Microbial Hazards in Foods: Food-Borne Infections and Intoxications 493not think of E. coli as a food - borne pathogen;
however, recent research and information
indicates that some strains of E. coli can
indeed cause severe food - borne diseases. The
sensational outbreak of E. coli O157 : H7 in
1993 in the United States, involving hun-
dreds of people and resulting in four deaths,
was caused by the consumption of under-
cooked hamburger served by a fast - food
chain; it awakened the general public to the
realization of the importance of food safety.
Food industries, academic communities, reg-
ulatory agencies, and consumer groups have
been actively working on solving the problem
of E. coli O157 : H7 ever since that outbreak.
Although much has been learned about this
organism, far more needs to be done to deter-
mine its habitat, detection, and control.
E. coli is a Gram - negative, facultative
anaerobic, non - spore - forming rod that occurs
widely in nature as well as in the intestines
of humans and animals. It is glucose - and
lactose - positive and indole and methyl red
positive but Voges - Proskauer and citrate
negative. The most useful way to classify the
species is by serotyping, using antibodies
against O, H, and K antigens of various
strains of E. coli.
Most E. coli isolated from the environ-
ment are not pathogenic. However, there are
six classes of pathogenic and diarrheagenic
E. coli. They are enterohemorrhagic (EHEC),
enterotoxigenic (ETEC), enteroinvasive
(EIEC), enteroaggregative (EaggEC), entero-
pathogenic (EPEC), and diffusely adherent
(DAEC) E. coli.
EHEC or enterohemorrhagic E.coli was
fi rst identifi ed as a human pathogen in 1982.
The most important serotype is O157 : H7.
Other serotypes in this group are O26 : H11,
O103, O104, O111, and others. E. coli
O157 : H7 causes the most concern world-
wide because of its unusual cultural charac-
teristics and pathogenicity. Unlike most E.
coli, this serotype does not ferment sorbitol
within 24 hours, does not possess beta -
glucuronidase activity, and does not have thelaboratory, the enzyme Oxyrase was found to
greatly stimulate the growth of this organism
even in the absence of special gas mixtures,
thus facilitating its rapid and convenient
detection and isolation. The incubation time
of C. jejuni food poisoning ranges from 2 to
5 days; the duration of the sickness may be
up to 10 days. The patient will exhibit enteri-
tis, fever, malaise, abdominal pain, and head-
ache. The stools become liquid and foul
smelling. Blood, bile, and mucus discharge
may occur in serious cases. The organism has
a worldwide distribution, with outbreaks
related to milk, poultry, eggs, red meat, pork,
and water reported. It has been isolated in
50% to almost 100% of poultry carcasses in
several studies. Competitive exclusion proto-
cols have been devised to prevent the attach-
ment and growth of C. jejuni by inoculating
large numbers of natural intestine microor-
ganisms in newly hatched chicks. Detection
of this organism is by suitable liquid and
solid growth media designed for the organ-
ism and rapid tests involving ELISA, PCR,
Ribotyping, etc. One complication in study-
ing this organism is the presence of viable but
nonculturable populations of C. jejuni in the
environment.
Proper food - processing techniques (heat-
ing, cooling, chemical treatment of foods,
etc.) will control this fragile organism. Its
prevalence as a food - borne pathogen can
be attributed to post - processing contamina-
tions of food. Again, good sanitation and
hygiene should reduce the incidence of this
organism in our food supplies. Because of
increased outbreaks and cases related to this
organism, much research is being conducted
worldwide to monitor the organism. C. jejuni
may be the next major food - borne disease -
causing organism to be faced by food micro-
biologists around the world.
Escherichia coli
Escherichia coli is one of the most common
bacteria in our environment. Most people do