Species specificity and lack of production of STb enterotoxin by Escherichia coli strains isolated from humans with diarrheal illness.

Escherichia coli strains produce at least two heat-stable enterotoxins, STa and STb. STa is well known to be important in the pathogenesis of human diarrheal disease; the role of STb has not been defined. Fifty-two E. coli strains recovered from human diarrheal illness in northeast Brazil or Bangladesh were examined in weaned porcine ligated intestinal segments for STb activity. A total of 113 E. coli strains from human diarrheal disease in northeast Brazil and 28 E. coli strains from Bangladesh were examined for DNA hybridization to a STb gene probe. None of these strains produced STb as detected by enterotoxic activity or by the gene probe. We also examined adult human ileal mucosa for responses to STb in the Ussing chamber in vitro. In contrast to piglet jejunum, which consistently responds electrogenically to crude STb, human ileal tissue showed no response to STb but responded electrogenically to theophylline (10 mM). These results suggest that STb-producing E. coli strains are not a major cause of diarrheal illness in humans.