A 5-year-old develops bloody diarrhea followed by hemolytic uremic syndrome (microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure). Stool cultures on Sorbitol-MacConkey agar shows colorless (sorbitol non-fermenting) colonies. Which toxin causes the renal injury?
- A Heat-labile toxin (LT)
- B Shiga toxin (Stx2) binding to Gb3 receptors on renal endothelium ✓
- C Heat-stable toxin (ST) activating guanylate cyclase
- D Cytotoxic necrotizing factor (CNF)
Explanation
Enterohemorrhagic E. coli (EHEC) serotype O157:H7 produces Shiga toxins (Stx1 and Stx2; Stx2 is more potent). These toxins bind to globotriaosylceramide (Gb3) receptors abundantly expressed on renal glomerular endothelium and intestinal epithelium, are endocytosed, and inhibit protein synthesis by cleaving the 28S rRNA. Endothelial injury triggers the thrombotic microangiopathy of HUS — thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure. Antibiotics are contraindicated in EHEC diarrhea as they may precipitate toxin release and increase HUS risk.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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