Immunoprotective Potential of Adenylosuccinate Synthetase Protein (PurA) in Streptococcus equi ssp. zooepidemicus Infections

Background: Streptococcus equi ssp. zooepidemicus (SEZ) is one important pathogen. There are still sporadic outbreaks in China, northern United States and the Netherlands. Adenylosuccinate synthetase PurA, a newly discovered protein in prior research, requires further assessment of its protective effectiveness. Methods: In this study, we focused on the expression of recombinant PurA from SEZ ATCC 35246. We evaluated the immunoreactivity of this recombinant protein using convalescent minipig sera. Additionally, we conducted experiments in mice to assess its immunogenic properties. Results: Our findings revealed that the recombinant PurA triggered a substantial antibody response in mice, resulting in an 80% protection rate against SEZ infection. Notably, mice immunized with PurA exhibited significantly reduced bacterial colonization in all organs compared to the PBS control group. Furthermore, the levels of IL-6, IL-8, IL-1β, and TNF-α in mouse serum were significantly elevated in the PurA-immunized group compared to the control group. Hyperimmune sera targeting PurA effectively eliminated SEZ in bactericidal tests. Remarkably, antibodies against PurA demonstrated a significant inhibitory effect on developing SEZ biofilm. Conclusion: Immunization with PurA elicited robust humoral and cellular immune responses in mice. These promising results suggest the potential utility of PurA in developing SEZ vaccine immunogens, providing a valuable avenue for further research into SEZ infection prevention and control.