(See related pages)
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| M cell | Specialized cell of the intestinal mucosa and other sites, such as the urogenital tract, that delivers the antigen from the apical face of the cell to lymphocytes clustered within the pocket in its basolateral face. (See page(s) 710) |
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| macrolide antibiotic (mak_ro-lùõd) | An antibiotic containing a macrolide ring, a large lactone ring with multiple keto and hydroxyl groups, linked to one or more sugars. (See page(s) 817) |
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| macromolecule (mak²ro-mol_ùe-køul) | A large molecule that is a polymer of smaller units joined together. (See page(s) 205) |
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| macromolecule vaccine | A vaccine made of specific, purified macromolecules derived from pathogenic microorganisms. (See page(s) 767) |
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| macronucleus (mak²ro-nu_kle-us) | The larger of the two nuclei in ciliate protozoa. It is normally polyploid and directs the routine activities of the cell. (See page(s) 585) |
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| macrophage (mak_ro-føaj) | The name for a large mononuclear phagocytic cell, present in blood, lymph, and other tissues. Macrophages are derived from monocytes. They phagocytose and destroy pathogens; some macrophages also activate B cells and T cells. (See page(s) 705) |
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| maduromycosis (mah-du_ro-mi-ko_sis) | A subcutaneous fungal infection caused by Madurella mycetoma; also termed an eumycotic mycetoma. (See page(s) 945) |
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| madurose | The sugar derivative 3-O-methyl-D-galactose, which is characteristic of several actinomycete genera that are collectively called maduromycetes. (See page(s) 548) |
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| magnetosomes | Magnetite particles in magnetotactic bacteria that are tiny magnets and allow the bacteria to orient themselves in magnetic fields. (See page(s) 52) |
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| maintenance energy | The energy a cell requires simply to maintain itself or remain alive and functioning properly. It does not include the energy needed for either growth or reproduction. (See page(s) 121) |
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| major histocompatibility complex (MHC) | A large set of cell surface molecules in each individual, encoded by a family of genes, that serves as a unique biochemical marker of individual identity. It can trigger T-cell responses that may lead to rejection of transplanted tissues and organs. MHC molecules are also involved in the regulation of the immune response and the interactions between immune cells. (See page(s) 745) |
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| malaria (mah-la_re-ah) | A serious infectious illness caused by the parasitic protozoan Plasmodium. Malaria is characterized by bouts of high chills and fever that occur at regular intervals. (See page(s) 954) |
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| malt (mawlt) | Grain soaked in water to soften it, induce germination, and activate its enzymes. The malt is then used in brewing and distilling. (See page(s) 983) |
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| Marburg viral hemorrhagic fever | An acute infection caused by a virus that produces varying degrees of hemorrhage, shock, and sometimes death. (See page(s) 877) |
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| mash | The soluble materials released from germinated grains and prepared as a microbial growth medium. (See page(s) 983) |
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| mashing | The process in which cereals are mixed with water and incubated in order to degrade their complex carbohydrates (e.g., starch) to more readily usable forms such as simple sugars. (See page(s) 982) |
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| mast cell | A bone marrow-derived cell present in a variety of tissues that resembles peripheral blood-borne basophils and contains an Fc receptor for IgE. It undergoes IgE-mediated degranulation. (See page(s) 707) |
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| mean growth rate constant (k) | The rate of microbial population growth expressed in terms of the number of generations per unit time. (See page(s) 116) |
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| measles (rubeola; me_zelz) | A highly contagious skin disease that is endemic throughout the world. It is caused by a morbilli virus in the family Paramyxoviridae, which enters the body through the respiratory tract or through the conjunctiva. (See page(s) 873) |
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| medical mycology (mi-kol_o-je) | The discipline that deals with the fungi that cause human disease. (See page(s) 942) |
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| meiosis (mi-o_sis) | The sexual process in which a diploid cell divides and forms two haploid cells. (See page(s) 88) |
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| melting temperature (Tm) | The temperature at which double-stranded DNA separates into individual strands; it is dependent on the G 1 C content of the DNA and is used to compare genetic material in microbial taxonomy. (See page(s) 430) |
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| membrane attack complex (MAC) | The complex complement components (C5b-C9) that create a pore in the plasma membrane of a target cell and leads to cell lysis. C9 probably forms most of the actual pore. (See page(s) 716, 758) |
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| membrane-disrupting exotoxin | A type of exotoxin that lyses host cells by disrupting the integrity of the plasma membrane. (See page(s) 797) |
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| membrane filter technique | The use of a thin porous filter made from cellulose acetate or some other polymer to collect microorganisms from water, air, and food. (See page(s) 118, 654) |
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| memory B cell | A lymphocyte capable of initiating the antibody-mediated immune response upon detection of a specific antigen molecule for which it is genetically programmed. It circulates freely in the blood and lymph and may live for years. (See page(s) 741) |
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| meningitis (men_in-ji_tis) | A condition that refers to inflammation of the brain or spinal cord meninges (membranes). The disease can be divided into bacterial (septic) meningitis (caused by bacteria) and aseptic meningitis syndrome (caused by nonbacterial sources). (See page(s) 902) |
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| mesophile (mes_o-føõl) | A microorganism with a growth optimum around 20 to 45°C, a minimum of 15 to 20°C, and a maximum about 45°C or lower. (See page(s) 126) |
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| messenger RNA (mRNA) | Single-stranded RNA synthesized from a DNA template during transcription that binds to ribosomes and directs the synthesis of protein. (See page(s) 230) |
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| metabolic channeling (mùet_ah-bol_ik) | The localization of metabolites and enzymes in different parts of a cell. (See page(s) 165) |
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| metabolic control engineering | Modification of the controls for biosynthetic pathways without altering the pathways themselves in order to improve process efficiency. (See page(s) 997) |
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| metabolic pathway engineering (MPE) | The use of molecular techniques to improve the efficiency of pathways that synthesize specific products. (See page(s) 997) |
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| metabolism (me-tab_o-lizm) | The total of all chemical reactions in the cell; almost all are enzyme catalyzed. (See page(s) 173) |
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| metachromatic granules (met_ah-kro-mat_ik) | Granules of polyphosphate in the cytoplasm of some bacteria that appear a different color when stained with a blue basic dye. They are storage reservoirs for phosphate. Sometimes called volutin granules. (See page(s) 52) |
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| metastasis (mùe-tas_tah-sis) | The transfer of a disease like cancer from one organ to another not directly connected with it. (See page(s) 411) |
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| methanogens (meth_@-no-jens_) | Strictly anaerobic archaeons that derive energy by converting CO2, H2, formate, acetate, and other compounds to either methane or methane and CO2. (See page(s) 458) |
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| methylotroph | A bacterium that uses reduced one-carbon compounds such as methane and methanol as its sole source of carbon and energy. (See page(s) 491, 502) |
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| Michaelis constant (Km; mùõ-ka_lis) | A kinetic constant for an enzyme reaction that equals the substrate concentration required for the enzyme to operate at half maximal velocity. (See page(s) 163) |
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| microaerophile (mi_kro-a_er-o-føõl) | A microorganism that requires low levels of oxygen for growth, around 2 to 10%, but is damaged by normal atmospheric oxygen levels. (See page(s) 127) |
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| microarray technology | Profiling of gene expression by measuring binding of RNA from growing cells to an array of function-specific oligonucleotides attached to an inert surface. (See page(s) 354, 1018) |
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| microbial dietary adjuvant | A substance added to the diet to stimulate specific microbial processes and populations. (See page(s) 986) |
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| microbial ecology | The study of microorganisms in their natural environments, with a major emphasis on physical conditions, processes, and interactions that occur on the scale of individual microbial cells. (See page(s) 596) |
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| microbial transformation (mi-kro_be-al) | See bioconversion. (See page(s) 1009) |
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| microbial loop | The mineralization of organic matter synthesized by photosynthetic phytoplankton through the activity of microorganisms such as bacteria and protozoa. This process "loops" minerals and carbon dioxide back for reuse by the primary producers and makes the organic matter unavailable to higher consumers. (See page(s) 608, 638) |
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| microbial mat | A firm structure of layered microorganisms with complementary physiological activities that can develop on surfaces in aquatic environments. (See page(s) 621) |
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| microbiology (mi_kro-bi-ol_o-je) | The study of organisms that are usually too small to be seen with the naked eye. Special techniques are required to isolate and grow them. (See page(s) 2) |
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| microbivory | The use of microorganisms as a food source by organisms that can ingest or phagocytose them. (See page(s) 672) |
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| microenvironment (mi_kro-en-vi_ron-ment) | The immediate environment surrounding a microbial cell or other structure, such as a root. (See page(s) 619) |
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| microfilaments (mi_kro-fil_ah-ments) | Protein filaments, about 4 to 7 nm in diameter, that are present in the cytoplasmic matrix of eucaryotic cells and play a role in cell structure and motion. (See page(s) 77) |
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| micronucleus (mi_kro-nu_kle-us) | The smaller of the two nuclei in ciliate protozoa. Micronuclei are diploid and involved only in genetic recombination and the regeneration of macronuclei. (See page(s) 585) |
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| micronutrients | Nutrients such as zinc, manganese, and copper that are required in very small quantities for growth and reproduction. Also called trace elements. (See page(s) 96) |
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| microorganism (mi²kro-or_gan-izm) | An organism that is too small to be seen clearly with the naked eye. (See page(s) 2) |
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| microtubules (mi²kro-tu_buls) | Small cylinders, about 25 nm in diameter, made of tubulin proteins and present in the cytoplasmic matrix and flagella of eucaryotic cells; they are involved in cell structure and movement. (See page(s) 78) |
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| miliary tuberculosis (mil_e-a-re) | An acute form of tuberculosis in which small tubercles are formed in a number of organs of the body because of dissemination of M. tuberculosis throughout the body by the bloodstream. Also known as reactivation tuberculosis. (See page(s) 908) |
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| mineralization | The release of inorganic nutrients from organic matter during microbial growth and metabolism. (See page(s) 504, 613) |
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| minimal inhibitory concentration (MIC) | The lowest concentration of a drug that will prevent the growth of a particular microorganism. (See page(s) 809) |
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| minimal lethal concentration (MLC) | The lowest concentration of a drug that will kill a particular microorganism. (See page(s) 809) |
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| minus, or negative, strand | The virus nucleic acid strand that is complementary in base sequence to the viral mRNA. (See page(s) 374) |
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| missense mutation | A single base substitution in DNA that changes a codon for one amino acid into a codon for another. (See page(s) 250) |
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| mitochondrion (mi_to-kon_dre-on) | The eucaryotic organelle that is the site of electron transport, oxidative phosphorylation, and pathways such as the Krebs cycle; it provides most of a nonphotosynthetic cell's energy under aerobic conditions. It is constructed of an outer membrane and an inner membrane, which contains the electron transport chain. (See page(s) 83) |
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| mitosis (mi-to_sis) | A process that takes place in the nucleus of a eucaryotic cell and results in the formation of two new nuclei, each with the same number of chromosomes as the parent. (See page(s) 87) |
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| mixed acid fermentation | A type of fermentation carried out by members of the family Enterobacteriaceae in which ethanol and a complex mixture of organic acids are produced. (See page(s) 181, A-17) |
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| mixotrophic (mik_so-trof_ik) | Refers to microorganisms that combine autotrophic and heterotrophic metabolic processes (they use inorganic electron sources and organic carbon sources). (See page(s) 98) |
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| modified atmosphere packaging (MAP) | Addition of gases such as nitrogen and carbon dioxide to packaged foods in order to inhibit the growth of spoilage organisms. (See page(s) 966) |
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| mold | Any of a large group of fungi that cause mold or moldiness and that exist as multicellular filamentous colonies; also the deposit or growth caused by such fungi. Molds typically do not produce macroscopic fruiting bodies. (See page(s) 556) |
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| molecular chaperones | Proteins that aid in the proper folding of unfolded polypeptides or partly denatured proteins and often also help transport proteins across membranes. (See page(s) 272) |
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| molecular chronometers | Nucleic acid and protein sequences that gradually change over time in a random fashion and at a steady rate, and which therefore can be used to determine phylogenetic relationships. (See page(s) 432) |
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| monoclonal antibody (MAb; mon_o-kløon_al) | An antibody of a single type that is produced by a population of genetically identical plasma cells (a clone); a monoclonal antibody is typically produced from a cell culture derived from the fusion product of a cancer cell and an antibody-producing cell (a hybridoma). (See page(s) 743) |
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| monocyte (mon_ o-søõt) | A mononuclear phagocytic leukocyte that circulates briefly in the bloodstream before migrating to the tissues where it becomes a macrophage. (See page(s) 705) |
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| monocyte-macrophage system | The collection of fixed phagocytic cells (including macrophages, monocytes, and specialized endothelial cells) located in the liver, spleen, lymph nodes, and bone marrow. This system is an important component of the host's general nonspecific defense against pathogens. (See page(s) 705) |
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| monokine (mon_o-køõn) | A generic term for a cytokine produced by mononuclear phagocytes (macrophages or monocytes). (See page(s) 720) |
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| monotrichous (mon-ot_rùõ-kus) | Having a single flagellum. (See page(s) 63) |
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| morbidity rate (mor-bid_i-te) | Measures the number of individuals who become ill as a result of a particular disease within a susceptible population during a specific time period. (See page(s) 849) |
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| mordant (mor_dant) | A substance that helps fix dye on or in a cell. (See page(s) 28) |
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| mortality rate (mor-tal_i-te) | The ratio of the number of deaths from a given disease to the total number of cases of the disease. (See page(s) 849) |
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| most probable number (MPN) | The statistical estimation of the probable population in a liquid by diluting and determining end points for microbial growth. (See page(s) 654) |
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| mucociliary blanket | The layer of cilia and mucus that lines certain portions of the respiratory system; it traps microorganisms up to 10 mm in diameter and then transports them by ciliary action away from the lungs. (See page(s) 711) |
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| mucosal-associated lymphoid tissue (MALT) | The defensive immune lymphoid tissue located in the intestinal mucosa. (See page(s) 710) |
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| multi-drug-resistant strains of tuberculosis (MDR-TB) | A multi-drug-resistant strain is defined as Mycobacterium tuberculosis resistant to isoniazid and rifampin, with or without resistance to other drugs. (See page(s) 908) |
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| mumps | An acute generalized disease that occurs primarily in school-age children and is caused by a paramyxovirus that is transmitted in saliva and respiratory droplets. The principal manifestation is swelling of the parotid salivary glands. (See page(s) 875) |
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| murein | See peptidoglycan. (See page(s) 55) |
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| must | The juices of fruits, including grapes, that can be fermented for the production of alcohol. (See page(s) 982) |
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| mutagen (mu_tah-jen) | A chemical or physical agent that causes mutations. (See page(s) 246) |
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| mutation (mu-ta_shun) | A permanent, heritable change in the genetic material. (See page(s) 244) |
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| mutualism (mu_tu-al-izm_) | A type of symbiosis in which both partners gain from the association and are unable to survive without it. The mutualist and the host are metabolically dependent on each other. (See page(s) 598) |
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| mutualist (mu_tu-al-ist) | An organism associated with another in a relationship that is beneficial to both (and often obligatory). (See page(s) 598) |
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| mycelium (mi-se_le-um) | A mass of branching hyphae found in fungi and some bacteria. (See page(s) 43, 556) |
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| mycobiont | The fungal partner in a lichen. (See page(s) 598) |
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| mycolic acids | Complex 60 to 90 carbon fatty acids with a hydroxyl on the b-carbon and an aliphatic chain on the a-carbon; found in the cell walls of mycobacteria. (See page(s) 543) |
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| mycologist (mi-kol_o-jist) | A person specializing in mycology; a student of mycology. (See page(s) 553) |
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| mycology (mi-kol_o-je) | The science and study of fungi. (See page(s) 553) |
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| mycoplasma (mi²ko-plaz_mah) | Bacteria that are members of the class Mollicutes and order Mycoplasmatales; they lack cell walls and cannot synthesize peptidoglycan precursors; most require sterols for growth; they are the smallest organisms capable of independent reproduction. (See page(s) 520) |
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| mycoplasmal pneumonia (mi²ko-plaz_mal nu-mo_ne-ah) | A type of pneumonia caused by Mycoplasma pneumoniae. Spread involves airborne droplets and close contact. (See page(s) 917) |
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| mycorrhizosphere | The region around a mycorrhizal fungus in which nutrients released from the fungus increase the microbial population and its activities. (See page(s) 681) |
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| mycosis (mi-ko_sis; pl., mycoses) | Any disease caused by a fungus. (See page(s) 553, 942) |
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| mycotoxicology (mi-ko_tok²si-kol_o-je) | The study of fungal toxins and their effects on various organisms. (See page(s) 553) |
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| myeloma cell (mi²e-lo_mah) | A tumor cell that is similar to the cell type found in bone marrow. Also, a malignant, neoplastic plasma cell that produces large quantities of antibodies and can be readily cultivated. (See page(s) 743) |
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| myositis (mi²o-si_tis) | Inflammation of a striated or voluntary muscle. (See page(s) 904) |
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| myxamoeba (mik-sah-me_bah; pl., myxamoebae) | A free-living amoeboid cell that can aggregate with other myxamoeba to form a plasmodium or pseudoplasmodium. Found in cellular slime molds and the myxomycetes. (See page(s) 565) |
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| myxobacteria | A group of gram-negative, aerobic soil bacteria characterized by gliding motility, a complex life cycle with the production of fruiting bodies, and the formation of myxospores. (See page(s) 512) |
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| myxospores (mik_so-spøors) | Special dormant spores formed by the myxobacteria. (See page(s) 512) |
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| napkin (diaper) candidiasis | Typically found in infants whose diapers are not changed frequently and are therefore not kept dry. Caused by Candida species of fungi. (See page(s) 950) |
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| narrow-spectrum drugs | Chemotherapeutic agents that are effective only against a limited variety of microorganisms. (See page(s) 808) |
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| natural attenuation | The decrease in the level of an enviromental contaminant that results from natural chemical, physical, and biological processes. (See page(s) 1016) |
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| natural classification | A classification system that arranges organisms into groups whose members share many characteristics and reflect as much as possible the biological nature of organisms. (See page(s) 426) |
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| natural killer (NK) cell | A non-T, non-B lymphocyte present in nonimmunized individuals that exhibits MHC-independent cytolytic activity against tumor cells. (See page(s) 723, 760) |
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| naturally acquired active immunity | The type of active immunity that develops when an individual's immunologic system comes into contact with an appropriate antigenic stimulus during the course of normal activities; it usually arises as the result of recovering from an infection and lasts a long time. (See page(s) 729) |
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| naturally acquired passive immunity | The type of temporary immunity that involves the transfer of antibodies from one individual to another. (See page(s) 729) |
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| necrotizing fasciitis (nek_ro-tøõz²ing fas²e-i_tis) | A disease that results from a severe invasive group A streptococcus infection. Necrotizing fasciitis is an infection of the subcutaneous soft tissues, particularly of fibrous tissue, and is most common on the extremities. It begins with skin reddening, swelling, pain, and cellulitis, and proceeds to skin breakdown and gangrene after 3 to 5 days. (See page(s) 904) |
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| negative staining | A staining procedure in which a dye is used to make the background dark while the specimen is unstained. (See page(s) 28) |
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| Negri bodies (na_gre) | Masses of viruses or unassembled viral subunits found within the brain neurons of rabies-infected animals. (See page(s) 888) |
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| neurotoxin (nu²ro-tok_sin) | A toxin that is poisonous to or destroys nerve tissue; especially the toxins secreted by C. tetani, Corynebacterium diphtheriae, and Shigella dysenteriae. (See page(s) 797) |
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| neustonic (nu_ston²ik) | The microorganisms that live at the atmospheric interface of a water body. (See page(s) 571) |
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| neutrophil (noo_tro-fil) | A mature white blood cell in the granulocyte lineage formed in bone marrow. It has a nucleus with three to five lobes and is very phagocytic. (See page(s) 123, 707) |
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| neutrophile (nu_tro-føõl²) | Microorganisms that grow best at a neutral pH range between pH 5.5 and 8.0. (See page(s) 123) |
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| niche (nich) | The function of an organism in a complex system, including place of the organism, the resources used in a given location, and the time of use. (See page(s) 619) |
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| nicotinamide adenine dinucleotide (NAD1; nik²o-tin_ah-møõd) | An electron-carrying coenzyme; it is particularly important in catabolic processes and usually donates its electrons to the electron transport chain under aerobic conditions. (See page(s) 157) |
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| nicotinamide adenine dinucleotide phosphate (NADP1; nik²o-tin_ah-møõd) | An electron-carrying coenzyme that most often participates as an electron carrier in biosynthetic metabolism. (See page(s) 158) |
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| nitrification (ni²trùõ-fùõ-ka_shun) | The oxidation of ammonia to nitrate. (See page(s) 193, 495, 615) |
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| nitrifying bacteria (ni_trùõ-fi²ing) | Chemolithotrophic, gram-negative bacteria that are members of the family Nitrobacteriaceae and convert ammonia to nitrate and nitrite to nitrate. (See page(s) 193, 493) |
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| nitrogenase (ni_tro-jen-øas) | The enzyme that catalyzes biological nitrogen fixation. (See page(s) 213) |
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| nitrogen fixation | The metabolic process in which atmospheric molecular nitrogen is reduced to ammonia; carried out by cyanobacteria, Rhizobium, and other nitrogen-fixing bacteria. (See page(s) 212, 616, 676) |
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| nitrogen oxygen demand (NOD) | The demand for oxygen in sewage treatment, caused by nitrifying microorganisms. (See page(s) 657) |
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| nitrogen saturation point | The point at which mineral nitrogen, when added to an ecosystem, can no longer be incorporated into organic matter through biological processes. (See page(s) 686) |
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| nocardioforms | Bacteria that resemble members of the genus Nocardia; they develop a substrate mycelium that readily breaks up into rods and coccoid elements (a quality sometimes called fugacity). (See page(s) 544) |
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| nomenclature (no_men-kla²tøur) | The branch of taxonomy concerned with the assignment of names to taxonomic groups in agreement with published rules. (See page(s) 422) |
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| noncyclic photophosphorylation (fo²to-fos²for-i-la_shun) | The process in which light energy is used to make ATP when electrons are moved from water to NADP1 during photosynthesis; both photosystem I and photosystem II are involved. (See page(s) 198) |
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| nongonococcal urethritis (NGU) (u²r@-thri_tis) | Any inflammation of the urethra not caused by Neisseria gonorrhoeae. (See page(s) 918) |
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| nonsense codon | A codon that does not code for an amino acid but is a signal to terminate protein synthesis. (See page(s) 241, 270) |
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| nonsense mutation | A mutation that converts a sense codon to a nonsense or stop codon. (See page(s) 251) |
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| nonspecific immune response (innate or natural immunity) | See nonspecific resistance. (See page(s) 705) |
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| nonspecific resistance | Refers to those general defense mechanisms that are inherited as part of the innate structure and function of each animal; also known as nonspecific, innate or natural immunity. (See page(s) 705) |
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| normal microbiota (also indigenous microbial population, microflora, microbial flora; mi²kro-bi-o_tah) | The microorganisms normally associated with a particular tissue or structure. (See page(s) 699) |
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| nosocomial infection (nos²o-ko_me-al) | An infection that develops within a hospital (or other type of clinical care facility) and is produced by an infectious organism acquired during the stay of the patient. (See page(s) 866) |
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| nuclear envelope (nu_kle-ar) | The complex double-membrane structure forming the outer boundary of the eucaryotic nucleus. It is covered by pores through which substances enter and leave the nucleus. (See page(s) 86) |
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| nucleic acid hybridization (nu-kle_ik) | The process of forming a hybrid double-stranded DNA molecule using a heated mixture of single-stranded DNAs from two different sources; if the sequences are fairly complementary, stable hybrids will form. (See page(s) 431) |
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| nucleocapsid (nu²kle-o-kap_sid) | The nucleic acid and its surrounding protein coat or capsid; the basic unit of virion structure. (See page(s) 369) |
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| nucleoid (nu_kle-oid) | An irregularly shaped region in the procaryotic cell that contains its genetic material. (See page(s) 54) |
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| nucleolus (nu-kle_o-lus) | The organelle, located within the eucaryotic nucleus and not bounded by a membrane, that is the location of ribosomal RNA synthesis and the assembly of ribosomal subunits. (See page(s) 87) |
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| nucleoside (nu_kle-o-søõd²) | A combination of ribose or deoxyribose with a purine or pyrimidine base. (See page(s) 217) |
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| nucleosome (nu_kle-o-søom²) | A complex of histones and DNA found in eucaryotic chromatin; the DNA is wrapped around the surface of the beadlike histone complex. (See page(s) 235) |
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| nucleotide (nu_kle-o-tøõd) | A combination of ribose or deoxyribose with phosphate and a purine or pyrimidine base; a nucleoside plus one or more phosphates. (See page(s) 217) |
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| nucleus (nu_kle-us) | The eucaryotic organelle enclosed by a double-membrane envelope that contains the cell's chromosomes. (See page(s) 86) |
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| numerical aperture | The property of a microscope lens that determines how much light can enter and how great a resolution the lens can provide. (See page(s) 20) |
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| numerical taxonomy | The grouping by numerical methods of taxonomic units into taxa based on their character states. (See page(s) 426) |
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| nutrient (nu_tre-ent) | A substance that supports growth and reproduction. (See page(s) 96) |
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| nystatin (nis_tah-tin) | A polyene antibiotic from Streptomyces noursei that is used in the treatment of Candida infections of the skin, vagina, and alimentary tract. (See page(s) 820) |
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| O antigen | A polysaccharide antigen extending from the outer membrane of some gram-negative bacterial cell walls; it is part of the lipopolysaccharide. (See page(s) 58) |
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| obligate aerobes | Organisms that grow only in the presence of oxygen. (See page(s) 127) |
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| obligate anaerobes | Microorganisms that cannot tolerate the presence of oxygen and die when exposed to it. (See page(s) 127) |
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| odontopathogens | Dental pathogens. (See page(s) 933) |
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| Okazaki fragments | Short stretches of polynucleotides produced during discontinuous DNA replication. (See page(s) 239) |
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| oligotrophic environment (ol_ùõ-go-trof_ik) | An environment containing low levels of nutrients, particularly nutrients that support microbial growth. (See page(s) 131, 648) |
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| oncogene (ong_ko-jøen) | A gene whose activity is associated with the conversion of normal cells to cancer cells. (See page(s) 411) |
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| one-step growth experiment | An experiment used to study the reproduction of lytic phages in which one round of phage reproduction occurs and ends with the lysis of the host bacterial population. (See page(s) 383) |
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| onychomycosis (on_i-ko-mi-ko_sis) | A fungal infection of the nail plate producing nails that are opaque, white, thickened, friable, and brittle. Also called ringworm of the nails and tinea unguium. Caused by Trichophyton and other fungi such as C. albicans. (See page(s) 950) |
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| oocyst (o_o-sist) | Cyst formed around a zygote of malaria and related protozoa. (See page(s) 591) |
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| oogonia (o_o-go_ne-a) | Mitotically dividing female structures that produce primary oocytes and gametes. (See page(s) 574) |
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| oomycetes (o_o-mi-se_tøez) | A collective name for members of the division Oomycota; also known as the water molds. (See page(s) 565) |
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| open reading frame (ORF) | A reading frame sequence not interrupted by a stop codon; it is usually determined by nucleic acid sequencing studies. (See page(s) 347) |
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| operator | The segment of DNA to which the repressor protein binds; it controls the expression of the genes adjacent to it. (See page(s) 276) |
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| operon (op_er-on) | The sequence of bases in DNA that contains one or more structural genes together with the operator controlling their expression. (See page(s) 277) |
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| ophthalmia neonatorum (of-thal_me-ah ne_o-nat-or-um) | A gonorrheal eye infection in a newborn, which may lead to blindness. Also called conjunctivitis of the newborn. (See page(s) 916) |
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| opportunistic microorganism or pathogen | A microorganism that is usually free-living or a part of the host's normal microbiota, but which may become pathogenic under certain circumstances, such as when the immune system is compromised. (See page(s) 704, 789, 948) |
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| opsonization (op_so-ni-za_shun) | The action of opsonins in making bacteria and other cells more readily phagocytosed. Antibodies, complement (especially C3b), and fibronectin are potent opsonins. (See page(s) 718, 756) |
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| optical tweezer | The use of a focused laser beam to drag and isolate a specific microorganism from a complex microbial mixture. (See page(s) 627) |
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| oral candidiasis | See thrush. (See page(s) 949) |
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| orchitis (or-ki_tis) | Inflammation of the testes. (See page(s) 875) |
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| organelle (or_gah-nel_) | A structure within or on a cell that performs specific functions and is related to the cell in a way similar to that of an organ to the body. (See page(s) 76) |
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| organotrophs | Organisms that use reduced organic compounds as their electron source. (See page(s) 97) |
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| ornithosis | See psittacosis. (See page(s) 919) |
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| osmophilic microorganisms (oz_mo-fil_ik) | Microorganisms that grow best in or on media of high solute concentration. (See page(s) 965) |
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| osmosis (oz-mo_sis) | The movement of water across a selectively permeable membrane from a dilute solution (higher water concentration) to a more concentrated solution. (See page(s) 61) |
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| osmotolerant Organisms that grow over a | fairly wide range of water activity or solute concentration. (See page(s) 122) |
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| Ouchterlony technique | See double diffusion agar assay. (See page(s) 780) |
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| outbreak | The sudden, unexpected occurrence of a disease in a given population. (See page(s) 849) |
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| outer membrane | A special membrane located outside the peptidoglycan layer in the cell walls of gram-negative bacteria. (See page(s) 55) |
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| oxidation-reduction (redox) reactions | Reactions involving electron transfers; the reductant donates electrons to an oxidant. (See page(s) 157) |
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| oxidative phosphorylation (fos_for-ùõ-la_shun) | The synthesis of ATP from ADP using energy made available during electron transport. (See page(s) 184) |
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| oxidizing agent or oxidant (ok_sùõ-dant) | The electron acceptor in an oxidation-reduction reaction. (See page(s) 157) |
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| oxygenic photosynthesis | Photosynthesis that oxidizes water to form oxygen; the form of photosynthesis characteristic of eucaryotic algae and cyanobacteria. (See page(s) 199, 468) |
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| pacemaker enzyme | The enzyme in a metabolic pathway that catalyzes the slowest or rate-limiting reaction; if its rate changes, the pathway's activity changes. (See page(s) 169) |
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| pandemic (pan-dem_ik) | An increase in the occurrence of a disease within a large and geographically widespread population (often refers to a worldwide epidemic). (See page(s) 849) |
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| Paneth cell (pah_ net) | The granular cell located at the base of glands in the small intestine; it produces the enzyme lysozyme. (See page(s) 711) |
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| pannus (pan_us) | A superficial vascularization of the cornea with infiltration of granulation tissue. (See page(s) 926) |
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| panzootic (pan_zo-ot_ik) | The wide dissemination of a disease in an animal population. (See page(s) 849) |
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| paralytic shellfish poisoning (par_@-lit_ik) | Dinoflagellates (Gonyaulax spp.) produce a powerful neurotoxin called saxitoxin. Shellfish accumulate saxitoxin and are poisonous when consumed by animals and humans. Saxitoxin paralyzes the striated respiratory muscles by inhibiting sodium transport. Paralytic shellfish poisoning is characterized by numbness of the mouth, lips, face, and extremities. (See page(s) 580) |
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| parasite (par_ah-søõt) | An organism that lives on or within another organism (the host) and benefits from the association while harming its host. Often the parasite obtains nutrients from the host. (See page(s) 788) |
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| parasitism (par_ah-si_tizm) | A type of symbiosis in which one organism adversely affects the other (the host), but cannot live without it. (See page(s) 609, 788) |
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| parenteral route (pah-ren_ter-al) | A route of drug administration that is nonoral (e.g., by injection). (See page(s) 812) |
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| parfocal (par-fo_kal) | A microscope that retains proper focus when the objectives are changed. (See page(s) 20) |
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| paronychia (par_o-nik_e-ah) | Inflammation involving the folds of tissue surrounding the nail; usually caused by Candida albicans. (See page(s) 950) |
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| passive diffusion | The process in which molecules move from a region of higher concentration to one of lower concentration as a result of random thermal agitation. (See page(s) 100) |
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| passive immunization | The induction of temporary immunity by the transfer of immune products, such as antibodies or sensitized T cells, from an immune vertebrate to a nonimmune one. (See page(s) 765) |
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| Pasteur effect (pas-tur_) | The decrease in the rate of sugar catabolism and change to aerobic respiration that occurs when microorganisms are switched from anaerobic to aerobic conditions. (See page(s) 189) |
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| pasteurization (pas_ter-ùõ-za_shun) | The process of heating milk and other liquids to destroy microorganisms that can cause spoilage or disease. (See page(s) 142, 970) |
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| pathogen (path_o-j@n) | Any virus, bacterium, or other agent that causes disease. (See page(s) 698, 789) |
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| pathogenicity (path_o-je-nis_ùõ-te) | The condition or quality of being pathogenic, or the ability to cause disease. (See page(s) 698, 789) |
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| pathogenicity island | A large segment of DNA in some pathogens that contains the genes responsible for virulence; often it codes for the type III secretion system that allows the pathogen to secrete virulence proteins and damage host cells. A pathogen may have more than one pathogenicity island. (See page(s) 794) |
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| pathogenic potential | The degree that a pathogen causes morbid signs and symptoms. (See page(s) 790) |
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| pathway architecture | The analysis, design, and modification of biochemical pathways to increase process efficiency. (See page(s) 997) |
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| pŽbrine (pa-brøen_) | An infectious disease of silkworms caused by the protozoan Nosema bombycis. (See page(s) 591) |
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| ped | A natural soil aggregate, formed partly through bacterial and fungal growth in the soil. (See page(s) 670) |
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| pellicle (pel_ùõ-k_l) | A relatively rigid layer of proteinaceous elements just beneath the plasma membrane in many protozoa and algae. The plasma membrane is sometimes considered part of the pellicle. (See page(s) 89, 576, 585) |
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| pelvic inflammatory disease (PID) | A severe infection of the female reproductive organs. The disease that results when gonococci and chlamydiae infect the uterine tubes and surrounding tissue. (See page(s) 915, 918) |
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| penicillins (pen_ùõ-sil-ins) | A group of antibiotics containing a b-lactam ring, which are active against gram-positive bacteria. (See page(s) 61, 814) |
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| penton or pentamer | A capsomer composed of five protomers. (See page(s) 370) |
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| pentose phosphate pathway (pen_tøos) | The pathway that oxidizes glucose 6-phosphate to ribulose 5-phosphate and then converts it to a variety of three to seven carbon sugars; it forms several important products (NADPH for biosynthesis, pentoses, and other sugars) and also can be used to degrade glucose to CO2. (See page(s) 177, A-14) |
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