Enterobacteriacea and E.coli Lecture Notes

• Lactose fermenters





• Non-lactose fermenters




LARGEST COLLECTION OF MEDICALLY IMPORTANT BACTERIA causing 35% septicemias,more than 70% UTI infections and many intestinal infections.are part of the normal intestinal flora.

Salmonella typhi,shigella always associated with diisease e.coli ,kliebsiella,Proteus are members of the normal flora that can cause opportunistic infections.

Diseases caused by E.coli

• SSI.surgical site infection These occur as a result of bacteria entering the body when it is opened up in surgery.

• Because they get inside the body, the bacteria circumvent the protection provided by the skin.

• They multiply – and as the patient’s immune system is weaker, the body is less able to fight them off.

• An estimated 400,000 NHS patients in England were affected last year, although the real figure could be much higher as many SSIs are not recorded because they emerge after the patient has been discharged from hospital.

by making sure proper hygiene rules are followed,

• equipment is properly decontaminated

• and the patient is well looked after before, during and after surgery – it could reduce post-surgery infections by 56 per cent.

•Travellers diarrhoea

• (due to production of enterotoxins results in outpouring of fluid and electrolytes into the gut lumen

• Urinary tract infections with E.coli most common in cystitis

• Important cause of hospital acquired infection

• Infections of wounds ,peritonitis,sepsis and endotoxin induced shock

• Neonatal meningitis

• Haemorrhagic colitis

• cholecystitis, bacteremia,

. cholangitis



- Complicated UTI and pyelonephritis are observed in elderly patients with structural abnormalities or obstruction such as prostatic hypertrophy or neurogenic bladders or in patients with urinary catheters.

Escherichia coli

• Microscopy

• Gram negative bacilli

• Motile with flagella

• Some strains are capsulated

• Cultural characteristics

• Rose pink colonies on Macconkeys medium lactose fermenters

Laboratory diagnosis e.coli

•Specimens according to the site of infection

• pus




•Specimen inoculated on MacConkeys medium,lactose fermenting colonie s identified by morphology,

•.Biochemical tests-indole positive

• serotyping (anti-O antisera in gastroenteritis)

•Antimicrobial sensitivity tests


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