Mab : Monoclonal antibody.

MAC : Mycobacterium avium complex.

MAC : MacConkey (agar plate).

MAC EIA : IgM antibody capture EIA.

Macromolecule : A large molecule formed from the connection of a number of small molecules.

Macroconidium (pl. macroconidia) : The larger, multicelled conidium in those fungi with smaller conidia (microconidia) or conidia of two sizes. Example: Fusarium.

Macronucleus : Large, kidney bean-shaped nucleus in Balantidium coli (shape is not always consistent).

Macrophage : Motile, phagocytic, mononuclear cell that originates in the tissues and may be confused morphologically with protozoan trophozoites (particularly those of Entamoeba histolytica).

Macular : Pertaining to lesions which are flat and which are often only detected because of a change in color or texture of the lesion from surrounding, normal tissue.

Maculopapular : Pertaining to lesions with properties which are both macular and papular.

Magnetosome : Small particle of Fe3O4 present in cells that exhibit magnetotaxis.

Magnetotaxis : Movement toward the magnetic poles due to the presence of magnetosomes.

Magnetotactic bacteria : Bacteria that can orient themselves in the earth's magnetic field due to the presence of magnetosomes.

Major histocompatability complex (MHC) : A cluster of genes coding for cell surface proteins important in antigen presentation to T cells.

Malabsorptive diarrhea : An increase in the total number or volume of stools due to a decrease in the absorption of nutrients (especially fats) in the small intestine.

Malabsorption : Poor fat absorption in upper small bowel (giardiasis).

Malaise : Vague feeling of discomfort throughout the whole body; tiredness.

Malarial pigment : Composed of hematin and excess protein left over from the metabolism of hemoglobin; will appear as a brownish pigment after Giemsa staining (Plasmodium spp.).

Malignant : In reference to a tumor, an infiltrating metastasizing growth no longer under normal growth control.

Malignant tertian malaria : Malaria caused by Plasmodium falciparum.

Mass spectrometry : Method for determining composition of a substance by observing its volatile products during disintegration and comparing them with known standards.

Mast cell : A type of connective tissue cell adjoining blood vessels throughout the body. It secretes histamine, heparin, and other biologically active products and participates in immediate type hypersensitivity reactions and in the inflammatory response.

Maurer's dots or clefts : Irregular dots occur infrequently in red blood cells infected with Plasmodium falciparum (dots tend to be more blue after Giemsa staining than are the Schuffner's dots).

MBC : Minimum bactericidal concentration.

MCV : Mean corpuscular volume.

MD : Maintenance dose.

Me : Methyl.

Meconium : Pasty greenish mass in intestine of fetus; made up of mucus, desquamated cells, bile, and such.

Media, differential : Media that permit ready recognition of a particular organism or group of organisms by virtue of facilitating recognition of a natural product of the organism being sought or by incorporating an appropriate substrate and indicator system so that organisms possessing certain enzymes will be readily recognized.

Media, enrichment : Media, usually liquid, that favor the growth of one or more organisms while suppressing most of the competing flora in a specimen with a mixture of organisms.

Media, selective : Culture media that contain inhibitory substances or unique growth factors such that one particular organism or group of organisms that may be found in a mixture. Efficient selective media will select out only the organism or organisms being sought, with little or no growth of other types of organisms.

Media, supportive : Culture media that provide adequate nutrition for most nonfastidious microorganisms and that permit each organism to grow normally without conferring any special advantage to one organism over another.

Mediastinum : Space in the middle of the chest between the medial surface of the two pleurae.

Medium (plural media) : Any liquid or solid materials which is prepared for the growth, maintenance, or storage of microorganisms. There are different types of media according to the purposes

Megacolon : Dilation of the colon (Chagas' disease).

Megaesophagus : Dilation of the esophagus (Chagas' disease).

MEIA : Microparticle enzyme Immunoassay.

Meiosis : In eukaryotes, reduction division, the process by which the change from diploid to haploid occurs.

Melena : Excretion of black, tarry stools containing blood that has been altered by intestinal substances.

Meleney's ulcer : A chronic undermining ulcerative lesion of the subcutaneous tissue, usually caused by streptococcal infection.

Memory cell : A differentiated B lymphocyte capable of rapid conversion to an antibody-producing plasma cell upon subsequent stimulation with antigen.

Menaquinones : Vitamins K. 2-Methyl-3-all-tans-polyprenol-1-4-naphthoquinones possessing side chains varying length from C5--C65. Menaquinones function as electron carriers.

Meninges : Thin, tough tissue surrounding the brain and spinal cord.

Meningitis : Inflammation of the meninges, the membranes that cover the brain and spinal cord (e.g., bacterial meningitis).

Asceptic : Low number of white cells in cerebrospinal fluid, predominantly lymphocytes, most frequently caused by infection by viruses or fungi.

Septic : High number of white cells, predominantly neutrophils, due to infection by bacteria.

Meningoencephalitis : Inflammation of the brain and its surrounding membranes (trypanosomiasis, malaria, Naegleria and Angiostrongylus cantonensis infections).

mEq : Milliequivalent.

mEq/L : Milliequivalent per liter.

Merosporangium (pl. merosporangia) : A cylindrical small sporangium containing a few spores in a row.

Merozoite : Product of schizogonic cycle in malaria that will invade red blood cells.

Mesenteric adenitis : Inflammation of mesenteric lymph nodes.

Mesentery : A fold of the peritoneum that connects the intestine with the posterior abdominal wall.

Mesophile : Organism living in the temperature range around that of warm-blooded animals, usually between 20-45 degrees C.

Mesophilic : Growing best at a moderate temperature range (25-40C).

Messenger RNA (mRNA) : An RNA molecule transcribed from DNA which contains the information to direct the synthesis of a particular protein.

Metabolism : All biochemical reactions in a cell, both anabolic and catabolic.

Metacercaria : The infective, encysted larval form of a trematode; found within the tissues of an intermediate host or on plant material (Paragonimus, Clonorchis, and Fasciolopsis spp.).

Metaphyseal : Relating to the conical portion of long bones that lies between the epiphysis and diaphysis.

Metastasis : The occurrence of disease from and not connected directly with the site where the disease first appeared; this process is seen with many tumors and infections.

Metastatic : Spread of an infectious (or other) process from a primary focus to a distant one via the bloodstream or lymphatic system.

Methanogen : A methane-producing prokaryote; member of the Archaea.

Methanogenesis : The biological production of methane.

Methanogenic : Producing Methane.

Methanotroph : An organism capable of oxidizing methane.

Methylotroph : An organism capable of oxidizing organic compounds which do not contain carbon-carbon bonds; if able to oxidize methane, also a methanotroph.

Metula (pl. metulae) : The structure below the phialides of some Aspergillus and Penicillium spp.

mg : Microgram(s).

mg : Milligram(s).

mg/ml : Micrograms/milliliter.

Mg : Magnesium.

MHA-TP : Microhemagglutination test for antibody to Treponema pallidum.

MHC Class I Protein : The antigen-presenting molecule found on all nucleated vertebrate cells.

MHC Class II Protein : The antigen-presenting molecule found primarily on macrophages and B lymphocytes.

MIC : Minimum inhibitory concentration.

Microaerobic : Requiring a partial pressure of oxygen less than that of atmospheric oxygen for growth. New term for "microaerophillic."

Microaerophile : An organism that is capable of oxygen-dependent growth but cannot grow in the presence of a level of oxygen equivalent to that present in an air atmosphere (21% oxygen). Oxygen-dependent growth occurs only at low oxygen levels. In addition to being able to respire with oxygen, some microaerophiles may be capable of respiring anaerobically with electron accepters other than oxygen.

Microaerophile, obligate : Microorganism that grows only under reduced oxygen tension and cannot grow aerobically and anaerobically.

Microaerophilic : Requiring oxygen but at a level lower than atmospheric.

Microaerotolerant anaerobe : An organism that grows in an anaerobic system and a microaerophillic environment (5% oxygen) but does not grow in a CO2 incubator (15% oxygen) or in air (about 21% oxygen).

Microangiopoathic hemolytic anemia : The destruction or breakdown of red blood cells as a result of diseases or disorders of the capillaries.

Microbiology : The study of microbioorganisms.

Microcalorimetry : Study of microcalories, a measure of heat production.

Microconidium (pl. microconidia) : The smaller of two types of conidia in a fungus that produces both large and small conidia; usually single celled and round, ovoid, pear shaped, or club shaped. (See Conidium).

Microenvironment : The immediate physical and chemical surroundings of a microorganism.

Microfilaria : Embryos produced by filarial worms and found in the blood or tissue of individuals with filariasis.

Micro-IF : Micro-immunofluorescence.

Micro-Immunofluorescence (Micro-IF) , is really multiple Indirect Flourescent Antibody (IFA). Several different substrates are arranged in specific locations on a single microscope slide well allowing a rapid, simultaneous IFA on each substrate.

Micrometer (micron) : Unit of measure equal to 0.001mm; abbreviate mml.

Micron : See Micrometer.

Micronucleus : Small, dotlike nucleus found in Balantidium coli; often very difficult to see, even in stained preparations.

Microorganism : A living organism too small to be seen with the naked eye; includes bacteria, fungi, protozoans, and microscopic algae; also includes viruses.

Microparticle Enzyme Immunoassay (MEIA) , is a technique in which the solid-phase support consists of very small microparticles in liquid suspension. Specific reagent antibodies are covalently bound to the microparticles. Antigen, if present, is then "sandwiched" between bound antibodies and antigen-specific, enzyme-labeled antibodies. Antigen-antibody complexes are detected and quantitated by analysis of fluorescence from the enzyme-substrate interaction.

Microplasmodesmata : Fine pores occurring in the septa of certain filamentous prokaryotes, such as actinomycetes and cyanobacterial trichomes. These pores are used for communication (exchange of metabolites) between two adjacent cells which are separated by septa.

Microtubules : Tubes that are the structural entity for eukaryotic flagella, have a role in maintaining cell shape, and function as mitotic spindle fibers.

Miliary : Of the size of a millet seed (0.5 to 1.0mm); characterized by the formation of numerous lesions of the above size distributed rather uniformly throughout one or more organs.

min : Minute(s).

Minimum bactericidal concentration (MBC) : The minimum concentration of antimicrobial agent needed to yield a 99.9% reduction in viable colony forming units of a bacterial or fungal suspension.

Minimum inhibitory concentration (MIC) : The minimum concentration of antimicrobial agent needed to prevent visually discernible growth of a bacterial or fungal suspension.

Minus (negative)-strand nucleic acid : An RNA or DNA strand which has the opposite sense of (would be complementary to) the mRNA of a virus.

Miracidium : Free-living, ciliated larva released from a trematode egg and infective for the snail intermediate host.

Mitochondrion (plural mitochondria) : Eukaryotic organelle responsible for processes of respiration and electron-transport phosphorylation.

Mitogen : A substance which is able to induce mitosis of certain eukaryotic cells.

Mitosis : A highly ordered process by which the nucleus divides in eukaryotes.

Mitral regurgitation : Any condition of the mitral valve between the left atrium and left ventricle that allows blood to flow back into the atrium when the ventricle contracts; normally, the valve shuts tightly, allowing no flow of blood back into the atrium; often heard as a heart murmur during auscultation.

Mitral valve prolapse : A defect in the valve between the left atrium and ventricle caused by a weakening of the tough connective tissue of the valve leaflets, which allows the valve to project beck into the left atrium; during normal function, the valve closes tightly during ventricular contraction.

Mixed culture (pure culture) : More than one organism growing in or on the same culture medium, as opposed to a single organism in pure culture.

Mixotroph : An organism able to assimilate organic compounds as carbon sources while using inorganic compounds as electron donors. Compare with autotroph and heterotroph.

ml : Milliliter(s).

MLC : Minimum lethal concentration.

mM : Micromolar.

mo : Month.

Molasses : A brownish, syrupy by-product which is produced during the sugar refining procedure, i.e., crystallization of sucrose from sugar-cane or sugar beet. Molasses primarily consists of sucrose, water and inorganic components. Because of its cheap price, it is commercially used as a substrate for producing other microbial products.

Mold : A filamentous fungus composed of filaments that generally form a colony that may be either fuzzy, powdery, wooly, velvety, or relatively smooth.

Molecule : The result of two or more atoms combining by chemical bonding.

Molecular oxygen : A biradical molecular containing two oxygen atoms. The molecule has two unpaired electrons which exist in two states: a ground state and a singlet state. The singlet state is much more reactive than the ground state and has electrons that spin in opposite directions. In the ground state both electrons have the same spin direction.

Molluscicide : A chemical substance used for the destruction of snails and other molluscs.

Monoarticular : Occurring in only one joint.

Monoclonal antibody : Antibody that is derived from a single cell producing one antibody molecule type that reacts with a single epitope.

Monocyte : Circulating white blood cell which contains many lysosomes and can differentiate into a macrophage.

Monocytosis : Increase in the number of monocytes in the peripheral blood; may be found in both helminth and protozoan infections.

Monoecious : Both male and female reproductive organs occur in the same individual (hermaphroditic) (trematodes, cestodes).

Monolayer : A confluent layer of tissue culture cells one cell thick.

Monomer : A building block of a polymer.

Monomorphic : In this guide, refers to fungi having the same type of morphology in culture at both 25-30 degrees C. and 35-37 degrees C. (i.e., if growth occurs at both temperature ranges; some saprophytes are inhibited at 35-37 degrees C.).

Monotrichous : Having a single polar flagellum.

Montenegro test : Delayed hypersensitivity skin test; injection of leishmanial antigen; read after 72h; positive reaction in cured individuals, negative in early cases (visceral and mucocutaneous leishmaniasis).

Morbidity : Incidence of disease in a population, including both fatal and nonfatal cases.

Morbidity rate : An incidence rate (q.v.) used to include all persons in the population under consideration who become clinically ill during the period of time stated. The population may be limited to a specific gender or age group, or to those with certain other characteristics.

Morbilliform rash : Rash which resembles the flat to slightly raised (maculopapular) lesions seen in measles.

Morphotype : A term used in reference to a specific morphological appearance; can be used in reference to colony appearance (colony morphotype) or Gram stain appearance (cellular morphotype). A given organism (e.g. Fusobacterium nucleatum) could have more than one colony morphotype.

Mortality : Incidence of disease in population.

Mortality rate : A rate calculated in the same way as an incidence rate (q.v.), by dividing the number of deaths occurring in the population during the stated period of time, usually a year, by the number of persons at risk of dying during the period. A total or crude mortality rate utilizes deaths from all causes, usually expressed as deaths per 1,000. A disease-specific mortality rate covers deaths due to only one disease and is often reported on the basis of 100,000 persons. The population base may be defined by gender, age or other characteristics. The mortality rate must not be confused with case-fatality rate (q.v.) (Synonym: death rate).

mos : Months.

Motility : The property of movement of a cell under its own power.

MOTT : Mycobacteria other than Mycobacterium tuberculosis.

MPC : Mucopurulent cervicitis.

mRNA : Messenger RNA.

MRI : Magnetic resonance imagery.

MRSA : Methicillin-resistant Staphylococcus aureus.

MSAIDs : Nonsteroidal antiinflammatory drugs.

MU : Million units.

Mucilage : A gumlike material covering some bacteria (e.g. cyanobacteria) to prevent the water loss during the dryness.

Mucocutaneous : Involving the skin and mucous membranes.

Mucopurulent : Term used to describe material containing both mucus and pus (e.g. mucopurulent sputum).

Mucosa : A mucous membrane.

Multilocular cyst : Cyst containing many cavities (Echinococcus multilocularis).

Multiple myeloma : Malignancy involving antibody producing plasma cells.

Murein : See peptidoglycan.

Muriform : A multicelled, transverse and longitudinal septate conidium.

Murmur : Abnormal sounds heard on auscultation of the heart, lungs, or vessels; this is a physical finding that has a variety of causes.

Mushroom : A filamentous fungus that produces large, sometimes edible structure, called fruiting body.

Mutagen : A substance which causes the mutation of genes. Compare with carcinogen.

Mutant : Refers to an organism, population, gene, or chromosome, etc., which differs from the corresponding wild type by one or more mutations.

Mutation : An inheritable change in the base sequence of the DNA of an organism.

Mutualism : A type of interaction in which two or more organisms living together benefit each other.

MW : Molecular weight.

Myalgia : Soreness or aching of muscles.

Mycelia Sterilia : An order of the Fungi Imperfecti consisting of fungi that do not produce conidia or spores.

Mycelium (pl. mycelia) : A large mass of hyphae forming the vegetative (somatic) portion of the fungus.

Mycetoma : A localized, chronic cutaneous or subcutaneous infection classically characterized by draining sinuses, granules, and swelling.

Mycology : The study of fungi and their biology.

Mycoplasma : A group of bacteria without a cell wall. They are grouped together with gram-positive bacteria not because they are stained positive but because they are phylogenetically close to the clostridia. The other important feature of mycoplasma is that they are very small, probably the smallest organisms capable of autonomous growth.

Mycorrhiza : A symbiotic association between a fungus and the roots of a plant.

Mycosis (pl. mycoses) : A disease caused by a fungus.

Myeloma : A malignant tumor of a plasma cell (antibody-producing cell).

Myiasis : Infestation with maggots (fly larvae).

Myocarditis : Inflammation of the heart muscle.

Myositis : Inflammation of a muscle, sometimes caused by infection as in pyomyositis, an infection caused by Staphylococcus aureus that leads to small abscesses within the muscle substance.