Colonization in the fish intestinal tract and production of inhibitory substances in intestinal mucus and faecal extracts by Carnobacterium sp. strain K1

A non-virulent Carnobacterium sp., designated strain K1, isolated from the gastrointestinal tract of Atlantic salmon, Salmo salar L., which produced inhibitory substances against bacterial fish pathogens, was examined in vitro for characteristics important for the colonization of the fish gastrointestinal tract and in vivo for persistence in the tract after oral dosing. In vitro growth experiments showed that the cells of this strain were metabolically active in both the intestinal mucus and faeces from salmonids. The production of growth inhibitors against the two common fish pathogens Vibrio anguillarum and Aeromonas salmonicida by Carnobacterium sp. strain K1 was demonstrated in vitro in mucus and faecal extracts. Furthermore, it was demonstrated that the Carnobacterium cells remained viable in the gastrointestinal tract for several days and that no detrimental effect to the fish was observed as a result of the presence of the bacterium.