Clonal relationships among classic enteropathogenic Escherichia coli (EPEC) belong to different O groups.

Fifty Escherichia coli strains belonging to nine classic EPEC (enteropathogenic E. coli) O:H serotypes from infantile diarrhea were examined for enzyme polymorphism and typed according to their multilocus genotypes. They were further examined for lipopolysaccharide (LPS) patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining, for localized adhesion to HEp2 cells, and for their outer membrane protein (OMP) pattern. A very close relationship was detected among electrophoretic type, O:H serotype, biotype, LPS type, and OMP pattern. Most likely these characteristic EPEC groups (all type I) each represented bacterial clones, and furthermore they could be grouped into two genetically closely related clusters. In each cluster the only phenotypic character that differed among strains was the O antigen, which might suggest that the genetic background for the LPS side chains can be transferred horizontally among EPEC strains. The results support the idea that O:H serotyping is useful for studies of epidemiologic linkages between cases of EPEC diarrhea.