Effect of tobramycin supplementation to medium on isolation of Flavobacterium psychrophilum from ayu Plecoglossus altivelis

The effect of the addition of the aminoglycoside antibiotic tobramycin to the culture medium on selective isolation of Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease, from ayu Plecoglossus altivelis was examined. The minimum inhibitory concentrations of tobramycin against all 37 strains of F. psychrophilum tested were more than 6.3 micro g/ mL. The addition of tobramycin to medium at a concentration of 5 micro g/mL was a better method for the isolation of F. psychrophilum, because the overgrowth of other bacteria was inhibited and the isolation rates of F. psychrophilum were improved. Especially, the use of tobramycin-supplemented medium could be effective in the examination of the external organs of carrier fish, in which viable bacterial counts of F. psychrophilum are lower than those of other bacteria.