Pre-treatment of Nile tilapia (Oreochromis niloticus) with ozone nanobubbles improve efficacy of heat-killed Streptococcus agalactiae immersion vaccine

Abstract

Nanobubble technology has shown appealing technical benefits and potential applications in aquaculture. We recently found that treatment with ozone nanobubbles (NB-O3) activated expression of several immune-related genes leading to effective response to subsequent exposure to fish pathogens. In this study, we investigated whether pre-treatment of Nile tilapia (Oreochromis niloticus) with NB-O3 can enhance specific immune responses and improve efficacy of immersion vaccination against Streptococcus agalactiae. Spleen and head kidney of fish in the vaccinated groups showed a substantial upregulation in expression levels of three immunoglobulin classes(IgM, IgD, and IgT) compared with the unvaccinated control groups. At day 21 post-immunization, the relative expression was greatest (approx. 3.2 to 4.1 folds). Both systemic and mucosal IgM antibodies were elicited in vaccinated groups. As the result, the cumulative survival rate of the vaccinated groups was found to be higher than that of the unvaccinated groups, with a relative percent survival (RPS) ranging from 52.9-70.5%. However, fish in the vaccinated groups that received pre-treatment with NB-O3, bacterial antigen uptakes, expression levels of IgM, IgD, and IgT, as well as the specific-IgM antibody levels and percent survival, were all slightly or significantly higher than that of the vaccinated group without pre-treatment with NB-O3. Taken together, our findings suggest that utilizing pre-treatment with NB-O3 may improve the immune response and efficacy of immersion vaccination in Nile tilapia.HighlightsImmune response and efficacy of a heat-killed Streptococcus agalactiae immersion vaccine for Nile tilapia with and without pre-treatment with NB-O3 were accessed.Bacterial antigen uptake in the NB-O3-VAC compared to the AT-VAC groups was increased 1.32 and 1.80-fold at 3 and 6 h post-vaccination, respectively.Vaccinated group that received pre-treatment with NB-O3 had slightly to significantly higher levels of IgM, IgD, and IgT mRNA expression; IgM levels; and survival rate.Pre-treatment with NB-O3 may be a novel strategy for improving efficacy of immersion vaccine in aquaculture

Current status and development prospects of aquatic vaccines

“…The hyperosmotic method is to soak the fish in 3% ~5% salt solution for 5 minutes, then move the fish herd to the vaccine solution for immersing, to force the antigen to infiltrate into the fish by the change of osmotic pressure (248, 266). Ultrasonic treatment can increase the permeability of biological tissues such as skin and muscles, and the number of antigens entering a fish's body can be significantly increased by ultrasound in spray (267,268). Although hypertonic and spray methods can improve the efficacy of immersion vaccines, their application is limited by stress on fish bodies.…”