Efficacy of mucoadhesive nanoemulsion-based immersion vaccine against Streptococcus agalactiae and Edwardsiella tarda infections in Nile tilapia (Oreochromis niloticus)

Information from the abstract

Streptococcosis and edwardsiellosis caused by Streptococcus agalactiae and Edwardsiella tarda , respectively, are amongst the most economically devastating bacterial diseases in Nile tilapia ( Oreochromis niloticus ) aquaculture, compounded by the escalating prevalence of multidrug-resistant strains and the associated risks to both aquaculture productivity and public health. This study developed and evaluated the efficacy of mucoadhesive nanoemulsion immersion vaccines formulated against each pathogen (NE- Sa and NE- Et ) in Nile tilapia fingerlings using a two-dose protocol comprising primary vaccination at Day 0 and a booster at Day 30. Each vaccine was formulated as a cationic oil-in-water nanoemulsion using a medium-chain triglyceride oil core stabilized with non-ionic (Tween 80, Span 80) and cationic (benzalkonium chloride) surfactants. Both formulations exhibited nanoscale particle sizes (143 ± 5.68 and 126 ± 6.02 nm), positive zeta potentials, and polydispersity index (PDI) values below 0.5, confirming successful cationic nanoemulsion formation. Vaccinated fish demonstrated significantly elevated serum lysozyme and bactericidal activity maintained across both pre- and post-challenge time points, indicating sustained innate immune priming throughout the experimental period. Pathogen-specific IgM antibody levels in serum, skin mucus, gills, and head kidney were significantly elevated and maintained from pre- to post-challenge in vaccinated fish, confirming durable humoral immune responses across both mucosal and systemic compartments. Significant upregulation of immunoglobulin genes ( ighm , ight , and ighd ) in gills and head kidney at both sampling time points provided molecular evidence for sustained activation of multi-isotype adaptive immunity in mucosal and lymphoid tissues. Immersion challenge with S. agalactiae and E. tarda at Day 60 yielded relative percent survival (RPS) values of 51.90% and 53.33%, respectively, with significantly reduced cumulative mortality in vaccinated fish compared with controls throughout the 14-day observation period ( P = 0.0078 and P = 0.0010). These findings collectively support mucoadhesive nanoemulsion immersion vaccination as a practical, needle-free, and scalable alternative to antibiotic-based disease management in commercial Nile tilapia aquaculture.

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Related topics: Aquaculture disease management and microbiota · Advanced Drug Delivery Systems · Antimicrobial Peptides and Activities