The enterotoxins of both Vibrio cholerae Ol and noninvasive (toxigenic) strains of Escherichia coli produce serious diarrhea by what mechanism?

• A. Stimulation of adenylate cyclase, which gives rise to excessive fluid secretion by the cells of the small intestine
• B. Penetration of the bowel mucosa
• C. Stimulation of colicin production
• D. Elaboration of a dermonecrotizing toxin

Answer: (A)

Secretory diarrhea from these enterotoxins happens because they turn on adenylate cyclase in the intestinal lining. The toxin modifies a G protein (Gs) to stay active, which drives a sustained rise in cAMP inside enterocytes. Elevated cAMP keeps the CFTR chloride channels open, so chloride (and with it sodium and water) is secreted into the intestinal lumen. The result is large volumes of watery stools without tissue invasion or inflammation. This contrasts with invasive toxins or those causing tissue damage, which would present differently.