Review of selected bacterial enterotoxins and their role in gastroenteritis.

The study of enterotoxins began in earnest approximately 30 years ago with characterization of the cholera toxin. So far, more enterotoxins have been associated with Gram-negative rather than Gram-positive bacteria. These substances can be roughly divided into the cytotonic variety, which primarily interfere with intestinal cell metabolism, and those which are cytotoxic, responsible for cell destruction. Most cytotonic enterotoxins activate cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP) producing watery diarrhea, resulting from fluid and electrolyte flux. This typically results after binding to a toxin-specific receptor site on the small intestinal epithelium. Cytotoxic enterotoxins may interfere with protein synthesis in cells of the colonic epithelium and cause bloody, sometimes fatal dysentery. As more enterotoxins are discovered, it is becoming apparent that such variables as anatomic site and mode of action may not, in fact, be definitive criteria for classifying these substances. As a result, no universally acceptable classification scheme has yet been devised. Moreover, the biochemical and physiological characteristics of many enterotoxins and their role in gastroenteritis and other disorders remain speculative.