Comparative evaluation of bacterial culture and two ELISA techniques for the detection of Renibacterium salmoninarum antigens in salmonid kidney tissues

Abstract

Soluble antigens from Renibacterium salmoninarum (Rs) incorporated into immunostimulating complexes (iscoms) induced polyclonal antibodies directed to the heat-stable, 57 kDa antigen complex of Rs. The antibodies were used in an enzyme-linked immunosorbent assay (ELISA) for the detection of Rs antigens in salmonid kidney samples. The negative-positive threshold value in the ELISA was determined to be 0.10 based on the analyses of 408 samples from rainbow trout Oncorhynchus mykiss, Arctic char Salvelinus alpinus, Baltic salmon Salmo salar, and brown trout Salmo trutta, all negative for Rs by bacterial culture. The Rs organism was isolated on selective kidney disease medium (SKDM) after up to 12 wk of incubation from 45% of the samples collected from fish farms having enzootic bacterial kidney disease (BKD), and from fish in populations with clinical signs of BKD (n = 260). Soluble antigens of Rs were detected with the polyclonal ELISA in 50% of these samples. In a comparative evaluation of 3 diagnostic techniques (bacterial culture, the polyclonal ELISA described here, and a commercially available ELISA based on monoclonal antibodies), 167 kidney samples were individually analyzed. The results of the diagnostic tests (positive or negative) were identical for 95% of the examined samples. A higher sensitivity of the polyclonal ELISA when compared with the monoclonal method was indicated in this study.