Establishment Of Serum Bactericidal Assay Against Streptococcus Suis Type 2 And Their Correlation Analysis With ELISA

Streptococcus suis(SS),a Gram-positive bacterium,is a zoonotic agent causing serious symptom that are pneumonia,septicemia,meningitis,arthritis,endocarditis and so on.The disease has been popular all over the world,resulting in serious outbreaks.Serotype2 is the most toxic Streptococcus suis.The pathogenic process of Streptococcus suis includes adhesion,invasion,transmission through the bloodstream and breakthrough of the blood-brain barrier.It can cause bacteremia during blood diffusion.At present,antibody of Streptococcus suis can be detected by Enzyme-Linked Immunosorbent Assay(ELISA).This method can only detect immunoglobulins that specifically bind to antigens,and the serum bactericidal assay(SBA)is a method for measuring functional antibody titers against all kinds of bacteria,and can directly detect the bactericidal activity of the antibody,and thus more accurately evaluate the protective effect of immunity.In the present study,a suspicious strain was isolated from the heart of a sick pig.by culture and observation of bacteria,Gram staining and microscopic observation,biochemical test and polymerase chain reaction(PCR),the isolated strain was identified as Streptococcus suis type 2(SS2).The Tibetan pig serum immunized with Streptococcus suis type 2 bacterial vaccine was used as positive serum.In addition,the complement control test was performed with negative serum.The serum bactericidal assay of Streptococcus suis type 2 was established by gradient tests,and it was showed that the specificity and reproducibility were good.The commercial ELISA kit and serum bactericidal assay were used to detect the antibody of the first immunized serum and the second immunized serum from the80-day-old Tibetan pigs without Streptococcus suis type 2 then immunized with bacterial vaccine.The results of testing 36 immunized serum samples by two methods were in extremely significant linear relationship.The correlation was good(r=0.841,P<0.001).