Objectives: To determine variation at the genome level in Escherichia coli ST131 clinical isolates previously shown to be phenotypically diverse.
Methods: The genomes of 10 ST131 isolates extensively characterized in previous studies were sequenced using combinations of Illumina and 454 sequencing technology. Whole-genome comparisons and phylogenetic comparisons were then performed across the strain set and with other closely related extraintestinal pathogenic E. coli (ExPEC) strain types.
Results: E. coli ST131 is overrepresented in a collection of clinical isolates, and there is large phenotypic variation amongst isolates. In contrast, genome sequencing of a selection of non-related clinical isolates shows almost no genetic variation between ST131 strains, and E. coli ST131 shows evidence of a genetically monomorphic pathogen showing a similar evolutionary trend to hypervirulent Clostridium difficile.
Conclusions: A dominant circulating clone of E. coli ST131 has been identified in unrelated clinical urine samples in the UK. The clone splits into two distinct subgroups on the basis of antimicrobial resistance levels and carriage of extended-spectrum β-lactamase plasmids. This provides the most comprehensive snapshot to date of the true molecular epidemiology of ST131 clinical isolates.