Phenotypic and molecular characterization of 5 novel CTX-M enzymes carried by Klebsiella pneumoniae and Escherichia coli

• 来源期刊: 中国药理学报（英文版）
• 关键词: novel CTX-M-β-lactamases sequence analysis prokaryotic expression antimicrobial susceptibility kinetic parameter isoelectric focusing plasmid profiling pulsed-field gel electrophoresis
• 年，卷（期）: 2008,（2）
• 页码范围: 217-225
• 页数: 9页
• 语种: 英文
• DOI: 10.1111/j.1745-7254.2008.00736.x

摘要

Aim: The aim of the present study was to study the phenotypic and molecular characterization of 5 novel CTX-M-β-lactamases carried by 5 Klebsiella pneumoniae isolates and 3 Escherichia coli isolates collected from 4 hospitals in Hefei, China. Methods: The purified PCR products were ligated with pGEM-Teasy vectors, expressed, and sequenced. The complete genes of the CTX-M-β-lactamases were ligated with the pHSG398 vector to express prokaryotic recombi-nant proteins. Plasmids were extracted by rapid alkaline lysis protocol, and the PCR method was performed to determine whether the prokaryotic expression was successful or not. Antimicrobial susceptibility was tested and the phenotypes of transformants were determined according to criteria recommended by the Clinical and Laboratory Standards Institute. The kinetic parameters of enzymes were confirmed. The isoelectric points (pI) were determined by isoelectric focusing assay. Pulsed-field gel electrophoresis and plasmid profiling were performed. Results: The PCR products had 1101 nucleotides and were determined as CTX-M-46, CTX-M-47, CTX-M-48, CTX-M-49, and CTX-M-50. All strains were resistant to cefotaxime, but most of them were susceptible or intermediate to ceftazidime. The phenotypes of novel enzymes were determined as extended-spectrum β-lactamases (ESBL). Penicillin G, cephalothin, cefuroxime, and cefotaxime were determined to good substrates, whereas ceftazidime hydrolysis was not detected. The pI of the 5 novel CTX-M-βlactamases were 8.0. CTX-M-derivatives could be the multiplex genesis in our area. Conclusion: This is the first report of these 5 novel plasmid-mediated CTX-M ESBL produced from China in the world. Mo-lecular typing reveals notably different origin in genes encoding different CTX-M variants of 8 strains.