Protective Efficacy and Immunogenicity of Vi‐Porin Conjugate against Salmonella typhi

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Abstract
A conjugate vaccine against Salmonella typhi was prepared by covalently binding capsular polysaccharide (Vi) with porin, both isolated from S. typhi. First, Vi and porins were extracted. The Vi was purified from S. typhi Ty2. The purified Vi conformed to the requirements of the World Health Organization. Porins were purified from S. typhi 0901. The Vi was bound to the porins by a heterobifunctional cross‐linking reagent, N‐succinimidyl‐3‐(2‐pyridyl dithio)‐propionate (SPDP). After preparing the Vi‐porin conjugate, its protective ability and immunogenicity were studied in mice following systemic immunization. The results showed that the conjugate is 6.5‐fold more protective than Vi alone against S. typhi. The mice immunized with conjugate elicited higher anti‐Vi antibody (IgG) levels (PS. typhi than Vi alone.