Photobacterium damselae subsp. piscicida (PDP) is the causative agent of fish
pasteurellosis, a
bacterial disease causing important losses in marine aquaculture.
Vaccines against the pathogen can be a way to control the
infection and avoid
antibiotic treatments. However, a satisfactory protective
vaccine against fish
pasteurellosis is not commercially available. In this study, a biotechnogical approach based on reverse vaccinology has been used to identify potential
vaccine candidates for the development of a recombinant
subunit vaccine. Genome sequencing of clones from a genomic cosmid library of PDP and in silico selection of the surface exposed
proteins were the initial steps in
vaccine candidate identification. From 370 open reading frames (ORF) eight potential
antigens were selected, expressed as
recombinant proteins and purified. These
vaccine candidates were used to generate specific polyclonal
antibodies in mice. Each antibody was then screened in vitro by inhibition adherence assay of live PDP on chinook salmon embryo cells (CHSE-214). A
lipoprotein, found to be involved in the adherence of the bacterium to epithelial cells and annotated as PDP_0080, was then selected. The
recombinant protein was further investigated in fish vaccination and challenge experiments to assess its ability to protect sea bass, Dicentrarchus labrax, against PDP
infection. Immunisation with PDP_0080
recombinant protein elicited high specific antibody titres. Furthermore, the survival rate of fish immunized with the 25 μg dose of
protein was significantly higher compared to the control group. The results of the study suggest that the PDP_0080
protein could be a promising candidate for the design of a
recombinant vaccine against
pasteurellosis.