The mechanism study of plasmid-mediated quinolone resistance in clinical isolates of Enterobacteriaceae from nine teaching hospitals in China / 中华检验医学杂志

ABSTRACT

Objective To investigate the prevalence of plasmid-mediated quinolone resistance qnr and aac(6')-Ib-cr in Enterobacteriaceac in Chiha.Methods A total of 197 clinical isolates with ciprofloxacin≥0.25μg/ml,cefotaxime≥2.0μg/ml and ceftriaxone≥2.0 μg/ml were screened from the 421 non-repetitive clinical isolates of Enterobac teriaceae(Escherichia coli,Klebsiella pneumoniae,Citrobacter freundii,and Enterobacter cloacae)from the nine teaching hospitals in China.qnrA,qnrB,qnrS and aac(6')-Ib gene were detected by PCR.aac(6')-Ib-cr gene was further identified by the digestion with BtsCI followed by sequencing.Conjugation experiments were done.The MIC of ciprofloxacin and other antibacterial agents in donor strain and acceptor strain were determined by agar dilution.Results Qnr was present in 42%(83/197)of isolares,and among these,17 isolates carried qnrA(9%),46 isolates carried qnrB(23%),24 isolates carried qnrS(12%),2 isolates carried qnrA and qnrB,and 2 isolates carried qnrB and qnrS.aac(6')-Ib was present in 46%(90/197)of isolates,40%(36/90)of which carried the cr variant responsible for low-level ciprofloxacin resistance.18 isolates carried qnr and aac(6')-Ib-cr.Qnr wag present in 66% of Enterobacter cloacae isolates,66% of Klebsiella pneumoniae isolates,63% of Citrobacter freundii isolates,and 6% of Escheriehia coil isolates,respectively,aac(6')-Ib-cr was present in 9% of Enterobacter cloacae isolates,22% of Klebsiella pneumoniae isolates,27% of Citrohacter freundii isolates,and 17% of Escherichia coil isolates,respectively,qnr and aac(6')-Ib-cr were present in 20% (83/421)and 9% (36/421) of all isolates respectively. The 13 transconjugants showed 16 to 125 fold increases in the MICs of ciprofloxacin and 16 to 31 fold increases in the MICs of levofloxacin relative to that of the recipient Conclusion Transferable plasmid-medlated low level quinolone resistance associated with qnr and aac(6')-Ib-cr widely exists in the enterobacteriaceae strains and perhaps this may contribute to the rapid increase of bacterial resistance to quinolones in China.