Novel transfersome-based vaccine delivery for red tilapia: Enhancing immunization against Francisella orientalis...

Emerging infectious diseases caused by Francisella orientalis (Fo) pose significant challenges to aquaculture. This study aimed to develop and evaluate a novel transfersome-based nanovaccine (T-FoBCFSVac) formulated with bacteriocin cell-free supernatant (BCFS) derived from F. orientalis. The characteristics of T-FoBCFSVac including size, zeta potential and morphology were analyzed using dynamic light scattering (DLS) and transmission electron microscope (TEM). The vaccine was then assessed for safety, protection and immune responses in tilapia vaccinated for 7 and 14 days, with sampling at week 8 post-vaccination following disease resistance analysis against F. orientalis. The T-FoBCFSVac vaccine exhibited uniform particle sizes (∼100 nm) with a narrow polydispersity index (∼0.24) and stable negative zeta potential (-55 to -58 mV). The optimized formulation preserved the structural integrity of bacteriocin and antigen components through mild ultrasonication processing. Immunological analyses revealed significantly elevated IgM titers, enhanced serum lysozyme activity, and upregulated immunoglobulin-related genes, including IgM, IgT and IgD and intestinal mucosal responses. Pathway enrichment analysis demonstrated progressive activation of innate and adaptive immune pathways, notably phagosome, cell adhesion molecules, cytokine-cytokine receptor interaction, ubiquitin mediated proteolysis, RIG-l-like receptor signaling pathway, and intestinal immune network for Ig production. Protective efficacy studies showed significantly lower bacterial loads, improved survival rates (60-67.5%), and high relative percent survival (51.25-60.32%) in T-FoBCFSVac-treated fish compared to the controls. Importantly, no significant changes in blood biochemistry or tissue pathology were observed, which confirmed the nanovaccine's safety and biocompatibility. These findings suggest that T-FoBCFSVac offers a robust and safe prophylactic strategy against F. orientalis, with potential applications for disease management in aquaculture.