| 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 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 817)
|
|
|
|
| macromolecule (mak²ro-mol_ùe-køul) | A large molecule that is a polymer of smaller units joined together.
(See 205)
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|
| macromolecule vaccine | A vaccine made of specific, purified macromolecules derived from pathogenic microorganisms.
(See 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 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 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 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 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 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 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 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 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 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 877)
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| mash | The soluble materials released from germinated grains and prepared as a microbial growth medium.
(See 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 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 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 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 873)
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| medical mycology (mi-kol_o-je) | The discipline that deals with the fungi that cause human disease.
(See 942)
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| meiosis (mi-o_sis) | The sexual process in which a diploid cell divides and forms two haploid cells.
(See 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 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 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 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 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 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 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 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 230)
|
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|
| metabolic channeling (mùet_ah-bol_ik) | The localization of metabolites and enzymes in different parts of a cell.
(See 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 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 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 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 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 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 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 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 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 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 354, 1018)
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| microbial dietary adjuvant | A substance added to the diet to stimulate specific microbial processes and populations.
(See 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 596)
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| microbial transformation (mi-kro_be-al) | See bioconversion.
(See 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 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 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 2)
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| microbivory | The use of microorganisms as a food source by organisms that can ingest or phagocytose them.
(See 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 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 77)
|
|
|
|
| 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 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 96)
|
|
|
|
| microorganism (mi²kro-or_gan-izm) | An organism that is too small to be seen clearly with the naked eye.
(See 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 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 908)
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|
| mineralization | The release of inorganic nutrients from organic matter during microbial growth and metabolism.
(See 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 809)
|
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| minimal lethal concentration (MLC) | The lowest concentration of a drug that will kill a particular microorganism.
(See 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 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 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 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 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 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 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 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 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 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 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 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 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 705)
|
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|
|
| monokine (mon_o-køõn) | A generic term for a cytokine produced by mononuclear phagocytes (macrophages or monocytes).
(See 720)
|
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|
|
| monotrichous (mon-ot_rùõ-kus) | Having a single flagellum.
(See 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 849)
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|
| mordant (mor_dant) | A substance that helps fix dye on or in a cell.
(See 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 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 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 711)
|
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|
|
| mucosal-associated lymphoid tissue (MALT) | The defensive immune lymphoid tissue located in the intestinal mucosa.
(See 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 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 875)
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| murein | See peptidoglycan.
(See 55)
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|
| must | The juices of fruits, including grapes, that can be fermented for the production of alcohol.
(See 982)
|
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|
|
| mutagen (mu_tah-jen) | A chemical or physical agent that causes mutations.
(See 246)
|
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|
|
| mutation (mu-ta_shun) | A permanent, heritable change in the genetic material.
(See 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 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 598)
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|
|
| mycelium (mi-se_le-um) | A mass of branching hyphae found in fungi and some bacteria.
(See 43, 556)
|
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| mycobiont | The fungal partner in a lichen.
(See 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 543)
|
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|
|
| mycologist (mi-kol_o-jist) | A person specializing in mycology; a student of mycology.
(See 553)
|
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|
|
| mycology (mi-kol_o-je) | The science and study of fungi.
(See 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 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 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 681)
|
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|
|
| mycosis (mi-ko_sis; pl., mycoses) | Any disease caused by a fungus.
(See 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 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 743)
|
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|
|
| myositis (mi²o-si_tis) | Inflammation of a striated or voluntary muscle.
(See 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 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 512)
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|
|
| myxospores (mik_so-spøors) | Special dormant spores formed by the myxobacteria.
(See 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 950)
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|
|
| narrow-spectrum drugs | Chemotherapeutic agents that are effective only against a limited variety of microorganisms.
(See 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 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 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 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 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 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 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 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 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 797)
|
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|
|
| neustonic (nu_ston²ik) | The microorganisms that live at the atmospheric interface of a water body.
(See 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 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 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 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 157)
|
|
|
|
| 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 158)
|
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|
|
| nitrification (ni²trùõ-fùõ-ka_shun) | The oxidation of ammonia to nitrate.
(See 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 193, 493)
|
|
|
|
| nitrogenase (ni_tro-jen-øas) | The enzyme that catalyzes biological nitrogen fixation.
(See 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 212, 616, 676)
|
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|
|
| nitrogen oxygen demand (NOD) | The demand for oxygen in sewage treatment, caused by nitrifying microorganisms.
(See 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 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 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 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 198)
|
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|
|
| nongonococcal urethritis (NGU) (u²r@-thri_tis) | Any inflammation of the urethra not caused by Neisseria gonorrhoeae.
(See 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 241, 270)
|
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|
|
| nonsense mutation | A mutation that converts a sense codon to a nonsense or stop codon.
(See 251)
|
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|
|
| nonspecific immune response (innate or natural immunity) | See nonspecific resistance.
(See 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 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 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 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 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 431)
|
|
|
|
| nucleocapsid (nu²kle-o-kap_sid) | The nucleic acid and its surrounding protein coat or capsid; the basic unit of virion structure.
(See 369)
|
|
|
|
| nucleoid (nu_kle-oid) | An irregularly shaped region in the procaryotic cell that contains its genetic material.
(See 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 87)
|
|
|
|
| nucleoside (nu_kle-o-søõd²) | A combination of ribose or deoxyribose with a purine or pyrimidine base.
(See 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 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 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 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 20)
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| numerical taxonomy | The grouping by numerical methods of taxonomic units into taxa based on their character states.
(See 426)
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| nutrient (nu_tre-ent) | A substance that supports growth and reproduction.
(See 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 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 58)
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| obligate aerobes | Organisms that grow only in the presence of oxygen.
(See 127)
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| obligate anaerobes | Microorganisms that cannot tolerate the presence of oxygen and die when exposed to it.
(See 127)
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| odontopathogens | Dental pathogens.
(See 933)
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| Okazaki fragments | Short stretches of polynucleotides produced during discontinuous DNA replication.
(See 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 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 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 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 950)
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| oocyst (o_o-sist) | Cyst formed around a zygote of malaria and related protozoa.
(See 591)
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| oogonia (o_o-go_ne-a) | Mitotically dividing female structures that produce primary oocytes and gametes.
(See 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 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 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 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 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 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 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 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 627)
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| oral candidiasis | See thrush.
(See 949)
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| orchitis (or-ki_tis) | Inflammation of the testes.
(See 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 76)
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| organotrophs | Organisms that use reduced organic compounds as their electron source.
(See 97)
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| ornithosis | See psittacosis.
(See 919)
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| osmophilic microorganisms (oz_mo-fil_ik) | Microorganisms that grow best in or on media of high solute concentration.
(See 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 61)
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| osmotolerant Organisms that grow over a | fairly wide range of water activity or solute concentration.
(See 122)
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| Ouchterlony technique | See double diffusion agar assay.
(See 780)
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| outbreak | The sudden, unexpected occurrence of a disease in a given population.
(See 849)
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| outer membrane | A special membrane located outside the peptidoglycan layer in the cell walls of gram-negative bacteria.
(See 55)
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| oxidation-reduction (redox) reactions | Reactions involving electron transfers; the reductant donates electrons to an oxidant.
(See 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 184)
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| oxidizing agent or oxidant (ok_sùõ-dant) | The electron acceptor in an oxidation-reduction reaction.
(See 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 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 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 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 711)
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| pannus (pan_us) | A superficial vascularization of the cornea with infiltration of granulation tissue.
(See 926)
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| panzootic (pan_zo-ot_ik) | The wide dissemination of a disease in an animal population.
(See 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 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 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 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 812)
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| parfocal (par-fo_kal) | A microscope that retains proper focus when the objectives are changed.
(See 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 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 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 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 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 142, 970)
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| pathogen (path_o-j@n) | Any virus, bacterium, or other agent that causes disease.
(See 698, 789)
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