Protective efficacy of Interferon-γ and β-glucan adjuvanted formalin killed vaccines in Nile tilapia against Edwardsiella tarda infection

Aquaculture is a central commercial commodity for low-to middle-income countries and a promising source of economically important food and livelihood. Indian aquaculture faces challenges with the onset of several upcoming fish diseases. The antimicrobial resistance (AMR) pathogen Edwardsiella tarda infection is one of the serious threats affecting worldwide aquaculture. Replacing antibiotics, vaccines can be used as a safe treatment for multidrug-resistant E. tarda. The present study focuses on creating a formalin killed vaccine incorporated with IFN-γ and β-glucan as adjuvants, that confers protection against E. tarda infection in Nile tilapia (Oreochromis niloticus). The isolated virulent strain was cultivated in marine nutrient broth and inactivated by 0.5 % formalin treatment. To increase the immunogenicity, the bacterial suspension was mixed with IFN-γ and β-glucan. Fish were intraperitoneally immunized with IFN-γ and β-glucan -adjuvanted formalin killed vaccine (FKV), followed by sampling at a fixed time. After 28 days from the first immunization, the fish were challenged with E. tarda at a dose of 1 x 10⁷ CFU/fish. Blood from the immunized fish was sampled weekly to measure immunochemical parameters, including sodium oxide dismutase (SOD), myeloperoxidase (MPO), lysozyme activity (LZM), and bactericidal activity. Fish serum IgM titre values were measured on the 14th and 28 day post-vaccination (d.p.v.), and both showed that the adjuvanted vaccinated groups had higher antibody levels than the control group. The vaccinated groups with IFN-γ and β-glucan showed considerably higher expressions immune genes, including IgM, TCR β, MHC II. The study emphasizes that β-glucan and IFN-γ adjuvanted inactivated vaccine is a potentially plausible approach toward novel vaccination strategies for sustainable aquaculture.