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Objectives To determine the population structure of E. coli ST73 isolated from human bacteraemia and urinary tract infections Methods The genomes of 22 E. coli ST73 isolates were sequenced using the Illumina HiSeq platform. High resolution SNP typing was used to create a phylogenetic tree. Comparative genomics were also performed using a pangenome approach. In silico and S1-PFGE plasmid profiling was conducted, and isolates were checked for their ability to survive exposure to human serum Results E. coli ST73 isolates circulating in clinically unrelated episodes show a high degree of diversity at a whole genome level, though exhibit conservation in gene content, particularly in virulence associated gene carriage. The isolates also contain a highly diverse plasmid pool that confers multi-drug resistance via carriage of CTX-M genes. All strains are highly serum resistant and uniformly carry genes shown to be essential for serum resistance. Conclusions Our data shows that a rise in incidence of multi-drug resistant E. coli ST73 clinical isolates is not due to a circulating outbreak strain as in E. coli ST131. Rather the ST73 circulating strains are distantly related and carry a diverse set of resistance plasmids. This suggests that the evolutionary events behind emergence of drug resistant E. coli differ between lineages, and suggests that all ST73 strains are capable of accessing a diverse group of resistance plasmids and becoming successful human pathogens. |