Study of E. coli on the basis of Morphological, Cultural, Biochemical, clinical and pathological characteristics

1. Presentation by,
Prof. Abullais Ansari
Department of Microbiology

2. Index
1. Introduction
2. Morphology of E. coli
3. Cultural characteristics
4. Biochemical characteristics
5. Antigens
6. Pathogenicity & Virulence factors
7. Pathogenesis
8. Laboratory Diagnosis
9. Treatment

3. Escherichia coli
• This genus is named after Escherichia who was the first to describe the colon bacillus
under the name Bacterium coli commune (1885).
• Based on minor differences in biochemical characteristic, colon bacilli were described
under various names but in the view of the mutability of the biochemical properties in
this group, they have all been included in one species Escherichia coli which is further
subdivided into biotypes and serotypes (classification of microorganisms by surface
antigen)
• A few other species have been described in the genus but they are of little medical
importance. These include E. fergusonii, E. harmanii and E. vulneris which have been
isolated infrequently from clinical specimens. E. blattae found in the gut of
cockroaches is biochemically different in being indole and betagalactosidase
negative. It has not been isolated by clinical specimens.
• Unlike other coliforms, E. coli is a parasite living only in humans or animal intestine.
Voided in faeces, it remains viable in the environment only for some days. Detection of
E. coli in drinking water therefore, is taken as evidence of recent pollution with human
or animal faeces.

4. Morphology of E.coli
• E. coli is gram-negative (-ve) rod-shaped bacteria.
• It is 1-3 x 0.4-0.7 µm in size and 0.6 to 0.7 µm in volume.
• It is arranged singly or in pairs.
• It is motile due to peritrichous flagella.
• Some strains are non-motile.
• Some strains may be fimbriated. The fimbriae are of type 1
(hemagglutinating & mannose-sensitive) and are present in both motile
and non-motile strains.
• Some strains of E. coli isolated from extra-intestinal infections have a
polysaccharide capsule.
• They are non-sporing.
• They have a thin cell wall with only 1 or 2 layers of peptidoglycan.
• They are facultative anaerobes.
• Growth occurs over a wide range of temperatures from 15-45°C.

6. Cultural characteristics
E. coli are facultative anaerobic, Gram-negative, motile bacilli that will ferment lactose
to produce hydrogen sulfide. Up to 10% of isolates have historically been reported to
be slow or non-lactose fermenting, though clinical differences are unknown.
EMB Agar
Metallic green sheen represent E.coli
MacConkey Agar
Red colour colony represent lactose
fermenting E.coli

7. Biochemical characteristics
Tests Escherichia
Gas from glucose +
Acid from lactose +
Acid in sucrose d
Growth in KCN -
Indole +
MR +
VP -
Citrate -
H2S -
Urease -
Phenylalanine
deaminase (PPA) -
Arginine
dehydrolase d
Lysine
decarboxylase +
Ornithine
decarboxylase d
(d) differs, (+) present, (-) absent

8. Antigens
Sr. No Antigen Types Diversity Comment
1 O Somatic antigen
(Somatic
lipopolysaccharide)
173 •Protect bacteria from phagocytosis and
complement system.
•Heat stable, resistant to boiling up to 2 hrs. 30
minutes
•Occur on the surface of the outer membrane
•An integral part of the cell wall
•Endotoxic activity
2 K Capsular antigen
(Acidic polysaccharide)
100 •Protect bacteria from phagocytosis and
antibacterial factors present in serum
•Heat labile
•Acidic polysaccharide antigen present in the
envelope
•Boiling removes the K antigen
•103 ‘K’ antigens have been recognized
3 H Flagellar antigen 75 •Heat and alcohol labile protein
•Present on the flagella
•Genus specific
•Present as monophasic.
4 F Fimbrial Antigen •Heat labile proteins
•Present in the fimbriae
•K88, K99 antigens
• Serotyping of E. coli is based on the following Antigens

9. Pathogenicity & Virulence factors
• Virulence of E. coli is based on following factors.
Virulence Factor
Surface Antigens O, K, H, F
Toxins
Hemolysins
Enterotoxins
Heat labile toxin
(LT)
Heat stable toxin
(ST)
Verotoxin (VT) /
Shiga- like toxin
(SLT)

10. E. coli possesses a broad range of virulence factors. In addition to the general factors
possessed by all members of the family Enterobacteriaceae, Escherichia strains possess
specialized virulence factors that can be placed into two general categories: adhesins and
exotoxins.
ETEC (Enterotoxigenic E. coli):
• Colonization factor antigens (CFA/I, CFA/II, CFA/III)
• Heat-labile toxin (LT-1); heat-stable toxin (STa)
EPEC (Enteropathogenic E. coli):
• Bundle Forming Pili (BFP); intimin
EAEC (Enteroaggregative E. coli):
• Aggregative adherence fimbriae (AAF/I, AAF/II, AAF/III)
• Enteroaggregative heat-stable toxin; plasmid-encoded toxin
STEC (Shiga toxin-producing E. coli):
• BFP; intimin
• Shiga toxins (Stx1, Stx2)
EIEC (Enteroinvasive E. coli):
• Invasive plasmid antigen
• Hemolysin (HlyA)
Uropathogens:
• P pili
• Dr fimbriae

11. Pathogenesis
Gastroenteritis
• watery or bloody diarrhoea
• vomiting
• cramps
• nausea
• low-grade fever
• dehydration
• abdominal cramps
Urinary tract infection
• The most common bacteria found to cause UTIs is Escherichia coli (E. coli). Other bacteria can cause UTI,
but E. coli is the culprit about 90 percent of the time. The major manifestations of the infection include:
• A strong, persistent urge to urinate
• A burning sensation when urinating
• Pelvic pressure
• Lower abdomen discomfort
• Frequent, painful urination
• Blood in urine
Acute bacterial meningitis
• Newborns with E. coli meningitis present with fever and failure to thrive or abnormal neurologic signs.
• Other findings in neonates include jaundice, decreased feeding, periods of apnea, and listlessness.
• Patients younger than 1 month present with irritability, lethargy, vomiting, lack of appetite, and seizures

12. Laboratory Diagnosis
• Bacteriuria can be detected microscopically using Gram staining of
uncentrifuged urine specimens, Gram staining of centrifuged
specimens, or direct observation of bacteria in urine specimens.
• On staining, E coli appear as non-spore-forming, Gram-negative
rod-shaped bacterium
• Routine urine cultures should be plated using calibrated loops for
the semi-quantitative method.
Note: The most commonly used criterion for defining significant
bacteriuria is the presence of ⩾105 CFU per milliliter of urine.
• The types of media used for routine cultures should be limited to
blood agar and MacConkey’s agar.
• ELISA is commonly used to detect the antigen and toxins present
on the cell surface of bacteria.

13. Treatment
• The sulfonamides, ampicillin, cephalosporins, fluoroquinolones, and
aminoglycosides have marked antibacterial effects against the enterics, but
variation in susceptibility is great, and laboratory tests for antibiotic susceptibility
are essential.
• E. coli meningitis requires antibiotics, such as third-generation cephalosporins (eg,
ceftriaxone).
• E. coli pneumonia requires respiratory support, adequate oxygenation, and
antibiotics, such as third-generation cephalosporins or fluoroquinolones.
• In most cases of diarrheal disease, antibiotics are not prescribed. The best way to
treat E coli infection is to drink plenty of fluids to avoid dehydration and to get as
much rest as possible. However, patients should avoid dairy products because
those products may induce temporary lactose intolerance, and therefore make
diarrhea worse.

14. Prevention and Control
• It is widely recommended that caution be observed in regard to food and
drink in areas where environmental sanitation is poor and that early and
brief treatment (eg: with ciprofloxacin or trimethoprim-sulfamethoxazole)
be substituted for prophylaxis.
• Their control depends on hand washing, rigorous asepsis, sterilization of
equipment, disinfection, restraint in intravenous therapy, and strict
precautions in keeping the urinary tract sterile (ie, closed drainage).