Enterotoxigenic E. coli (ETEC) produces two toxins, LT and ST. Heat-stable toxin (STa) differs from LT in that STa acts by:

• A ADP-ribosylation of Gs protein with increased intracellular cAMP
• B Insertion into the host membrane forming pores with loss of potassium
• C Inhibition of 60S ribosomal subunit by removal of adenine
• D Activation of guanylate cyclase with increased intracellular cGMP ✓

Explanation

STa is a small peptide that binds guanylate cyclase C on the enterocyte brush border, raising cGMP, which inhibits NaCl absorption and stimulates chloride secretion through CFTR, causing watery diarrhea. LT, like cholera toxin, ADP-ribosylates Gs and raises cAMP, so option A describes LT rather than STa. Ribosome inhibition describes Shiga toxin and pore formation describes RTX-type cytolysins.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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