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Title: Renibacterium salmoninarum p57 antigenic variation is restricted in geographic distribution and correlated with genomic markers

item Wiens, Gregory - Greg

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2008
Publication Date: 2/12/2009
Citation: Wiens, G.D., Dale, O. 2009. Renibacterium salmoninarum p57 antigenic variation is restricted in geographic distribution and correlated with genomic markers. Diseases of Aquatic Organisms. 83:123-131.

Interpretive Summary: Renibacterium salmoninarum (Rs) is the causative agent of bacterial kidney disease and a significant threat to the healthy and sustainable production of salmonid fish in the United States. This bacterium produces a 57-kDa protein (p57) that is a virulence factor and is a reliable diagnostic marker of infection. We have previously identified variants of this protein that may increase infectivity. Here, we investigate the prevalence and distribution of strains producing this variant protein. Our screening results indicate that the variant is prevalent only in isolates originating from Norway and that these isolates are homogenous at other genomic loci. These results suggest that antigenic variation is geographically restricted in distribution.

Technical Abstract: The 57 kDa protein (p57) is an important diagnostic antigen that is implicated in the pathogenesis of salmonid bacterial kidney disease. Little is known about the nature and extent of antigenic variation in p57. Previously, we reported that p57 produced by Renibacterium salmoninarum Strain 684 contains a mutation that disrupts monoclonal antibody (MAb) 4C11 binding. We examined MAb binding to a panel of 23 additional R. salmoninarum isolates obtained from diverse geographic locations to examine the prevalence of this variant and whether additional variability exists within other p57 epitopes. Six p57-specific Mabs (4C11, 4D3, 3H1, 4H8, 4D10 and 1A1) were used to probe dot and western blots to determine the relative expression, size and cellular association of p57. Full-length p57 was produced by all isolates, and for each isolate, the protein was associated with the bacterial cell surface. The epitopes recognized by 4 MAbs, 4D3, 4H8, 3H1 and 1A1, were conserved among all strains tested. The 4C11 epitope was absent in 5 of 8 strains originating from Norway, while the 4D10 epitope was partially disrupted in one isolate from British Columbia, Canada. The 5 Norwegian antigenic-variant strains appeared to be clonally related as they shared the following characteristics: one tandem repeat in the ETRA locus, a sequovar-four 16-23S rRNA intervening DNA sequence, a larger XhoI fragment in the msa1 5’ region, and absent msa3 gene. These results indicate that limited antigenic and genomic variation exists between strains and this variation appears geographically restricted in distribution.