Characterization of the properties of human- and dairy-derived probiotics for prevention of infectious diseases in fish

The present study aimed to investigate the potential probiotic properties o f six lactic acid bacteria (LAB) intended for human use, Lactobacillus rham nosus ATCC 53103, Lactobacillus casei Shirota, Lactobacillus bulgaricus, L, rhamnosus LC 705, Bifidobacterium lactis Bb12, and Lactobacillus johnsonii La1, and one for animal use, Enterococcus faecium Tehobak for use as a fis h probiotic, The strains for human use were specifically chosen since they are known to be safe for human use, which is of major importance because th e fish are meant for human consumption. The selection was carried out by fi ve different methods: mucosal adhesion, mucosal penetration, inhibition of pathogen growth and adhesion, and resistance to fish bile, The adhesion abi lities of the seven LAB and three fish pathogens, Vibrio anguillarum, Aerom onas salmonicida, and Flavobacterium psychrophilum, were determined to mucu s from five different sites on the surface or in the gut of rainbow trout. Five of the tested LAB strains showed considerable adhesion to different fi sh mucus types (14 to 26% of the added bacteria). Despite their adhesive ch aracter, the LAB strains were not able to inhibit the mucus binding of A, s almonicida, Coculture experiments showed significant inhibition of growth o f A. salmonicida, which was mediated by competition for nutrients rather th an secretion of inhibitory substances by the probiotic bacteria as measured in spent culture liquid. All LAB except L, casei Shirota showed tolerance against fish bile. L, rhamnosus ATCC 53103 and L. bulgaricus were found to penetrate fish mucus better than other probiotic bacteria. Based on bile re sistance, mucus adhesion, mucus penetration, and suppression of fish pathog en growth, L. rhamnosus ATCC 53103 and L, bulgaricus can be considered for future in vivo challenge studies in fish as a novel and safe treatment in a quaculture.