Correlation of fluoroquinolone resistance with expression of qnrA gene in Kluyvera spp

The objective of the present study was to examine whether the expression of qnrA may contribute to a high level of resistance among parent and induced strains of Kluyvera spp. Two clinical isolates of ciprofloxacin-resistant Kluyvera spp. were obtained from livers of diseased chickens, and upon induction with ciprofloxacin, six strains with increased resistance were produced. Point mutations in qnrA, aac(6')-Ib-cr, gyrA, gyrB, parC, and parE were investigated by polymerase chain reaction (PCR) amplification and DNA sequencing, and expression levels of acrAB and qnrA in all strains were investigated by quantitative real-time PCR (qRT-PCR). The induced strains contained the same mutations in quinolone resistance-determining region as those of the parent strains. qRT-PCR showed that the expression of the acrA gene was not detected in any strain and acrB gene expression was unchanged between induced and parental strains. However, difference in expression of qnrA was observed, which correlated well with the level of quinolone resistance in the parent and induced strains. The induced high resistance was not affected by mutations in qnrA and aac(6')-Ib-cr, by new mutations in the quinolone resistance-determining region of gyrA, gyrB, parC, and parE, or by the expression level of acrAB. These data suggest that the expression of qnrA may be a factor contributing to the high level of resistance among parent and induced strains of Kluyvera spp.