The complete genome sequence of five pre-2013 Escherichia coli sequence type (ST)1193 strains reveals insights into an emerging pathogen.

Fluoroquinolone-resistant Escherichia coli sequence type (ST)1193 is a profound, emerging lineage associated with systemic, urinary tract and neonatal infections. Humans, companion animals and the environment are reservoirs for ST1193, which has been disseminated globally. Following its detection in 2007, ST1193 has been identified repeatedly amongst fluoroquinolone-resistant clones in Australia. However, despite the growing importance of ST1193, only three complete genomes are published in the literature, none of which are from Australia. Here we expand on the available ST1193 resources with the complete genomes of five ST1193 strains sequenced using Oxford Nanopore Technologies and Illumina. Using in silico genotyping, we found that all strains were multi-drug resistant, including resistances to fluoroquinolones and cephalosporins. In vitro antibiotic susceptibility testing mostly correlated with individual genotypes. The exception was MS8320, which had additional in vitro resistance to piperacillin/tazobactam, ampicillin/sulbactam, cefazolin and doripenem (carbapenem). Further investigation identified seven additional copies of an IS26 transposable unit carrying a bla _TEM-1B beta-lactamase gene, suggesting this tandem amplification is associated with extended resistance phenotypes. Uropathogenicity factors, including three separate siderophore-encoding loci, were conserved in chromosomal and plasmid regions. Using all complete genomes, we further elucidated the recombination events surrounding the previously described K5/K1 capsular locus switch. Phenotypic confirmation of differing capsules in Australian ST1193 strains, coupled with genetic analysis revealing insertions downstream of the capsular locus, underscored the genetic distinctions between K5 and K1 capsule encoding strains. This study provides five new reference ST1193 genomes from Australia. These include the earliest complete K5-capsule ST1193 genomes on record (collected 2007), alongside our reference genome (MS10858), a clinical isolate obtained early during the ST1193 expansion and representative of the predominant K1-associated clade. These findings lay the foundations for further genomic and molecular analyses that may help understand the underlying reasons for the rapid global expansion of ST1193.