Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 1101
Title: Interpreting dual ELISA and qPCR data for bacterial kidney disease of salmonids
Author: Shelly L. Nance, Michael Riederer, Tyler Zubkowski, Marc Trudel, L. D. Rhodes
Publication Year: 2010
Journal: Diseases of Aquatic Organisms
Volume: 91
Issue: 2
Pages: 113-119
DOI: 10.3354/dao02252
Keywords: bacterial kidney disease, Renibacterium salmoninarum, diagnostic assays, ELISA, real-time TaqMan PCR assay, infection state
Abstract: Although there are a variety of methods available for the detection of Renibacterium salmoninarum, the causative agent of bacterial kidney disease in salmon and trout, the enzyme-linked immunosorbent assay (ELISA) is probably the most widely used method. However, ELISA measures bacterial antigen, which does not necessarily reflect the number of cells present. We hypothesized that dual analysis of kidney tissue by ELISA and a quantitative real-time polymerase chain reaction assay (qPCR) would provide complementary information about antigen level and the number of bacterial genomes. We found that DNA extracted from the insoluble fraction of the ELISA tissue preparation produced the same qPCR value as DNA extracted directly from frozen tissue, permitting true dual analysis of the same tissue sample. Tissue from both free-ranging juvenile Chinook salmon and antibiotic-treated captive subadult salmon revealed three patterns of results. Among the majority of fish, there was a strong correlation between ELISA value and the qPCR value across the full range of ELISA values. However, subsets of fish exhibited either low ELISA values with elevated qPCR values or higher ELISA values with very low qPCR values. We propose an interpretation model suggesting that the latter results may provide information about the state of infection. This conceptual model may have utility in broodstock programs that currently apply egg-culling practices based on ELISA alone.
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