Pathophysiology of Salmonella Diarrhea in the Rhesus Monkey: Intestinal Transport, Morphological and Bacteriological Studies

Diarrhea caused by Vibrio cholerae and some Escherichia coli is the result of enterotoxin-induced abnormalities in small intestinal fluid and electrolyte transport. In contrast to these so-called “toxigenic diarrheas,” the pathophysiology of diarrhea caused by bacteria which invade the gastrointestinal mucosa, but do not elaborate enterotoxin, is obscure. In vivo jejunal, ileal, and colonic water and electrolyte transport was studied in Salmonella typhimurium-infected rhesus monkeys, and alterations in transport correlated with changes in intestinal morphology and with intraluminal salmonella concentrations. In controls, net water absorption was seen in the jejunum, ileum, and colon. All salmonella-infected monkeys with diarrhea had severe colitis associated with either a marked inhibition of colonic water absorption or net colonic secretion. In addition, monkeys with mild diarrhea had mildly impaired ileal and markedly impaired jejunal transport. In contrast, monkeys with severe watery diarrhea demonstrated net secretion in the jejunum, ileum, and colon. Sodium and chloride transport paralleled water transport in magnitude and direction. In the ileum, the severity of morphological damage and the intraluminal salmonella concentrations correlated with the degree of transport abnormalities and with the severity of the observed diarrhea. Despite a transport defect in the jejunum however, bacterial invasion was never seen, and morphological changes were minimal, as were intraluminal salmonella concentrations. These observations suggest that in salmonella-infected monkeys, mild diarrhea may be the result of the inability of the colon to reabsorb the fluid load presented to it by the small intestine, but that severe diarrhea may be the result of profound transport abnormalities in both the jejunum and ileum superimposed on that in the colon. Unlike enterotoxin-mediated diarrheas, salmonella diarrhea seems to involve both the small and large intestine, and is regularly accompanied by both ileitis and colitis.