Protection of mice from Brucella infection by immunization with attenuated Salmonellaenterica serovar typhimurium expressing A L7/L12 and BLS fusion antigen of Brucella

This study describes the potential use of attenuated Salmonella enterica serovar Typhimurium Strains (S. typhimurium) to express and deliver a L7/L12 and BLS fusion antigen of Brucella as a vaccination strategy to prevent Brucella infection in mice. S. typhimurium X4072 that contained a pTrc99A-BLS-L7/L12 plasmid, designated X4072bl, can deliver a L7/L12 and BLS fusion antigen expressed by the bacterium itself, while S. typhimurium X4550 that contained an asd-pVAX1-BLS-L7/L12 (asd-pBL) plasmid, designated X4550bl, can deliver the antigen to be expressed in target eukaryotic cells. When orally administered to BALB/c mice, both attenuated carrier strains were able to elicit mucosal and systemic immunity, which induced protection against B. abortus 544 infection in mice. The immunogenicity and protective efficacy of X4072bl and X4550bl were compared with a recombinant BLS-L7/L12 fusion protein vaccine (rBL) and a pVAX1-BLS-L7/L12 DNA vaccine (pBL) in this study. When rBL and pBL were intramuscularly injected into mice, both vaccines could also elicit comparable humoral and cellular immune responses, but not mucosal immunity, which therefore induced lower protection. Taken together, Salmonella-based subunit vaccines are a promising vaccine strategy in the prevention of Brucella infection.