Phylogenetic analysis of multidrug-resistant Escherichia coli clones isolated from humans and poultry

Chicken products represent a source for multidrug-resistant Escherichia coli causing extraintestinal infections (ExPEC) in humans. We applied phylogenetic analysis to a collection of E. coli strains from both hosts (poultry/humans) to improve our understanding of the origin and spread of ExPEC in humans. The dataset consisted of 58 sequences among 172 E. coli strains from human extraintestinal infections and avian species. Human phylogenetic tree analysis showed a major clade, within which ST clones belonging to groups A and B1 were largely intermixed, and two clusters, each exclusively including B2 or D clones. The avian tree exhibited greater heterogeneity between and within clades/clusters. In the Bayesian tree, consisting of sequences from both human and avian E. coli, the B2 and D human ST clones were clustered together separate from the avian strains, whereas B1 and A ST clones (frequently associated with multidrug resistance) were intermixed with avian strains. This study suggests that a subgroup of E. coli clones, A and B1, associated with multidrug resistance, is potentially exchangeable between poultry and humans. Such a subgroup may be of public health concern. On the contrary, E. coli clones included in B2 and D appeared clearly separate between human and avian sources, suggesting a minor zoonotic potential of these phylotypes.