Background: Brucellosis vaccines are designed to induce cellular immunity. An effective brucellosis vaccine could induce both cellular and humoral immunity. Serum Bactericidal Assay (SBA) is an important method for determining vaccine humoral immunity. This study is the first to observe humoral immunity in brucellosis by SBA.

Methods: Extracted Brucella abortus (B. abortus) Lipopolysaccharide (LPS) and Outer Membrane Proteins (OMPs) were injected into rabbits. Group 1 was injected with 25 µg of LPS, Group 2 was injected with 50 µg of OMPs, and Group 3 was injected with 1 ml of combined vaccine, 3 times every 2 weeks. The groups were challenged with B. abortus 544 in the second injection. Sera were separated 2 weeks after the last injection. SBA was performed, and each well was streak-cultured into a plate of Brucella agar. A colony count was done for each plate.

Results: Results have shown, the third injection of the combined vaccine had the highest titer of 1/64, and the efficacy of the vaccine was 87.71%.

Conclusion: As a conclusion, the results of this study showed that LPS and OMP's from B. abortus can provide acceptable immunity.