O:K:H:F serotypes of fimbriated Escherichia coli strains isolated from infants with diarrhea.

Bacterial agglutination and crossed immunoelectrophoresis were compared as techniques for the subdivision of mannose-resistant hemagglutinating Escherichia coli fimbrial antigens. A total of 22 fimbrial strains, 15 of which had earlier been grouped into two fimbrial agglutination groups, were examined for the presence of fimbrial antigens F7 go F12 by crossed immunoelectrophoresis. Most of the strains were isolated from infants with diarrhea; they were neither enteropathogenic nor enterotoxigenic serotypes. Of the 10 strains in agglutination group 1, 4 had fimbrial antigens F7 and 1C, 4 had antigens F8 and 1C, and in 1 strain, only antigen 1C was demonstrated. The tenth strain did not, by the crossed immunoelectrophoresis test, fit into agglutination group 1. Agglutination group 2 comprised five strains. Four of these had antigens in common with the still unnumbered fimbrial antigens of an O4:K12:H5 strain. In the fifth strain, no known F antigens were demonstrated. The previously found correlation between some O:K:H serotypes and fimbrial antigens in strains from urinary tract infections was confirmed in this study in strains from diarrhea cases. We concluded that, although the agglutination test can indicate the presence of certain fimbriae, it cannot be used presently for an exact demonstration of these antigens because each strain often produces several different fimbriae.