CTX-M-137, a hybrid of CTX-M-14-like and CTX-M-15-like β-lactamases identified in an Escherichia coli clinical isolate.
OBJECTIVE
To characterize a novel CTX-M chimera, CTX-M-137, from Escherichia coli clinical isolates in China.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, 74 Zhongshan 2nd Road, Guangzhou 510080, China Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China.
Guo-Bao
GB
Tian
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, 74 Zhongshan 2nd Road, Guangzhou 510080, China Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China.
Ying-Min
YM
Huang
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, 74 Zhongshan 2nd Road, Guangzhou 510080, China Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China.
Zhi-Li
ZL
Fang
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, 74 Zhongshan 2nd Road, Guangzhou 510080, China Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China.
Yun
Y
Qing
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, 74 Zhongshan 2nd Road, Guangzhou 510080, China Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China.
Xue-Fei
XF
Zhang
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, 74 Zhongshan 2nd Road, Guangzhou 510080, China Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China huangxi6@mail.sysu.edu.cn.
Xi
X
Huang
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001398:Aztreonam / Q000494:pharmacology; D002439:Cefotaxime / Q000494:pharmacology; D002442:Ceftazidime / Q000494:pharmacology; D019818:Clavulanic Acid / Q000494:pharmacology; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000188:drug therapy* / Q000382:microbiology; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D008969:Molecular Sequence Data; D050506:Mutant Chimeric Proteins / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D014552:Urinary Tract Infections / Q000382:microbiology*; D018440:beta-Lactam Resistance / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics*
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D050506:Mutant Chimeric Proteins; D019818:Clavulanic Acid; D002442:Ceftazidime; C456080:beta-lactamase CTX-M-14; C473109:beta-lactamase CTX-M-15; D001618:beta-Lactamases; D001398:Aztreonam; D002439:Cefotaxime
E. coli; ESBLs; IncI1 plasmids; ST354; blaCTX-M-137; extended-spectrum β-lactamases; sequence type 354