Enterotoxigenic E. coli (ETEC) produces two enterotoxins, LT and ST. The heat-stable toxin (STa) causes secretory diarrhea by which intracellular mechanism?

• A ADP-ribosylation of the Gs alpha subunit with sustained adenylate cyclase activation
• B Activation of intestinal guanylate cyclase leading to increased cyclic GMP ✓
• C Activation of phospholipase C generating IP3 and diacylglycerol
• D ADP-ribosylation of elongation factor 2 with inhibition of protein synthesis

Explanation

STa binds guanylin receptors on enterocytes and directly activates particulate guanylate cyclase, raising intracellular cGMP. cGMP reduces sodium chloride absorption and stimulates chloride secretion through CFTR, producing watery diarrhea without mucosal invasion. Option A describes LT, which is structurally homologous to cholera toxin and works through ADP-ribosylated Gs and cAMP. Option D describes diphtheria toxin, not an enterotoxin.

Reference: Ananthanarayan and Paniker Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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