Study On Quinolone ╟ Resistance And Resistant Genes In Clinical Isolates Of Acinetobater Baumannii

Background:quinolone antibiotics,such as Ciprofloxacin,Levofloxacin and Gatifloxacin are chemically distinct, but have similar effects on bacterial protein synthesis. Treatment of Gram negative bacilli infections using quinolone antibiotics is commonplace but it is often accompanied by increased numbers of resistant strains.The mechanisms responsible for resistance to quinolone antibiotics in Gram negative bacilli are target site modification and active drug efflux.The purpose of this study was to investigate the prevalence of quinolone–resistance in clinical isolates of Acinetobacter baumanii in the First Affiliated Hospital of Anhui Medical University, to examine the genetic mechanisms of resistance by molecular methods.Objective: To investate the distribution and drug resistance of Acinetobacter baumanii strains isolated in our hospital , to examine the genetic mechanisms of resistance by molecular methods and to provide evidence for the clinical therapy of infections.Methods:Microorganisms were identified by VITEK System and K-B disk diffusion mothod was used for the antibiotics susceptibility test,MICs of Levofloxaein,Ciprofloxacin and Gatifloxacin were determined using agar dilution method.Genes gyrA, parC and qnrA,B,S,aac(6')-Ib,qepA on plasmid were amplified by polymerase chain reaction(PCR),and some PCR products were sequenced.A total of 120 clinical isolates were analyzed based on WHONET 5.3 software.Results:A total of 120 strains of Acinetobacter baumanii species were collected from October 2007 to October 2009,The strains of multi-drug resistance(MDR)Acinetobacter baumanii accouted for 80.0%(96/120)of total strains,The percentage of isolated bacteria in intensive care unit,respiratory department and emergency center was 28.3 %,24.2%,12.5%respectively.The resistance rate of Acinetobacter baumanii isolates to Ciprofloxacin,Levofloxacin and Gatifloxacin were 78.3 %,58.3 %和40.0% respectively.multi-drug resistance Acinetobacter baumanii(MDR-AB)have a higher resistance rate than others.Polymerase chain reaction(PCR) and DNA sequencing indicated that all strains of Acinetobacter baumanii have PCR products of gyrA and parC genes ,but no products of qnrA,B,S and qepA genes on plasmid;the postive rate of PCR products of aac(6')-Ib is 29.2%(35/120),but there were no aac(6')-Ib-Cr genes on plasmid by DNA sequencing;there were the point mutations in gyrA genes at codon 83 of quinolones resistant strains but no such mutation in sensitive strains.We found the new point mutations in gyrA and parC genes of resistant strains to that with the Genbank number of DQ270238 and EU977576,respectively.Conclusion:The current status of resistance to quinolones among Acinetobater baumannii and MDR-ABA strains in Hefei region of China is serious,and the resistance is related to the point mutations within gyrA and parC genes,but isn't related to genes qnrA,B,S,aac(6')-Ib-Cr and qepA on plasmid.Surveillance of bacterial resistance is of great important to rational selection of antibiotics and preventing the abuse of antibiotics and the emergence of new drug-resistant strains.