Monoclonal Antibody-Based Analysis of the Renibacterium salmoninarum p57 Protein in Spawning Chinook and Coho Salmon

Abstract

Renibacterium salmoninarum, causative agent of bacterial kidney disease of salmonid fish, produces large amounts of soluble proteins during infection and broth culture. An enzyme-linked immunosorbent assay (ELISA) based on monoclonal antibodies was developed for the precise quantification of p57, a major component of these proteins. Kidney, spleen, blood, and reproductive fluids of adult Pacific salmon Oncorhynchus spp. were examined by means of the assay. Kidney and spleen harbored the highest concentrations of this antigen. In the populations of returning salmon tested, 5–25% of the fish had p57 concentrations above a baseline level of 3 ng antigenig tissue, and antigen concentrations as high as 200 μg/g tissue were detected in kidneys of individual fish. The ELISA was compared to direct fluorescent antibody analysis, in which rabbit anti-R. salmoninarum antiserum was used to identify infected fish. There was 99% agreement (199 of 201 examined fish) between the two methods. Western blot analysis was used to demonstrate that antigenic proteins present in infected fish were similar to those seen from antigen prepared from broth culture of R. salmoninarum, although less degradation of p57 appears to occur in vivo.