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Escherichia
coli, a gram-negative bacillus that is part of the intestinal flora,
is also an important opportunistic pathogen, causing diarrhea and
dysentery, urinary tract infection, pneumonia and neonatal meningitis.
Visit: Shigellosis ;
Amoebiasis (Entamoeba histolytica)
;
Cholera
;
Hookworm Infection
;
Giardiasis
;
Salmonellosis (Gastroenteritis and Septicemia)
;
Necrotizing Enteritis (pig-bel)
;
Yersiniosis.
E. coli causes
various patterns of human enteric diseases caused by different
varieties of E.Coli.
Some of these are -
Enterotoxigenic ; Enteroinvasive ; Enteroadherent ;
Enterohemorrhagic.
Enterotoxigenic E. coli causes
diarrheal disease by elaborating two plasmid-mediated enterotoxins.
The
heat-labile toxin is antigenically, structurally and functionally
related to the cholera toxin, although the toxin of E. coli is less
potent than that of
cholera
. The heat-labile toxin also binds to DM1 ganglioside on the intestinal epithelial cells. As in cholera,
resulting activation of adenyl cyclase produces a hypersecretory
diarrhea.
The heat-stable toxin of E. coli is different from cholera
toxin and apparently acts to impair sodium and chloride absorption and
to reduce the motility of small intestine through a mechanism
dependent on cyclic GMP.
Dehydration and electrolyte imbalance is a
significant cause of morbidity and mortality when appropriate rehydration is lacking.
Enterotoxigenic E. coli is also responsible for
50% of traveller’s diarrhea.
Enteroinvasive E. coli produces a dysentery-like disease resembling
shigellosis , although it is less severe and requires a much larger
infecting dose of organisms. Enteroinvasive E. coli invades the
intestinal mucosa and causes local tissue destruction and sloughing of
necrotic mucosa. Bloody mucoid stools contain neutrophils.
Enteroadhesive
E. coli has been associated with diarrheal diseases. Enteroadhesiveness is plasmid-dependent and is apparently mediated by
pili, which bind tightly to receptors of the intestinal epithelial
cells. The mechanism of diarrhea is unknown.
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The most common strain of
enterohemorrhagic E. coli is 0157:H7.
This organism
adheres to intestinal epithelial cells and produces a cytotoxin
similar to that produced by
Shigella dysenteriae.
Contaminated meat is the most frequent mode of transmission, but
infection may also occur through contaminated water, milk, produce,
and person-to-person contact.
The
symptoms include bloody diarrhea with severe abdominal cramps and mild
or no fever. Non bloody, watery diarrhea may occur . Some patients
have fecal leukocytes. Patients are at risk for the hemolytic-uremic
syndrome or thrombotic thrombocytopenic purpura. Children and elderly
patients are at particular risk of serious illness.
Patients
may have colonic edema, erosions, ulcers, and hemorrhage, and the
right colon is usually more severely affected.
The lamina propria and
submucosa contain marked edema and hemorrhage, with associated mucosal
acute inflammation, cryptitis, crypt abscesses, ulceration, and
necrosis. Microthrombi may be seen within small vessels, and
pseudomembranes are occasionally present.
About 80% of all
infections of the urinary tract in humans, ranging from mild cystitis
to fatal pyelonephritis, are caused by E. coli.
In addition, E. coli
is the etiologic agent in many caes of nosocomial pneumonia, most
often in elderly patients with underlying chronic disease.
Aspirates
of endogenous oral flora containing E. coli appear to be the cause of
this
bronchopneumonia , although in bacteremic patients pneumonia may
result from seeding by septic emboli.
Empyema is a common
complication, especially in patients with disease lasting more than a
week.
Only rarely does
E. coli cause meningitis in adults, but it is a major cause of
neonatal meningitis.
Between 40% and 80% of infants with E. coli
meningitis die, and the survivors frequently suffer from neurologic or
developmental anomalies.
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