Protection and safety of aluminum hydroxide adjuvant and chimeric antigen containing predicted epitopes from bacteria murC gene in Aeromonas hydrophila fish infection.

Aquaculture is a food production system based on fish, amphibians, crustaceans, molluscs, plant and algae production that promotes significant positive impacts on the world economy and human nutrition. Aeromonas hydrophila, a gram-negative zoonotic bacterium associated with outbreaks in aquaculture, threatens fish production, resulting in fish disease and mortality. The aim of this work was to evaluate zebrafish protection against A. hydrophila infection using an immunoinformatically predicted recombinant antigen based on a cytoplasmic enzyme involved in cell wall biosynthesis, as well as to assess the toxic impacts of aluminum hydroxide adjuvant. The chimeric recombinant antigen was constructed based on the murC gene product and subjected to B and T cell prediction before being expressed in a bacterial system. The zebrafish protection assay was evaluated after administration of an LD50 dose of A. hydrophila. Organs were harvested for histopathological analysis and qRT-PCR. The results showed an acute toxic profile of A. hydrophila in vivo with high mortality within 24 h. An antigenic profile from the chimeric antigen was registered with no toxic damage to fish and a targeted immune response in the spleen based on up-regulation of IL10, IFN1, MHCII and IL6, although 0.5 % aluminum hydroxide showed a toxic profile resulting in fish mortality, tissue damage and acute inflammation. In conclusion, new targets from the mur family and other cytoplasmic enzymes should be explored to establish their immunogenic profile against aquaculture pathogenic bacteria. Additionally, novel adjuvants for aquatic vaccines should be developed as sustainable alternatives with no toxicity profile.