Detection of plasmid-mediated IMP-1 metallo-beta-lactamase and quinolone resistance determinants in an ertapenem-resistant Enterobacter cloacae isolate.
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 urea-sodium 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 microg/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. Urea-SDS-PAGE analysis of OMPs showed that ZY106 lacked an OMP of approximately 38 kDa.


CONCLUSIONS
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.
Clinical Laboratory Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310009, China.
Li-rong
LR
Chen
Hong-wei
HW
Zhou
Jia-chang
JC
Cai
Rong
R
Zhang
Gong-xiang
GX
Chen
D016972:Enterobacter cloacae / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D000077727:Ertapenem; D010957:Plasmids / Q000235:genetics*; D015363:Quinolones / Q000008:administration & dosage*; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*; D047090:beta-Lactams / Q000008:administration & dosage*
D015363:Quinolones; D047090:beta-Lactams; C409201:beta-lactamase IMP-1; D001618:beta-Lactamases; D000077727:Ertapenem