Detection Of QnrA Gene And Effect Of Ciprofloxacin Concentration On Escherichia Coli

Objective: To investigate the prevalence of qnrA gene in Escherichia coli in DaLian, study the mechanism of the resistance.And to study the mutation of ciprofloxacin concentration selection pressure on the gyrA gene with qnrA gene positive strains and the MPC.Methods: A total of 213 clinical isolates of quinolone resistance in Escherichia coli were collected.The qnrA genes were amplified by PCR and DNA sequencing. Kirby-Bauer disk diffusion method was used to test the in vitro susceptibility of the isolates to antimicrobial agents.ESBLs produced by qnrA genes positive strains were detected with the double disk synergistic method.Plasmid conjugation experments were done in order to investigate the qnrA genes can transfer or not. And MIC values were determind for transconjugants.By plasmid conjugation experiments,PCR then analyzed by restriction endonuclease selected strains which with qnrA genes and gyrA genes were not mutation.And observed gyrA genes mutation under ciprofloxacin concentration selection pressure.Results: The qnrA genes were identified in 2 clinical isolates and the qnrA gene sequence matched that of GenBank with 100%.One was resistant to many antimicrobial agents and produced ESBLs,another was not.The plasmid conjugation tests were carried out in the both strains and one was not succeed. The qnrA genes were more stability in transconjugants. The gyrA genes with qnrA genes positive strains were more apt to mutation under ciprofloxacin concentration selection pressure and produced high MPC than qnrA genes negative strains.Conclusions: The qnrA genes had been existing in DaLian.The serious situation of complex resistance mechanism should be highly concerned in clinics. The gyrA genes with qnrA genes positive strains were more apt to mutation under ciprofloxacin concentration selection pressure.So the strains with the qnrA genes played an important role in the high-level quinolone resistance and high MPC.