Characterization of turbot (Scophthalmus maximus) associated bacteria with inhibitory effects against the fish pathogen Vibrio anguillarum.

More than 400 isolates from the intestine and the external surface of farmed turbot, as well as from fish food and hatchery water were screened for inhibitory effects against the fish pathogen Vibrio anguillarum HI 11345 and seven other fish pathogens. The bacteria with inhibitory effects were then characterized with regards to their sites of colonization, especially the intestinal regions and sites within each region. No correlations between the different biochemical phena, site of colonization and inhibitory effect could be found. The potential of seven of these strains for adhesion to intestinal mucus from turbot was studied. Rapid growth of V. anguillarum in intestinal mucus was measured, hence it is feasible that the intestinal tract is a site for V. anguillarum multiplication. Strains isolated from the intestine showed greater capacity for in vitro adhesion to and growth in fish intestinal mucus than did the pathogen and skin mucus isolates. Two of the strains isolated from the intestine were studied for their inhibitory kinetics and one strain for the potential of in vivo colonization. The molecular weight of the inhibitory component was below 1000 dalton in 65% of the strains isolated. For the other 35% the inhibitory component ranged between 1000 D-6000 D in dialysis cut off experiments. One week after oral administration, one such isolate still accounted for 45% of the total c.f.u. in the intestinal mucus of 5 g turbot. In preliminary experiments we demonstrated that it is possible to detect the pathogen in intestinal mucus with a fluorescently labelled oligonucleotide probe directed against a specific part of the intracellular rRNA of V. anguillarum.