Evaluate the potential use of TonB-dependent receptor protein as a subunit vaccine against Aeromonas veronii infection in Nile tilapia(Oreochromis niloticus)

Aeromonas veronii is an emerging bacterial pathogen that causes serious systemic infectionsi n cultured Nile tilapia(Oreochromisniloticus),leading to massive deaths.Therefore,there is an urgent need to identify effective vaccine candidates tocontrol the spread of this emerging disease.TonB-dependentreceptor(Tdr)of A.veronii,which plays a role in the virulence factor of the organism,could be useful interms of protective anti-gens for vaccine development.This study aims to evaluate the potential use of Tdr protein as a novel subunit vaccine against A.veronii infection in Nile tilapia.TheTdr gene from A.veronii wascloned into thepET28b expression vector,and the recombinant protein wassubsequently produced in Escherichia coli strainBL21(DE3).Tdr was expressed as an insoluble protein and purified by affinity chromatography.Antigenicity test indicated that this protein was recognized by serum fromA.veronii infected fish.When Nile tilapia wereimmunized with theTdr protein,specific antibody levels increased significantly (p-value<0.05) at7days post-immunization(dpi),and peaked at21dpi compared to antibody levels at 0 dpi.Furthermore,bacterial agglutination activity was observed in the fish serum immunized with theTdr protein,indicating that specific antibodies in the serum can detect Tdr on the bacterial cellsurface.These results suggest that Tdr protein has po-tential as a vaccine candidate.However,challenging tests with A.veronii in Nile tilapia needs to be investigated to thoroughly evaluate its protective efficacy for future applications.