Qualitative differences in the immune response of rabbit, mouse and sea bass,Dicentrarchus labrax, L. toPhotobacterium damselasubsp.piscicida, the causative agent of fish Pasteurellosis

Sera raised in rabbits, mice and sea bass againstPhotobacterium damselasubsp.piscicida(Ph.d.p.) cultured both in normal laboratory medium and under iron-limited conditions were analysed by Western blot. Sera collected from sea bass after injection with both live and heat-killedPh.d.p.cells were also analysed. All analysed sera reacted with two groups ofPh.d.p.cell antigens, one (an array of products) assigned as a high molecular weight group and another (lipopolysaccharide and/or lipoprotein) assigned as a low molecular weight group. Each serum tested differed in its reaction by Western blot. Cells cultured under iron-limited conditions demonstrated, both qualitatively and quantitatively, elevated immunogenicity. Great variation among the sera was evident with reference to the recognition of antigens in the high molecular weight group ofPh.d.p.products, with the sea bass serum raised against live cells demonstrating reaction against a wider range of cell material. Lipopolysaccharide and/or lipoprotein situated in the low molecular weight group products appeared to be the most immunogenic material in the bacterial cell. A 15·5 kDa antigen was recognised only from sea bass serum raised against live cells. The findings of this study are discussed in relation to future vaccine development.