CTX-M-137, a hybrid of CTX-M-14-like and CTX-M-15-like β-lactamases identified in an Escherichia coli clinical isolate

To characterize a novel CTX-M chimera, CTX-M-137, from Escherichia coli clinical isolates in China. Isolates were collected from five hospitals between 22 February 2009 and 20 December 2011. Resistance genes were investigated by PCR. bla(CTX-M-137) was cloned and purified for kinetic measurements. Conjugation experiments, S1-PFGE and Southern blotting were performed to study the plasmid harbouring bla(CTX-M-137). The genetic environment of bla(CTX-M-137) was determined by genomic cloning and sequencing. A total of 247 cephalosporin-resistant E. coli were identified. bla(CTX-M) group genes were the most prevalent extended-spectrum beta-lactamase (ESBL) genes, with 71 isolates harbouring bla(CTX-M-1) group genes and 137 isolates harbouring bla(CTX-M-9) group genes. A novel chimera of CTX-M-14-like and CTX-M-15-like ESBLs, designated CTX-M-137, was identified from a 60-year-old man with a urinary tract infection. The N-terminus of CTX-M-137 matched CTX-M-14 and the C-terminus matched CTX-M-15. CTX-M-137 conferred resistance to ceftazidime, cefotaxime and aztreonam. Purified CTX-M-137 showed good hydrolytic activity against ceftazidime and cefotaxime, and was inhibited by clavulanic acid. The bla(CTX-M-137) was carried on an similar to 83 kb IncI1 plasmid. bla(CTX-M-137) was carried on a complete transposition unit ISEcp1-bla(CTX-M-137)-Delta orf477 inserted into yagA, which is part of the IncI1 plasmid backbone. We identified a novel CTX-M chimera, CTX-M-137, with a CTX-M-14-like N-terminus and a CTX-M-15-like C-terminus. Our findings suggest an ongoing diversification of CTX-M-type ESBLs through recombination events.