A 3-year-old child develops bloody diarrhoea followed by oliguria, microangiopathic haemolytic anaemia, and thrombocytopenia. Stool culture grows sorbitol-non-fermenting E. coli on sorbitol-MacConkey agar. The pathogenic mechanism involves:

• A Heat-labile toxin (LT) stimulating adenylate cyclase via ADP-ribosylation of Gs protein
• B Invasion plasmid antigen (Ipa proteins) mediating intracellular invasion of colonocytes
• C CNF1 (cytotoxic necrotizing factor) causing persistent Rho GTPase activation
• D Shiga-like toxin (Stx1/Stx2) cleaving 28S rRNA of host ribosomes causing microangiopathy ✓

Explanation

Haemolytic uraemic syndrome (HUS) is caused by E. coli O157:H7 (STEC — Shiga-toxin producing E. coli), which does not ferment sorbitol and is identifiable on sorbitol-MacConkey agar. Shiga-like toxin (Stx1/Stx2) binds to Gb3 receptors on renal endothelial cells, cleaves 28S rRNA inhibiting protein synthesis, causing cell death, microangiopathic haemolysis, thrombocytopenia and renal failure (HUS). LT is the cholera-like toxin of ETEC. IpaB proteins characterize EIEC/Shigella. CNF1 is associated with uropathogenic E. coli.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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