Objective  Epidemiology and mechanism of quinolone-related drug resistance genes of Riemerella anatipestifer found in ducks in Putian, Fujian were investigated.

  Method  The K-B method was applied to examine 55 strains of R. anatipestifer to determine their resistance to 6 types of quinolones. PCR was employed to detect and analyze the quinolone resistance determining region (QRDR) and plasmid mediated quinolone resistance (PMQR) genes.

  Result   More than half of the 55 strains examined were multi-resistant and highly resistant to pipemidic acid, norfloxacin, enrofloxacin, and ciprofloxacin; and more than 90% of them highly sensitive to ofloxacin. PCR did not find the 4 PMQRs, i.e., qnrA, qnrB, qnrS, and oqxA, in the specimens. On the other hand, 6 QRDR mutations in the deduced amino acid sequences of gyrA, including S83R and S83I, S84P, D87A and D87G, A183V, N202E, and Y211H were detected. Among them, S83I, N202E, and Y211H had the highest mutation rates of 98.18% (54/55), 92.73% (51/55), and 90.91% (50/55), respectively. Of which, the S83I (38/39) and S83R (1/39) mutations were found in gyrA of 39 enrofloxacin-resistant strains, and the S83I mutations also in that of 3 enrofloxacin-sensitive strains. There was only one enrofloxacin-intermediated strain that had the F155S mutation in parC, which was not previously reported to exist in R. anatipestifer.

  Conclusion   The quinolone-resistance of R. anatipestifer found in ducks in Putian was severe. No PMQR was detected in the samples, but the S83I mutation in gyrA of QRDR could be the major culprit that involved in the drug resistance of R. anatipestifer.