University of Jyväskylä, Faculty of Mathematics and Science
The Department of Biological and Environmental Science
Lotta-Riina Sundberg: Flavobacterium columnare
Abstracts (first author)
Nutrient and bacterial doses affect virulence and host-specificity of the opportunistic fish pathogen Flavobacterium columnare
Flavobacterium columnare is a gram-negative bacterial pathogen that causes columnaris disease in freshwater aquaculture. Columnaris outbreaks occur at fish farms during summer months and may cause mortality up to 100 %. Virulence of environmental isolates of F. columnare has been found to be lower than those isolated during disease outbreaks at fish farms. In order to understand factors selecting for the higher virulence at fish farms, we studied if the bacterial dose, exposure time (transient or continuous), or nutrients have an effect on the virulence of F. columnare.
Three F. columnare strains were used in two separate experiments: a non-virulent strain B398 isolated from the lake and two virulent strains from disease outbreaks (B185 and B67). In the first experiment zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss) fingerlings were individually infected with bath immersion (transient challenge) with 9 different doses of bacterial strains B185, B398, and a mixture of these strains. In the second experiment the bacteria (strains B185, B398 and B67) were added in three doses directly into aquaria (continuous challenge) where zebrafish and rainbow trout were maintained. Longevity of fish was monitored for five days in both experiments, and the infection verified by bacterial culture from gills.
We found bacterial dose to have a positive effect on mortality of both fish species. Increase in nutrients had a significantly positive effect on columnaris infection and fish mortality. The non-virulent strain was able to infect the fish when introduced in continuous exposure, but not in transient challenge. Our results suggest that the continuous exposure to bacteria at fish farms combined with a high nutrient level can promote virulence also in environmental non-virulent bacteria. In addition, the zebrafish can be used as a functional model host to study F. columnare virulence and infection dynamics in the laboratory.