Which bacterium employs enterotoxin production as a mechanism of disease in the GI tract?

• A. Campylobacter jejuni
• B. Yersinia enterocolitica
• C. Escherichia coli
• D. Salmonella species

Answer: (C)

Enterotoxin production that drives secretory diarrhea is a classic mechanism by which certain gut pathogens cause disease. Enterotoxigenic E. coli releases toxins that disrupt the normal ion transport in enterocytes, increasing chloride secretion and water into the intestinal lumen. This results in watery, nonbloody stools and is a well-known cause of traveler's diarrhea. The toxins are of two types: a heat-labile toxin that raises cAMP and a heat-stable toxin that raises cGMP, both leading to secretion rather than tissue invasion.

Other organisms on the list cause diarrhea mainly through mucosal invasion and inflammation rather than toxin-induced secretion. Campylobacter jejuni tends to cause invasive, inflammatory diarrhea with possible fever and sometimes blood. Yersinia enterocolitica often presents with mesenteric adenitis and inflammatory symptoms. Salmonella species primarily provoke disease via invasion and inflammation of the intestinal mucosa rather than a dominant enterotoxin effect.

So, the bacterium best explained by enterotoxin-mediated disease in the GI tract is enterotoxigenic E. coli.