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.