A 2-year-old child presents with bloody diarrhoea and oliguria. CBC shows microangiopathic haemolytic anaemia and thrombocytopenia. Stool culture grows E. coli that ferments sorbitol slowly. Which E. coli pathotype and toxin are responsible?
- A Enteropathogenic E. coli (EPEC); bundle-forming pilus
- B Enterohaemorragic E. coli (EHEC) O157:H7; Shiga toxin (Stx1 and/or Stx2) ✓
- C Enterotoxigenic E. coli (ETEC); heat-labile toxin (LT)
- D Enteroaggregative E. coli (EAEC); EAST1 toxin
Explanation
Haemolytic uraemic syndrome (HUS) — the triad of MAHA, thrombocytopenia, and acute renal failure — is the classic complication of EHEC O157:H7 infection. The pathogen is identified by its failure to ferment sorbitol on MacConkey sorbitol agar (sorbitol MacConkey, SMAC). Shiga toxin (Stx, particularly Stx2) inhibits protein synthesis in renal endothelial cells, causing microvascular thrombosis and GFR reduction. Antibiotics are AVOIDED in EHEC HUS as they may increase Stx release. EPEC causes infantile watery diarrhoea via attaching-effacing lesions. ETEC causes traveller's diarrhoea with watery stools.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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