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

• Published in: Journal of antimicrobial chemotherapy 2014-08, Vol.69 (8), p.2081-2085
• Main Authors: Tian, Guo-Bao, Huang, Ying-Min, Fang, Zhi-Li, Qing, Yun, Zhang, Xue-Fei, Huang, Xi
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; Aztreonam - pharmacology; beta-Lactam Resistance - genetics; beta-Lactamases - genetics; Cefotaxime - pharmacology; Ceftazidime - pharmacology; Clavulanic Acid - pharmacology; DNA, Bacterial - genetics; Escherichia coli - drug effects; Escherichia coli - genetics; Escherichia coli - isolation & purification; Escherichia coli Infections - drug therapy; Escherichia coli Infections - microbiology; Humans; Male; Microbial Sensitivity Tests; Middle Aged; Molecular Sequence Data; Mutant Chimeric Proteins - genetics; Plasmids - genetics; Urinary Tract Infections - microbiology
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dku126

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. blaCTX-M-137 was cloned and purified for kinetic measurements. Conjugation experiments, S1-PFGE and Southern blotting were performed to study the plasmid harbouring blaCTX-M-137. The genetic environment of blaCTX-M-137 was determined by genomic cloning and sequencing. A total of 247 cephalosporin-resistant E. coli were identified. blaCTX-M group genes were the most prevalent extended-spectrum β-lactamase (ESBL) genes, with 71 isolates harbouring blaCTX-M-1 group genes and 137 isolates harbouring blaCTX-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 blaCTX-M-137 was carried on an ∼83 kb IncI1 plasmid. blaCTX-M-137 was carried on a complete transposition unit ISEcp1-blaCTX-M-137-Δorf477 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.