Objective： To investigate the mechanism of carbapenem resistance and the occurrence ofplasmid-mediated quinolone resistance determinants qnr and aac（6＇）-Ib-cr in a clinical isolate of Enterobacter cloacae. Methods...Objective： To investigate the mechanism of carbapenem resistance and the occurrence ofplasmid-mediated quinolone resistance determinants qnr and aac（6＇）-Ib-cr in a clinical isolate of Enterobacter cloacae. Methods： An ertapenem-resistant E. cloacae ZY106, which was isolated from liquor puris of a female gastric cancer patient in a Chinese hospital, was investigated. Antibiotic susceptibilities were determined by agar dilution method. Conjugation experiments, isoelectric focusing, polymerase chain reaction （PCR）, and DNA sequence analyses of plasmid-mediated carbapenemases and quinolone resistance determinants were preformed to confirm the genotype. Outer membrane proteins （OMPs） were examined by urea-sodium dodecyl sulfate- polyacrylamide gel electrophoresis （Urea-SDS-PAGE）. Results： Minimum inhibitory concentrations （MICs） of imipenem, mer- openem, and ertapenem for ZY 106 were 2, 4, and 16 pg/ml, respectively. Conjugation studies with Escherichia coli resulted in the transfer of significantly reduced carbapenem susceptibility. ZY106 produced IMP-1 metallo-β-lactamase and CTX-M-3 extended-spectrum β-1actamase, and E. coli transconjugant produced IMP-1. Plasrnid-mediated quinolone resistance determinant qnrS1 was detected in ZY106. Transfer of the qnrSl-encoding-plasmid into E. coli by conjugation resulted in intermediate resistance to ciprofloxacin in E. coli transconjugant. Urea-SDS-PAGE analysis of OMPs showed that ZYI06 lacked an OMP of approximately 38 kDa. Conclusion： It is the first IMP-l-producing Enterobacteriaceae in China and the first report of a clinical isolate that harbors both blalMP and qnrS genes as well. The blalMP-1, blaCTX-M-3, and qnrS1 are encoded at three different plasmids. IMP-1 combined with the loss of an OMP possibly resulted in ertapenem resistance and reduced imipenem and mero- penern susceptibility in E. cloacae.展开更多
文摘Objective： To investigate the mechanism of carbapenem resistance and the occurrence ofplasmid-mediated quinolone resistance determinants qnr and aac（6＇）-Ib-cr in a clinical isolate of Enterobacter cloacae. Methods： An ertapenem-resistant E. cloacae ZY106, which was isolated from liquor puris of a female gastric cancer patient in a Chinese hospital, was investigated. Antibiotic susceptibilities were determined by agar dilution method. Conjugation experiments, isoelectric focusing, polymerase chain reaction （PCR）, and DNA sequence analyses of plasmid-mediated carbapenemases and quinolone resistance determinants were preformed to confirm the genotype. Outer membrane proteins （OMPs） were examined by urea-sodium dodecyl sulfate- polyacrylamide gel electrophoresis （Urea-SDS-PAGE）. Results： Minimum inhibitory concentrations （MICs） of imipenem, mer- openem, and ertapenem for ZY 106 were 2, 4, and 16 pg/ml, respectively. Conjugation studies with Escherichia coli resulted in the transfer of significantly reduced carbapenem susceptibility. ZY106 produced IMP-1 metallo-β-lactamase and CTX-M-3 extended-spectrum β-1actamase, and E. coli transconjugant produced IMP-1. Plasrnid-mediated quinolone resistance determinant qnrS1 was detected in ZY106. Transfer of the qnrSl-encoding-plasmid into E. coli by conjugation resulted in intermediate resistance to ciprofloxacin in E. coli transconjugant. Urea-SDS-PAGE analysis of OMPs showed that ZYI06 lacked an OMP of approximately 38 kDa. Conclusion： It is the first IMP-l-producing Enterobacteriaceae in China and the first report of a clinical isolate that harbors both blalMP and qnrS genes as well. The blalMP-1, blaCTX-M-3, and qnrS1 are encoded at three different plasmids. IMP-1 combined with the loss of an OMP possibly resulted in ertapenem resistance and reduced imipenem and mero- penern susceptibility in E. cloacae.
