Microbiology, 2021

1196 E • Glossary
bacterial reproduction until it excises and
enters a lytic phase of the life cycle
lysogeny process of integrating the phage
into the host genome
lysosome an organelle of the
endomembrane system that contains
digestive enzymes that break down
engulfed material such as foodstuffs,
infectious particles, or damaged cellular
components
lytic cycle infection process that leads to
the lysis of host cells
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
meiosisa two-stage nuclear division
process that results in four genetically
distinct gametes
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 heatsensitive
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
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