Escherichia coli ST457: an emerging extended-spectrum β-lactam resistant lineage with reservoirs in wildlife and food-producing animals

Silver gulls carry phylogenetically diverse Escherichia coli including globally dominant ExPEC sequence types and pandemic ExPEC-ST131 clades, however our large-scale study (504 samples) on silver gulls nesting off the coast of New South Wales identified E. coli ST457 as the most prevalent. A phylogenetic analysis of whole-genome sequences (WGS) of 138 ST457 comprising of 42 from gulls, two from humans (Australia) and 14 from poultry farmed in Paraguay were compared with 80 WGS deposited in public databases from diverse sources and countries. E. coli ST457 strains are phylogenetic group F, carry fimH145 and partition into five main clades in accordance to predominant flagella H-antigen carriage. Although we identified considerable phylogenetic diversity among the 138 ST457 strains, closely related subclades (< 100 SNPs) suggested zoonotic or zooanthroponosis transmission between humans, wild birds and food-producing animals. Australian human clinical and gull strains in two of the clades were closely related (≤ 80 SNPs). Regarding plasmid content, country or country-source specific connections were observed including I1/ST23, I1/ST314 and I1/ST315 disseminating bla CMY-2 in Australia, I1/ST113 carrying bla CTX-M-8 and mcr-5 in Paraguayan poultry and F2:A-:B1 plasmids of Dutch origin across multiple ST457 clades. We identified a high prevalence of nearly identical I1/ST23 plasmids carrying bla CMY-2 among Australian gull and clinical human strains. In summary, ST457 is a broad host range, geographically-diverse E. coli lineage that can cause human extraintestinal disease including urinary tract infection and displays a remarkable ability to capture mobile elements that carry and transmit genes encoding resistance to critically important antibiotics.