THE MINIMUM INHIBITORY CONCENTRATION OF ANTIBIOTICS AGAINST NOCARDIA SERIOLAE ISOLATION FROM DISEASED FISH IN TAIWAN

Abstract

Nocardia seriolae infections pose a significant economic threat to Taiwan’s aquaculture. It is therefore important to find the most effective antibiotics to treat these infections. However, a standardized method to determine the most suitable minimal inhibitory concentration (MIC) values of antibiotics againist N. seriolae has not yet to be agreed. This study tested 7 antibiotics on 80 N. seriolae isolates, using the disk diffusion and broth diffusion methods described by Alderman and Smith to find their MIC values. All the isolates were found to be sensitive to trimethoprim and oxytetracycline, which showed that these drugs could treat nocardiosis in fish. Among the seven drugs tested, amoxicillin was found to have very high MIC90 value, which was [Formula: see text]128[Formula: see text][Formula: see text]g/mL and flumequine had the highest MIC50 value, which was 51.06[Formula: see text][Formula: see text]g/mL. MIC50 and MIC90 values were very low in erythromycin, which was [Formula: see text]0.12 and 0.41[Formula: see text][Formula: see text]g/mL, respectively. N. seriolae isolates were sensitive to florfenicol (98.8%), erythromycin (97.5%), thiamphenicol (68.8%), amoxicillin (8.8%) and flumequin (0%), separately. This study has found that oxytetracycline, trimethoprim or erythromycin, florfenicol, thiamphenicol are good drugs to treat N. seriolae infection in fish.