What is the mechanism by which ETEC causes diarrhea?

Enterotoxigenic Escherichia coli (ETEC) is a significant cause of diarrhea, particularly in developing countries and among travelers. The mechanism by which ETEC induces diarrhea primarily involves the production of two types of enterotoxins: heat-labile toxin (LT) and heat-stable toxin (ST).

Heat-labile toxin is an AB5-type toxin that activates adenylate cyclase, leading to increased levels of cyclic adenosine monophosphate (cAMP) within intestinal epithelial cells. This elevation in cAMP causes the cells to secrete excessive amounts of chloride and inhibits sodium absorption, resulting in a net loss of water and electrolytes into the intestinal lumen, which manifests as watery diarrhea.

Heat-stable toxin, on the other hand, also stimulates intestinal fluid secretion but through a different pathway. It activates guanylate cyclase, increasing cyclic guanosine monophosphate (cGMP) levels, contributing further to the loss of fluids.

The combination of these toxins disrupts the normal absorption mechanisms of the intestine, leading to significant fluid loss and diarrhea, characteristic of ETEC infections. This dual mechanism involving toxin production is fundamental to understanding how ETEC causes diarrhea, differentiating it from other bacterial pathogens that