Evidence for the immune recognition of two haemolysins of Renibacterium salmoninarum by fish displaying clinical symptoms of bacterial kidney disease (BKD)

Little is known of the pathogenicity of Renibacterium salmoninarum, in particular, the complexity of interactions that must occur between the host and the pathogen during the course of an infection. Previously, researchers have shown that during the course of either an experimental or natural infection the salmonid immune system recognises p57, the major secretory antigen produced by R. salmoninarum. Two haemolytic components are known to be produced by R. salmoninarum, a metalloprotease (HLY) encoded by gene hly and a haemolysin (RSH) encoded by gene rsh. In order to simplify further research into the role of these components in vivo, and to remove the dependence upon time consuming in vitro cultures of R. salmoninarum, fusion proteins have been produced using Escherichia coli host/vector systems. These methods entailed the translational fusion of either maltose-binding protein (MBP) or beta -galactosidase to the R. salmoninarum proteins and subsequent purification using affinity chromatography to sepecifically bind the fusion proteins. The present study reports the recognition of epitopes of the fusion proteins by sera taken from fish experiencing a natural outbreak of bacterial kidney disease (BKD) and, for comparison, from immunised fish.