0.5 Glossary  (Page 11/18)

M

• M protein a streptococcal cell wall protein that protects the bacteria from being phagocytized. It is associated with virulence and stimulates a strong immune response
• macrolides class of protein synthesis inhibitors containing a large, complex ring structure that binds to the 50S subunit, inhibiting peptide bond formation
• macromolecule polymer assembled from of individual units, monomers, that bind together like building blocks
• macronucleus larger nucleus in ciliate protists that have two nuclei; polyploid with a reduced genome of metabolic genes and derived from the micronucleus
• macronutrient element required in abundance in cells; account for approximately 99% of the cell’s dry weight
• macrophages monocytes that have left the bloodstream and differentiated into tissue-specific phagocytes
• mad cow disease form of transmissible spongiform encephalopathy primarily affecting cattle; can be transmitted to humans by consumption of contaminated cattle products
• magnetosomes inclusions in certain bacterial cells containing magnetic iron oxide or iron sulfide, which allows bacteria to align along a magnetic field by magnetotaxis
• magnetotaxis directional movement of bacterial cells using flagella in response to a magnetic field
• magnification the power of a microscope (or lens) to produce an image that appears larger than the actual specimen, expressed as a factor of the actual size
• major histocompatibility complex (MHC) collection of genes that code for MHC glycoproteins expressed on the surface of all nucleated cells
• malaise a general feeling of being unwell
• malaria potentially fatal, mosquito-borne protozoan infection caused by several species of Plasmodium and characterized by a relapsing fever, nausea, vomiting, and fatigue
• mast cells granulocytes similar in origin and function to basophils, but residing in tissues
• matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF) technique in which the sample (e.g., a microbe colony) is mixed with a special matrix and irradiated with a high-energy laser to generate characteristic gaseous ions that are subjected to mass spectral analysis, yielding mass spectra that may be compared to reference data for identification purposes
• maturation assembly of viral components to produce a functional virus
• mature naïve T cell a T cell that has exited the thymus after thymic selection but has not yet been activated
• maximum growth pH highest pH value that an organism can tolerate for growth
• maximum growth temperature highest temperature at which a microorganism will divide or survive
• maximum permissible oxygen concentration highest concentration of oxygen at which an organism will grow
• measles highly contagious respiratory disease caused by the measles virus (MeV); marked by an intense macular rash and high fever; also known as rubeola
• mebendazole antihelminthic drug of the benzimidazole class that binds to helminthic β-tubulin, preventing microtubule formation
• mechanical transmission transfer of a pathogen between hosts by a mechanical vector
• mechanical vector an animal that transfers a pathogen from one host to another or from a reservoir to a host without being infected by the pathogen itself
• median infectious dose (ID ₅₀ ) concentration of pathogen that will produce active infection in 50% of test animals inoculated
• median lethal dose (LD ₅₀ ) concentration of pathogen that kills 50% of infected test animals
• medulla loosely packed layer of fungal filaments located underneath the cortex of a lichen
• membrane attack complex (MAC) ring structure formed from complement proteins C6 through C9 that penetrates the membranes of a targeted cell, causing cell lysis and death
• membrane filtration method to remove bacteria from liquid, typically heat-sensitive solutions, using filters with an effective pore size of 0.2 µm or smaller, depending on need
• membrane filtration technique known volumes are vacuum filtered aseptically through a membrane with a pore size small enough to trap microorganisms, which are counted after growth on plates
• membrane-bound ribosome 80S eukaryotic ribosome attached to rough endoplasmic reticulum
• membrane-disrupting toxin toxin that affects cell membrane function by either forming pores or disrupting the phospholipid bilayer
• memory B cell an activated and differentiated B cell that is programmed to respond to secondary exposures to a specific antigen
• memory helper T cell a long-lived T cell programmed to recognize and quickly mount a secondary response to a specific pathogen upon re-exposure
• memory the ability of the specific adaptive immune system to quickly respond to pathogens to which it has previously been exposed
• meninges membranes that surround the brain
• meningitis inflammation of the meningeal membranes that surround the brain
• meningococcal meningitis bacterial infection caused by Neisseria meningitidis that results in an inflammation of the meninges
• meningoencephalitis inflammatory response that involves both the brain and the membranes that surround it
• MERS Middle East respiratory syndrome; first described in Saudi Arabia in 2013; caused by a zoonotic coronavirus that results in flu-like symptoms
• mesophile a microorganism that grows best at moderate temperatures, typically between about 20 °C and 45 °C
• metabolism all of the chemical reactions inside of cells
• metachromatic granule a type of inclusion containing volutin, a polymerized inorganic phosphate that appears red when stained with methylene blue
• metagenomics the sequencing of genomic fragments from microbial communities, allowing researchers to study genes from a collection of multiple species
• metatranscriptomics the science of studying a collection of mRNA molecules produced from microbial communities; involves studying gene expression patterns from a collection of multiple species
• methanogen microorganism that produces gaseous methane
• methicillin-resistant Staphylococcus aureus (MRSA) pathogen resistant to all β-lactams through acquisition of a new low-affinity penicillin-binding protein, and often resistant to many other drug classes
• metronidazole antibacterial and antiprotozoan drug of the nitroimidazole class that is activated in anaerobic target cell and introduces DNA strand breakage, thus interfering with DNA replication in target cells
• MHC I molecule glycoprotein expressed on the surface of all nucleated cells and involved in the presentation of normal “self” antigens and foreign antigens from intracellular pathogens
• MHC II molecule glycoprotein expressed only on the surface of antigen-presenting cells and involved in the presentation of foreign antigens from pathogens ingested by phagocytosis
• micelle simple spherical arrangement of amphipathic lipid molecules with nonpolar tails aggregated within the interior and polar heads forming the outer surface
• microaerophile organism that requires oxygen at levels lower than atmospheric concentration
• microarray analysis a technique used to compare two samples of genomic DNA or cDNA; the DNA or cDNA fragments are immobilized on a chip and labeled with different fluorescent dyes, allowing for comparison of sequences or gene-expression patterns
• microbe generally, an organism that is too small to be seen without a microscope; also known as a microorganism
• microbial death curve graphical representation of the progress of a particular microbial control protocol
• microbial ecology study of the interactions between microbial populations microbiology the study of microorganisms
• microbiome all prokaryotic and eukaryotic microorganisms that are associated with a certain organism
• microfilament cytoskeletal fiber composed of actin filaments
• microinjection the direct injection of DNA into the cytoplasm of a eukaryotic cell using a glass micropipette
• micronucleus smaller nucleus in ciliate protists that have two nuclei; diploid, somatic, and used for sexual reproduction through conjugation
• micronutrient indispensable element present in cells in lower amounts than macronutrients; also called trace element
• microorganism generally, an organism that is too small to be seen without a microscope; also known as a microbe
• microsporidia fungi that lack mitochondria, centrioles, and peroxisomes; some can be human pathogens
• microtiter plates plastic dishes with multiple small wells
• microtubule hollow tube composed of tubulin dimers (α and β tubulin); the structural component of the cytoskeleton, centrioles, flagella, and cilia
• miliary tuberculosis hematogenous dissemination and spread of Mycobacterium tuberculosis from tubercles
• minimal bactericidal concentration (MBC) lowest antibacterial drug concentration that kills ≥99.9% of a starting inoculum of bacteria
• minimal inhibitory concentration (MIC) lowest concentration of an antibacterial drug that inhibits visible growth of a bacterial strain
• minimum growth pH lowest pH value that an organism can tolerate for growth
• minimum growth temperature lowest temperature at which a microorganism will divide or survive
• minimum permissible oxygen concentration lowest concentration of oxygen at which an organism will grow
• missense mutation point mutation that results in a different amino acid being incorporated into the resulting polypeptide
• mitochondrial matrix the innermost space of the mitochondrion enclosed by two membranes; the location of many metabolic enzymes as well as the mitochondrial DNA and 70S ribosomes
• mitochondrion (plural: mitochondria) large, complex organelle that is the site of cellular respiration in eukaryotic cells
• mode of action way in which a drug affects a microbe at the cellular level
• moist-heat sterilization protocol that involves steam under pressure in an autoclave, allowing the steam to reach temperatures higher than the boiling point of water
• mold a multicellular fungus, typically made up of long filaments
• molecular cloning the purposeful fragmentation of DNA followed by attachment to another piece of DNA to produce a recombinant molecule, followed by introduction of this recombinant molecule into an easily manipulated host to allow for the creation of multiple copies of a gene of interest
• monoclonal antibodies (mAbs) antibodies produced in vitro that only bind to a single epitope
• monocular having a single eyepiece
• monocytes large, agranular, mononuclear leukocytes found in the peripheral blood; responsible for phagocytosis of pathogens and damaged cells
• monoecious refers to sexually reproducing organisms in which individuals have both male and female reproductive organs
• monomer small organic molecule that binds with like molecules, forming a polymer or macromolecule
• monosaccharide monomer for the synthesis of carbohydrate polymers; the simplest carbohydrate, called a simple sugar
• monotrichous having one flagellum, typically located on one end of the bacterial cell
• morbidity a state of illness
• Morbidity and Mortality Weekly Report ( MMWR ) the trade/industry publication for epidemiologists, reporting US public health data compiled by the CDC
• morbidity rate the number of cases of a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000
• mordant a chemical added to a specimen that sets a stain
• mortality death
• mortality rate the number of deaths from a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000
• most probable number (MPN) statistical value representing the viable bacterial population in a sample obtained after a series of dilutions and multiple tube inoculations
• mRNA short-lived type of RNA that serves as the intermediary between DNA and the synthesis of protein products
• mucociliary escalator system by which mucus and debris are propelled up and out of the respiratory tract by the beating of respiratory cilia and the mechanical actions of coughing or swallowing
• mucormycosis rare form of pneumonia that can be caused by an invasive infection of different fungi in the order Mucorales, such as Rhizopus or Mucor
• mucous membrane moist layer of epithelial cells and interspersed goblet cells that lines the inner surfaces of the body, usually bathed in antimicrobial secretions from the cells of the membrane
• mucus viscous secretion produced by cells and glands in various mucous membranes throughout the body; helps trap and remove microbes and debris from the body
• multidrug-resistant microbes (MDR) group of pathogens that carry one or more resistance mechanisms, making them resistant to multiple antimicrobials; also called superbugs
• multidrug-resistant Mycobacterium tuberculosis (MDR-TB) strains of M. tuberculosis that are resistant to both rifampin and isoniazid, the drug combination typically prescribed for the treatment of tuberculosis
• multiple sclerosis autoimmune attack on the myelin sheaths and nerve cells in the central nervous system
• mumps a viral illness that causes swelling of the parotid glands; rare in the United States because of effective vaccination
• murine typhus fleaborne infection caused by Rickettsia typhi and characterized by fever, rash, and pneumonia
• mutagen type of chemical agent or radiation that can induce mutations
• mutant organism harboring a mutation that often has a recognizable change in phenotype compared to the wild type
• mutation heritable change in the DNA sequence of an organism
• mutualism type of symbiosis in which two populations benefit from, and depend on, each other
• myasthenia gravis autoimmune disease affecting the acetylcholine receptors in the neuromuscular junction, resulting in weakened muscle contraction capability
• mycelium vegetative network of branched, tubular hyphae
• mycolic acids waxy molecules associated with peptidoglycan in some gram-positive, acid-fast bacteria, chiefly mycobacteria
• mycology the study of fungi
• Mycoplasma pneumonia also known as walking pneumonia; a milder form of atypical pneumonia caused by Mycoplasma pneumoniae
• mycoses (mycosis, sing.) refers to diseases caused by fungi
• mycotoxin biologically active product of pathogenic fungi that causes adverse changes in the host cells
• myelin sheath insulating layer that surrounds the axon of some neurons and helps to promote signal propagation
• myocarditis inflammation of the heart muscle tissues