- Escherichia coli (E. coli) is a common bacteria that normally lives in the intestines of humans and animals. However, some strains of E. coli can cause illness, including diarrhea. - E. coli that causes diarrhea is divided into six groups that produce diarrhea through different pathogenic mechanisms, such as the production of heat-stable or heat-labile toxins. One group, enterotoxigenic E. coli (ETEC), commonly causes travelers' diarrhea. - In addition to diarrhea, E. coli can cause other illnesses like urinary tract infections, wound or blood infections, and even sepsis. The type of specimen collected for testing depends on the suspected infection.

3. - The name of the genus is
given after Escherich who
first isolated the bacilli (1885)
from faeces of infants
suffering from diarrhoea.
- E. coli is a parasite
inhabiting only in human and
animal intestine.

6. E. coli causing diarrhoeal
diseases are divisible into
five groups . They
produce diarrhoea with
different pathogenic
mechanism.

10. Enterotoxigenic E .coli (ETEC) :
 Cause travellers diarrhoea.
 ETEC infection is commonly acquired
by consuming contaminated food or
water.
 Adheres to epithelium of the small
intestine.
 Produce heat stable/ heat labile toxin.
 Heat labile like cholera toxin.
 Causes accumulation of fluid.

16. - E. coli forms a part of normal intestinal
flora of man and animals.
- E. coli is excreted in faeces of man and
animals in very large numbers and
contaminate soil and water . Infection
acquired by consuming contaminated food
or water .
- Some strains of E. coli produce
enterotoxin, hemolysin and verocytotoxin.

18. Enterotoxigenic strains of E. coli (ETEC) Produce
two different toxins. .
. Heat labile toxin (LT).
. Heat stable toxin (ST).
A. Heat labile toxin:
- It is a heat labile protein.
- It is destroyed by heating at 650 C for 30
min.
- It is composed of A sub unit and 5
identical B sub unit.

21. B. Heat stable toxin:
- ST is a low molecular weight
polypeptide and poorly immunogenic.
- Two major classes of E. coli ST are
known. ST-I and ST-II.
- ST-I is not destroyed by heating at
1000 C for 30 min.

22. - It activates guanylate cyclase causing the
increased production of cyclic guanosine
mono phosphate (cGMP) and subsequent
hypersecretion.
- ST-II is produced by some strains of E. coli
.
- The mechanism of action of ST-II is not
known but it appears not to act via cAMP or
cGMP
- The enterotoxin alone is not sufficient to
cause diarrhoea.

23. Haemolysin:
- Many strains of E. coli produce a
haemolysin which can bring about lysis of
RBCs of some species.
- In experimental animals, hemolytic
strains found to be more virulent than non
hemolytic ones.
- It is likely that hemolytic strains of E.
coli obtain iron from lysed erythrocytes of
the host.

24. Verocytotoxin :
- E. coli produces cytotoxin identical to the
Shiga toxin (Stx) produced by S. dysentriae
type I.
- The best known of these strains is
0157:H7.
- This causes HUS (hemolytic Uremic
Syndrome) and food borne illness.

25. - The verocytotoxin is
cytotoxic to Vero cells
(African Green Monkey
Kidney cell), hence the
term Verocytotoxin.
- It also reacts with and is
neutralized by the antibody
against Shiga toxin.

26. It can cause four main types of clinical
syndrome.
. Urinary tract infection
. Diarrhoea and dysentry.
. Pyogenic infection.
. Septicaemia.

27. 1. Urinary Tract infection:
- E. coli is the commonest organism
causing Urinary Tract infection.(UTI) .
- E. coli that causes UTI often originate
in the gut of the patient .The bacteria may
gain access to the urinary tract by the
ascending or the haematogenous route. The
bacteria from the fecal flora spread to the
perineum and from there they ascend into
the bladder.

28. 2. Diarrhoea and dysentry:
E. coli causing diarrhoeal disease are
divisible into six groups . They produce diarrhoea
with different pathogenic mechanism.
. Enteropathogenic E. coli (EPEC)
. Enterotoxigenic E. coli (ETEC)
. Enteroinvasive E. coli (EIEC)
. Enterohaemorrhagic E. coli (EHEC)
. Enteroaggregative E. coli (EAEC ).
. Verocytotoxigenic E. coli (VTEC).

29. 3. Pyogenic infections:
E. coli may cause wound infection,
peritonitis, biliary tract infection and
meningitis. E. coli is the common cause of
meningitis in the new born, but is much so
less in older patients.

30. Septicaemia:
E. coli is a very common
cause of septicaemia in many
hospitals. It leads to fever,
hypotension and disseminated
intravascular coagulation. This
condition is usually develops in
debiliated patients.

31. Specimen:
Specimen to be collected
depending upon the type of lesion.
- In urinary tract infection:
. Clean voided mid-stream sample of
urine is employed for culture.
- In acute diarrhoea:
. Faeces or rectal swab.

32. - In pyogenic infection:
. Pus from wound,
wound swab, CSF, blood
- In case of septicaemia:
. Blood

33. - Microscopic examination of urine is done to
detect the presence of increased number of
polymorphs (pyuria) which is an indication of UTI.
- Centrifuged urine can be examined under
microscope to find out presence of pus cells, red
blood cells and bacteria.
- Presence of more than 3 pus cells/hpf is
suggestive of infection.

34. Fresh specimen should be inoculated directly on
Mac Conkey agar and Blood agar plates and
incubated overnight at 370