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