differentiation by PCR of 5 different
categories of diarrheagenic
E. coli -- ETEC, EHEC, EIEC, EPEC and EAEC.
diseases are a major cause of death for children under 5 years
of age in developing countries; the estimated death toll is
12,600 children per day. Causes of diarrhea include a wide range
of viruses, bacteria, and parasites. Among the bacterial
pathogens, various strains of
Escherichia coli are
the major culprits.
E. coli is the
predominant nonpathogenic facultative anaerobic member of the
human intestinal microflora, some
E. coli strains can
cause diseases of the gastrointestinal, urinary, and central
nervous systems in humans. The intestinal tracts of almost all
birds and mammals, including nonhuman primates and horses, are
colonized by E. coli.
Infections by pathogenic strains of
E. coli also occur in many domestic and wild
symptoms induced by these diarrheagenic
E. coli can be due
to production of toxins or other virulence traits.
E. coli strains that
induce diarrhea in their hosts can be divided into five main
categories on the basis of distinct epidemiological and clinical
features and specific virulence determinants:
E. coli: Produce heat-labile toxin (LT)
and heat-stable toxin (ST).
Enterohemorrhagic E. coli:
shiga-like toxins (SLT) I and II.
Enteroinvasive E. coli:
invade and destroy the bowel mucosa.
Enteropathogenic E. coli:
bowel mucosa with characteristic attaching and effacing
lesions mediated by a protein encoded by a gene called the
attaching and effacing locus (eal).
Enteroaggregative E. coli:
epidemiology and pathogenicity of these strains have not yet
been clearly defined, but the presence of a large 60 kD
plasmid encoding several virulence factors and toxins is
important for their virulence.
induce a watery diarrhea in infected hosts by action of the two
toxins, LT and ST. The LT enterotoxin is very similar to cholera
toxin in both structure and mode of action. ST is known to bind
to and activate a guanylate cyclase enzyme located on apical
membranes of host cells. This leads to secretion of fluid and
electrolytes resulting in a watery diarrhea. Incubation period
is approximately 1-2 days and illness can last 3 days to several
are mostly represented by a single strain, serotype O157:H7,
which causes a diarrheal syndrome with copious bloody discharge
and no fever. There is a toxic effect on the kidneys, and
diarrhea caused by this strain can be fatal, particularly in
infants, due to acute kidney failure. Infection in humans is
often associated with ingestion of inadequately cooked hamburger
meat. Incubation period is approximately 3 to 4 days and
duration of illness is about 1 week.
are similar to Shigella in their pathogenic mechanism and
clinical symptoms. EIEC bacteria penetrate and multiply within
epithelial cells of the colon causing widespread cell
destruction. The clinical syndrome is identical to Shigella
dysentery and includes a dysentery-like diarrhea with fever.
EIEC do not produce LT or ST toxin and, unlike Shigella, do not
produce shiga toxin. The incubation period is less than 24
cause a watery diarrhea similar to ETEC, but do not produce ST
or LT toxins. These strains are a principal cause of infant
diarrhea in developing countries. The illness typically lasts 1
to 3 days.
adhere to epithelial cells in a characteristic stacked-brick
pattern known as the aggregative adherence (AA) pattern. When
they adhere to small and large bowel mucosal surfaces they
stimulate mucus production, leading to a thick mucus-containing
biofilm encrusted with EAEC. They can also secrete toxins, such
as heat-stable enterotoxin 1 (EAST1), Pet and Pic, which are
associated with damage to the mucosa. EAEC were originally
recognized as one of the predominant etiologic agents of
persistent diarrhea in developing countries and they remain an
important cause of acute as well as protracted diarrhea in many
parts of the world, including industrialized countries.
assays are available for detection of diarrheagenic
E. coli, including
biochemical reactions, serotyping and phenotypic assays based on
virulence characteristics. However, molecular detection by PCR
has become a commonly-used method to detect and identify these
bacteria because the method gives rapid and reliable results in
addition to its high sensitivity and specificity (Bellin et al.,
2001; Stacy-Phipps et al., 1995).
Help confirm the disease causing agent
Selection of appropriate treatment regimen
Shorten the time required to confirm a clinical
Help ensure that colonies are free of diarrheagenic
Early prevention of spread of diarrheagenic
E. coli among a
Minimize personnel exposure to diarrheagenic
Safety monitoring of biological products that derive
Bellin, T., Pulz, M., Matussek, A., Hempen, H.G. and Gunzer, F.
(2001) Rapid detection of enterohemorrhagic Escherichia coli by
real-time PCR with fluorescent hybridization probes. J. Clin.
Stacy-Phipps, S., Mecca, J.J. and
Weiss, J.B. (1995) Multiplex PCR assay and simple preparation
method for stool specimens detect enterotoxigenic Escherichia
coli DNA during course of infection. J. Clin. Microbiol.
Rectal swab, or 0.2 ml feces, or 0.2 ml bacterial culture,
specimen - 0.2 ml whole
blood in EDTA (purple top) or ACD (yellow top) tube.
types other than those listed here, please call to confirm
specimen acceptability and shipping instructions.
specimen types, if there will be a delay in shipping, or during
very warm weather, refrigerate specimens until shipped and ship
with a cold pack unless more stringent shipping requirements are
specified. Frozen specimens should be shipped so as to remain
frozen in transit. See shipping
instructions for more information.
3 business days