Abstract: Aeromonas are known to cause several diseases in turtles.Antimicrobial agents,such as fluoroquinolones,are used to prevent and curtail bacterial infections.However,prolonged abuse of antimicrobials agents could result in the selection of fluoroquinolone-resistant Aeromonas.Quinolone resistance is due principally to chromosomal mutations or efflux pump.Mutations in the quinolone resistance-determining regions(QRDRs)of the gyrA and parC genes have been shown to be related to quinolone resistance in Aeromonas spp.Plasmid-mediated quinolone resistance(PMQR)determinants(qnrA,qnrB,qnrS and aac(6')-Ib-cr)have been identified exclusively in Enterobacteriaceae,but have very rarely been identified in Aeromonas.In order to determine antimicrobial susceptibility,the relationship of PMQR,QRDR and resistance profiles in clinical isolates of Aeromonas from turtles in Guangdong province,67 isolates were collected from diseased turtles in 1996-2013.All the isolates were tested for resistance to 23 antimicrobial agents by K-B agar disc diffusion method.The PMQR genes qnrA,qnrB,qnrS,qepA and aac(6')-Ib-cr in all these strains were screened by PCR.Then,mutations in QRDR of the gyrA and parC genes and the plasmids were detected in the PMQR positive strains.All the 67 strains were highly resistant to ampicillin,cephalothin and sulfonamides,the resistance rates of which were 100%,92.54% and 83.58%,respectively;it showed medium resistance to quinolones,whose rates were 19.40%-64.18%; the isolates were more susceptible to imipenem,nitrofurantoin,amikacin and cefotaxime,with the resistance rates below 10%.79.10%(53/67)strains showed multiple-resistance to at least three classes of agents.Of these 67 Aeromonas isolates,19.40%(13/67)harbored PMQR genes.PCR and DNA sequence results showed that 8.96%,5.97% and 7.46% were positive for genes qnrS1,qnrS2 and aac(6')-Ib-cr,respectively,and two strains carried both qnrS2 and aac(6')-Ib-cr.All the 13 PMQR positive strains carried 1-4 plasmids,the sizes of which were between 0.8 kb to 15 kb.Among the 13 isolates with PMQR genes,6 strains showed mutations in both gyrA and parC genes,3 strains carried point mutation in gyrA gene,and no mutations of both genes were found in 4 strains.These results indicated that Aeromonas isolated from turtles in Guangdong were of high level multiple-resistance to widely used drugs.The existence of PMQR genes implied a more widespread dissemination of resistance to quinolones in aquaculture,and this should attract more attention.