Abstract:

[Objective] The aims of the present study were to identify the bacterial pathogens causing the disease in a duck farm in Guangdong Province, to characterize the antimicrobial susceptibility and the presence of NDM resistance genes of the isolated strains, and to screen the single traditional Chinese medicine with in vitro bacteriostatic effects against the isolated strains. [Method] The clinical samples of liver and spleen from the diseased ducks were collected for bacterial isolation and cultivation. The PCR amplification, sequencing and similarity comparison of 16S rDNA gene were used to identify the species of the isolated strains. The susceptibility test of the isolated strains to 13 antibacterial agents was carried out with K-B disk diffusion method. The PCR assay was used to detect the distribution of 10 NDM resistance genes in the isolated strains. The broth double dilution method was employed to determine the minimum inhibitory concentration （MIC） of 14 single Chinese traditional medicines against the isolated strains. [Result] Two bacterial strains were obtained from the clinical samples of the diseased ducks. Through Gram staining and microscopy examination, biochemical identification, as well as 16S rDNA sequence analysis, they were identified as Proteus mirabilis （SK1 strain） and Morganella morganii （SK2 strain）, respectively. Both SK1 and SK2 strains were susceptible to neomycin, ceftazidime, cefotaxime, and cefoperazone, and resistant to doxycycline, co-trimoxazole, enrofloxacin, flufenicol, and polymyxin B. None of the 10 NDM resistance genes were detected in SK1 strain. SK2 strain carried the bla_NDM-1 gene, while the other 9 NDM resistance genes were not detected. Macleaya cordata （Willd.） R. Br. had the best bacteriostatic effect against SK1 strain, with a MIC of 3.906 mg/mL. Forsythia suspensa （Thunb）. Vahl had the best bacteriostatic effect against SK2 strain, with a MIC of 3.906 mg/mL. [Conclusion] The main pathogens causing the disease in the duck farm were Proteus mirabilis and Morganella morganii. Neomycin, cephalosporin antibiotics, as well as traditional Chinese medicine Macleaya cordata （Willd.） R. Br. and Forsythia suspensa （Thunb）. Vahl were recommended to therapy the diseased ducks.

Key words: duck, isolation and identification, NDM resistance gene, Proteus mirabilis, Morganella morganii, traditional Chinese medicine, in vitro bacteriostatic effect