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Glossary M-R
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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)
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)
macromolecule (mak²ro-mol_ùe-køul)  A large molecule that is a polymer of smaller units joined together.
(See page(s) 205)
macromolecule vaccine  A vaccine made of specific, purified macromolecules derived from pathogenic microorganisms.
(See page(s) 767)
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)
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)
maduromycosis (mah-du_ro-mi-ko_sis)  A subcutaneous fungal infection caused by Madurella mycetoma; also termed an eumycotic mycetoma.
(See page(s) 945)
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)
magnetosomes  Magnetite particles in magnetotactic bacteria that are tiny magnets and allow the bacteria to orient themselves in magnetic fields.
(See page(s) 52)
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)
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)
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)
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)
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)
mash  The soluble materials released from germinated grains and prepared as a microbial growth medium.
(See page(s) 983)
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)
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)
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)
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)
medical mycology (mi-kol_o-je)  The discipline that deals with the fungi that cause human disease.
(See page(s) 942)
meiosis (mi-o_sis)  The sexual process in which a diploid cell divides and forms two haploid cells.
(See page(s) 88)
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)
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)
membrane-disrupting exotoxin  A type of exotoxin that lyses host cells by disrupting the integrity of the plasma membrane.
(See page(s) 797)
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)
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)
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)
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)
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)
metabolic channeling (mùet_ah-bol_ik)  The localization of metabolites and enzymes in different parts of a cell.
(See page(s) 165)
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)
metabolic pathway engineering (MPE)  The use of molecular techniques to improve the efficiency of pathways that synthesize specific products.
(See page(s) 997)
metabolism (me-tab_o-lizm)  The total of all chemical reactions in the cell; almost all are enzyme catalyzed.
(See page(s) 173)
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)
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)
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)
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)
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)
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)
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)
microbial dietary adjuvant  A substance added to the diet to stimulate specific microbial processes and populations.
(See page(s) 986)
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)
microbial transformation (mi-kro_be-al)  See bioconversion.
(See page(s) 1009)
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)
microbial mat  A firm structure of layered microorganisms with complementary physiological activities that can develop on surfaces in aquatic environments.
(See page(s) 621)
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)
microbivory  The use of microorganisms as a food source by organisms that can ingest or phagocytose them.
(See page(s) 672)
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)
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)
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)
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)
microorganism (mi²kro-or_gan-izm)  An organism that is too small to be seen clearly with the naked eye.
(See page(s) 2)
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)
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)
mineralization  The release of inorganic nutrients from organic matter during microbial growth and metabolism.
(See page(s) 504, 613)
minimal inhibitory concentration (MIC)  The lowest concentration of a drug that will prevent the growth of a particular microorganism.
(See page(s) 809)
minimal lethal concentration (MLC)  The lowest concentration of a drug that will kill a particular microorganism.
(See page(s) 809)
minus, or negative, strand  The virus nucleic acid strand that is complementary in base sequence to the viral mRNA.
(See page(s) 374)
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)
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)
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)
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)
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)
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)
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)
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)
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)
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)
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)
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)
monokine (mon_o-køõn)  A generic term for a cytokine produced by mononuclear phagocytes (macrophages or monocytes).
(See page(s) 720)
monotrichous (mon-ot_rùõ-kus)  Having a single flagellum.
(See page(s) 63)
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)
mordant (mor_dant)  A substance that helps fix dye on or in a cell.
(See page(s) 28)
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)
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)
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)
mucosal-associated lymphoid tissue (MALT)  The defensive immune lymphoid tissue located in the intestinal mucosa.
(See page(s) 710)
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)
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)
murein  See peptidoglycan.
(See page(s) 55)
must  The juices of fruits, including grapes, that can be fermented for the production of alcohol.
(See page(s) 982)
mutagen (mu_tah-jen)  A chemical or physical agent that causes mutations.
(See page(s) 246)
mutation (mu-ta_shun)  A permanent, heritable change in the genetic material.
(See page(s) 244)
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)
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)
mycelium (mi-se_le-um)  A mass of branching hyphae found in fungi and some bacteria.
(See page(s) 43, 556)
mycobiont  The fungal partner in a lichen.
(See page(s) 598)
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)
mycologist (mi-kol_o-jist)  A person specializing in mycology; a student of mycology.
(See page(s) 553)
mycology (mi-kol_o-je)  The science and study of fungi.
(See page(s) 553)
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)
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)
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)
mycosis (mi-ko_sis; pl., mycoses)  Any disease caused by a fungus.
(See page(s) 553, 942)
mycotoxicology (mi-ko_tok²si-kol_o-je)  The study of fungal toxins and their effects on various organisms.
(See page(s) 553)
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)
myositis (mi²o-si_tis)  Inflammation of a striated or voluntary muscle.
(See page(s) 904)
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)
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)
myxospores (mik_so-spøors)  Special dormant spores formed by the myxobacteria.
(See page(s) 512)
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)
narrow-spectrum drugs  Chemotherapeutic agents that are effective only against a limited variety of microorganisms.
(See page(s) 808)
natural attenuation  The decrease in the level of an enviromental contaminant that results from natural chemical, physical, and biological processes.
(See page(s) 1016)
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)
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)
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)
naturally acquired passive immunity  The type of temporary immunity that involves the transfer of antibodies from one individual to another.
(See page(s) 729)
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)
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)
Negri bodies (na_gre)  Masses of viruses or unassembled viral subunits found within the brain neurons of rabies-infected animals.
(See page(s) 888)
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)
neustonic (nu_ston²ik)  The microorganisms that live at the atmospheric interface of a water body.
(See page(s) 571)
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)
neutrophile (nu_tro-føõl²)  Microorganisms that grow best at a neutral pH range between pH 5.5 and 8.0.
(See page(s) 123)
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)
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)
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)
nitrification (ni²trùõ-fùõ-ka_shun)  The oxidation of ammonia to nitrate.
(See page(s) 193, 495, 615)
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)
nitrogenase (ni_tro-jen-øas)  The enzyme that catalyzes biological nitrogen fixation.
(See page(s) 213)
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)
nitrogen oxygen demand (NOD)  The demand for oxygen in sewage treatment, caused by nitrifying microorganisms.
(See page(s) 657)
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)
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)
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)
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)
nongonococcal urethritis (NGU) (u²r@-thri_tis)  Any inflammation of the urethra not caused by Neisseria gonorrhoeae.
(See page(s) 918)
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)
nonsense mutation  A mutation that converts a sense codon to a nonsense or stop codon.
(See page(s) 251)
nonspecific immune response (innate or natural immunity)  See nonspecific resistance.
(See page(s) 705)
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)
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)
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)
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)
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)
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)
nucleoid (nu_kle-oid)  An irregularly shaped region in the procaryotic cell that contains its genetic material.
(See page(s) 54)
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)
nucleoside (nu_kle-o-søõd²)  A combination of ribose or deoxyribose with a purine or pyrimidine base.
(See page(s) 217)
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)
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)
nucleus (nu_kle-us)  The eucaryotic organelle enclosed by a double-membrane envelope that contains the cell's chromosomes.
(See page(s) 86)
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)
numerical taxonomy  The grouping by numerical methods of taxonomic units into taxa based on their character states.
(See page(s) 426)
nutrient (nu_tre-ent)  A substance that supports growth and reproduction.
(See page(s) 96)
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)
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)
obligate aerobes  Organisms that grow only in the presence of oxygen.
(See page(s) 127)
obligate anaerobes  Microorganisms that cannot tolerate the presence of oxygen and die when exposed to it.
(See page(s) 127)
odontopathogens  Dental pathogens.
(See page(s) 933)
Okazaki fragments  Short stretches of polynucleotides produced during discontinuous DNA replication.
(See page(s) 239)
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)
oncogene (ong_ko-jøen)  A gene whose activity is associated with the conversion of normal cells to cancer cells.
(See page(s) 411)
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)
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)
oocyst (o_o-sist)  Cyst formed around a zygote of malaria and related protozoa.
(See page(s) 591)
oogonia (o_o-go_ne-a)  Mitotically dividing female structures that produce primary oocytes and gametes.
(See page(s) 574)
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)
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)
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)
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)
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)
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)
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)
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)
oral candidiasis  See thrush.
(See page(s) 949)
orchitis (or-ki_tis)  Inflammation of the testes.
(See page(s) 875)
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)
organotrophs  Organisms that use reduced organic compounds as their electron source.
(See page(s) 97)
ornithosis  See psittacosis.
(See page(s) 919)
osmophilic microorganisms (oz_mo-fil_ik)  Microorganisms that grow best in or on media of high solute concentration.
(See page(s) 965)
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)
osmotolerant Organisms that grow over a  fairly wide range of water activity or solute concentration.
(See page(s) 122)
Ouchterlony technique  See double diffusion agar assay.
(See page(s) 780)
outbreak  The sudden, unexpected occurrence of a disease in a given population.
(See page(s) 849)
outer membrane  A special membrane located outside the peptidoglycan layer in the cell walls of gram-negative bacteria.
(See page(s) 55)
oxidation-reduction (redox) reactions  Reactions involving electron transfers; the reductant donates electrons to an oxidant.
(See page(s) 157)
oxidative phosphorylation (fos_for-ùõ-la_shun)  The synthesis of ATP from ADP using energy made available during electron transport.
(See page(s) 184)
oxidizing agent or oxidant (ok_sùõ-dant)  The electron acceptor in an oxidation-reduction reaction.
(See page(s) 157)
oxygenic photosynthesis  Photosynthesis that oxidizes water to form oxygen; the form of photosynthesis characteristic of eucaryotic algae and cyanobacteria.
(See page(s) 199, 468)
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)
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)
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)
pannus (pan_us)  A superficial vascularization of the cornea with infiltration of granulation tissue.
(See page(s) 926)
panzootic (pan_zo-ot_ik)  The wide dissemination of a disease in an animal population.
(See page(s) 849)
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)
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)
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)
parenteral route (pah-ren_ter-al)  A route of drug administration that is nonoral (e.g., by injection).
(See page(s) 812)
parfocal (par-fo_kal)  A microscope that retains proper focus when the objectives are changed.
(See page(s) 20)
paronychia (par_o-nik_e-ah)  Inflammation involving the folds of tissue surrounding the nail; usually caused by Candida albicans.
(See page(s) 950)
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)
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)
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)
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)
pathogen (path_o-j@n)  Any virus, bacterium, or other agent that causes disease.
(See page(s) 698, 789)
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)
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)
pathogenic potential  The degree that a pathogen causes morbid signs and symptoms.
(See page(s) 790)
pathway architecture  The analysis, design, and modification of biochemical pathways to increase process efficiency.
(See page(s) 997)
p┼Żbrine (pa-brøen_)  An infectious disease of silkworms caused by the protozoan Nosema bombycis.
(See page(s) 591)
ped  A natural soil aggregate, formed partly through bacterial and fungal growth in the soil.
(See page(s) 670)
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)
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)
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)
penton or pentamer  A capsomer composed of five protomers.
(See page(s) 370)
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)
peplomer or spike (pep_lo-mer)  A protein or protein complex that extends from the virus envelope and often is important in virion attachment to the host cell surface.
(See page(s) 374)
peptic ulcer disease  A gastritis caused by Helicobacter pylori.
(See page(s) 918)
peptide interbridge (pep_tøõd)  A short peptide chain that connects the tetrapeptide chains in some peptidoglycans.
(See page(s) 56)
peptidoglycan (pep_tùõ-do-gli_kan)  A large polymer composed of long chains of alternating N-acetylglucosamine and N-acetylmuramic acid residues. The polysaccharide chains are linked to each other through connections between tetrapeptide chains attached to the N-acetylmuramic acids. It provides much of the strength and rigidity possessed by bacterial cell walls.
(See page(s) 55, 521)
peptidyl or donor site (P site)  The site on the ribosome that contains the peptidyl-tRNA at the beginning of the elongation cycle during protein synthesis.
(See page(s) 270)
peptidyl transferase  The enzyme that catalyzes the transpeptidation reaction in protein synthesis; in this reaction, an amino acid is added to the growing peptide chain.
(See page(s) 270)
peptones (pep_tøons)  Water-soluble digests or hydrolysates of proteins that are used in the preparation of culture media.
(See page(s) 105)
perforin pathway  The cytotoxic pathway that uses perforin protein, which polymerizes to form membrane pores that help destroy cells during cell-mediated cytotoxicity. Perforin is produced by cytotoxic T cells and NK cells and stored in granules that are released when a target cell is contacted.
(See page(s) 750)
period of infectivity  Refers to the time during which the source of an infectious disease is infectious or is disseminating the pathogen.
(See page(s) 854)
periodontal disease (per_e-o-don_tal)  A disease located around the teeth or in the periodontium-the tissue investing and supporting the teeth, including the cementum, periodontal ligament, alveolar bone, and gingiva.
(See page(s) 936)
periodontitis (per_e-o-don-ti_tis)  An inflammation of the periodontium.
(See page(s) 936)
periodontium (per²e-o-don_she-um)  See periodontal disease.
(See page(s) 936)
periodontosis (per²e-o-don-to_sis)  A degenerative, noninflammatory condition of the periodontium, which is characterized by destruction of tissue.
(See page(s) 936)
periplasm (per_ùõ-plaz-@m)  The substance that fills the periplasmic space.
(See page(s) 55)
periplasmic flagella  The flagella that lie under the outer sheath and extend from both ends of the spirochete cell to overlap in the middle and form the axial filament. Also called axial fibrils and endoflagella.
(See page(s) 479)
periplasmic space (per²i-plas_mik) or periplasm (per_ùõ-plazm)  The space between the plasma membrane and the outer membrane in gram-negative bacteria, and between the plasma membrane and the cell wall in gram-positive bacteria.
(See page(s) 55)
peritrichous (pùe-rit_rùõ-kus)  A cell with flagella evenly distributed over its surface.
(See page(s) 63)
permease (per_me-øas)  A membrane-bound carrier protein or a system of two or more proteins that transports a substance across the membrane.
(See page(s) 100)
pertussis (p@r-tus_is)  An acute, highly contagious infection of the respiratory tract, most frequently affecting young children, usually caused by Bordetella pertussis or B. parapertussis. Consists of peculiar paroxysms of coughing, ending in a prolonged crowing or whooping respiration; hence the name whooping cough.
(See page(s) 903)
petri dish (pe_tre)  A shallow dish consisting of two round, overlapping halves that is used to grow microorganisms on solid culture medium; the top is larger than the bottom of the dish to prevent contamination of the culture.
(See page(s) 108)
phage (føaj)  See bacteriophage.
(See page(s) 364)
phagocytic vacuole (fag²o-sit_ik vak_u-ol)  A membrane-delimited vacuole produced by cells carrying out phagocytosis. It is formed by the invagination of the plasma membrane and contains solid material.
(See page(s) 585)
phagocytosis (fag²o-si-to_sis)  The endocytotic process in which a cell encloses large particles in a membrane-delimited phagocytic vacuole or phagosome and engulfs them.
(See page(s) 80, 718)
phagolysosome (fag²o-li_so-søom)  The vacuole that results from the fusion of a phagosome with a lysosome.
(See page(s) 718)
phagovar (fag_o-var)  A specific phage type.
(See page(s) 842)
pharyngitis (far²in-ji_tis)  Inflammation of the pharynx, often due to a S. pyogenes infection.
(See page(s) 905)
phase-contrast microscope  A microscope that converts slight differences in refractive index and cell density into easily observed differences in light intensity.
(See page(s) 22)
phenetic system  A classification system that groups organisms together based on the similarity of their observable charactistics.
(See page(s) 426)
phenol coefficient test  A test to measure the effectiveness of disinfectants by comparing their activity against test bacteria with that of phenol.
(See page(s) 149)
phosphatase (fos_fah-tøas_)  An enzyme that catalyzes the hydrolytic removal of phosphate from molecules.
(See page(s) 210)
phosphate group transfer potential  A measure of the ability of a phosphorylated molecule such as ATP to transfer its phosphate to water and other acceptors. It is the negative of the DGo_ for the hydrolytic removal of phosphate.
(See page(s) 157)
photoautotroph (fo_to-aw_to-trøof)  See photolithotrophic autotrophs.
(See page(s) 97)
photolithotrophic autotrophs  Organisms that use light energy, an inorganic electron source (e.g., H2O, H2, H2S), and CO2 as a carbon source.
(See page(s) 97)
photoorganotrophic heterotrophs  Microorganisms that use light energy and organic electron donors, and also employ simple organic molecules rather than CO2 as their carbon source.
(See page(s) 98)
photoreactivation (fo_to-re-ak_tùõ-va_shun)  The process in which blue light is used by a photoreactivating enzyme to repair thymine dimers in DNA by splitting them apart.
(See page(s) 130, 254)
photosynthesis (fo_to-sin_thùe-sis)  The trapping of light energy and its conversion to chemical energy, which is then used to reduce CO2 and incorporate it into organic form.
(See page(s) 154, 195, 207)
photosystem I  The photosystem in eucaryotic cells that absorbs longer wavelength light, usually greater than about 680 nm, and transfers the energy to chlorophyll P700 during photosynthesis; it is involved in both cyclic photophosphorylation and noncyclic photophosphorylation.
(See page(s) 196)
photosystem II  The photosystem in eucaryotic cells that absorbs shorter wavelength light, usually less than 680 nm, and transfers the energy to chlorophyll P680 during photosynthesis; it participates in noncyclic photophosphorylation.
(See page(s) 196)
phototrophs  Organisms that use light as their energy source.
(See page(s) 97)
phycobiliproteins  Photosynthetic pigments that are composed of proteins with attached tetrapyrroles; they are often found in cyanobacteria and red algae.
(See page(s) 196)
phycobilisomes  Special particles on the membranes of cyanobacteria that contain photosynthetic pigments and electron transport chains.
(See page(s) 471)
phycobiont (fi_ko-bi_ont)  The algal or cyanobacterial partner in a lichen.
(See page(s) 599)
phycocyanin (fi_ko-si_an-in)  A blue phycobiliprotein pigment used to trap light energy during photosynthesis.
(See page(s) 196)
phycoerythrin (fi_ko-er_i-thrin)  A red photosynthetic phycobiliprotein pigment used to trap light energy.
(See page(s) 196)
phycology (fi-kol_o-je)  The study of algae; algology.
(See page(s) 571)
phyllosphere  The surface of plant leaves.
(See page(s) 674)
phylogenetic or phyletic classification system (fi_lo-jùe-net_ik, fi-let_ik)  A classification system based on evolutionary relationships rather than the general similarity of contemporary characteristics.
(See page(s) 428)
phylogenetic tree  A graph made of nodes and branches, much like a tree in shape, that shows phylogenetic relationships between groups of organisms and sometimes also indicates the evolutionary development of groups.
(See page(s) 433)
phytoplankton (fi²to-plank_ton)  A community of floating photosynthetic organisms, largely composed of algae and cyanobacteria.
(See page(s) 571, 638)
phytoremediation  The use of plants and their associated microorganisms to remove, contain, or degrade environmental contaminants.
(See page(s) 1014)
piedra (pe-a_drah)  A fungal disease of the hair in which white or black nodules of fungi form on the shafts.
(See page(s) 943)
pinocytosis (pi²no-si-to_sis)  The endocytotic process in which a cell encloses a small amount of the surrounding liquid and its solutes in tiny pinocytotic vesicles or pinosomes.
(See page(s) 80)
pitched  Pertaining to inoculation of a nutrient medium with yeast, for example, in beer brewing.
(See page(s) 983)
plague (pløag)  An acute febrile, infectious disease, caused by the bacillus Yersinia pestis, which has a high mortality rate; the two major types are bubonic plague and pneumonic plague.
(See page(s) 911)
plankton (plank_ton)  Free-floating, mostly microscopic microorganisms that can be found in almost all waters; a collective name.
(See page(s) 571, 584)
planktonic (adj.)  See plankton.
(See page(s) 571)
plaque (plak)  1. A clear area in a lawn of bacteria or a localized area of cell destruction in a layer of animal cells that results from the lysis of the bacteria by bacteriophages or the destruction of the animal cells by animal viruses. 2. The term also refers to dental plaque, a film of food debris, polysaccharides, and dead cells that cover the teeth. It provides a medium for the growth of bacteria (which may be considered a part of the plaque), leading to a microbial plaque ecosystem that can produce dental decay.
(See page(s) 364, 934)
plasma cell  A mature, differentiated B lymphocyte chiefly occupied with antibody synthesis and secretion; a plasma cell lives for only 5 to 7 days.
(See page(s) 709)
plasma membrane  The selectively permeable membrane surrounding the cell's cytoplasm; also called the cell membrane, plasmalemma, or cytoplasmic membrane.
(See page(s) 46)
plasmid (plaz_mid)  A double-stranded DNA molecule that can exist and replicate independently of the chromosome or may be integrated with it. A plasmid is stably inherited, but is not required for the host cell's growth and reproduction.
(See page(s) 54, 294, 819)
plasmid fingerprinting  A technique used to identify microbial isolates as belonging to the same strain because they contain the same number of plasmids with the identical molecular weights and similar phenotypes.
(See page(s) 843)
plasmodial (acellular) slime mold (plaz-mo_de-al)  A member of the division Myxomycota that exists as a thin, streaming, multinucleate mass of protoplasm, which creeps along in an amoeboid fashion.
(See page(s) 564)
plasmodium (plaz-mo_de-um; pl., plasmodia)  A stage in the life cycle of myxomycetes (plasmodial slime molds); a multinucleate mass of protoplasm surrounded by a membrane. Also, a parasite of the genus Plasmodium.
(See page(s) 565)
plasmolysis (plaz-mol_ùõ-sis)  The process in which water osmotically leaves a cell, which causes the cytoplasm to shrivel up and pull the plasma membrane away from the cell wall.
(See page(s) 61)
plastid (plas_tid)  A cytoplasmic organelle of algae and higher plants that contains pigments such as chlorophyll, stores food reserves, and often carries out processes such as photosynthesis.
(See page(s) 85)
pleomorphic (ple_o-mor_fik)  Refers to bacteria that are variable in shape and lack a single, characteristic form.
(See page(s) 44)
plus strand or positive strand  The virus nucleic-acid strand that is equivalent in base sequence to the viral mRNA.
(See page(s) 374)
pneumocystis pneumonia, Pneumocystis carinii pneumonia (PCP); (noo_mo-sis-tis)  A type of pneumonia caused by the protist Pneumocystis carinii.
(See page(s) 950)
pneumonic plague  See plague.
(See page(s) 911)
point mutation  A mutation that affects only a single base pair in a specific location.
(See page(s) 249)
polar flagellum  A flagellum located at one end of an elongated cell.
(See page(s) 63)
poliomyelitis (po_le-o-mi_e-li_tis)  An acute, contagious viral disease that attacks the central nervous system, injuring or destroying the nerve cells that control the muscles and sometimes causing paralysis; also called polio or infantile paralysis.
(See page(s) 892)
poly-b-hydroxybutyrate (hi-drok_se-bu_tùõ-røat)  A linear polymer of b-hydroxybutyrate used as a reserve of carbon and energy by many bacteria.
(See page(s) 49)
polymerase chain reaction (PCR)  An in vitro technique used to synthesize large quantities of specific nucleotide sequences from small amounts of DNA. It employs oligonucleotide primers complementary to specific sequences in the target gene and special heat-stable DNA polymerases.
(See page(s) 326)
polymorphonuclear leukocyte (PMN) (pol_e-mor_fo-noo_kle-@r)  A leukocyte that has a variety of nuclear forms.
(See page(s) 707)
polyphasic taxonomy  An approach in which taxonomic schemes are developed using a wide range of phenotypic and genotypic information.
(See page(s) 435)
polyribosome (pol_e-ri_bo-søom)  A complex of several ribosomes with a messenger RNA; each ribosome is translating the same message.
(See page(s) 83, 266)
Pontiac fever  A bacterial disease caused by Legionella pneumophila that resembles an allergic disease more than an infection. First described from Pontiac, Michigan. See Legionnaires' disease.
(See page(s) 902)
population  An assemblage of organisms of the same type.
(See page(s) 596)
porin proteins  Proteins that form channels across the outer membrane of gram-negative bacterial cell walls. Small molecules are transported through these channels.
(See page(s) 60)
postherpetic neuralgia  The severe pain after a herpes infection.
(See page(s) 872)
posttranscriptional modification  The processing of the initial RNA transcript, heterogeneous nuclear RNA, to form mRNA.
(See page(s) 263)
potable (po_tah-b_l)  Refers to water suitable for drinking.
(See page(s) 654)
pour plate  A petri dish of solid culture medium with isolated microbial colonies growing both on its surface and within the medium, which has been prepared by mixing microorganisms with cooled, still liquid medium and then allowing the medium to harden.
(See page(s) 107)
precipitation (or precipitin) reaction (pre-sip_ùõ-ta_shun)  The reaction of an antibody with a soluble antigen to form an insoluble precipitate.
(See page(s) 756)
precipitin (pre-sip_ùõ-tin)  The antibody responsible for a precipitation reaction.
(See page(s) 756)
prevalence rate  Refers to the total number of individuals infected at any one time in a given population regardless of when the disease began.
(See page(s) 849)
Pribnow box  A special base sequence in the promoter that is recognized by the RNA polymerase and is the site of initial polymerase binding.
(See page(s) 244, 262)
primary amebic meningoencephalitis  An infection of the meninges of the brain by the free-living amoebae Naegleria or Acanthamoeba.
(See page(s) 953)
primary (frank) pathogen  Any organism that causes a disease in the host by direct interaction with or infection of the host.
(See page(s) 789)
primary metabolites  Microbial metabolites produced during the growth phase of an organism.
(See page(s) 1002)
primary producer  Photoautotrophic and chemoautotrophic organisms that incorporate carbon dioxide into organic carbon and thus provide new biomass for the ecosystem.
(See page(s) 622)
primary production  The incorporation of carbon dioxide into organic matter by photosynthetic organisms and chemoautotrophic bacteria.
(See page(s) 622)
primary treatment  The first step of sewage treatment, in which physical settling and screening are used to remove particulate materials.
(See page(s) 658)
prion (pri_on)  An infectious particle that is the cause of slow diseases like scrapie in sheep and goats; it has a protein component, but no nucleic acid has yet been detected.
(See page(s) 416)
probe (prøob)  A short, labeled nucleic acid segment complementary in base sequence to part of another nucleic acid, which is used to identify or isolate the particular nucleic acid from a mixture through its ability to bind specifically with the target nucleic acid.
(See page(s) 322, 976)
probiotic  (1) The oral administration of either living microorganisms or substances to promote the health and growth of an animal or human. (2) A living organism that may provide health benefits beyond its nutritional value when it is ingested.
(See page(s) 703, 986)
procaryotic cells (pro_kar-e-ot_ik)  Cells that lack a true, membrane-enclosed nucleus; bacteria are procaryotic and have their genetic material located in a nucleoid.
(See page(s) 11, 91)
procaryotic species  A collection of strains that share many stable properties and differ significantly from other groups of strains.
(See page(s) 425)
prodromal stage (pro-dro_m@l)  The period during the course of a disease in which there is the appearance of signs and symptoms, but they are not yet distinctive and characteristic enough to make an accurate diagnosis.
(See page(s) 850)
progametangium (pro-gam-ùe²tan_je-um; pl., progametangia)  The cell that gives rise to a gametangium and a proximal suspensor during the early stages of sexual reproduction in zygomycetous fungi.
(See page(s) 560)
proliferative kidney disease (pro-lif_er-a-tiv)  A protozoan disease caused by an unclassified myxozoan in salmonids throughout the world.
(See page(s) 591)
promoter  The region on DNA at the start of a gene that the RNA polymerase binds to before beginning transcription.
(See page(s) 242, 262)
propagated epidemic  An epidemic that is characterized by a relatively slow and prolonged rise and then a gradual decline in the number of individuals infected. It usually results from the introduction of an infected individual into a susceptible population, and the pathogen is transmitted from person to person.
(See page(s) 851)
prophage (pro_føøaj)  The latent form of a temperate phage that remains within the lysogen, usually integrated into the host chromosome.
(See page(s) 308, 390)
prostheca (pros-the_kah)  An extension of a bacterial cell, including the plasma membrane and cell wall, that is narrower than the mature cell.
(See page(s) 490)
prosthetic group (pros-thet_ik)  A tightly bound cofactor that remains at the active site of an enzyme during its catalytic activity.
(See page(s) 161)
protease (pro_te-øas)  An enzyme that hydrolyzes proteins to their constituent amino acids. Also called a proteinase.
(See page(s) 192)
proteasome  A large, cylindrical protein complex that degrades ubiquitin-labeled proteins to peptides in an ATP-dependent process.
(See page(s) 82)
protein engineering (pro_tøen)  The rational design of proteins by constructing specific amino acid sequences through molecular techniques, with the objective of modifying protein characteristics.
(See page(s) 994)
protein splicing  The post-translational process in which part of a precursor polypeptide is removed before the mature polypeptide folds into its final shape; it is carried out by self-splicing proteins that remove inteins and join the remaining exteins.
(See page(s) 275)
proteobacteria (pro_te-o-bak-tøer_-e-ah)  A large group of bacteria, primarily gram-negative, that 16S rRNA sequence comparisons show to be phylogenetically related; proteobacteria contain the purple photosynthetic bacteria and their relatives and are composed of the a, b, g, d, and e subgroups.
(See page(s) 487)
proteome  The complete collection of proteins that an organism produces.
(See page(s) 356)
protists (pro_tist)  Eucaryotes with unicellular organization, either in the form of solitary cells or colonies of cells lacking true tissues.
(See page(s) 438)
protocooperation  A positive, but not obligatory, interaction between two different organisms in which both parties benefit.
(See page(s) 604)
protomer  An individual subunit of a viral capsid; a capsomer is made of protomers.
(See page(s) 369)
proton motive force (PMF)  The force arising from a gradient of protons and a membrane potential that is thought to power ATP synthesis and other processes.
(See page(s) 187)
protoplast (pro_to-plast)  A bacterial or fungal cell with its cell wall completely removed. It is spherical in shape and osmotically sensitive.
(See page(s) 49, 61)
protoplast fusion  The joining of cells that have had their walls weakened or completely removed.
(See page(s) 994)
protothecosis (pro_to-the-ko_sis; pl., protothecoses)  A disease of humans and animals produced by the green alga Prototheca moriformis.
(See page(s) 575)
prototroph (pro_to-trøof)  A microorganism that requires the same nutrients as the majority of naturally occurring members of its species.
(See page(s) 245)
protozoan or protozoon (pro_to-zo_an, pl. protozoa)  A microorganism belonging to the Protozoa subkingdom. A unicellular or acellular eucaryotic protist whose organelles have the functional role of organs and tissues in more complex forms. Protozoa vary greatly in size, morphology, nutrition, and life cycle.
(See page(s) 584)
protozoology (pro_to-zo-ol_o-je)  The study of protozoa.
(See page(s) 584)
proviral DNA  Viral DNA that has been integrated into host cell DNA. In retroviruses it is the double-stranded DNA copy of the RNA genome.
(See page(s) 407)
pseudomurein  A modified peptidoglycan lacking D-amino acids and containing N-acetyltalosaminuronic acid instead of N-acetylmuramic acid; found in methanogenic archaea.
(See page(s) 452)
pseudoplasmodium (soo_do-plaz-mo_de-um; pl., pseudoplasmodia)  A sausage-shaped amoeboid structure consisting of many myxamoebae and behaving as a unit; the result of myxamoebal aggregation in the cellular slime molds; also called a slug.
(See page(s) 565)
pseudopodium or pseudopod (soo_do-po_de-um)  A nonpermanent cytoplasmic extension of the cell body by which amoebae and amoeboid organisms move and feed.
(See page(s) 586)
psittacosis (ornithosis; sit_ah-ko_sis)  A disease due to a strain of Chlamydia psittaci, first seen in parrots and later found in other birds and domestic fowl (in which it is called ornithosis). It is transmissible to humans.
(See page(s) 919)
psychrophile (si_kro-føõl)  A microorganism that grows well at 0°C and has an optimum growth temperature of 15°C or lower and a temperature maximum around 20°C.
(See page(s) 126)
psychrotroph  A microorganism that grows at 0°C, but has a growth optimum between 20 and 30°C, and a maximum of about 35°C.
(See page(s) 126)
puerperal fever (pu-er_per-al)  An acute, febrile condition following childbirth; it is characterized by infection of the uterus and/or adjacent regions and is caused by streptococci.
(See page(s) 857)
pulmonary anthrax (pul_mo-ner_e)  A form of anthrax involving the lungs. Also known as woolsorter's disease.
(See page(s) 913)
pulmonary syndrome hantavirus  See hantavirus pulmonary syndrome.
(See page(s) 877)
pure culture  A population of cells that are identical because they arise from a single cell.
(See page(s) 106)
purine (pu_rin)  A basic, heterocyclic, nitrogen-containing molecule with two joined rings that occurs in nucleic acids and other cell constituents; most purines are oxy or amino derivatives of the purine skeleton. The most important purines are adenine and guanine.
(See page(s) 216)
purple membrane  An area of the plasma membrane of Halobacterium that contains bacteriorhodopsin and is active in photosynthetic light energy trapping.
(See page(s) 461)
putrefaction (pu_trùe-fak_shun)  The microbial decomposition of organic matter, especially the anaerobic breakdown of proteins, with the production of foul-smelling compounds such as hydrogen sulfide and amines.
(See page(s) 965)
pyrenoid (pi_rùe-noid)  The differentiated region of the chloroplast that is a center of starch formation in green algae and stoneworts.
(See page(s) 85, 573)
pyrimidine (pi-rim_i-døen)  A basic, heterocyclic, nitrogen-containing molecule with one ring that occurs in nucleic acids and other cell constituents; pyrimidines are oxy or amino derivatives of the pyrimidine skeleton. The most important pyrimidines are cytosine, thymine, and uracil.
(See page(s) 216)
Q fever  An acute zoonotic disease caused by the rickettsia Coxiella burnetii.
(See page(s) 912)
Quellung reaction  The increase in visibility or the swelling of the capsule of a microorganism in the presence of antibodies against capsular antigens.
(See page(s) 784)
quorum sensing  The process in which bacteria monitor their own population density by sensing the levels of signal molecules that are released by the microorganisms. When these signal molecules reach a threshold concentration, the population density has attained a critical level or quorum, and quorum-dependent genes are expressed.
(See page(s) 132)
rabies (ra_bøez)  An acute infectious disease of the central nervous system, which affects all warm-blooded animals (including humans). It is caused by an ssRNA virus belonging to the genus Lyssavirus in the family Rhabdoviridae.
(See page(s) 888)
racking  The removal of sediments from wine bottles.
(See page(s) 982)
radappertization  The use of gamma rays from a cobalt source for control of microorganisms in foods.
(See page(s) 972)
radioimmunoassay (RIA; ra_de-o-im_u-no-as_a)  A very sensitive assay technique that uses a purified radioisotope-labeled antigen or antibody to compete for antibody or antigen with unlabeled standard and samples to determine the concentration of a substance in the samples.
(See page(s) 783)
reactivation tuberculosis  See miliary tuberculosis.
(See page(s) 908)
reading frame  The way in which nucleotides in DNA and mRNA are grouped into codons or groups of three for reading the message contained in the nucleotide sequence.
(See page(s) 241)
reagin (re_ah-jin)  Antibody that mediates immediate hypersensitivity reactions. IgE is the major reagin in humans.
(See page(s) 768)
recombinant DNA technology  The techniques used in carrying out genetic engineering; they involve the identification and isolation of a specific gene, the insertion of the gene into a vector such as a plasmid to form a recombinant molecule, and the production of large quantities of the gene and its products.
(See page(s) 320)
recombinant-vector vaccine  The type of vaccine that is produced by the introduction of one or more of a pathogen's genes into attenuated viruses or bacteria. The attenuated virus or bacterium serves as a vector, replicating within the vertebrate host and expressing the gene(s) of the pathogen. The pathogen's antigens induce an immune response.
(See page(s) 767)
recombination (re_kom-bùõ-na_shun)  The process in which a new recombinant chromosome is formed by combining genetic material from two organisms.
(See page(s) 292)
recombination repair  A DNA repair process that repairs damaged DNA when there is no remaining template; a piece of DNA from a sister molecule is used.
(See page(s) 255)
Redfield ratio  The carbon-nitrogen-phosphorus ratio of aquatic microorganisms. This ratio is important for predicting limiting factors for microbial growth.
(See page(s) 638)
red tides  Red tides occur frequently in coastal areas and often are associated with population blooms of dinoflagellates. Dinoflagellate pigments are responsible for the red color of the water. Under these conditions, the dinoflagellates often produce saxitoxin, which can lead to paralytic shellfish poisoning.
(See page(s) 580)
reducing agent or reductant (re-duk_tant)  The electron donor in an oxidation-reduction reaction.
(See page(s) 157)
reductive dehalogenation  The cleavage of carbon-halogen bonds by anaerobic bacteria that creates a strong electron-donating environment.
(See page(s) 1010)
refraction (re-frak_shun)  The deflection of a light ray from a straight path as it passes from one medium (e.g., glass) to another (e.g., air).
(See page(s) 18)
refractive index (re-frak_tiv)  The ratio of the velocity of light in the first of two media to that in the second as it passes from the first to the second.
(See page(s) 18)
regulator T cell  Regulator T cells control the development of effector T cells. Two types exist: T-helper cells (CD41 cells) and T-suppressor cells. There are three subsets of T-helper cells: TH1, TH2, and TH0. TH1 cells produce IL-2, IFN-g, and TNF-b. They effect cell-mediated immunity and are responsible for delayed-type hypersensitivity reactions and macrophage activation. TH2 cells produce IL-4, IL-5, IL-6, IL-10, IL-13. They are helpers for B-cell antibody responses and humoral immunity; they also support IgE responses and eosinophilia. TH0 cells exhibit an unrestricted cytokine profile.
(See page(s) 751)
regulatory mutants  Mutant organisms that have lost the ability to limit synthesis of a product, which normally occurs by regulation of activity of an earlier step in the biosynthetic pathway.
(See page(s) 1005)
regulon  A collection of genes or operons that is controlled by a common regulatory protein.
(See page(s) 281)
replica plating  A technique for isolating mutants from a population by plating cells from each colony growing on a nonselective agar medium onto plates with selective media or environmental conditions, such as the lack of a nutrient or the presence of an antibiotic or a phage; the location of mutants on the original plate can be determined from growth patterns on the replica plates.
(See page(s) 252)
replication (rep_lùõ-ka_shun)  The process in which an exact copy of parental DNA or RNA is made with the parental molecule serving as a template.
(See page(s) 230)
replication fork  The Y-shaped structure where DNA is replicated. The arms of the Y contain template strand and a newly synthesized DNA copy.
(See page(s) 235)
replicative form  A double-stranded form of nucleic acid that is formed from a single-stranded virus genome and used to synthesize new copies of the genome.
(See page(s) 388, 406)
replicon (rep_lùõ-kon)  A unit of the genome that contains an origin for the initiation of replication and in which DNA is replicated.
(See page(s) 235, 294)
repressible enzyme  An enzyme whose level drops in the presence of a small molecule, usually an end product of its metabolic pathway.
(See page(s) 276)
repressor protein (re-pres_or)  A protein coded for by a regulator gene that can bind to the operator and inhibit transcription; it may be active by itself or only when the corepressor is bound to it.
(See page(s) 276)
reservoir (rez_er-vwar)  A site, alternate host, or carrier that normally harbors pathogenic organisms and serves as a source from which other individuals can be infected.
(See page(s) 791, 854)
reservoir host  An organism other than a human that is infected with a pathogen that can also infect humans.
(See page(s) 789)
residuesphere  The region surrounding organic matter such as a seed or plant part in which microbial growth is stimulated by increased organic matter availability.
(See page(s) 690)
resolution (rez_o-lu_shun)  The ability of a microscope to separate or distinguish between small objects that are close together.
(See page(s) 20)
respiration (res_ pùõ-ra_ sh@n)  An energy-yielding process in which the energy substrate is oxidized using an exogenous or externally derived electron acceptor.
(See page(s) 173)
respiratory burst  The respiratory burst occurs when an activated phagocytic cell increases its oxygen consumption to support the increased metabolic activity of phagocytosis. The burst generates highly toxic oxygen products such as singlet oxygen, superoxide radical, hydrogen peroxide, hydroxyl radical, and hypochlorite.
(See page(s) 720)
respiratory syncytial virus (RSV; sin-sish_al)  A member of the family Paramyxoviridae and genus Pneumovirus; it is a negative-sense ssRNA virus that causes respiratory infections in children.
(See page(s) 875)
restricted transduction  A transduction process in which only a specific set of bacterial genes are carried to another bacterium by a temperate phage; the bacterial genes are acquired because of a mistake in the excision of a prophage during the lysogenic life cycle.
(See page(s) 309)
restriction enzymes  Enzymes produced by host cells that cleave virus DNA at specific points and thus protect the cell from virus infection; they are used in carrying out genetic engineering.
(See page(s) 320, 386)
reticulate body (RB)  The form in the chlamydial life cycle whose role is growth and reproduction within the host cell.
(See page(s) 477)
retroviruses (re_tro-vi_rus-es)  A group of viruses with RNA genomes that carry the enzyme reverse transcriptase and form a DNA copy of their genome during their reproductive cycle.
(See page(s) 407)
reverse transcriptase (RT)  An RNA-dependent DNA polymerase that uses a viral RNA genome as a template to form a DNA copy; this is a reverse of the normal flow of genetic information, which proceeds from DNA to RNA.
(See page(s) 407, 879)
reversible covalent modification  A mechanism of enzyme regulation in which the enzyme's activity is either increased or decreased by the reversible covalent addition of a group such as phosphate or AMP to the protein.
(See page(s) 167)
Reye's syndrome  An acute, potentially fatal disease of childhood that is characterized by severe edema of the brain and increased intracranial pressure, vomiting, hypoglycemia, and liver dysfunction. The cause is unknown but is almost always associated with a previous viral infection (e.g., influenza or varicella-zoster virus infections).
(See page(s) 874)
R factors or R plasmids  Plasmids bearing one or more drug resistant genes.
(See page(s) 297, 819)
rheumatic fever (roo-mat_ik)  An autoimmune disease characterized by inflammatory lesions involving the heart valves, joints, subcutaneous tissues, and central nervous system. The disease is associated with hemolytic streptococci in the body. It is called rheumatic fever because two common symptoms are fever and pain in the joints similar to that of rheumatism.
(See page(s) 905)
rhizosphere  A region around the plant root where materials released from the root increase the microbial population and its activities.
(See page(s) 675)
rho factor (ro)  The protein that helps RNA polymerase dissociate from the terminator after it has stopped transcription.
(See page(s) 263)
rhoptry  Saclike, electron dense structure in the anterior portion of a zoite of a member of the phylum Apicomplexa; perhaps involved in the penetration of host cells.
(See page(s) 591)
ribonucleic acid (RNA; ri²bo-nu-kle_ik)  A polynucleotide composed of ribonucleotides joined by phosphodiester bridges.
(See page(s) 230)
ribosomal RNA (rRNA)  The RNA present in ribosomes; ribosomes contain several sizes of single-stranded rRNA that contribute to ribosome structure and are also directly involved in the mechanism of protein synthesis.
(See page(s) 261)
ribosome (ri_bo-søom)  The organelle where protein synthesis occurs; the message encoded in mRNA is translated here.
(See page(s) 52, 267)
ribotyping  Ribotyping is the use of E. coli rRNA to probe chromosomal DNA in Southern blots for typing bacterial strains. This method is based on the fact that rRNA genes are scattered throughout the chromosome of most bacteria and therefore polymorphic restriction endonuclease patterns result when chromosomes are digested and probed with rRNA.
(See page(s) 843)
ribulose-1,5-bisphosphate carboxylase (ri_bu-løos)  The enzyme that catalyzes the incorporation of CO2 in the Calvin cycle.
(See page(s) 208)
ringworm (ring_werm)  The common name for a fungal infection of the skin, even though it is not caused by a worm and is not always ring-shaped in appearance.
(See page(s) 943)
rise period or burst  The period during the one-step growth experiment when host cells lyse and release phage particles.
(See page(s) 383)
RNA polymerase  The enzyme that catalyzes the synthesis of mRNA under the direction of a DNA template.
(See page(s) 261)
Rocky Mountain spotted fever  A disease caused by Rickettsia rickettsii.
(See page(s) 913)
rolling-circle mechanism  A mode of DNA replication in which the replication fork moves around a circular DNA molecule, displacing a strand to give a tail that is also copied to produce a new double-stranded DNA.
(See page(s) 236)
root nodule  Gall-like structures on roots that contain endosymbiotic nitrogen-fixing bacteria (e.g., Rhizobium or Bradyrhizobium is present in legume nodules).
(See page(s) 676)
roseola infantum (ro-ze_o-l@)  A skin eruption that produces a rose-colored rash in infants. Caused by the human herpesvirus 6. The disease is short-lived and characterized by a high fever of 3 to 4 days' duration.
(See page(s) 887)
rubella  A moderately contagious skin disease that occurs primarily in children 5 to 9 years of age that is caused by the rubella virus, which is acquired by droplet inhalation into the respiratory system; German measles.
(See page(s) 875)
rubeola  See measles.
(See page(s) 873)
rumen (roo-men)  The expanded upper portion or first compartment of the stomach of ruminants.
(See page(s) 602)
ruminant (roo_mùõ-nant)  An herbivorous animal that has a stomach divided into four compartments and chews a cud consisting of regurgitated, partially digested food.
(See page(s) 602)
run  The straight line movement of a bacterium.
(See page(s) 67)

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