The socalled enteropathogenic Escherichia coli
(EPEC) O serogroups include typical and atypical EPEC, en-terohaemorrragic E. coli
, enterotoxigenic E. coli
, and enteroaggregative E. coli
. The aim of this article is to review the composition of each O serogroup and the major serotypes, clones, and additional virulence characteristics of each of these diarrheagenic categories. Their adherence patterns and genetic relationships are also presented. The review is based on the study of 805 strains of serogroups O26, O55, O86, O111, O114, O119, O125, O126, O1127, O128, and O142 most of which isolated in São Paulo from children with diarrhea between 1970 and 1990. Since some O serogroups include more than one diarrheagenic category O serogrouping only should be abandoned as a diagnostic method. However serotyping is a reliable method for those serotypes that correspond to clones.