ESCHERICHIA COLI

Enterobacteriaceae- ESCHERICHIA COLI

• Large family of gram-negative rods –
• Occur as free-living in nature OR
• As part of normal flora of colon of human and animals.

Four metabolic characteristics:
1. Facultative anaerobic
2. Ferment glucose
3. Oxidase - negative
4. Nitrate - positive

Grouping on the basis of lactose fermentation:

A. Lactose fermenters
Produce pink-red colonies on MacConkey agar:
? Escherichia
? Klebsiella Coliforms
? Citrobacter
? Enterobacter
? Serratia

B. Non-lactose fermenters
Pale-colour colonies on MacConkey agar
? Salmonella
? Shigella
? Proteus.

ESCHERICHIA COLI

• Gram-negative bacilli
• Motile
• Some strains capsulated
• Normal flora of colon in man and animals
° Excreted in stool
° contamination of water supplies – used as indicator to test faecal contamination of water
°
ANIGENIC STRUCTURE
1. Somatic (O) antigen
2. Capsular (K) antigen
3. Flagellar (H) antigen
4. Pili : help in attachment and virulence

• Bind to D-mannose residues on surface of cells.
• Pyelonephritis associated pili (Pap) and
• Intestinal colonization factor antigen

Virulence factors for UTI:
° Adherence to uroepithelial cells by Pap pili
° Capsule (K-antigen)
° Siderophore – help survival of E.coli in iron-poor environment of human body fluids

DISEASES CAUSED BY E.COLI
1. Urinary Tract Infection (UTI)
• Commonest cause (70-90%)
• More common in females due to shorter urethra
• 105 bacteria / ml of urine is significant
• Common cause of hospital-acquired UTI
due to urinary catheters
Cystitis (infection of bladder)
• Pain (dysuria)
• Frequency of micturation
• More common in females due to shorter urethra
Pyelonephritis (infection of kidney)
• Fever (chills)
• Flank pain
2. INTESTINAL INFECTIONS
a) Enterotoxigenic E.coli (ETEC)
• Virulence due to enterotoxins
• Act on small intestine
• Watery diarrhoea (common cause of traveler’s diarrhoea)
• Transmitted by contaminated food and water
b) Enteropathogenic E.coli (EPEC)
° Adhere to enterocytes, cause destruction of
microvilli of small intestine.
° Infantile and childhood diarrhoea (20% of bottle-fed)
° Stool : watery, non-purulent, no blood
c) Enteroinvasive E.coli (EIEC)
° Cause invasion of enterocytes in large intestine
° Necrosis, ulceration and inflammation.
° Stool : scanty, purulent & blood stained
d) Enterohaemorrhagic E.coli (EHEC)
• Due to verotoxin – causes destruction of microvilli
in large intestine.
• Produced by E.coli O157 : H7
• Haemorrhagic colitis with copious bloody stool
without pus cells.
e) Enteroaggregative E.coli (EAEC)

3. Meningitis in newborns
From mother’s genital tract (colonized with E.coli)

4. Opportunistic Infections
• Peritonitis due to intestinal trauma
• Wound infections
• Bacteremia gram-negative septic shock
- Beta-lactam antibiotics are not recommended?

5. Hospital-acquired infections
-Common cause

LAB IDENTIFICATION OF E. COLI
Specimens : urine, stool, pus
Culture on:
• MacConkey agar – lactose fermenter
• EMB agar – green metallic sheen
• Indole +ve
• Citrate –ve
• TSI: Slant acid, Butt-acid
Serotyping for enteric pathogens
Coliform Count and Public Health?

TREATMENT OF E. COLI DISEASES
UTI : use antibiotics after C/S
Trimethoprim-sulphamethoxazole
Diarrhoea
° Oral rehydration + ciprofloxacin
Meningitis
• Ceftriaxone (3rd generation cephalosporin)
Others diseases : C/S
• Increasing Resistance in E.coli ?