Genomic and Virulence Heterogeneity of Enteroaggregative Escherichia coli

Abstract

This chapter focuses on study of Escherichia coli evolution, and examines what is understood concerning the diversity of this highly heterogeneous pathovar, recent insights from whole and partial genome sequences, and how these data may eventually be used to further clarify what factors make enteroaggregative E. coli (EAEC) pathogens. In 1999, a collaborative effort between Tom Whittam’s lab and Jim Nataro’s lab provided the first large-scale phylogenetic determination of a worldwide collection of EAEC isolates, as well as isolates previously identified as diffusely adherent E. coli (DAEC). In this study, isolates were screened by 20-locus multilocus enzyme electrophoresis (MLEE) as well as colony hybridizations to 10 plasmid-and chromosome-encoded virulence genes. These results provided for the first time a more complete picture of EAEC diversity, and several important points came to light. First, three phylogenetic groups containing EAEC strains were identified and designated EAEC1, EAEC2, and AA/DA. Second, even in cases where DAEC and EAEC strains intermingled within the same phylogenetic group, these strains were clearly distinguished by the fact that DAEC did not carry EAEC virulence determinants. Third, a few strains were classified as EAEC by the HEp-2 adherence assay but were DNA probe negative for all the screened EAEC virulence factors and clustered phylogenetically outside of EAEC1, EAEC2, and AA/DA. To date, two complete and one shotgun-assembled EAEC genome sequences are available, providing important data for comparative studies between typical and atypical EAEC, as well as EAEC from different phylogenetic groups.