Isolation And Identification Of Streptococcus Equi Subspecies Equi And The Preparation Of Strangles Inactivated Vaccine

Strangles is an acute contagious infection of equines caused by the host adapted Lancefield group C bacterium Streptococcus equi sub-species equi(S.equi). Strangles prevalent in pastoral areas, and infects ponies under two years. Strangles caused great economic losses of herders, but there were no effective preventions and control measures in China. In this study, an inactivated strangles vaccine was prepared with a wild isolated S.equi strain(HLJ2011), which caused serious clinical disease. The inactivated vaccine could prevent the mice from infection of HLJ2011.In this study, the biological characteristics of HLJ2011 and the protection of inactivated vaccine to infected mice were researched.1. The biological characteristics research of HLJ2011: In this study, the S.equi strain(HLJ2011) was isolated from the festering mandibular lymph nodes of a strangles horse. The following characteristics of HLJ2011 were studied, such as 16 S rRNA identification of the bacteria, biochemical identification, different inoculum concentrations of the growth curve, relationship of colony forming units(CFU) and the OD value, Strangles Streptococcus Virulence. The results shows as following:(1) HLJ2011 was S.equi by 16 S rRNA identification and biochemical identification;(2) The growth curve of different concentrations of bacteria inoculation showed that the concentration of the growth curve is substantially the same, the higher the inoculation concentration, the shorter the logarithmic growth phase;(3) 1% inoculation concentration after 8 h ~ 10 h culture, the CFU maximum up to 1 × 109 CFU;(4)The 8-week-old Balb/c mice were challenged by intraperitoneal inoculation with 1 × 107 CFU of HLJ2011, the mortality rate were 100% in 5 d. The median lethal dose of the bacteria to were 5 × 105 CFU calculated by modified Karber method.2. The protection of inactivated vaccine to infected mice. In this study, the inactivated vaccine of strangles were produced with different temperature and concentration of formaldehyde. The protection of inactivated vaccine to the HLJ2011 infected mice were studied. The two results were shown as following:(1) Different concentrations of formaldehyde at 4℃、28℃ and 37℃ were used to inactivate the HLJ2011,the results showed that the higher temperature and formaldehyde concentration, the shorter inactivated time were cost.(2) The S.equi strain HLJ2011 was inactivated with 1% formaldehyde after 12 h at 28℃, and then mixed with a polymer adjuvant. Five groups of mice were immunized with different doses of the produced inactivated vaccine, then the mice were infected with different doses of HLJ2011. The result shows that the mice will get 80% of vaccine protection after 106 CFU inactivated vaccine immunity.In this work, the biological characteristics of a S.equi wild isolated strain HLJ2011 were studied, the inactivated vaccine were produced with HLJ2011, as well as the protection on bacteria infected mice were studied. These work would be the basics of pathongens study of strangles and the strangles vaccine researches.