A 3-year-old child presents with bloody diarrhoea, pallor, and oliguria 5 days after eating contaminated beef. Peripheral blood smear shows fragmented red cells (schistocytes). Serum creatinine is 4 mg/dL. Stool culture grows E. coli O157:H7. Which virulence factor is primarily responsible for the haemolytic uraemic syndrome (HUS)?

• A Heat-stable toxin (ST) activating guanylyl cyclase
• B Intimin-mediated intimate attachment causing A/E lesions
• C Haemolysin A (HlyA) lysing red blood cells directly
• D Shiga toxin (Stx2) cleaving 28S rRNA of endothelial cells in glomerular microvasculature ✓

Explanation

Shiga toxin-producing E. coli (STEC/EHEC), classically O157:H7, produces Shiga toxins (Stx1 and Stx2). Stx2 is more strongly associated with HUS. Stx enters endothelial cells via Gb3 receptor (highly expressed in renal glomerular endothelium), inhibits 28S ribosomal RNA translation, causing endothelial cell death, platelet activation, microthrombi, microangiopathic haemolytic anaemia, thrombocytopaenia, and acute kidney injury. Intimin mediates colonisation (A/E lesions) but does not cause HUS directly. ST toxin causes secretory diarrhoea without haemolysis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.