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Antimicrob Agents Chemother. 2016 Sep 23;60(10):6121-6. doi: 10.1128/AAC.00822-16. Print 2016 Oct.

Characterization of CTX-M-140, a Variant of CTX-M-14 Extended-Spectrum β-Lactamase with Decreased Cephalosporin Hydrolytic Activity, from Cephalosporin-Resistant Proteus mirabilis.

Author information

1
Program of Immunology, Affiliated Guangzhou Women and Children's Medical Center, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China Key Laboratory of Tropical Diseases Control, Sun Yat-sen University, Ministry of Education, Guangzhou, China.
2
BGI Genomics Co., Ltd., Shenzhen, Guangdong, China.
3
Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China Key Laboratory of Tropical Diseases Control, Sun Yat-sen University, Ministry of Education, Guangzhou, China Department of Laboratory, Central Hospital of Panyu District, Shiqiao, Guangzhou, Guangdong, China.
4
Department of Clinical Laboratory, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, China.
5
Program of Immunology, Affiliated Guangzhou Women and Children's Medical Center, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China Department of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China Key Laboratory of Tropical Diseases Control, Sun Yat-sen University, Ministry of Education, Guangzhou, China huangxi6@mail.sysu.edu.cn.

Abstract

CTX-M-140, a novel CTX-M-type extended-spectrum β-lactamase (ESBL), was identified in cephalosporin-resistant clinical isolates of Proteus mirabilis CTX-M-140 contained an alanine-to-threonine substitution at position 109 compared to its putative progenitor, CTX-M-14. When it was expressed in an Escherichia coli isogenic background, CTX-M-140 conferred 4- to 32-fold lower MICs of cephalosporins than those with CTX-M-14, indicating that the phenotype was attributable to this single substitution. For four mutants of CTX-M-14 that were constructed by site-directed mutagenesis (A109E, A109D, A109K, and A109R mutants), MICs of cephalosporins were similar to those for the E. coli host strain, which suggested that the alanine at position 109 was essential for cephalosporin hydrolysis. The kinetic properties of native CTX-M-14 and CTX-M-140 were consistent with the MICs for the E. coli clones. Compared with that of CTX-M-14, a lower hydrolytic activity against cephalosporins was observed for CTX-M-140. blaCTX-M-140 is located on the chromosome as determined by I-CeuI pulsed-field gel electrophoresis (I-CeuI-PFGE) and Southern hybridization. The genetic environment surrounding blaCTX-M-140 is identical to the sequence found in different plasmids with blaCTX-M-9-group genes among the Enterobacteriaceae Genome sequencing and analysis showed that P. mirabilis strains with blaCTX-M-140 have a genome size of ∼4 Mbp, with a GC content of 38.7% and 23 putative antibiotic resistance genes. Our results indicate that alanine at position 109 is critical for the hydrolytic activity of CTX-M-14 against oxyimino-cephalosporins.

PMID:
27480855
PMCID:
PMC5038311
DOI:
10.1128/AAC.00822-16
[Indexed for MEDLINE]
Free PMC Article

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