Evaluation of the safety and immune protection of OMPAC, PAPF, and EBPSs recombinant subunit vaccines Developed for Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae in mice.

Bacterial mastitis in dairy cow is often caused by a combination of bacterial infections, such as Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae. Currently, there is no effective vaccine against the disease. Therefore, we constructed a recombinant subunit vaccine by fusing gene fragments of E. coli OMPA and OMPC, S. aureus EBPS, and S. agalactiae PGK, AP1, AP2, and FBSA. These gene fragments were combined into three fusion proteins: OMPAC, EBPSs, and PAPF. Mice were immunized with the three fusion proteins either alone or in combination. The test results showed that immunization with OMPAC, EBPSs, and PAPF individually or in combination could induce high titers of antibodies in the mice. Additionally, 21 days post-immunization, IFN-γ levels were significantly increased in all groups of mice, suggesting that immunization with OMPAC, EBPSs, and PAPF, whether alone or in combination, was effective in inducing antibody production. This indicates that OMPAC, EBPSs, and PAPF were effective in inducing both humoral and cellular immunity in mice. Furthermore, immunization with OMPAC, EBPSs, and PAPF individually or in combination were effective in protecting mice from E. coli, S. aureus, and S. agalactiae infections. Importantly, a mixture of the three fusion proteins was relatively safe for pregnant female mice. In conclusion, we successfully constructed and expressed recombinant subunit vaccines of OMPAC, EBPSs and PAPF and verified that these vaccines rapidly induced high levels of specific antibodies while reducing bacterial loads in the organs of mice. This lays the theoretical foundation and data support for the development of novel subunit vaccines against mastitis in dairy cows.