High prevalence of plasmid-mediated quinolone resistance genes qnr and aac(6')-Ib-cr in clinical isolates of Enterobacteriaceae from nine teaching hospitals in China.
Yang H, Chen H, Yang Q, Chen M, Wang H.
Quinolone resistance is an emerging problem in China. To investigate the prevalence of the plasmid-mediated quinolone resistance genes qnr and aac(6')-Ib-cr, a total of 265 clinical isolates of Escherichia coli, Klebsiella pneumoniae, Citrobacter freundii, and Enterobacter cloacae with ciprofloxacin MICs of > or =0.25 microg/ml were screened at nine teaching hospitals in China. The qnrA, qnrB, qnrS, and aac(6')-Ib genes were detected by PCR. The aac(6')-Ib-cr gene was further identified by digestion with BtsCI and/or direct sequencing. The qnr gene was present in significantly smaller numbers of isolates with cefotaxime MICs of <2 microg/ml than isolates with higher MICs (> or =2.0 microg/ml) (20.6% and 42.1%, respectively; P < 0.05). aac(6')-Ib-cr was present in 17.0% of the isolates tested, and 7.9% of the isolates carried both the qnr and the aac(6')-Ib-cr genes. Among the isolates with cefotaxime MICs of > or =2.0 microg/ml, qnr and aac(6')-Ib-cr were present in 65.7% and 8.6% of E. cloacae isolates, respectively; 65.5% and 21.8% of K. pneumoniae isolates, respectively; 63.3% and 26.7% of C. freundii isolates, respectively; and 6.5% and 16.9% of E. coli isolates, respectively. The 20 transconjugants showed 16- to 128-fold increases in ciprofloxacin MICs, 14 showed 16- to 2,000-fold increases in cefotaxime MICs, and 5 showed 8- to 32-fold increases in cefoxitin MICs relative to those of the recipient due to the cotransmission of bla(CTX-M-14), bla(CTX-M-3), bla(DHA-1), bla(SHV-2), and bla(SHV-12) with the qnr and aac(6')-Ib-cr genes. Southern hybridization analysis showed that these genes were located on large plasmids of different sizes (53 to 193 kb). These findings indicate the high prevalence of qnr and aac(6')-Ib-cr in members of the family Enterobacteriaceae and the widespread dissemination of multidrug resistance in China.