Evaluation of polymeric adjuvants associated with cadidate vaccine strain Brucella ovis ∆abcBA in a murine model of Brucella ovis infection.

Brucellosis is an infectious disease caused by facultative intracellular Gram-negative bacteria, of great importance in animal and human health. An ideal vaccine against brucellosis should induce protection, not cause disease in animals or humans, and not interfere with serological diagnosis. Vaccine adjuvants can improve the immune response, leading to a more intense and prolonged protection, improving its effectiveness. The Brucella ovis ΔabcBA strain encapsulated in alginate provides an experimental vaccine formulation that protects against Brucella spp. infection. However, the investigation of other polymers such as adjuvants is important for optimizing the efficiency of the candidate vaccine B. ovis ∆abcBA. Therefore, this study aimed to evaluate the vaccine potential of the B. ovis ∆abcBA associated with different polymeric adjuvants in mice challenged with B. ovis. We observed that B. ovis ∆abcBA encapsulated by alginate with chitosan, but not copolymer Poloxamer 407, resulted in the lowest bacterial recovery in both the spleen and liver of challenged animals compared to non-vaccinated mice. While copolymer Poloxamer 407 did not induce significant humoral immune response, the alginate and chitosan vaccine formulation induced higher levels of Immunoglobulin G, with an increase in the IgG2b subclass, indicating a Th1 type of response, which is known to play a critical role in controlling infections by intracellular agents.