ARS | Publication request: Development of a reproducible challenge model to investigate the virulence of Flavobacterium columnare genomovars in rainbow trout Oncorhynchus mykiss (Walbaum)

Submitted to: American Fisheries Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 25, 2012
Publication Date: July 31, 2012
Citation: Lafrentz, B.R., Lapatra, S.E., Shoemaker, C.A., Klesius, P.H. 2012. Development of a reproducible challenge model to investigate the virulence of Flavobacterium columnare genomovars in rainbow trout Oncorhynchus mykiss (Walbaum)[abstract]. American Fisheries Society Annual Meeting. p. 25.

Technical Abstract: Flavobacterium columnare is a Gram-negative bacterium that causes columnaris disease and has significant economic impacts on aquaculture production worldwide. Molecular analyses have demonstrated that there is genetic diversity among F. columnare isolates. A review of the published literature that used restriction fragment length polymorphism analysis of the 16S rRNA gene revealed that all isolates typed from salmonids were genomovar I. The objective of this study was to develop a laboratory challenge model for F. columnare in rainbow trout Oncorhynchus mykiss (Walbaum) and use the model to determine the virulence of genomovar I and II isolates in rainbow trout. Six F. columnare isolates were obtained from rainbow trout experiencing losses due to columnaris disease and were determined to be genomovar I. Three of these were chosen for a preliminary assessment of virulence and isolate 051-10-S5 was chosen for additional experiments to determine the reproducibility of the waterborne challenge model. In two independent experiments, cumulative percent mortalities (CPM) were 49 and 50 % and the standard deviations between replicate groups were ± 10 and 19 %, respectively. The challenge model was then used to compare the virulence of genomovar I and II F. columnare isolates (two per genomovar) in rainbow trout. The results demonstrated a difference in the CPM of fish challenged with the genomovars, with the genomovar II isolates inducing significantly higher CPM. In summary, a reproducible waterborne challenge model for columnaris disease in rainbow trout was developed which will be useful to investigate host-pathogen interactions, vaccine development, and other potential control strategies. This research also provides a basis for further defining the molecular diversity and virulence associated with F. columnare genomovars in rainbow trout and other salmonid species.