A new recombinant SsnA protein combined with aluminum hydroxide protects mouse against Streptococcus suis

An experimental challenge in a mouse model was used to select the most effective adjuvant in a vaccine formulation with the surface-anchored DNA-nuclease (SsnA). We used a protocol based on clinical, histopathological, bacterial kinetics and immune response against S. suis serotype 2 in infected animals. The three adjuvants used, aluminum hydroxide (ALOH), incomplete Freund's adjuvant (FIA), oil-in-water adjuvant (OW) showed a protective effect against death by S. suis serotype 2 in this mouse model, although aluminum hydroxide revealed as the best option. Subsequently, in a second experimental assay, we showed that a recombinant SsnA protein combined with ALOH as adjuvant allowed a significant decrease of clinical and lesional findings in animals, faster reduction of the bacteria from organs and a highest humoral response against S. suis after 3 days post-infection. The results show that this combination (rSsnA + AlOH) could be a good vaccine formulation against S. suis, although further studies are necessary to evaluate their use for swine and human species.