Pathogenesis of acute bacterial diarrheal disorders

Acute bacterial diarrheal disease is a worldwide problem of enormous magnitude. In recent years a number of bacteria have been added to the list of recognized etiologic agents causing acute diarrheal disease. This was made possible by our increased understanding of the mechanisms by which such bacteria cause diarrhea and by the development of methods to detect these bacterial enteropathogens. We are now able to define an etiologic agent in 50-80% of cases of acute diarrhea, depending on the particular population. The bacterial agents recently incriminated as important causes of diarrhea include E coli Y. enterocolitica, B. cereus, C. fetus, V. parahemolyticus, and many other coliform organisms. Establishment of an enteric infection depends upon a complex interplay between host defense mechanisms and bacterial virulence factors adapted to overcome these defenses. Bacterial enteropathogens cause diarrhea primarily by elaborating enterotoxins (which also requires the organisms to adhere to the surface of the intestinal cell) and by invading the intestinal mucosa. The number of known bacterial enterotoxins has rapidly increased. Enterotoxins cause intestinal secretion and diarrhea by stimulating the adenyl cyclase system or the guanyl cyclase system and by other mechanisms yet to be defined. The ability of enterotoxigenic bacteria to adhere to the intestine involves a specific binding interaction between bacterial structures called pili or fimbriae and specific receptors on the surface of intestinal cells. Both bacterial pili and the intestinal receptors are under genetic control. A variety of other bacteria, Salmonellae, Shigellae, Y. enterocolitica etc, must invade the mucosa to cause diarrheal disease. The ability to invade is essential to the pathogenesis of disease and requires particular surface characteristics of the bacterium as well as the active participation of both the bacterium and the host cell. The bacteria probably elaborate substances that signal the host cell to initiate the invasive process, i.e. endocytosis. The mechanism by which invasive bacteria evoke intestinal secretion is uncertain but is probably a multifactorial process involving products elaborated by the mucosal acute inflammatory reaction and enterotoxins elaborated by the bacteria.