Substantial protective immunity conferred by a combination of Brucella abortus recombinant proteins; SodC, RibH, Ndk, L7/L12 and MDH against Brucella abortus 544 infection in BALB/c mice.

Chronic infection with intracellular Brucella abortus ( B. abortus ) in livestock remains to be a major problem worldwide. Thus, the search for an ideal vaccine is still ongoing. In this study, we evaluated the protection efficacy of a combination of B. abortus recombinant proteins; superoxide dismutase (rSodC), riboflavin synthase subunit beta (rRibH), nucleoside diphosphate kinase (rNdk), 50S ribosomal protein (rL7/L12) and malate dehydrogenase (rMDH) cloned and expressed into a pMal vector system and DH5α, respectively and further purified and applied intraperitoneally into BALB/c mice. After first immunization and two boosters, mice were infected intraperitoneally (IP) with 5×10⁴ CFU of virulent B. abortus 544. Spleens were harvested and bacterial loads were evaluated at two-week post-infection. Results revealed that this combination showed significant reduction in bacterial colonization in the spleen with a log protection unit of 1.31 which is comparable to the average protection conferred by the widely used live attenuated vaccine RB51. Cytokine analysis exhibited enhancement of cell-mediated immune response as IFN-γ is significantly elevated while IL-10 which is considered beneficial to the pathogen's survival was reduced compared to control group. Furthermore, both titers of IgG1 and IgG2a were significantly elevated at three and four-week time points from first immunization. In summary, our in vivo data revealed that vaccination with a combination of five different proteins conferred a heightened host response to Brucella infection through cell-mediated immunity which is desirable in the control of intracellular pathogens. Thus, this combination might be considered for further improvement as potential candidate vaccine against Brucella infection.