Design, expression, and immunogenicity evaluation of a novel multi-epitope chimeric protein (SOMP) against Salmonella Typhimurium.

The emergence of multidrug-resistant Salmonella enterica serovar Typhimurium highlights an urgent need for effective vaccines. This study developed SOMP, a novel multi-epitope chimeric vaccine, by integrating conserved immunogenic domains from OmpA, OmpC, OmpF, and FliC using a rational immunoinformatics approach. The designed construct demonstrated high antigenicity (VaxiJen: 0.98) and favorable physicochemical properties. The gene was codon-optimized, synthesized, and expressed in E. coli, yielding a ∼ 65.9 kDa protein purified via Ni-NTA chromatography. BALB/c mice immunized with SOMP formulated with Montanide ISA 720 adjuvant elicited a robust IgG response, with endpoint titers reaching 1:102,400. Crucially, the vaccine conferred significant protection against a lethal challenge, achieving 70% survival at 100× LD₅₀ and 100% survival at 1× LD₅₀ of wild-type S. typhimurium, compared to 0% in control groups (p < 0.0001). These results demonstrate that the SOMP chimera is a highly immunogenic and protective vaccine candidate. Our integrated pipeline, combining computational design with efficient prokaryotic production, offers a promising, scalable strategy for developing effective subunit vaccines against antibiotic-resistant bacterial pathogens.