Salmonella typhimurium-based inactivated vaccine containing a wide spectrum of bacterial antigens which mimics protein expression changes during different stages of an infection process

Salmonella infections are still considered a persistent problem in veterinary medicine. Vaccination is one of the tools for decreasing the burden of many pathogens on animals. However, the efficiency of available commercial or experimental vaccines against non-typhoid Salmonella strains is not yet sufficient. We followed the path of an inactivated vaccine that is safe and well accepted, but whose presented antigen spectrum is limited. We improved this issue by using diverse cultivation conditions mimicking bacterial protein expression during the natural infection process. The cultivation process was set up to simulate the host environment to enhance the expression of SPI-1 (Salmonella pathogenicity island) proteins, SPI-2 proteins, siderophore-related proteins, and flagellar proteins. Three different cultivation media were used and subsequent cultures were mixed together, inactivated, and used for the immunization of post-weaned piglets. A mixture of recombinant Salmonella proteins was also used as a recombinant vaccine for comparison. The clinical symptoms during the subsequent experimental infection, antibody response, and organ bacterial loads were examined. One day after the infection, we observed an increased rectal temperature in the group of unvaccinated animals and the animals vaccinated with the recombinant vaccine. The increase in the temperature of the pigs vaccinated with the inactivated Salmonella mixture was significantly lower. In the same group, we also found lower bacterial loads in the ileum content and the colon wall. The IgG response to several Salmonella antigens was enhanced in this group, but it did not reach the titers of the group vaccinated with the recombinant vaccine. To summarize, the pigs vaccinated with an inactivated mixture of Salmonella cultures mimicking protein expression changes during the natural infection exhibited less serious clinical symptoms and lower bacterial load in the body after the experimental infection compared to the unvaccinated pigs and the pigs vaccinated with a mixture of recombinant Salmonella proteins.