Serotypes of enterotoxigenic Escherichia coli isolated in the United States.

Strains of enterotoxigenic Escherichia coli isolated from humans in the United States were found in 11 of 16 serotypes that previously were documented in the international literature as associated with enterotoxin production. Of 68 strains belonging to these 11 serotypes, 28 (41%) were enterotoxigenic; none of 46 strains belonging to 5 other previously implicated serotypes was enterotoxigenic. Control cultures of various serotypes were selected for comparison and found to contain 0 to 7% enterotoxigenic E. coli. E. coli belonging to documented enterotoxin-associated serotypes, characterized by both O and H antigens, were selected for toxin testing to determine their prevalence and potential pathogenicity in this country. In this study, a strain possessing any combination of an enterotoxin-associated serotype O antigen and H antigen was more likely to be enterotoxigenic than strains possessing only the specific O antigen or H antigen or neither. Five E. coli strains belonging to undocumented enterotoxin-associated serotypes did contain a combination of previously reported enterotoxin-associated serotype O and H antigens and did produce enterotoxin.