ColV plasmids are mobile genetic elements that were first identified in E. coli in the 1970s. ColV carrying strains were noted for their ability to rapidly dominate mammalian faecal flora and for displaying increased extra-intestinal virulence. Carriage of multiple iron-acquisition gene operons as part of their highly conserved backbone was postulated as the underlying genetic basis for these apparently disparate functions. More recently, numerous molecular studies have revealed their high incidence in avian pathogenic E. coli affecting poultry as well as subsets of E. coli isolated from human urinary tract infections and associated pathologies.
Genomic characterisation of large genome collections of emergent and globally dominant extra-intestinal pathogenic E. coli (ExPEC) lineages including sequence types (ST) ST58 and ST95, revealed a high frequency of ColV plasmid carriage within specific sub-lineages of each ST. These sub-lineages also contained more poultry strains than other parts of the respective phylogenies. Our results supported sharing of ColV carrying strains between poultry and humans, raising questions about the role of poultry production in evolution and expansion of pathogenic lineages of E. coli.
Expansion of our analysis to 34,364 E. coli genomes revealed that whilst ColV plasmids are present in 16% of all ExPEC across the species, they are primarily distributed in E. coli from food production animals, particularly poultry (55%) and pigs (20%). Although gastrointestinal colonisation is an obvious explanation for their success across hosts, the higher abundance in poultry is not fully understood. Are poultry-adapted lineages of E. coli simply receptive to uptake and maintenance of these plasmids, with selection acting on the benefits to the bacteria, or are they under selection for some other function in the host microbiome?
Overall, our work highlights the potential for mobile genetic elements under selection in non-human niches to contribute to human disease. Furthermore, it highlights a significant knowledge gap in the ecology of E. coli in different hosts and the role of mobile genetic elements in their host distribution, colonisation ability and pathogenicity.