DEVELOPMENT OF RIFAMPICIN AND NOVOBIOCIN RESISTANT Aeromonas salmonicida STRAINS AND THEIR POTENTIAL AS LIVE ATTENUATED VACCINE CANDIDATES

Aeromonas salmonicida, the causative agent of furunculosis, poses a significant threat to a diverse range of hosts in both fresh and marine fish. Currently, there are no commercial vaccines available to treat furunculosis in non-salmonid fish. Limited vaccine options exist to prevent furunculosis in sablefish specifically. This problem is evident as sablefish aquaculture has intensified in the Pacific Northwest, furunculosis continues to cause high mortality rates during production. The primary objective of this study is to develop a live-attenuated vaccine suitable for immersion administration, aiming to effectively treat furunculosis in sablefish for commercial aquaculture production. Attenuated strains of typical and atypical A. salmonicida were generated using rifampicin and novobiocin through successive passages on TSA with escalating concentrations of the antibiotics, reaching up to 400 mg/ml for both rifampicin and novobiocin. Resulting isolates were cultured at temperatures up to 30 for additional attenuation. Partial and full attenuation of A. salmonicida strains was confirmed through in vivo virulence challenges in sablefish and rainbow trout. Subsequently, an in vivo vaccine trial was conducted with the attenuated typical A. salmonicida Isolate (A5) in rainbow trout. The vaccination trial using the A5 isolate showed significant A. salmonicida specific IgM titers for both immersion and injection vaccination methods. Overall, the proposed live-attenuated vaccine candidates to prevent furunculosis in sablefish and rainbow trout could become an asset to sustainable aquaculture management if proven effective with further vaccination trials.