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Objective:To investigate the mechanism of carbapenem resistance and the occurrence of plasmid-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 ureasodium dodecyl sulfatepolyacrylamide gel electrophoresis(Urea-SDS-PAGE).Results:Minimum inhibitory concentrations(MICs) of imipenem,meropenem,and ertapenem for ZY106 were 2,4,and 16 μg/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-lactamase,and E.coli transconjugant produced IMP-1.Plasmid-mediated quinolone resistance determinant qnrS1 was detected in ZY106.Transfer of the qnrS1-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 ZY106 lacked an OMP of approximately 38 kDa.Conclusion:It is the first IMP-1-producing Enterobacteriaceae in China and the first report of a clinical isolate that harbors both blaIMP and qnrS genes as well.The blaIMP-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 meropenem susceptibility in E.cloacae.
Objective: To investigate the mechanism of carbapenem resistance and the occurrence of plasmid-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 analyzes of plasmid-mediated carbapenemases and quinolone resistance determinants were preformed to confirm the genotype. Outer membrane proteins (OMPs) were examined by ureasodium dodecyl sulfate polyacrylamide gel electrophoresis (Urea-SDS-PAGE). Results: Minimum inhibitory concentrations (MICs) of imipenem, meropenem, and ertapenem for ZY106 were 2,4, and 16 μg / ml, respectively. Conjugation studies with Escherichia coli resulted in the transfer of significantly reduced carbapenem susceptibility. ZY106 produced IMP-1 metallo-beta-lactamase and CTX-M-3 extended-spectrum beta-lactamase, and E. coli transconjugant produced IMP-1.Plasmid- mediated quinolone resistance determinant qnrS1 was detected in ZY106.Transfer of the qnrS1-encoding-plasmid into E. coli by conjugation resulted in intermediate resistance to ciprofloxacin in E. coli transconjugant. Region-SDS-PAGE analysis of OMPs showed that ZY106 lacked an OMP of approximately 38 kDa. Conlusion: It is the first IMP- 1-producing Enterobacteriaceae in China and the first report of a clinical isolate that harbors both blaIMP and qnrS genes as well. BlaIMP-1, blaCTX-M-3, and qnrS1 are encoded at three different plasmids. loss of an OMP due resulted in ertapenem resistance and reduced imipenem and meropenem susceptibility in E. cloacae.