Streptococcus suis is one of the major pathogens of pigs circulating worldwide, and the development of vaccines will help to effectively control streptococcosis in swine. In this study, we evaluated the potential of three membrane associated proteins, histidine kinase (HK), glycosyltransferase family 2 (Gtf-2) and phosphate binding protein (PsbP) of S. suis as subunit vaccines. Bioinformatics analysis shows that protein ABC is highly conserved in S. suis. To verify the protective effects of these proteins in animal models, recombinant protein HK, Gtf-2 and PsbP were used to immunize BALB/c mice separately. The results showed that these proteins immunization in mice can effectively induce strong humoral immune responses, protect mice from cytokine storms caused by S. suis infection, and have a significant protective effect against lethal doses of S. suis infection. Furthermore, antibodies with opsonic activity exist in the recombinant proteins antiserum to assist phagocytic cells in killing S. suis. Overall, these results indicated that these recombinant proteins all elicit good immune protective effect against S. suis infection and can be represent promising candidate antigens for subunit vaccines against S. suis.

Streptococcus suis serotype 2 (S. suis 2) is an important zoonotic pathogen that can also cause epidemics of life-threatening infections in humans. Surface proteins of pathogens play a critical role in the interaction with host system or environment, as they take part in processes like virulence, cytotoxicity, adhesion, signaling or transport, etc. Thus, surface proteins identified by the screening of immunoproteomic techniques are promising vaccine candidates or diagnostic markers. In this study, four membrane associated proteins (MAP) identified by immunoproteomic method were cloned and expressed as recombinant proteins with his-tag. Screening for vaccine candidates were firstly performed by protection assay in vivo and immunization with Sbp markedly protected mice against systemic S. suis 2 infection. The immune responses and protective of Sbp were further evaluated. The results showed that Sbp could elicit a strong humoral antibody response and protect mice from lethal challenge with S. suis 2. The antiserum against Sbp could efficiently impede survival of bacterial in whole blood killing assay and conferred significant protection against S. suis 2 infection in passive immunization assays. The findings indicate that Sbp may serve as an important factor in the pathogenesis of S. suis 2 and would be a promising subunit vaccine candidate.