Phylogenetic analysis of enteroaggregative and diffusely adherent Escherichia coli

The phylogenetics of the various pathotypes of diarrheagenic Escherichia co li are not completely understood. In this study, we identified several plas mid and chromosomal genes in the pathogenic enteroaggregative a call (EAEC) prototype strain 042 and determined the prevalence of these loci among EAE C and diffusely adherent E. call strains. The distribution of these genes i s analyzed within an evolutionary framework provided by the characterizatio n of allelic variation in housekeeping genes via multilocus enzyme electrop horesis. Our data reveal that EAEC strains are heterogeneous with respect t o chromosomal and plasmid-borne genes but that the majority harbor a member of a conserved family of virulence plasmids. Comparison of plasmid and chr omosomal relatedness of strains suggests clonality of chromosomal markers a nd a limited transfer model of plasmid distribution.