Plasmid-mediated quinolone resistance in clinical isolates of gram-negative bacilli / 中国感染与化疗杂志

ABSTRACT

Objective To investigate the importance of plasmid-mediated quinolone resistance in the development of quinolone resistance in clinical isolates of gram-negative bacteria.Methods A total of 541 consecutive clinical isolates of gram-negative ba- cilli resistant or intermediate to ciprofloxacin were screened for the qnrA gene by PCR.Conjugation experiments were carried out with azide-resistant E.coli J53 as a recipient.The aac(6')-Ib-cr gene was detected.The mutations in the quinolone-resist- ance-determining region (QRDR) of the gyrA and parC genes were identified in qnrA positive strains.Results qnrA was identi- fied in 7 of the 541 strains.Among the qnrA positive strains,5 were Enterobacter cloacae.No qnrA was detected in nonfer- menters.Quinolone resistance was transferred in 4 of 7 qnrA positive strains.Transconjugants had 12-to 125-fold increases in MIC of ciprofloxacin relative to that of the recipient.Seven strains contained qnrA with a nucleotide sequence identical to that originally reported.Two transconjugants with higher ciprofloxacin MICs contained aac(6')-Ib-cr gene.Mutations occurred in the QRDR of the gyrA and parC genes in 5 PCR-positive clinical strains.Conclusions Transferable plasmid-mediated quinolone resistance associated with qnrA is highly prevalent in clinical strains of Enterobacter spp.aac(6')-Ib-cr gene and mutations in the quinolone targets may co-exist with qnrA,which may contribute to the further increase of resistance to quinolones.