Recombinant Aeromonas hydrophila outer membrane protein 48 (Omp48) induces a protective immune response against Aeromonas hydrophila and Edwardsiella tarda

The gene coding for an outer membrane protein Omp48 of Aeromonas hydrophila isolated from an infected fish was cloned and sequenced. Analysis of nucleotide sequence showed the omp48 gene to be an adhesin encoding a protein of 426 amino acids with high identity to the omp48 gene of Aeromonas veronii, another fish pathogen. The gene belonged to the maltoporin group of porins and had high similarity to LamB porins of A. hydrophila, Aeromonas salmonicida and Vibrio parahaemolyticus. The expressed purified recombinant protein had an estimated molecular weight of 48 kDa. Further, rabbit hyperimmune sera against the recombinant protein reacted with A. hydrophila, Aeromonas sobria and A. veronii whole cell proteins at the region of 48 kDa, in western blotting. The recombinant protein was immunogenic in the fish Labeo rohita Hamilton. Fish immunized with recombinant protein, when challenged with virulent A. hydrophila and another bacterial fish pathogen, Edwardsiella tarda, showed relative percent survivals of 69 and 60, respectively. Our results suggest that Omp48 of A. hydrophila could be used as a potential vaccine candidate for protection not only against A. hydrophila infection, but also against the fish pathogen E. tarda.