Protection of Atlantic salmon (Salmo salarL.) against an experimental infection ofAeromonas salmonicidassp.achromogenes

To assess the protective role of cell-associated and extracellular antigens ofAeromonas salmonicidassp.achromogenes, Atlantic salmon were immunised either with detoxified extracellular products (d-ECP), formalin killed cells (f-Cells) or a mixture of both. In an experimental challenge ECPs were found to elicit better protection than whole bacteria. The protection strongly correlated with the detection of antibodies directed against a toxic metallo-caseinase, AsaP1, in fish sera. Passive immunisation of Atlantic salmon with rainbow trout or rabbit anti-AsaP1 antisera conferred significant protection against challenge with a virulentA. salmonicidassp.achromogenesstrain. In an equivalent experiment neither rainbow trout nor rabbit antisera containing antibodies to the A-layer protein ofA. salmonicidawere found to be protective for passively immunised Atlantic salmon. The results demonstrate the importance of humoral antibodies and neutralisation of bacterial toxins in protecting Atlantic salmon againstA. salmonicidassp.achromogenes