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Studies on enterotoxin from Escherichia coli associated with acute diarrhea in man.

Abstract Escherichia coli was isolated in nearly pure culture from the upper small bowel and stool of 3 human patients with acute diarrhea from Calcutta, India. The serotypes of the somatic antigens were 078, 06, and 015; these strains are not generally considered enteropathogenic. Cell-free broth filtrates of the strains produced dilation and fluid accumulation in isolated intestinal loops of rabbits, similar to that observed with "cholera-toxin." When prepared as a cell-free filtrate, E. coli enterotoxin is heat stable (15 minutes at 100 °C.). However, when prepared as a lyophilized whole-cell lysate (WCL) by sonication of a slant culture, it is heat labile (15 minutes at 60 °C.). The 50 per cent effective dose (ED 50 ) or 1 unit (as defined by Burrows and Musteikis 14 ) was determined in the rabbit intestinal loop for WCL prepared from the 3 E. coli strains. One unit equalled 0.08, 0.2 and 0.25 mg., respectively. Similar studies with strains of V. cholerae reveal that crude E. coli enterotoxin is as potent and often more potent than "cholera-toxin." Antiserum was prepared in rabbits either by hyperimmunization with WCL or with WCL combined with Freund's adjuvant. Antitoxin neutralization titers were relatively low: 1:20 to 1:30 dilutions gave 50 per cent protection compared to a 1:2,000 titer achieved with "cholera-toxin." The 3 E. coli strains showed cross-neutralization. Rabbits immunized with 2 injections of WCL (25 U.) plus adjuvant were subsequently challenged by rabbit loop inoculations with small doses of WCL. No protection could be demonstrated in the immunized animals. Thus, crude E. coli enterotoxin is extremely potent in the rabbit intestinal loop model. However, as an antigen this material elicits a poor antibody response, and immunization does not confer significant protection to an intestinal loop challenge.