Regional survey of CTX-M-type extended-spectrum β-lactamases among Enterobacteriaceae reveals marked heterogeneity in the distribution of the ST131 clone.

OBJECTIVES: To establish the prevalence and diversity of clinically significant extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae harbouring bla(CTX-M) in the West Midlands region of the UK.
METHODS: During a 2 month period, 370 consecutive, non-duplicate isolates were collected from 13 laboratories. Isolates were screened for the presence of bla(CTX-M) by multiplex PCR and genotyped using denaturing HPLC (DHPLC). Clonal relationships were studied by PFGE and O25b-ST131 Escherichia coli were identified by PCR.
RESULTS: Two hundred and ninety-four out of 345 ESBL-producing isolates (85.2%) carried bla(CTX-M). CTX-M group 1 enzymes were expressed in 284 (96.6%) isolates, with the other 10 carrying group 9, 2 and 25/26 genes. All group 1 isolates had bla(CTX-M-15) DHPLC profiles. The bla(CTX-M) E. coli were split into 23 PFGE clusters. The largest cluster (RE1) was indistinguishable from the previously described strain A and all but one harboured bla(CTX-M-15.) A total of 66% of E. coli were O25b-ST131 positive.
CONCLUSIONS: The CTX-M-15-producing RE1 clone (strain A) is the predominant clone in the West Midlands. This clone has spread throughout the region since its emergence in an outbreak 3 years earlier. Most, but not all, RE1 isolates belong to the O25b-ST131 lineage, providing further evidence that this lineage plays a pivotal role in the clonal dispersal of CTX-M-15-producing Enterobacteriaceae. Strain A was found to be considerably more heterogeneous than when first described and has acquired greater resistance to gentamicin. Approximately one-third of CTX-M producers represented a wide variety of unrelated strains. The study shows the rapid spread and diversification of CTX-M-producing Enterobacteriaceae over a 3 year period.