Ultrasensitive qualitative detection of
E. coli strain
O157:H7 by real time polymerase chain reaction. This assay does
not detect other unrelated
E. coli strains.
Test B0059 is
- waterborne pathogens screening panel
serotype O157:H7 is a gram-negative, rod-shaped bacterium and is
one of hundreds of serotypes of the bacterium
E. coli. While most
strains are harmless and are found normally in the intestines of
mammals, strain O157:H7 produces shiga-like toxins, causes
severe illness, and is a member of a class of pathogenic E. coli
known as enterohemorrhagic Escherichia
coli (EHEC). They are sometimes also referred to by
their toxin producing capabilities, eg “verocytotoxin producing
E. coli” (VTEC)
or “shiga-like toxin producing
E. coli” (STEC).
O157:H7 differs from other pathogenic
E. coli in that it
is not invasive, elaborates no colonization factors (CFA/I nor
CFA/II), does not produce heat stable or heat labile toxins and
is non-hemolytic. In addition,
E. coli O157:H7 is
sorbitol negative whereas 93% of all
E. coli ferment
sorbitol. E. coli
O157:H7 also does not hydrolyze
4-methylumbelliferyl-ß-D-glucuronide (MUG), nor does it grow at
45ºC in the presence of 0.15% bile salts. Because of the latter
characteristic this serotype cannot be isolated by using
standard fecal coliform methods that include incubation at 45ºC.
O157:H7 can be transmitted in food or drinking water, and
outbreaks of E. coli
O157:H7 infection have been attributed to the presence of
this bacterium in groundwater and surface water (Chalmers et al.
2000; Lee et al. 2002). A likely source of contamination of
aquatic systems is cattle manure and agricultural runoff. The
intestinal cells of cattle, swine and deer lack the highly
specific surface receptors that the toxin requires in order to
attach and enter the cell. Therefore these animals do not
exhibit disease when infected (Pruimboom-Brees et al. 2000) and
can be carriers, shedding the organism in their feces.
O157:H7 persists in cattle manure (Wang et al. 1996; Bolton et
al. 1999; Fukushima et al. 1999; Osek 2002) and manure-amended
soil (Jiang et al. 2002) and experiments with models have
suggested that it may leach through soil (Gagliardi and Karns
2000). Meat can become contaminated during slaughter, and the
organisms can be thoroughly mixed into beef when it is ground.
Bacteria present on cows’ udders or on equipment may get into
raw milk. Although the number of organisms required to cause
disease is not known, it is suspected to be very small.
source of human infection is undercooked ground beef; other
sources include consumption of unpasteurized milk and juice, raw
sprouts, lettuce and salami, as well as contact with infected
live animals. Waterborne transmission occurs through swimming in
contaminated lakes or pools, or drinking inadequately treated
water. The organism is easily transmitted from person to person
and has been difficult to control in child daycare centers.
Infection often causes severe, acute bloody diarrhea (although
nonbloody diarrhea is also possible) and abdominal cramps.
Usually little or no fever is present, and the illness resolves
in 5 to 10 days. It can also be asymptomatic.
methods to detect E. coli
O157:H7 are important to identify the source of
outbreaks. Both molecular and culture-based methods have been
used for the detection of E.
coli O157:H7. Culture-based methods developed for
clinical samples have been applied to environmental samples.
These methods rely on enrichment cultures followed by
confirmation based on metabolic and antigenic properties. A
disadvantage of this approach is the lack of complete
correlation of these antigenic and metabolic properties with
Shigella toxin (stx) production (Karch and Bielaszewska 2001).
Also, culture-based methods for the detection of O157:H7 are
slow and labor intensive, so they are not ideal for analysis of
the large numbers of samples that must be tested when possible
environmental sources of an outbreak are being investigated.
infectious dose is very small and the number of cells
contaminating environmental samples or food may be low,
immunomagnetic capture with anti-O157 antibody has been
suggested as a means to concentrate and detect the target cells
(Pyle et al. 1999). However, this approach is limited to cells
displaying a specific antigen, making it unsuitable for other
STEC. Molecular approaches for bacterial detection avoid the
need for culture and can be designed to be more specific.
Primers targeting stx1, stx2 and other genes specific to
E. coli O157:H7 have
been used in PCR and real time PCR (Olsvik and Strockbine 1993;
Fratamico et al. 2000; Fortin et al. 2001; Li and Drake 2001;
Ibekwe et al. 2002; Ibekwe and Grieve 2003). Specific, rapid
diagnosis of E. coli
O157:H7 is possible using PCR techniques (Al-Ajmi et al., 2006;
Holicka et al., 2006).
Help confirm the disease causing agent
Shorten the time required to confirm a clinical
diagnosis of E. coli
Help ensure that horse populations are free of
E. coli O157:H7
Early prevention of spread of this bacterial strain
Minimize human exposure to this bacterial strain
Al-Ajmi, D., Padmanabha, J., Denman, S.E., Gilbert, R.A., Al
Jassim, R.A. and McSweeney, C.S.(2006) Evaluation of a PCR
detection method for Escherichia coli O157:H7/H- bovine faecal
samples. Lett Appl Microbiol. 42:386-391.
Guy, R.A., Kapoor, A., Shepherd, D. and Horgen, P.A. (2006) A
rapid (one day), sensitive real-time polymerase chain reaction
assay for detecting Escherichia coli O157:H7 in ground beef. Can
J Microbiol. 52:992-8.
Rectal swab, or 0.2 ml feces, or 0.2 ml bacterial culture,
or environmental swab.
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.
2 business days
real time PCR