Evaluation Of The Immune Protection Effect Of The Dual Multivalent Subunit Candidate Vaccine Of Streptococcus Suis-Extra-Intestinal Pathogenic Escherichia Coli

Streptococcus suis（S.suis）disease is an important zoonotic disease that can cause symptoms such as sepsis,toxic shock,and meningitis.S.suis is divided into multiple serotypes.In the past,the most common serotype in swine infection in China was type 2.In recent years,epidemiological investigation shows that type 9 infection has become more common.The serotype of extraintestinal pathogenic Escherichia coli（Ex PEC）is complex,which can colonize and infect various tissues and organs outside the intestine,leading to sepsis,meningitis,pneumonia,endocarditis,etc.In the pig industry,the mixed infection of streptococcus suis and Ex PEC is serious.There is no commercial vaccine that can be used to prevent infection caused by mixing of these two bacterial currently.Subunit vaccines not only show good safety and immunogenicity but also provide cross-protection against multiple serotypes.Therefore,this study carried out the evaluation of the immune protection effect of the dual multivalent subunit candidate vaccine based on the previous research in the laboratory.（1）Protective effects of immunization with candidate proteins separately against different bacteriaMice were immunized with the vaccines of inactivated S.suis serotype 2,9 and proteins IF-2 GTPase（IF-2）and SSU05-1022（1022）,respectively.The results indicated that the level of antibodies in mice in the protein mixture group was higher than that in mice in the single-protein group,and compared with the blank control group,the level of antibodies of mice in the immunized groups was higher（p<0.001）.The datas of the determination of antibodies and their subclasses show that proteins can induce high titers of Ig G 1 and Ig G 2a.Mice were challenged with the strain at a dose of 5LD₅₀.The experimental results showed that IF-2 and 1022 proteins provided 80%and 60%protection for mice infected with SS2（SC19）strain,while IF-2 and 1022 proteins provided 70%and 80%protection for mice infected with SS9（S29）strain.When these two proteins are mixed and used for immunization,the mixed proteins can provide 90%protection for mice against SC19 challenge and provided 90%protection for mice against S29 challenge.Furthermore,I tried to immunize mice with a mixture of proteins Groe L,Omp C and Omp F,and challenged mice with a 5LD₅₀ dose of the strain,and found that it provided 80%protection for mice infected with the PCN033 strain.And after immunization,the antibody titers in mice changed extremely significantly（p<0.001）.（2）Immune protection effect of candidate proteins after mixingThe above five proteins were mixed to immunize mice,and immune protection effect produced by mixing the protein against Streptococcus suis and pig extraintestinal pathogenic Escherichia coli.The results indicated that the mice in immunized group exhibited an obvious humoral antibody response and good protection effect against SC19,S29,PCN033 and E49 challenge,which can provided 80%,90%,90%and 80%protection for mice against lethal doses of PCN033,E49,SC19 and S29 strain respectively,compared to mice in the control group.Compared with the blank control group,the titer of specific antibodies in immunized mice was higher（p<0.001）.The levels of serum interferon（IFN）-gamma,IL-2,and IL-4 were significantly elevated in vaccinated mice,compared to those in unvaccinated mice（p<0.001）.Histopathological observation showed that the degree of disease in mice in the control group was significantly higher than that in mice in the immune group.Compared with the blank control group,the amount of bacteria in tissues of mice in the immuned group was extremely lower.