Strain B represented the most common haplotype,

comprising 18 R. salmoninarum isolates from Atlantic salmon and rainbow trout farmed in Scotland and Norway over a period of more than 20 years. Strain B was one of five closely related strains (A, B, C, D, E) differing from each other at a single locus. Figure 1 Relationship among the observed high throughput screening haplotypes described in Table 2 . Group 1 includes haplotypes A to L and Group 2 includes haplotypes M to Q. Bootstrap values indicate the level of support for clusters if higher than 50%. Group 2 represents R. salmoninarum isolates obtained uniquely from Atlantic salmon originating from Scotland and Norway. These isolates differed from group 1 at loci BKD396 and BKD1935. A moderately supported cluster within group 2, comprising EVP4593 strains O-Q, represented isolates exclusively from wild Atlantic salmon, including the Dee disease isolates NCIMB 1114 and 1116 associated with first occurrence of BKD in Scotland. Similar clustering of R. salmoninarum isolates Selleckchem Ruboxistaurin into two main groups was achieved using the eBURST algorithm based on either 16 or 6 polymorphic loci (Figure 2A,B). Using 16 polymorphic loci, a large radial cluster of 7 closely related haplotypes (A-G) was defined. Haplotype B was assigned as the most parsimonious “founder” of this group. Group 2 haplotypes

occurred as a single pair O/P representing the Dee disease isolates and three singletons (L,M,N). Using eBURST, a loss in resolving Silibinin power of the genotyping system was observed when the number of polymorphic loci included was reduced to 6 (Figure 2B). Figure 2 eBURST diagram of R. salmoninarum population derived from the allelic variation in (A) 16 polymorphic loci or (B) 6 polymorphic loci. The present VNTR

typing scheme was also applied to investigate whether Scottish R. salmoninarum isolates can be distinguished from isolates originating from Norway. Within group 1, some association with country of origin was observed for haplotypes A, C, and G, uniquely obtained from Scottish aquaculture, while haplotype E represented R. salmoninarum from Norway. On the contrary, the most common haplotype B contained isolates obtained from aquaculture establishments in both countries. Discussion The present study describes development and application of a VNTR typing system for R. salmoninarum, a bacterium affecting salmonid aquaculture worldwide and discusses the potential implications for disease management. In comparison to other genotyping methods used to study R. salmoninarum such as RAPD, tDNA-ILPs [20–23], multilocus VNTR typing offers a considerable improvement. Using a combination of sixteen VNTRs, 17 different haplotypes can be identified among 41 R. salmoninarum isolates. The discriminatory power of the present combined VNTR scheme was high, characterized by HGDI index of 0.81, indicating that two unrelated isolates will on 81% of occasions fall into different haplotypes.