Panphut, W. | bioRxiv Science

bioRxiv2021

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

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. HighlightsO_LIImmune response and efficacy of a heat-killed Streptococcus agalactiae immersion vaccine for Nile tilapia with and without pre-treatment with NB-O3 were accessed. C_LIO_LIBacterial 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. C_LIO_LIVaccinated 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. C_LIO_LIPre-treatment with NB-O3 may be a novel strategy for improving efficacy of immersion vaccine in aquaculture C_LI

molecular biology↗

bioRxiv2020

Ozone nanobubble treatment effectively reduced pathogenic Gram positive and negative bacteria in freshwater and safe for tilapia

High concentrations of pathogenic bacteria in water usually results in outbreaks of bacterial diseases in farmed fish. Here, we explored the potential application of an emerging nanobubble technology in freshwater aquaculture. Specifically, we aimed to determine if this technology was effective at reducing the concentration of pathogenic bacteria in the water, and to assess whether it was safe for fish. An ozone nanobubble (NB-O3) treatment protocol was established based on examination of nanobubble size, concentration, disinfection property, and impact on fish health. A 10-min treatment with NB-O3 in 50 L water generated approximately 2-3 x 107 bubbles with majority sizes less than 130 nm and ozone level of [~]800 mV ORP. A single treatment with water contaminated with either Streptococcus agalactiae or Aeromonas veronii effectively reduced 96.11-97.92 % of the bacterial load. This same protocol was repeated 3 times with 99.93-99.99 % reduction in the bacterial concentration. In comparison, bacterial concentration the control tanks remained the same level during the experiments. In fish-cultured water with the presence of organic matter (e.g. mucus, feces, bacterial flora, feed, etc.), the disinfection property of NB-O3 was reduced i.e bacterial concentration was reduced by 42.94 %, 84.94 % and 99.27 % after the first, second and third treatments, respectively. To evaluate the safety of NB-O3 to fish, juvenile Nile tilapia were exposed to NB-O3 treatment for 10 minutes. No mortality was observed during the treatment or 48 h post treatment. Gill histology examination revealed that a single NB-O3 treatment caused no alteration morphology. However, damage in the gill filaments was noticed in the fish receiving two or three consecutive exposures within the same day. Results of all the experiments conducted in this study suggest that NB-O3 technology is promising for controlling pathogenic bacteria in aquaculture systems, and may be useful at reducing the risk of bacterial disease outbreaks in farmed fish.

microbiology↗