Evaluation of immunogenicity and safety of genetic engineering attenuated strains for Salmonella enteritidis

Abstract:

[Background] Compared with inactivated vaccines and attenuated vaccines, the superiority of Salmonella genetically engineered live attenuated vaccines has gradually emerged, and research has continued to deepen. [Objective] To explore the immunogenicity and biological safety of four gene-deleted strains of Salmonella enteritidis G9 strain:G9(ΔhilA), G9(ΔhilD), G9(ΔssrABhilA) and G9(ΔssrABhilAhilD).[Methods] Salmonella enteritidis strain G9 and gene deletion strains G9(ΔhilA), G9(ΔhilD), G9(ΔssrABhilA) and G9(ΔssrABhilAhilD) were inoculated with the optimal immunization doses to mice, and then used indirect ELISA and flow cytometry, MTT method, mouse challenge test and pouring plate method to evaluate the immunogenicity and safety of each deletion strain.[Results] G9(ΔhilD) induced the highest titer of serum IgG antibody, G9(ΔhilD) and G9(ΔssrABhilAhilD) produced the highest titer of intestinal mucosal IgA antibody, and 4 strains of deletion bacteria induced IL-4, IL-10, IFN-γ, TNF-β, MCP-1 cytokine capacity was not significantly different from that of the parent strain G9 (P>0.05), the ratio of CD4⁺/CD3⁺, CD8⁺/CD3⁺ T cells showed an upward trend, and G9(ΔssrABhilA) and G9(ΔssrABhilAhilD) were the highest; G9(ΔssrABhilAhilD) induced the highest proliferation index of splenic lymphocytes; after immunization of mice, the protection rate of the four deletion strains against G9 challenge was 80%-100%. The structure of the spleen and small intestine villi was relatively complete without obvious pathological changes. The protection rate against Salmonella typhimurium challenge is 50% to 80%; 12 days after inoculation, the colonizing strains in the liver, spleen and small intestine of mice could be basically eliminated. And it could be continuously and stably passaged for 30 generations in vitro.[Conclusion] G9(ΔhilA), G9(ΔhilD), G9(ΔssrABhilA) and G9(ΔssrABhilAhilD) had good immune effects and biological safety in mice, and they had the possibility of becoming genetically engineered live attenuated vaccines of Salmonella enteritidis.