Immunization with Brucella abortus S19Δ per Conferred Protection in Water Buffaloes against Virulent Challenge with B. abortus Strain S544.

Vaccination of cattle and buffaloes with Brucella abortus strain 19 has been the mainstay for control of bovine brucellosis. However, vaccination with S19 suffers major drawbacks in terms of its safety and interference with serodiagnosis of clinical infection. Brucella abortus S19∆ per , a perosamine synthetase wbk B gene deletion mutant, overcomes the drawbacks of the S19 vaccine strain. The present study aimed to evaluate the potential of Brucella abortus S19Δ per vaccine candidate in the natural host, buffaloes. Safety of S19∆ per , for animals use, was assessed in guinea pigs. Protective efficacy of vaccine was assessed in buffaloes by immunizing with normal dose (4 × 10 10 colony forming units (CFU)/animal) and reduced dose (2 × 10 9 CFU/animal) of S19Δ per and challenged with virulent strain of B. abortus S544 on 300 days post immunization. Bacterial persistency of S19∆ per was assessed in buffalo calves after 42 days of inoculation. Different serological, biochemical and pathological studies were performed to evaluate the S19∆ per vaccine. The S19Δ per immunized animals showed significantly low levels of anti-lipopolysaccharides (LPS) antibodies. All the immunized animals were protected against challenge infection with B. abortus S544. Sera from the majority of S19Δ per immunized buffalo calves showed moderate to weak agglutination to RBPT antigen and thereby, could apparently be differentiated from S19 vaccinated and clinically-infected animals. The S19Δ per was more sensitive to buffalo serum complement mediated lysis than its parent strain, S19. Animals culled at 6-weeks-post vaccination showed no gross lesions in organs and there was comparatively lower burden of infection in the lymph nodes of S19Δ per immunized animals. With attributes of higher safety, strong protective efficacy and potential of differentiating infected from vaccinated animals (DIVA), S19Δ per would be a prospective alternate to conventional S19 vaccines for control of bovine brucellosis as proven in buffaloes.