UK epidemic Escherichia coli strains A-E, with CTX-M-15 β-lactamase, all belong to the international O25:H4-ST131 clone

Uropathogenic and invasive Escherichia coli O25:H4-ST131 isolates producing CTX-M-15 extended-spectrum beta-lactamase (ESBL) enzymes have recently been shown to be disseminated across the globe. In the UK, many CTX-M-15 ESBL-producing E. coli strains have been previously defined as belonging to the epidemic strains A-E, as determined by PFGE. The present study was carried out to define the relationship between these two groups of pathogenic E. coli. Multilocus sequence typing and PFGE were used for molecular characterization of a collection of 61 ESBL-producing E. coli isolates from across the UK. Strains A to E all belonged to the ST131 clone, further underscoring the epidemiological importance of this lineage. The future spread of the ST131 clone, and its UK variants, should be monitored closely and the pathogenic mechanisms explaining their success should be investigated.