一株猪丹毒杆菌的分离鉴定及其对小鼠的致病性研究OACSTPCD

To determine the cause of pig death in a pig farm in Hunan Province,a strain of Gram-posi-tive bacterium was isolated and purified in the collected tissues.The strain was identified through biochemical characteristics and 16S rDNA sequencing,antimicrobial susceptibility test was used to verify drug resistance of the isolated bacteria.Further sequencing analysis was conducted to determine the genetic variation of virulence factor genes of the isolated strain.In addition,the pathogenicity of the strain in mice was studied.The results showed that the isolated bacterium was characterized by needlepoint-sized,translucent colonies,and identified as Erysipelothrix rhusiopathiae.The isolated strain was sensitive to 15 antibiotics such as penicillin,oxacillin,ampicillin and etc.The 16S rDNA sequence analysis revealed that the isolated strain was 100％homology to the vaccine strain G4T10.The sequence of the hypervariable region in spaA gene showed four nucleotide mutations in the sites of A509C,C510A,A924C and C925T compared with the G4T10 strain,with three mutations in its amino acids including P170H,D308E and F309L.However,sequences of other virulence factor genes,including sialidase gene,capsular polysaccharide A,B,and C gene,remained unchanged.The animal experiment showed that all mice exhibited systemic sepsis with 100％of mortality when the mice were challenged with 1.466 × 103 CFU or higher titers of the isolate,indicating that the isolated strain is highly virulent.Bacteria were isolated from the tissues of the dead mice which were consistent with the morphological characteristics of the strain.In this study,a high virulence strain of E.rhusiopathiae was successfully isolated and identified,the data could provide a reference for the epidemiology and pathogenicity of swine erysipelas in Hunan Province.