THERAPEUTIC EFFECT OF FOSFOMYCIN ON EXPERIMENTALLY-INDUCED PSEUDOTUBERCULOSIS IN YELLOWTAIL

In vitro antibacterial activity of fosfomycin (FOM), a cell-wall synthesis inhibitor, was investigated against Pasteurella piscicida, the causative agent of pseudotuberculosis in yellowtail Seriola quinqueradiata. Minimum inhibitory concentrations (MIC) of FOM against 68 isolates of P. piscicida, including strains resistant to other antibiotics, ranged from 1.56 to 3.13 mug/ml. Bactericidal activity of FOM was evident at the MIC level. Therapeutic effect of FOM was studied in yellowtail experimentally infected with P. piscicida. The cumulative mortalities among infected fish after oral administration of FOM at doses of 0, 5, 10, 10, 30 and 40 mg/kg/day for 5 consecutive days from 1 h after infection were 60, 45, 45, 15, 5 and 0%, respectively. Based on the results obtained in this study, FOM may be a new therapeutic agent against pseudotuberculosis in yellowtail.