Molecular Evolution of Typical EnteropathogenicEscherichia coli: Clonal Analysis by Multilocus Sequence Typing and Virulence Gene Allelic Profiling

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Abstract
EnteropathogenicEscherichia coli(EPEC) infections are a leading cause of infantile diarrhea in developing nations. Typical EPEC isolates are differentiated from other types of pathogenicE. coliby two distinctive phenotypes, attaching effacement and localized adherence. The genes specifying these phenotypes are found on the locus of enterocyte effacement (LEE) and the EPEC adherence factor (EAF) plasmid. To describe how typical EPEC has evolved, we characterized a diverse collection of strains by multilocus sequence typing (MLST) and performed restriction fragment length polymorphism (RFLP) analysis of three virulence genes (eae,bfpA, andperA) to assess allelic variation. Among 129 strains representing 20 O-serogroups, 21 clonal genotypes were identified using MLST. RFLP analysis resolved nineeae, ninebfpA, and fourperAalleles. EachbfpAallele was associated with only oneperAallele class, suggesting that recombination has not played a large role in shuffling thebfpAandperAloci between separate EAF plasmids. The distribution ofeaealleles among typical EPEC strains is more concordant with the clonal relationships than the distribution of the EAF plasmid types. These results provide further support for the hypothesis that the EPEC pathotype has evolved multiple times withinE. colithrough separate acquisitions of the LEE island and EAF plasmid.