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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #322056

Research Project: Integrated Research to Improve On-Farm Animal Health in Salmonid Aquaculture

Location: Cool and Cold Water Aquaculture Research

Title: Virulence and molecular variation of Flavobacterium columnare affecting rainbow trout in ID, USA

item Evenhuis, Jason
item Mohammad, Haitham - University Of Auburn
item Lapatra, Scott - Clear Springs Foods, Inc
item Welch, Timothy - Tim
item Arias, Covadonga - University Of Auburn

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2016
Publication Date: 6/22/2016
Citation: Evenhuis, J., Mohammad, H., Lapatra, S.E., Welch, T.J., Arias, C. 2016. Virulence and molecular variation of Flavobacterium columnare affecting rainbow trout in ID, USA. Aquaculture. 464:106-110. doi: 10.1016/j.aquaculture.2016.06.017.

Interpretive Summary: Columnaris disease is an emerging problem for the rainbow trout producing region of Idaho. An initial study looking at the diversity of Flavobacterium columnare isolates, the causative agent for columnaris disease, suggested that the outbreaks occurring in the region were the result of a highly successful expansion of a family of closely related F. columnare. Herein we further characterize 11 isolates associated with disease outbreaks from 5 different rainbow trout farms in Idaho. Genetic and virulence variations were found based on genomic fingerprinting, gene sequence and immersion challenges against rainbow trout. Genomic similarity between isolates were as low as 60% based on fingerprinting analysis. Sequence analysis of a gene associated with the LPS matrix 3 different forms exist including the apparent lack of the gene in 6 of the isolates and two single nucleotide polymorphisms in the isolates that did encode the gene. The most virulent strains tested were upto 8 times as virulent as the least virulent strains based on the number of colony forming bacteria that required to achieve 50% death in rainbow trout. These results show that the F. columnare causing disease outbreaks in the Idaho region are more diverse genetically and phenotypically than originally thought.

Technical Abstract: Columnaris disease is an emerging problem in the rainbow trout (Oncorhychus mykiss) aquaculture industry of Idaho. The epidemiology of this pathogen in the area, and for rainbow trout, is all isolates taken from disease outbreaks are genomovar I and similar based on basic typing protocols. Virulence phenotyping of 11 isolates, taken from 5 different farms, suggests a measurable amount of variation in virulence toward rainbow trout with the most highly virulent strains having an LD50 of 1x106 CFU/ ml-1. The least virulent strain required 8x106 CFU/ ml-1 to get an LD50. AFLP fingerprinting of these strains and the resulting phylogenetic tree shows that all of the strains tested had similarity, at the genomic level, of greater than 75%, save one, the MS-FC-4 strain had less than 60% identity to all of the other strains tested. An example of variation at a gene level shows that the Alpha-L-Rha alpha-1,3-L-rhamnosyltransferase (welB) gene is differentially encoded between all strains tested. Six of the 12 strains tested were devoid of this gene entirely while the other 6 stains encoded one of two versions of the gene. These results suggest strains taken from disease outbreaks in rainbow trout have a higher degree of diversity than previously thought.