In vitro adherence of two candidate probiotics from Atlantic cod and their interference with the adhesion of two pathogenic bacteria

The potential of two candidate probiotic bacteria (GP21 and GP12), isolated from the gut of Atlantic cod, to adhere to primary cultures of the epithelial cells from the different regions of the intestine and to interfere with the adhesion of two pathogens, Vibrio anguillarum and Aeromonas salmonicida subsp. salmonicida were investigated. The intestinal isolates showed clear preference in adhering to the cells from the different intestine segments. GP12 adhered strongly to the fore- and mid intestine cells. The adherence of GP21 was most to the cells from the hind intestine followed by those from the mid-segment. The adhesion of V. anguillarum was affected by both GP21 and GP12; GP12 interfered through competition, but a specific mode of action was not observed for GP21. In the case of A. salmonicida, competition was the principal mechanism by which GP21 interfered with their adhesion, while exclusion mechanism was favoured by GP12. In addition, GP21 was more auto-aggregative than GP12, but the latter was more co-aggregative with both the pathogens. The isolates were also capable of lowering lactate dehydrogenase activity compared to that by the pathogen and they reduced the caspase-3 activity in the epithelial cells from the hind intestine, to which the pathogens adhered the most. Thus it could be concluded that the adhesion of the candidate probiotics is segment-specific and their interference with the adhesion of pathogens is dependent on both source of the epithelial cells and the mechanism adopted by the isolates. This information is novel in the case of fish and the manner in which potential probiotic organisms interfere with the pathogen adhesion provides supportive information for disease control.