494 Chapter 28
attaching to the epitheleal cells before E. coli
O157 : H7 can have a chance to interact with
them. Much research on this organism is
being conducted around the world. In 2002,
there were 84 outbreaks, 3,260 cases, and
8 deaths reported that were attributed to
Escherichia coli (the serotype was not speci-
fi ed, but it was probably O157 : H7).
Much is now known about the character-
istics of this organism. It grows well at 37 ° C
but poorly at 44 – 45 ° C, a temperature usually
used to isolate E. coli. It can grow between
8 – 45 ° C and can survive in ground beef at
− 20 ° C for nine months. It can grow in neutral
pH ranges of 5.5 to 7.5 but can also grow in
pH 4.0 to 4.5 range, and more recent data
indicated that it can survive in apple cider in
the range of pH 3.6 to 4.0. The organism is
heat sensitive. Proper cooking temperatures
of 71 ° C will destroy the organism in foods.
The organism is quite salt tolerant, with the
ability to grow at 8% NaCl at 37 ° C; however,
at a lower incubation temperature of 10 ° C,
growth was inhibited to 4% to 6%. This
organism grows well in water activity around
0.99, with a minimum at 0.95.
Outbreaks of E. coli O157 : H7 have been
reported from water, meat, poultry, dairy
products, salad, apple cider, and even fer-
mented meats and mayonnaise. Detection
methods include conventional culture pro-
cedures designed specifi cally for E. coli
O157 : H7, a variety of diagnostic kits, sero-
logic tests, ELISA. PCR, and Ribotyping.
The aim is to accurately and rapidly screen
for the presence or absence of the organisms
in 25 grams of food. A 24 - hour negative
screening protocol is now available. Some
commercial companies developed an 8 - hour
protocol. Research from Fung ’ s laboratory
perfected a 5.25 - hour test to detect this
organism using the Pathatrix system. This
involved a short incubation period, followed
by a circulating system to concentrate the
target E. coli O157 : H7 by immunomagnetic
separation technology and complete the pro-
cedure by using a 25 - minute ELISA test.ability to hydrolyze 4 - methylumbelliferyl -
beta - D - glucuronide (MUG), which is an
important diagnostic characteristic of most
other E. coli strains. Because of these differ-
ences in routine microbiological manipula-
tions, E. coli O157 : H7 has been excluded in
the protocol for common E. coli. The organ-
ism produces one or more Shiga - like toxins
(SLT; also known as verotoxin, VT) and it
possesses an attaching and effacing gene ( eae
gene ) and a large plasmid (60 MDA). The
organism causes several illness, especially in
children and immunocompromised patients.
There are three manifestations of the disease:
hemorrhagic colitis (HC), hemolytic uremic
syndrome (HUS), and thrombotic thrombo-
cytogenic purpura (TTP). Symptoms of HC
occur within 1 to 2 days after consuming
contaminated foods. The initial symptoms
are mild, nonbloody diarrhea followed by
severe abdominal pain and a short fever or
no fever. The watery diarrhea will last for 24
to 48 hours, followed by 4 to 10 days of
bloody diarrhea, severe abdominal pain, and
dehydration. Patients with HC may develop
more severe life - threatening complications
such as HUS or TTP. HUS symptoms are
characterized by microangiopathic hemolytic
anemia (pallor, intravascular destruction of
red blood cells), thrombocytopenia (depressed
platelet counts), and acute renal failure that
may lead to death. TTP affects mostly adults
and is a rare syndrome of E. coli O157 : H7
infection. It causes neurological abnormali-
ties such as nervous system deterioration,
seizures, and strokes. Patients will often
develop blood clots in the brain and may die.
The infectious dose of E. coli O157 : H7 is
between 2 and 200 cells.
Adhesion of the organisms to the intesti-
nal walls is important, but it does not enter
the circulatory system. The organism colo-
nizes the intestinal tract, where toxins are
produced and then become active in the
colon. For this reason, much research is
being conducted to achieve competitive
exclusion by nonpathogenic organisms