Nima Shiry - Division of Aquatic Animal Health, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran;
Siyavash Soltanian - Division of Aquatic Animal Health, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran;
Mostafa Akhlaghi - Division of Aquatic Animal Health, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran;

Introduction and Objectives: The present study was intended to assessing the in vitro efficacy of some used antibiotics in aquaculture for inhibiting Lactococcus garvieae isolated from the reared rainbow trout (Oncorhynchus mykiss) in Fars Province. Materials and Methods: For this purpose, the antibiotic susceptibility test (AST) was performed by disk diffusion on the Fars isolates, which previously were identified and reported. Then, the minimum inhibitory/bacteriocidal concentration (MIC & MBC) were determined by microdilution methods via reading the opacity degree of each dilution (by microplate reader) and recultivating them on plates. Results: According to findings, the isolated Lactococcus garvieae from the diseased fish of Fars province was susceptible to enrofloxacin (ENR), erythromycin (E) and florfenicol (FFC). In general, this bacterial pathogen showed resistance to 54.5% of the studied antibiotics. Regarding results, MIC and MBC of FFC for the assessed bacteria were recorded 1.2 and 5 μg/ml, respectively. Conclusion: It seems that for treatment and control of lactococcosis in fish, use of FDA-approved antibiotic (FFC), would be more efficient. As if, fortunately, based on evidence, FFC is still effective on both pathogen species in Fars Province and other parts of the country.

Minimum inhibitory concentration (MIC), Minimum bacteriocidal concnetration (MBC), Rainbow trout (Oncorhynchus mykiss), Lactococcus garvieae, Florfenicol (FFC).