Enolase-based nanovaccine immersion immunization induces robust immunity and protection against Streptococcus infection in tilapia

Streptococcal disease is one of the most serious diseases in tilapia, causing huge economic losses to the tilapia farming industry. Streptococcus agalactiae (S. agalactiae) and Streptococcus iniae (S. iniae) are the two main pathogens of tilapia streptococcosis. Vaccination has been proved to be an effective measure to control fish bacterial diseases. In this study, we selected the Enolase (Eno) as the candidate vaccine antigen, which is the common antigen of S. agalactiae and S. iniae with high similarity (97.2%), the rEno was obtained and the CNT-rEno nanocarrier vaccine system was constructed by connecting the rEno protein with functionalized carbon nanotubes (CNTs), the immersion immune effect against S. agalactiae and S. iniae infection was evaluated. The results showed that, compared with the control group, CNT-rEno significantly enhanced the serum antibody production, related enzyme activities and immune-related genes expression. It was worth noting that CNT-rEno demonstrated better immunoprotection against S. agalactiae and S. iniae infection, with relative percent survivals of 73.68% (S. agalactiae) and 68.96% (S. iniae), respectively, which were both much higher than those of rEno groups (36.84% and 31.03%, respectively). Our study indicated that the CNT-rEno nanovaccine had the ability to elicit robust immune responses in tilapia by immersion immunization, and had the potential to offer cross-protection against S. agalactiae and S. iniae infection. •Enolase (Eno) is a common and conserved antigen between S. agalactiae and S. iniae.•CNT-rEno significantly increases the serum specific antibody level and related enzyme activities.•CNT-rEno can regulate immune-related genes expression to enhance immune response.•CNT-rEno provides cross-protection against S. agalactiae and S. iniae infection in tilapia by immersion immunization.