Identification and characterization of OmpL as a potential vaccine candidate for immune-protection against salmonellosis in mice

• OmpL is a widely distributed and conserved outer membrane protein.
• rOmpL induces protective immunity against S. Typhimurium infection.
• Anti-OmpL antibodies mediated killing of invasive S. Typhimurium.
• Anti-rOmpL serum harbors a high bactericidal activity for Salmonella.

Salmonella is gram-negative flagellated bacteria that can cause food and waterborne gastroenteritis and typhoid fever in humans. Despite the importance of Salmonella infections in human and animal health, the target antigens of Salmonella-specific immunity remain poorly defined, the effectiveness of the currently available vaccines is also limited. Outer membrane proteins (OMPs) of Salmonella have been considered possible candidates for conferring protection against salmonellosis. OMPs interface the cell with the environment, thus representing important potential vaccine candidate for pathogen infection. We showed that the outer membrane porin L (OmpL) is a transmembrane β barrel (TMBB) protein, which forms 12 transmembrane β-strands. OmpL of S. Typhimurium is highly immunogenic, OmpL could evoke humoral and cell-mediated immune responses, and confer 100% protection to immunized mice against challenge with very high doses of S. Typhimurium. Besides, very efficient clearance of bacteria from the reticuloendothelial systems of immunized mice was seen. The homology search further revealed that OmpL is widely distributed and conserved, homologous proteins were identified in S. Typhi and Paratyphi by RT-PCR and western blot. We also found that anti-rOmpL serum harber a high bactericidal activity for Salmonella serovars tested in this study. Therefore, OmpL provide a promising target for the development of a candidate vaccine against Salmonella infection.