The Effect of Zataria multiflora Boiss. and Rosmarinus officinalis Essential Oil on Streptococcus iniae Isolated from Rainbow Trout Farms

The aim of this study was to investigate serotypes and bacterial capsule presence of Streptococcus iniae starins، the cause of streptococcosis in rainbow trout farms of Iran. The study also aimed to identify the minimum inhibitory concentrations (MICs) of Zataria multiflora and Rosmarinus officinalis essential oil against these strains and to assess the growth behavior of them. The results showed، most strains from rainbow trout farms were serotype I and all serotypes had complete bacterial capsule. The MIC of Z. multiflora to Streptococcus iniae serotype I and serotype II was 0. 06 µl/ml and the minimum bactericidal concentrations (MBCs) were 0. 5 and 0. 12-0. 25 µl/ml. minimum inhibitory concentrations of R. officinalis to serotype I and II were in range 0. 12 to 0. 25 µl/ml and 0. 12 µl/ml، respectively. MBCs of R. officinalis against serotype I and II were >1 µl/ml and 0. 5-1 µl/ml According to disk diffusion assay results، antimicrobial activity of Z. multiflora essential oil is significantly higher than R. officinalis. The growth of strains was reduced by increasing essential oils concentration. Our results suggested that Z. multiflora and R. officinalis essential oils could be effective for the inhibition of streptococcosis in rainbow trout farms.