Escherichia coli
Download
Report
Transcript Escherichia coli
Escherichia coli
Escherichia coli
Named for Theodor Escherich a
German physician (1885)
Normal flora of the mouth and
intestine.
Protects the intestinal tract from
bacterial infection.
Produces small amounts of vitamins
B12 and K
Colonizes newborns GI tract within
hours after birth.
Properties:
Gram-negative
Facultative
short rod.
anaerobe
Member of the
Enterobacteriaceae family.
It is present normally in high
concentrations (108/g) in normal
human feces.
Motile and ferments lactose.
It has three antigens
1. O, or cell wall, antigen
2. H, or flagellar, antigen
3. K, or capsular, antigen.
Diseases in general:
Urinary
tract infection (UTI), Sepsis,
Neonatal meningitis, and "traveler's
diarrhea" are most common.
E.coli
Pathogenesis:
Reservoir:
Humans
and animals( cattle).
The source of E. coli that causes UTI
is the patient's own colonic flora.
The source of E. coli that causes
neonatal meningitis is the mother's
birth canal.
E. coli that causes traveler's
diarrhea is acquired by ingestion of
contaminated food or water.
It causes pathogenesis by.
I.
Pili and capsule
II.
Endotoxin.
III.
Three exotoxins (enterotoxins).
1.
Labile toxin
2.
Stable toxin
3.
Verotoxin that causes bloody
diarrhea and hemolytic-uremic
syndrome.
A.
B.
1.
Clinical disease:
Intestinal:
Caused by four different strains
Enteropathogenic E coli
Watery diarrhea primarily in
infants by endotoxin.
Enterotoxigenic Escherichia Coli
Causes traveler's diarrhea in all
age-groups.
Two enterotoxins are responsible
for traveler diarrhea.
The heat-labile toxin (LT)
stimulates adenylate cyclase.
C.
It in turn causes increased cyclic
AMP which causes outflow of
chloride ions and water, resulting
in diarrhea.
The heat-stable toxin (ST) causes
diarrhea by stimulating guanylate
cyclase.
Enterohemorrhagic Escherichia
Coli
Causes Hemorrhagic Colitis and
Hemolytic-Uremic Syndrome.
Verotoxin (a cytotoxin)
responsible for hemorrhagic colitis
and hemolytic uremic syndrome.
Hemorrhagic
colitis: A severe form
of bloody diarrohea.
Hemolytic uremic syndrome. A
potentially life-threatening acute
renal failure.
D. Enteroinvasive E. coil
Cause a dysentery-like syndrome
with fever and bloody stools.
Extraintestinal disease:
1. UTI.
E. coil is the most common cause
of cystitis and pyelonephritis.
Women are particularly at risk for
infection.
2. Neonatal meningitis: E. coli is a
major cause of disease occurring
within the first month of life.
3.
The K (capsular) antigen is
particularly associated.
Nosocomial (hospital-acquired)
infections: These include sepsis
endotoxic shock, and
pneumonia.
1.
2.
Laboratory Diagnosis:
Specimens suspected of
containing E. coli, are grown on
A blood agar plate and
On a differential medium, such as
EMB agar or MacConkey's agar.
E. coli, which ferments lactose,
forms pink colonies, whereas
lactose-negative organisms are
colorless.
Pure culture of E.coli.
Detection from stool is difficult but
easier from specimens like CSF and
urine