Microbiology, 2021

1188 E • Glossary
quantification or identification of the
antigen bound by the antibody
enzyme-linked immunosorbent assay
(ELISA) specialized form of EIA in which
either the primary antibody or the antigen
is first attached to a solid surface such as
the well of a microtiter plate
eosinophils leukocytes with granules
containing histamine and major basic
protein; facilitate allergic responses and
protection against parasitic protozoa and
helminths
epidemic disease an illness with a higherthan-expected
incidence in a given period
within a given population
epidemic typhus severe and sometimes
fatal infection caused by Rickettsia
prowazekii and transmitted by body lice
epidemiology the study of where and
when infectious diseases occur in a
population and how they are transmitted
and maintained in nature
epidermis the outermost layer of human
skin
epididymis coiled tube that collects sperm
from the testes and passes it on to the vas
deferens
epididymitis inflammation of the
epididymis caused by a bacterial infection
epigenetic regulation chemical
modification of DNA or associated
histones to influence transcription
epiglottis flap of cartilage that covers the
larynx during swallowing; diverts food to
the esophagus and prevents it from
entering the respiratory tract
epiglottitis inflammation of the epiglottis
epiphyte a plant that grows on another
plant
epitope smaller exposed region on an
antigen that is recognized by B-cell and T-
cell receptors and antibodies
Epsilonproteobacteria class of
Proteobacteria that are microaerophilic
equivalence zone region where the
antibody–antigen ratio produces the
greatest amount of precipitin in a
precipitin reaction
erysipelas a skin infection, typically
caused by Streptococcus pyogenes, that
presents as a red, large, intensely
inflamed patch of skin involving the
dermis, usually with clear borders,
typically on the legs or face
erythema nodosum a condition that
causes inflammation in the subcutaneous
fat cells of the hypodermis resulting in red
nodules
erythema redness at the site of
inflammation, usually due to dilation of
blood vessels in the area to help bring in
white blood cells
erythrocyte red blood cell
erythrogenic toxin exotoxin produced by
some strains of Streptococcus pyogenes;
activity of the toxin can produce the
characteristic rash of scarlet fever
erythromycin protein synthesis inhibitor
of the macrolide class that is often used as
an alternative to penicillin
eschar a localized mass of dead skin
tissue
Etest simple, rapid method for
determining MIC, involving commercially
available plastic strips that contain a
gradient of an antimicrobial and are
placed on an agar plate inoculated with a
bacterial lawn
etiologic agent the pathogen or substance
responsible for causing a particular
disease; causative agent
etiology the science of the causes of
disease
Eukarya the domain of life that includes
all unicellular and multicellular organisms
with cells that contain membrane-bound
nuclei and organelles
eukaryote an organism made up of one or
more cells that contain a membranebound
nucleus and organelles
eukaryotic cell has a nucleus surrounded
by a complex nuclear membrane that
contains multiple, rod-shaped
chromosomes
eustachian tube small passage between
the nasopharynx and the middle ear that
allows pressure to equalize across the
tympanic membrane
excystment the process of emerging from
a cyst
exergonic reaction chemical reaction that
does not require energy beyond activation
energy to proceed; releases energy when
the reaction occurs
exocytosis the release of the contents of
transport vesicles to the cell’s exterior by
fusion of the transport vesicle’s membrane
with the plasma membrane
exoenzyme secreted enzyme that
enhances the ability of microorganisms to
invade host cells
exon protein-coding sequence of a
eukaryotic gene that is transcribed into
RNA and spliced together to code for a
polypeptide
exonuclease enzymatic activity that
removes RNA primers in DNA introduced
by primase
exotoxin biologically active product that
causes adverse changes in the host cells
experimental epidemiology the use of
laboratory and clinical studies to directly
study disease in a population
experimental study a type of scientific
study that involves manipulation of the
study subjects by the researcher through
application of specific treatments
hypothesized to affect the outcome while
maintaining rigorously controlled
conditions
exposure contact between potential
pathogen and host; also called
contamination or contact
extended-spectrum β-lactamases
(ESBLs) β-lactamases carried by some
gram-negative bacteria that provide
resistance to all penicillins,
cephalosporins, monobactams, and β-
lactamase-inhibitor combinations, but not
carbapenems
extensively drug resistant
Mycobacterium tuberculosis (XDR-TB)
strains of M. tuberculosis that are resistant
to rifampin and isoniazid, and also are
resistant to any fluoroquinolone and at
least one of three other drugs (amikacin,
kanamycin, or capreomycin)
extracellular matrix material composed
of proteoglycans and fibrous proteins
secreted by some eukaryotic cells that lack
cell walls; helps multicellular structures
withstand physical stresses and
coordinates signaling from the external
surface of the cell to the interior of the cell
extracellular polymeric substances
(EPS) hydrated gel secreted by bacteria in
a biofilm containing polysaccharides,
proteins, nucleic acids, and some lipids
extrachromosomal DNA additional
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