) | The process of sulfate use as an oxidizing agent, which results in the accumulation of reduced forms of sulfur such as sulfide, or incorporation of sulfur into organic molecules, usually as sulfhydryl groups. (See page(s) 614) |
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| sulfonamide (sul-fon_ah-møõd) | A chemotherapeutic agent that has the SO2-NH2 group and is a derivative of sulfanilamide. (See page(s) 812) |
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| superantigen | Superantigens are bacterial proteins that stimulate the immune system much more extensively than do normal antigens. They stimulate T cells to proliferate nonspecifically through simultaneous interaction with class II MHC proteins on antigen-presenting cells and variable regions on the b chain of the T-cell receptor complex. Examples include streptococcal scarlet fever toxins, staphylococcal toxic shock syndrome toxin-1, and streptococcal M protein. (See page(s) 732) |
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| superinfection (soo²per-in-fek_shun) | A new bacterial or fungal infection of a patient that is resistant to the drug(s) being used for treatment. (See page(s) 819) |
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| superoxide dismutase (SOD; soo²per-ok_søõd dis-mu_tas) | An enzyme that protects many microorganisms by catalyzing the destruction of the toxic superoxide radical. (See page(s) 128) |
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| suppressor mutation | A mutation that overcomes the effect of another mutation and produces the normal phenotype. (See page(s) 248) |
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| Svedberg unit (sfed_berg) | The unit used in expressing the sedimentation coefficient; the greater a particle's Svedberg value, the faster it travels in a centrifuge. (See page(s) 52) |
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| swab (swahb) | A wad of absorbent material usually wound around one end of a small stick and used for applying medication or for removing material from an area; also, a dacron-tipped polystyrene applicator. (See page(s) 827) |
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| swarm cell | A flagellated cell; the term is usually applied to the motile cells of the Myxomycota. (See page(s) 565) |
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| symbiosis (sim_bi-o_sis) | The living together or close association of two dissimilar organisms, each of these organisms being known as a symbiont. (See page(s) 596) |
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| symbiosome | The final nitrogen-fixing form of Rhizobium that is active within root nodule cells. (See page(s) 676) |
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| symptom (simp_t@m) | A change during a disease that a person subjectively experiences (e.g., pain, bodily discomfort, fatigue, or loss of appetite). Sometimes the term symptom is used more broadly to include any observed signs. (See page(s) 850) |
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| syndrome | See disease syndrome. (See page(s) 850) |
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| synthetic medium | See defined medium. (See page(s) 105) |
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| syntrophism (sin_trøof-iz@m) | The association in which the growth of one organism either depends on, or is improved by, the provision of one or more growth factors or nutrients by a neighboring organism. Sometimes both organisms benefit. This type of mutualism is also known as cross-feeding or the satellite phenomenon. (See page(s) 604) |
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| syphilis (sif_ùõ-lis) | See venereal syphilis. (See page(s) 923) |
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| systematic epidemiology | The field of epidemiology that focuses on the ecological and social factors that influence the development of emerging and reemerging infectious diseases. (See page(s) 859) |
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| systematics (sis_te-mat_iks) | The scientific study of organisms with the ultimate objective being to characterize and arrange them in an orderly manner; often considered synonymous with taxonomy. (See page(s) 422) |
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| systemic lupus erythematosus (loo_pus er_ùõ-them-ah-to_sus) | An autoimmune, inflammatory disease that may affect every tissue of the body. (See page(s) 770) |
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| taxon (tak_son) | A group into which related organisms are classified. (See page(s) 422) |
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| taxonomy (tak-son_o-me) | The science of biological classification; it consists of three parts: classification, nomenclature, and identification. (See page(s) 422) |
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| TB skin test | Tuberculin hypersensitivity test for a previous or current infection with Mycobacterium tuberculosis. (See page(s) 771) |
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| T cell or T lymphocyte | A type of lymphocyte derived from bone marrow stem cells that matures into an immunologically competent cell under the influence of the thymus. T cells are involved in a variety of cell-mediated immune reactions. (See page(s) 705, 745) |
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| T-cell antigen receptor (TCR) | The receptor on the T cell surface consisting of two antigen-binding peptide chains; it is associated with a large number of other glycoproteins. Binding of antigen to the TCR, usually in association with MHC, activates the T cell. (See page(s) 745) |
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| T-dependent antigen | An antigen that effectively stimulates B-cell response only with the aid of T-helper cells that produce interleukin-2 and B-cell growth factor. (See page(s) 753) |
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| teichoic acids (ti-ko_ik) | Polymers of glycerol or ribitol joined by phosphates; they are found in the cell walls of gram-positive bacteria. (See page(s) 56) |
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| temperate phages | Bacteriophages that can infect bacteria and establish a lysogenic relationship rather than immediately lysing their hosts. (See page(s) 308, 390) |
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| template strand (tem_plat) | A strand of DNA or RNA that specifies the base sequence of a newly synthesized complementary strand of DNA or RNA. (See page(s) 242) |
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| terminator | A sequence that marks the end of a gene and stops transcription. (See page(s) 244, 263) |
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| tertiary treatment (ter_she-er-e) | The removal from sewage of inorganic nutrients, heavy metals, viruses, etc., by chemical and biological means after microorganisms have degraded dissolved organic material during secondary sewage treatment. (See page(s) 661) |
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| test | A loose-fitting shell of an amoeba. (See page(s) 590) |
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| tetanolysin (tet_ah-nol_ùõ-sin) | A hemolysin that aids in tissue destruction and is produced by Clostridium tetani. (See page(s) 925) |
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| tetanospasmin (tet_ah-no-spaz_min) | The neurotoxic component of the tetanus toxin, which causes the muscle spasms of tetanus. Tetanospasmin production is under the control of a plasmid gene. (See page(s) 924) |
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| tetanus (tet_ah-nus) | An often fatal disease caused by the anaerobic, spore-forming bacillus Clostridium tetani, and characterized by muscle spasms and convulsions. (See page(s) 924) |
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| tetracyclines (tet_rah-si_kløens) | A family of antibiotics with a common four-ring structure, which are isolated from the genus Streptomyces or produced semisynthetically; all are related to chlortetracycline or oxytetracycline. (See page(s) 815) |
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| tetrapartite associations (tet_rah-par_tøõt) | A mutualistic association of the same plant with three different types of microorganisms. (See page(s) 685) |
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| TH1 cell | See regulator T cell. (See page(s) 751) |
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| TH2 cell | See regulator T cell. (See page(s) 751) |
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| TH0 cell | See regulator T cell. (See page(s) 751) |
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| thallus (thal_us) | A type of body that is devoid of root, stem, or leaf; characteristic of some algae, many fungi, and lichens. (See page(s) 537, 554, 573) |
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| T-helper (TH) cell | A cell that is needed for T-cell-dependent antigens to be effectively presented to B cells. It also promotes cell-mediated immune responses. (See page(s) 751) |
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| theory | A set of principles and concepts that have survived rigorous testing and that provide a systematic account of some aspect of nature. (See page(s) 8) |
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| thermal death time (TDT) | The shortest period of time needed to kill all the organisms in a microbial population at a specified temperature and under defined conditions. (See page(s) 140) |
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| thymus (thi_m@s) | A primary lymphoid organ in the chest that is necessary in early life for the development of immunological functions. T-cell maturation takes place here. (See page(s) 708) |
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| thermoacidophiles | A group of bacteria that grow best at acid pHs and high temperatures; they are members of the Archaea. (See page(s) 457) |
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| thermophile (ther_mo-føõl) | A microorganism that can grow at temperatures of 55°C or higher; the minimum is usually around 45°C. (See page(s) 126) |
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| thrush (thrush) | Infection of the oral mucous membrane by the fungus Candida albicans; also known as oral candidiasis. (See page(s) 949) |
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| thylakoid (thi_lah-koid) | A flattened sac in the chloroplast stroma that contains photosynthetic pigments and the photosynthetic electron transport chain; light energy is trapped and used to form ATP and NAD(P)H in the thylakoid membrane. (See page(s) 85) |
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| thymine (thi_min) | The pyrimidine 5-methyluracil that is found in nucleosides, nucleotides, and DNA. (See page(s) 217) |
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| T-independent antigen | An antigen that triggers a B cell into immunoglobulin production without T-cell cooperation. (See page(s) 754) |
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| Ti or Ri plasmid | A plasmid obtained from Agrobacterium tumefaciens that is used to insert genes into plant cells. (See page(s) 339, 684) |
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| tinea (tin_e-ah) | A name applied to many different kinds of superficial fungal infections of the skin, nails, and hair, the specific type (depending on characteristic appearance, etiologic agent, and site) usually designated by a modifying term. (See page(s) 943) |
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| tinea capitis | A fungal infection of scalp hair caused by species of Trichophyton or Microsporum. (See page(s) 943) |
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| tinea corporis | A fungal infection of the smooth parts of the skin caused by either Trichophyton rubrum, T. mentagrophytes, or Microsporum canis. (See page(s) 943) |
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| tinea cruris | A fungal infection of the groin caused by either Epidermophyton floccosum, Trichophyton mentagrophytes, or T. rubrum; also known as jock itch. (See page(s) 944) |
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| tinea manuum | A fungal infection of the hand caused by Trichophyton rubrum, T. mentagrophytes, or E. floccosum. (See page(s) 944) |
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| tinea pedis | A fungal infection of the foot caused by Trichophyton rubrum, T. mentagrophytes, or E. floccosum; also known as athlete's foot. (See page(s) 944) |
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| tinea unguium | A fungal infection of the nail bed caused by either Trichophyton rubrum or T. mentagrophytes. (See page(s) 944) |
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| tinea versicolor | A fungal infection caused by the yeast, Malassezia furfur, that forms brownish-red scales on the skin of the trunk, neck, face, and arms. (See page(s) 943) |
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| titer (ti_ter) | Reciprocal of the highest dilution of an antiserum that gives a positive reaction in the test being used. (See page(s) 742) |
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| T lymphocyte | See T cell. (See page(s) 705) |
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| tonsillitis (ton_si-li_tis) | Inflammation of the tonsils, especially the palatine tonsils often due to S. pyogenes infection. (See page(s) 905) |
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| toxemia (tok-se_me-ah) | The condition caused by toxins in the blood of the host. (See page(s) 794) |
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| toxic shock-like syndrome (TSLS) | A disease caused by an invasive group A streptococcus infection that is characterized by a rapid drop in blood pressure, failure of many organs, and a very high fever. It probably results from the release of one or more streptococcal pyrogenic exotoxins. (See page(s) 904) |
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| toxic shock syndrome (tok_sik) | A staphylococcal disease that most commonly affects females who use certain types of tampons during menstruation. It is associated with the production of toxic shock syndrome toxin by certain strains of Staphylococcus aureus. (See page(s) 922) |
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| toxigenicity (tok_sùõ-jùe-nis_i-tøe) | The capacity of an organism to produce a toxin. (See page(s) 790) |
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| toxin (tok_sin) | A microbial product or component that can injure another cell or organism at low concentrations. Often the term refers to a poisonous protein, but toxins may be lipids and other substances. (See page(s) 794) |
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| toxin neutralization | The inactivation of toxins by specific antibodies, called antitoxins, that react with them. (See page(s) 756) |
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| toxoid (tok_soid) | A bacterial exotoxin that has been modified so that it is no longer toxic but will still stimulate antitoxin formation when injected into a person or animal. (See page(s) 767, 796) |
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| toxoplasmosis (tok_so-plaz-mo_sis) | A disease of animals and humans caused by the parasitic protozoan, Toxoplasma gondii. (See page(s) 957) |
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| trachoma (trah-ko_mah) | A chronic infectious disease of the conjunctiva and cornea, producing pain, inflammation and sometimes blindness. It is caused by Chlamydia trachomatis serotypes A-C. (See page(s) 925) |
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| transamination (trans_am-i-na_shun) | The removal of amino acid's amino group by transferring it to an a-keto acid acceptor. (See page(s) 192) |
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| transcriptase (trans-krip_tøas) | An enzyme that catalyzes transcription; in viruses with RNA genomes, this enzyme is an RNA-dependent RNA polymerase that is used to make RNA copies of the RNA genomes. (See page(s) 406) |
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| transcription (trans-krip_shun) | The process in which single-stranded RNA with a base sequence complementary to the template strand of DNA or RNA is synthesized. (See page(s) 230) |
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| transduction (trans-duk_shun) | The transfer of genes between bacteria by bacteriophages. (See page(s) 308) |
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| transfer host (trans_fer) | A host that is not necessary for the completion of a parasite's life cycle, but is used as a vehicle for reaching a final host. (See page(s) 789) |
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| transfer RNA (tRNA) | A small RNA that binds an amino acid and delivers it to the ribosome for incorporation into a polypeptide chain during protein synthesis. (See page(s) 261) |
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| transformation (trans_for-ma_shun) | A mode of gene transfer in bacteria in which a piece of free DNA is taken up by a bacterial cell and integrated into the recipient genome. (See page(s) 228, 305) |
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| transgenic animal or plant | An animal or plant that has gained new genetic information from the insertion of foreign DNA. It may be produced by such techniques as injecting DNA into animal eggs, electroporation of mammalian cells and plant cell protoplasts, or shooting DNA into plant cells with a gene gun. (See page(s) 335) |
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| transient carrier | See casual carrier. (See page(s) 854) |
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| transition mutations (tran-zish_un) | Mutations that involve the substitution of a different purine base for the purine present at the site of the mutation or the substitution of a different pyrimidine for the normal pyrimidine. (See page(s) 246) |
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| translation (trans-la_shun) | Protein synthesis; the process by which the genetic message carried by mRNA directs the synthesis of polypeptides with the aid of ribosomes and other cell constituents. (See page(s) 230) |
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| transmission electron microscope (trans-mish_un) | A microscope in which an image is formed by passing an electron beam through a specimen and focusing the scattered electrons with magnetic lenses. (See page(s) 30) |
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| transovarian passage (trans²o-va_re-an) | The passage of a microorganism such as a rickettsia from generation to generation of hosts through tick eggs. (No humans or other mammals are needed as reservoirs for continued propagation of the rickettsias.) (See page(s) 913) |
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| transpeptidation | 1. The reaction that forms the peptide cross-links during peptidoglycan synthesis. 2. The reaction that forms a peptide bond during the elongation cycle of protein synthesis. (See page(s) 223, 270) |
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| transposable elements | See transposon. (See page(s) 298) |
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| transposition (trans²po-zish_un) | The movement of a piece of DNA around the chromosome. (See page(s) 298) |
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| transposon (tranz-po_zon) A DNA segment | that carries the genes required for transposition and moves about the chromosome; if it contains genes other than those required for transposition, it may be called a composite transposon. Often the name is reserved only for transposable elements that also contain genes unrelated to transposition. (See page(s) 298) |
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| transversion mutations (trans-ver_zhun) | Mutations that result from the substitution of a purine base for the normal pyrimidine or a pyrimidine for the normal purine. (See page(s) 246) |
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| traveler's diarrhea | A type of diarrhea resulting from ingestion of certain viruses, bacteria, or protozoa normally absent from the traveler's environment. One of the major pathogens is enterotoxigenic Escherichia coli. (See page(s) 932) |
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| tricarboxylic acid cycle (TCA) | The cycle that oxidizes acetyl coenzyme A to CO2 and generates NADH and FADH2 for oxidation in the electron transport chain; the cycle also supplies carbon skeletons for biosynthesis. (See page(s) 183, A-16) |
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| trichome (tri_køom) | A row or filament of bacterial cells that are in close contact with one another over a large area. (See page(s) 472) |
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| trichomoniasis (trik²o-mo-ni_ah-sis) | A sexually transmitted disease caused by the parasitic protozoan Trichomonas vaginalis. (See page(s) 958) |
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| trickling filter | A bed of rocks covered with a microbial film that aerobically degrades organic waste during secondary sewage treatment. (See page(s) 659) |
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| trihalomethanes (THMs) | Halogenated one-carbon compounds formed during water disinfection; many of these compounds are potential carcinogens. (See page(s) 653) |
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| tripartite associations (tri-par_tøõt) | A mutualistic association of the same plant with two types of microorganisms. (See page(s) 685) |
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| trophozoite (trof² o-zo_øõt) | The active, motile feeding stage of a protozoan organism; in the malarial parasite, the stage of schizogony between the ring stage and the schizont. (See page(s) 586) |
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| tropism (tro_piz-@m) | The movement of living organisms toward or away from a focus of heat, light, or other stimulus. (See page(s) 791) |
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| trypanosome (tri-pan_o-søom) | A protozoan of the genus Trypanosoma. Trypanosomes are parasitic flagellate protozoa that often live in the blood of humans and other vertebrates and are transmitted by insect bites. (See page(s) 589, 957) |
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| trypanosomiasis (tri-pan²o-so-mi_ah-sis) | An infection with trypanosomes that live in the blood and lymph of the infected host. (See page(s) 957) |
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| tubercle (too_ber-k_l) | A small, rounded nodular lesion produced by Mycobacterium tuberculosis. (See page(s) 908) |
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| tuberculoid (neural) leprosy (too-ber_ku-loid) | A mild, nonprogressive form of leprosy that is associated with delayed-type hypersensitivity to antigens on the surface of Mycobacterium leprae. It is characterized by early nerve damage and regions of the skin that have lost sensation and are surrounded by a border of nodules. (See page(s) 916) |
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| tuberculosis (too-ber²ku-lo_sis) | An infectious disease of humans and other animals resulting from an infection by a species of Mycobacterium and characterized by the formation of tubercles and tissue necrosis, primarily as a result of host hypersensitivity and inflammation. Infection is usually by inhalation, and the disease commonly affects the lungs (pulmonary tuberculosis), although it may occur in any part of the body. (See page(s) 906) |
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| tuberculous cavity (too-ber_ku-lus) | An air-filled cavity that results from a tubercle lesion caused by M. tuberculosis. (See page(s) 908) |
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| tularemia (too²lah-re_me-ah) | A plaguelike disease of animals caused by the bacterium Francisella tularensis subsp. tularensis (Jellison type A), which may be transmitted to humans. (See page(s) 926) |
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| tumble | Random turning or tumbling movements made by bacteria when they stop moving in a straight line. (See page(s) 67) |
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| tumor (too_mor) | A growth of tissue resulting from abnormal new cell growth and reproduction (neoplasia). (See page(s) 411) |
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| turbidostat | A continuous culture system equipped with a photocell that adjusts the flow of medium through the culture vessel so as to maintain a constant cell density or turbidity. (See page(s) 121) |
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| twiddle | See tumble. (See page(s) 67) |
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| two-component phosphorelay system | A signal transduction regulatory system that uses the transfer of phosphoryl groups to control gene transcription and protein activity. It has two major components: a sensor kinase and a response regulator. (See page(s) 283) |
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| type I hypersensitivity | A form of immediate hypersensitivity arising from the binding of antigen to IgE attached to mast cells, which then release anaphylaxis mediators such as histamine. Examples: hay fever, asthma, and food allergies. (See page(s) 768) |
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| type II hypersensitivity | A form of immediate hypersensitivity involving the binding of antibodies to antigens on cell surfaces followed by destruction of the target cells (e.g., through complement attack, phagocytosis, or agglutination). (See page(s) 769) |
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| type III hypersensitivity | A form of immediate hypersensitivity resulting from the exposure to excessive amounts of antigens in which antibodies bind to the antigens and produce antibody-antigen complexes. These activate complement and trigger an acute inflammatory response with subsequent tissue damage. Examples: poststreptococcal glomerulonephritis, serum sickness, and farmer's lung disease. (See page(s) 770) |
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| type IV hypersensitivity | A delayed hypersensitivity response (it appears 24 to 48 hours after antigen exposure). It results from the binding of antigen to activated T lymphocytes, which then release cytokines and trigger inflammation and macrophage attacks that damage tissue. Type IV hypersensitivity is seen in contact dermititis from poison ivy, leprosy, and tertiary syphilis. (See page(s) 771) |
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| type III secretion system | See pathogenicity island. (See page(s) 794) |
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| typhoid fever (ti-foid) | A bacterial infection transmitted by contaminated food, water, milk, or shellfish. The causative organism is Salmonella typhi, which is present in human feces. (See page(s) 933) |
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| ultramicrobacteria | Bacteria that can exist normally in a miniaturized form or which are capable of miniaturization under low-nutrient conditions. They may be 0.2 mm or smaller in diameter. (See page(s) 640) |
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| ultraviolet (UV) radiation (ul²trah-vi_o-let) | Radiation of fairly short wavelength, about 10 to 400 nm, and high energy. (See page(s) 130, 144) |
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| uracil (u_rah-sil) | The pyrimidine 2,4-dioxypyrimidine, which is found in nucleosides, nucleotides, and RNA. (See page(s) 217) |
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| vaccine (vak_søen) | A preparation of either killed microorganisms; living, weakened (attenuated) microorganisms; or inactivated bacterial toxins (toxoids). It is administered to induce development of the immune response and protect the individual against a pathogen or a toxin. (See page(s) 764) |
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| vaccinomics | The application of genomics and bioinformatics to vaccine development. (See page(s) 766) |
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| valence (va_lens) | The number of antigenic determinant sites on the surface of an antigen or the number of antigen-binding sites possessed by an antibody molecule. (See page(s) 731) |
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| variable region (VL and VH) | The region at the N-terminal end of immunoglobulin heavy and light chains whose amino acid sequence varies between antibodies of different specificity. Variable regions form the antigen binding site. (See page(s) 734) |
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| vasculitis (vas²ku-li_tis) | Inflammation of a blood vessel. (See page(s) 909) |
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| vector (vek_tor) | 1. In genetic engineering, another name for a cloning vector. A DNA molecule that can replicate (a replicon) and is used to transport a piece of inserted foreign DNA, such as a gene, into a recipient cell. It may be a plasmid, phage, cosmid or artificial chromosome. 2. In epidemiology, it is a living organism, usually an arthropod or other animal, that transfers an infective agent from one host to another. (See page(s) 322, 791, 854) |
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| vector-borne transmission | The transmission of an infectious pathogen between hosts by means of a vector. (See page(s) 857) |
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| vehicle (ve_ùõ-k_l) | An inanimate substance or medium involved in the transmission of a pathogen. (See page(s) 857) |
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| venereal syphilis (ve-ne_re-al sif_ùõ-lis) | A contagious, sexually transmitted disease caused by the spirochete Treponema pallidum. (See page(s) 923) |
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| venereal warts | See anogenital condylomata. (See page(s) 894) |
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| verrucae vulgaris (v_ùe-roo_se vul-ga_ris; s. verruca vulgaris) | The common wart; a raised, epidermal lesion with horny surface caused by an infection with a human papillomavirus. (See page(s) 894) |
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| vibrio (vib_re-o) | A rod-shaped bacterial cell that is curved to form a comma or an incomplete spiral. (See page(s) 43) |
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| viral hemagglutination (vi_ral hem²ah-gloo²tùõ-na_shun) | The clumping or agglutination of red blood cells caused by some viruses. (See page(s) 776) |
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| viral neutralization | An antibody-mediated process in which IgA, IgM, and IgA antibodies bind to some viruses during their extracellular phase and inactivate or neutralize them. (See page(s) 756) |
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| viremia (vi-re_me-@) | The presence of viruses in the blood stream. (See page(s) 791) |
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| viricide (vir_i-søõd) | An agent that inactivates viruses so that they cannot reproduce within host cells. (See page(s) 138) |
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| virion (vi_re-on) | A complete virus particle that represents the extracellular phase of the virus life cycle; at the simplest, it consists of a protein capsid surrounding a single nucleic acid molecule. (See page(s) 363) |
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| virioplankton | Viruses that occur in waters; high levels are found in marine and freshwater environments. (See page(s) 643) |
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| viroid (vi_roid) | An infectious agent of plants that is a single-stranded RNA not associated with any protein; the RNA does not code for any proteins and is not translated. (See page(s) 416) |
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| virology (vi-rol_o-je) | The branch of microbiology that is concerned with viruses and viral diseases. (See page(s) 362) |
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| virulence (vir_u-lens) | The degree or intensity of pathogenicity of an organism as indicated by case fatality rates and/or ability to invade host tissues and cause disease. (See page(s) 790) |
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| virulence factor | A bacterial product, usually a protein or carbohydrate, that contributes to virulence or pathogenicity. (See page(s) 792) |
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| virulent bacteriophages (vir_u-lent bak-te_re-o-føajs²) | Bacteriophages that lyse their host cells during the reproductive cycle. (See page(s) 390) |
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| virus (vi_rus) | An infectious agent having a simple acellular organization with a protein coat and a single type of nucleic acid, lacking independent metabolism, and reproducing only within living host cells. (See page(s) 363) |
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| vitamin (vi_tah-min) | An organic compound required by organisms in minute quantities for growth and reproduction because it cannot be synthesized by the organism; vitamins often serve as enzyme cofactors or parts of cofactors. (See page(s) 99) |
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| volutin granules (vo-lu_tin) | See metachromatic granules. (See page(s) 52) |
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| wart (wort) An epidermal tumor of viral | origin. (See page(s) 894) |
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| wastewater treatment | The use of physical and biological processes to remove particulate and dissolved material from sewage and to control pathogens. (See page(s) 658) |
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| water activity (aw) | A quantitative measure of water availability in the habitat; the water activity of a solution is one-hundredth its relative humidity. (See page(s) 122) |
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| water mold | A common term for a member of the division Oomycota. (See page(s) 564) |
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| Weil-Felix reaction | A test for the diagnosis of typhus and certain other rickettsial diseases. In this test, the blood serum of a patient with suspected rickettsial disease is tested against certain strains of Proteus vulgaris (OX-2, OX-19, OX-K). The agglutination reactions, based on antigens common to both organisms, determine the presence and type of rickettsial infection. (See page(s) 910) |
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| white piedra | A fungal infection caused by the yeast Trichosporon beigelii that forms light-colored nodules on the beard and mustache. (See page(s) 943) |
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| whole-genome shotgun sequencing | An approach to genome sequencing in which the complete genome is broken into random fragments, which are then individually sequenced. Finally the fragments are placed in the proper order using sophisticated computer programs. (See page(s) 346) |
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| whole-organism vaccine | A vaccine made from complete pathogens, which can be of four types: inactivated viruses; attenuated viruses; killed microorganisms; and live, attenuated microorganisms. (See page(s) 766) |
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| Widal test (ve-dahl_) | A test involving agglutination of typhoid bacilli when they are mixed with serum containing typhoid antibodies from an individual having typhoid fever; used to detect the presence of Salmonella typhi and S. paratyphi. (See page(s) 775) |
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| Winogradsky column | A glass column with an anaerobic lower zone and an aerobic upper zone, which allows growth of microorganisms under conditions similar to those found in a nutrient-rich lake. (See page(s) 637) |
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| woolsorter's disease | See anthrax. (See page(s) 913) |
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| wort | The filtrate of malted grains used as the substrate for the production of beer and ale by fermentation. (See page(s) 982) |
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| xenograft (zen_o-graft) | A tissue graft between animals of different species. (See page(s) 773) |
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| xerophilic microorganisms (ze²ro-fil_ik) | Microorganisms that grow best under low aw conditions, and may not be able to grow at high aw values. (See page(s) 965) |
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| yeast (yøest) | A unicellular fungus that has a single nucleus and reproduces either asexually by budding or fission, or sexually through spore formation. (See page(s) 554) |
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| yeast artificial chromosome (YAC) | A stretch of DNA that contains all the elements required to propagate a chromosome in yeast and which is used to clone foreign DNA fragments in yeast cells. (See page(s) 335) |
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| yellow fever | An acute infectious disease caused by a flavivirus, which is transmitted to humans by mosquitoes. The liver is affected and the skin turns yellow in this disease. (See page(s) 878) |
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| YM shift | The change in shape by dimorphic fungi when they shift from the yeast (Y) form in the animal body to the mold or mycelial form (M) in the environment. (See page(s) 556) |
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| zooflagellates (zo²o-flùaj_-e-løats) | Flagellate protozoa that do not have chlorophyll and are either holozoic, saprozoic, or symbiotic. (See page(s) 588) |
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| zoonosis (zo²o-no_sis; pl. zoonoses) | A disease of animals that can be transmitted to humans. (See page(s) 849) |
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| zooplankton (zo²o-plank_ton) | A community of floating, aquatic, minute animals and nonphotosynthetic protists. (See page(s) 571) |
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| zoospore (zo_o-spøor) | A motile, flagellated spore. (See page(s) 573) |
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| zooxanthella (zo²o-zan-thel_ah) | A dinoflagellate found living symbiotically within cnidarians and other invertebrates. (See page(s) 579, 599) |
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| zoster | See shingles. (See page(s) 872) |
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| z value | The increase in temperature required to reduce the decimal reduction time to one-tenth of its initial value. (See page(s) 140) |
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| zygomycetes (zi²go-mi-se_tez) | A division of fungi that usually has a coenocytic mycelium with chitinous cell walls. Sexual reproduction normally involves the formation of zygospores. The group lacks motile spores. (See page(s) 560) |
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| zygospore (zi_go-spøor) | A thick-walled, sexual, resting spore characteristic of the zygomycetous fungi. (See page(s) 558) |
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| zygote (zi_gøot) | The diploid (2n) cell resulting from the fusion of male and female gametes. (See page(s) 574) |