ESCHERICHIA-COLI SEROGROUP O111 INCLUDES SEVERAL CLONES OF DIARRHEAGENIC STRAINS WITH DIFFERENT VIRULENCE PROPERTIES

Genetic variation among isolates of Escherichia coil O111 obtained mos tly from patients with diarrhea in Brazil was assessed by multilocus e nzyme electrophoresis to characterize chromosomal genotypes and by gen e probes and adherence assays to characterize virulence properties. Am ong the 152 isolates, we resolved 16 distinct electrophoretic types (E Ts), which differed on average at 40% of the enzyme loci. We identifie d four major bacterial O111 clones of different disease classes: ET 12 , which includes the bulk of the enteropathogenic E. coli strains, typ ically showing localized adherence and intimate attachment in tissue c ulture assays; ET 1, ,which includes strains,vith a different set of v irulence markers; ET 9, which includes strains that show intimate atta chment but lack localized adherence and Shiga-like toxin genes; and ET 8, which includes strains that are Shiga-like toxin producers and hav e the corresponding traits of enterohemorrhagic E. coli. Enteroaggrega tive strains constituted ET 10 and also occurred in ET 1. Isolates of the major clones were found in South and North America and matched in ET and virulence factors to previously described diarrheagenic clones that are widely disseminated in the human population. Because the majo r clones are genetically distantly related and exhibit different combi nations of virulence factors, we hypothesize that they have distinct m echanisms of pathogenesis. The results indicate that genetic divergenc e of bacteria with the O111 antigen, as measured by allelic variation in enzyme loci, is accompanied by divergence in virulence properties o f clones so that identification and classification of pathogenic E. co li strains cannot be based solely on serotyping or a single virulence factor.