Isolation,Identification,Pathogenicity Analysis and Inactivated Vaccine Preparation of a Strain of Riemerella anatipestifer Serotype 2
[Objective]The objective of this study was to analyze the biological characteristics and vaccine effectiveness of Riemerella anatipestifer isolated from a dead duckling,in order to provide guidance for the prevention and treatment of infectious serositis of duck.[Method]The brain,heart and liver tissues of the duckling were collected for bacterial isolation and culture.The strain was identified by colony morphology observation,Gram staining microscopy,16S rDNA PCR amplification and sequencing,and the genetic evolution relationship was analyzed.The serotype of the strain was identified by slide agglutination method,and the susceptibility to common antibiotics and pathogenicity of the strain were detected.The inactivated vaccine was prepared by the isolate and its immunoprotective effect was measured.[Result]The isolate showed semi-transparent,dewdrop-like round colonies on the blood plate.Gram staining showed multiple filamentous arrangement of negative short bacilli,and Wright's staining showed two stages of intensely stained short bacilli.16S rDNA sequencing showed that the isolate was in the same branch as the reference strain of Riemerella anatipestifer CZ-RA03,and the similarity was over 99.9％.Serotype identification showed that the isolate was Riemerella anatipestifer serotype 2.The results of drug sensitivity test showed that the isolate was resistant to ofloxacin,streptomycin and kanamycin,and sensitive to flufenicol,tetracycline and doxycycline.The results of pathogenicity test showed that the median lethal dose(LD50)of the isolate to 7-day-old duckling was 1.51×107 CFU,and the kidney bacterial load of infected duckling was the highest(2.15 × 106 CFU/g).The oil emulsion inactivated vaccine was used to immunize 7-day-old duckling,and the surviral rate was 86.67％.[Conclusion]In this study,a high pathogenicity strain of Riemerella anatipestifer serotype 2 was isolated and identified from infected ducklings,and the oil emulsion inactivated vaccine prepared by the strain had good immune protection effect.The results provided a theoretical basis for the prevention and treatment of infectious serositis of duck.
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