Role of Plasmids in the Ecology and Evolution of "High-Risk" Extraintestinal Pathogenic Escherichia coli Clones

Abstract

Bacterial plasmids have been linked to virulence in Escherichia coli and Salmonella since their initial discovery. Though the plasmid repertoire of these bacterial species is extremely diverse, virulence-associated attributes tend to be limited to a small subset of plasmid types. This is particularly true for extraintestinal pathogenic E. coli, or ExPEC, where a handful of plasmids have been recognized to confer virulence- and fitness-associated traits. The purpose of this review is to highlight the biological and genomic attributes of ExPEC virulence-associated plasmids, with an emphasis on high-risk dominant ExPEC clones. Two specific plasmid types are highlighted to illustrate the independently evolved commonalities of these clones relative to plasmid content. Furthermore, the dissemination of these plasmids within and between bacterial species is examined. These examples demonstrate the evolution of high-risk clones toward common goals, and they show that rare transfer events can shape the ecological landscape of dominant clones within a pathotype.

FIGURE 1

Key features of ColIa and ColV virulence-associated plasmids and the key high-risk sequence types possessing them among ExPEC. Note that there is evidence for ColV plasmid carriage among Salmonella and evidence for bidirectional transfer of these clones between poultry and humans.