Prevalence and expression of the plasmid-mediated quinolone resistance determinant qnrA1.
Since its discovery, qnrA has been found in most common Enterobacteriaceae. Ciprofloxacin MICs conferred by different qnrA-positive plasmids could range from 0.1 microg/ml to 2 microg/ml in Escherichia coli J53. The reasons for different ciprofloxacin MICs conferred by qnrA have not been fully clarified. Five hundred forty-one consecutive gram-negative clinical strains that were resistant or intermediate to ciprofloxacin and that were isolated in Shanghai in 2005 were screened for qnrA by PCR. For qnrA-positive isolates, the transferability of quinolone resistance was determined by conjugation and mutations within the quinolone resistance-determining region (QRDR) of gyrA and parC. aac(6')-Ib-cr was detected and qnrA RNA expression was determined using real-time reverse transcription-PCR for transconjugants with different ciprofloxacin MICs. The qnrA gene was detected in 7 of the 541 clinical isolates. Quinolone resistance was transferred in four strains by conjugation. Mutations in the QRDR of gyrA and parC were detected in five qnrA-positive clinical strains with higher ciprofloxacin MICs. Of four qnrA-bearing plasmids in E. coli J53, pHS4 and pHS5 conferred ciprofloxacin MICs of 0.094 to 0.125 microg/ml; pHS3, which harbored the aac(6')-Ib-cr gene as well, conferred a ciprofloxacin MIC of 0.25 microg/ml, and pHS6, which had both the aac(6')-Ib-cr gene and a high expression level of qnrA, had a ciprofloxacin MIC of 1.0 microg/ml. The prevalence of qnrA appeared to be higher in Enterobacter cloacae than in other Enterobacteriaceae. The coexistence of qnrA and aac(6')-Ib-cr in a single plasmid and increased qnrA expression can account for the different levels of ciprofloxacin resistance seen in transconjugants.
Xu
Xiaogang
X
Institute of Antibiotics, Huashan Hospital, Fudan University, 12 M. Wulumuqi Rd., Shanghai 200040, People's Republic of China.
Wu
Shi
S
Ye
Xinyu
X
Liu
Yang
Y
Shi
Wanliang
W
Zhang
Yingyuan
Y
Wang
Minggui
M
D000890:Anti-Infective Agents / Q000494:pharmacology; D001483:Base Sequence; D002939:Ciprofloxacin / Q000494:pharmacology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016972:Enterobacter cloacae / Q000187:drug effects / Q000235:genetics; D004755:Enterobacteriaceae / Q000187:drug effects / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial / Q000235:genetics; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics; D015363:Quinolones / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
D000890:Anti-Infective Agents; D004269:DNA, Bacterial; D015363:Quinolones; D002939:Ciprofloxacin