Evidence for convergent evolution of CTX-M-14 ESBL in Escherichia coli and its prevalence

A total of 2440 Escherichia coli strains isolated in 2003 at the Hospital de la Santa Creu i Sant Pau were evaluated for the presence of extended-spectrum beta-lactamases. Two different nucleotide sequences that encode the same beta-lactamase, CTX-M-14, were detected when the bla(CTX-M-14)-genes of 35 E. coli isolates were analysed. Thirty-two of the 35 had the previously described sequence of the bla(CTX-M-14) (AF252622), named bla(CTX-M-14a), and the remaining three isolates showed a nucleotide sequence identical to that of the bla(CTX-M-9) gene except for one nucleotide, named bla(CTX-M-14b). Characterisation of the regions surrounding the bla(CTX-M-14a) showed the ISEcp1 and the IS903 upstream and downstream, respectively, of the bla gene, whereas the regions surrounding the bla(CTX-M-14b) contained the genetic environment described for the bla(CTX-M-9) gene, the In60. Characterisation by hybridisation showed that the bla(CTX-M-14a) was present in IncK plasmids, whereas the bla(CTX-M-14b) was found in the HI2 Inc group. The CTX-M-14 ESBL in E. coli isolates is the result of the convergence of two different genes.