The Mechanism Of Quinolone Resistance In Riemerella Anatipestifer

The Riemerella anatipestifer infection, also known as duck infectious serositis, that isthe most important risk waterfowl breeding industry bacterial infections, fluoroquinolonesused clinically to treat the disease, however, Riemerella anatipesifer resistant tofluoroquinolones, and even the performance of multi-drug resistant R.anatipestifer isolatesdue to the unreasonable use of fluoroquinolones. Current literature on the mechanism ofquinolone resistance in R. anatipestifer rarely, this study aims to investigate the situation ofRA resistant to fluoroquinolones, and from both the active efflux systems and drug targetgene mutations sides to study the mechanism of fluoroquinolone resistance in R.anatipestifer, in order to control RA drug resistance and provide scientific basis.In this study,a total of31RA isolates were analyze the fluoroquinolones susceptibilitytested by K-B（Kirby-Bauer）method, the fluoroquinolones includes norfloxacin,enrofloxacin, ciprofloxacin, ofloxacin and levofloxacin, The ratios of the fluoroquinoloneantibiotics（FQNS）resistant strains were70.97%、64.52%、61.29%、48.39%and25.81%,the strains were most resistant to norfloxacin, the strains was most sensitive to levofloxacin,there are8RA isolates produce the antibiotic resistance to all the above drugs,18RAisolates（58.06%）produce the antibiotic resistance to two or more drugs. Visible, it iscommon multi-drug resistance to fluoroquinolones in RA.To study the active efflux mechanism of Riemerella anatipestifer for fluoroquinoloneantibiotics (FQNS) such as norfloxacin, enrofloxacin, ciprofloxacin, ofloxacin andlevofloxacin, the minimum inhibitory concentration (MIC) of25Riemerella anatipestiferisolates for FQNS was tested, and simultaneously the MIC was detected after addingcarbonylcyanide-m-chlorophenylhydrazone (CCCP). The ratios of the FQNS-resistantstrains were84%,72%,76%,68%and36%;76%of strains resistant to the two or moredrugs. CCCP increased the sensitivity of the drug-resistant bacteria to FQNS (exceptlevofloxacin), indicating that active efflux mechanism played an important role inresistance mechanisms to FQNS in Riemerella anatipestifer.In this research，the25R.anatipestifer isolates’ gyrA、gyrB、parC、parE genomes were detected by PCR respectively.Mutation analysis of the quinolone resistance-determiningregions (QRDRs) of25R.anatipestifer isolates and replace situations of amino acids.showed that mutations in gyrA were those resulting in the amino acid exchanges Ser83-Ile(n=15), followed by Ser83-Arg (n=9) and one isolate had no change, the existence of twogyrA mutation patterns were revealed. Enrofloxacin as the reference drug,15isolates had asingle mutation in gyrA（Ser83Ile）of18RA-resistant isolates, the percentage was83.3%,2resistant isolates Ser83Arg, one was not found change,6sensitive isolates and1middlesensitive isolates in gyrA mutations involving only one single mode (Ser83Arg). Allisolates containing QRDR mutations in gyrA（Ser83Ile）showed a high level fluoroquinoloneresistance with enrofloxacin MICs16-64μg mL-1respectively, showed that a single mutationin gyrA gene (Ser83Ile) can reduce the RA susceptibility to fluoroquinolones. All isolatesdon’t containing any QRDR mutations in parC, but there are12three-point amino acidmutations (Glu380Lys, Val397Met, Val586Thr) exist in parC outside QRDR, with othersreported consistent point mutations.3isolates exist Val456Glu, Met437Ile, Asp417Gly andIle423Thr point mutations in gyrB,15isolates outside the four levofloxacin resistance orhigh levels of fluoroquinolone-resistant strains which parE simultaneous double pointmutation (Val357Ile, His358Tyr). Results suggest the mechanism of quinolone resistancein RA, the hot point mutations in gyrA gene QRDR played a major role, parE QRDRsimultaneous double-gene mutations probably also played a role.In summary, overexpression of active efflux, mutations in drug target gene jointlymediated resistance to FQNS in RA.