ANTIBACTERIAL ABILITIES OF INTESTINAL BACTERIA IN FRESH-WATER CULTURED FISH

Intestinal bacteria isolated from seven freshwater cultured fish were examined for their antibacterial ability against 18 target strains, in cluding members of the genus Aeromonas and human pathogenic bacteria, using a double-layer method. A total of 304 isolates, including aerobi c and anaerobic bacteria, were classified into 18 taxonomic groups, Al l fish species harbored intestinal bacteria with antibacterial abiliti es. An average of 3.2% of tested strains exhibited antibacterial activ ity against 18 different species, including 12 Aeromonas species and p athogenic bacteria, but the activity varied with fish species, and tax onomic groups and strains of tested bacteria. All taxonomic groups tes ted, except for Acinetobacter spp., coryneforms and Staphylococcus spp ., contained strains exhibiting antibacterial activity. In particular, 7-12 target strains were inhibited by strains of Aeromonas caviae, A. hydrophila, Pseudomonas spp. and Clostridium spp. These results sugge st that the antibacterial ability of intestinal bacteria may protect h ost fish against pathogenic bacteria, to some extent.