Evaluation of a novel Vi conjugate vaccine in a murine model of salmonellosis

Immunisation of BALB/c mice with a vaccine containing Vi polysaccharide conjugated to the Klebsiella pneumoniae outer membrane 40 kDa protein (rP40), in combination with Escherichia coli heat-labile toxin adjuvant (LT), elicited anti-Vi IgG antibodies after administration using different routes. Testing of the immune serum in opsonisation assays demonstrated the specific enhancement of Vi-positive bacterial uptake by cultured murine bone marrow derived macrophages. Intra-peritoneal challenge of mice immunised with the Vi-based vaccine elicited a degree of protection against virulent Vi⁺ Salmonella enterica serovar typhimurium (S. typhimurium). In contrast, Vi vaccination did not confer protection against oral challenge with virulent Vi-positive S. typhimurium or S. dublin.