Protective efficacy of attenuated Salmonella Typhimurium strain expressing BLS, Omp19, PrpA, or SOD of Brucella abortus in goats

Background: Attenuated Salmonella strain can be used as a vector to transport immunogens to the host antigen-binding sites. Objectives: The study aimed to determine the protective efficacy of attenuated Salmonella strain expressing highly conserved Brucella immunogens in goats. Methods: Goats were vaccinated with Salmonella vector expressing individually lipoprotein outer-membrane protein 19 (Omp19), Brucella lumazine synthase (BLS), proline racemase subunit A (PrpA), Cu/Zn superoxide dismutase (SOD) at 5 × 10⁹ CFU/mL and challenge of all groups was done at 6 weeks after vaccination. Results: Among these vaccines inoculated at 5 × 10⁹ CFU/mL in 1 mL, Omp19 or SOD showed significantly higher serum immunoglobulin G titers at (2, 4, and 6) weeks post-vaccination, compared to the vector control. Interferon-γ production in response to individual antigens was significantly higher in SOD, Omp19, PrpA, and BLS individual groups, compared to that in the vector control (all p < 0.05). Brucella colonization rate at 8 weeks post-challenge showed that most vaccine-treated groups exhibited significantly increased protection by demonstrating reduced numbers of Brucella in tissues collected from vaccinated groups. Real-time polymerase chain reaction revealed that Brucella antigen expression levels were reduced in the spleen, kidney, and parotid lymph node of vaccinated goats, compared to the non-vaccinated goats. Besides, treatment with vaccine expressing individual antigens ameliorated brucellosis-related histopathological lesions. Conclusions: These results delineated that BLS, Omp19, PrpA, and SOD proteins achieved a definite level of protection, indicating that Salmonella Typhimurium successfully delivered Brucella antigens, and that individual vaccines could differentially elicit an antigen-specific immune response.