Differences in serological responses and excretion patterns of volunteers challenged with enterotoxigenic Escherichia coli with and without the colonization factor antigen.

Double-blind studies were performed to compare the virulence of enterotoxigenic Escherichia coli with and without the fimbriate colonization factor antigen (CFA), using young healthy adults (mean age, 23 years) as volunteers. In the first study one group of volunteers ingested 1 X 10(6) E. coli H-10407, the CFA-positive strain, and another group ingested 1 X 10(6) E. coli H-10407-P, the CFA-negative spontaneous derivative of strain H-10407. The second study was similar except that the test strains were administered at a dose of 1 X 10(8) viable cells. Three parameters of infection were monitored: (i) diarrhea and associated symptoms; (ii) excretion pattern of test strains; and (iii) humoral antibody response to CFA, somatic antigen, and heat-labile enterotoxin. Significant signs of illness occurred only in six of seven volunteers who ingested E. coli H-10407 at a dose of 1 X 10(8). At both doses, E. coli H-10407-P appeared in the stool on day 1 postchallenge and disappeared by day 4. In contrast, strain H-10407 was persistently excreted from the first to the last day of the study. Also, only those volunteers in the H-10407 challenge groups (12 of 13 analyzed) responded with a fourfold antibody titer rise to CFA, somatic antigen, and/or heat-labile enterotoxin. No reversion of H-10407-P to H-10407 was detected.