Evaluation of the chemical composition and in vitro antimicrobial activity of Rosmarinus officinalis, Zataria multiflora, Anethum graveolens and Eucalyptus globulus against Streptococcus iniae; the cause of zoonotic disease in farmed fish

There is a growing interest of industry to replace synthetic chemicals by natural products with bioactive properties from plant origin. The purpose of this study was to elucidate the factors affecting antimicrobial effectiveness of essential oils Rosmarinus officinalis, Zataria multiflora, Anethum graveolens and Eucalyptus globulus against food spoilage and pathogenic bacteria, Streptococcus iniae; the cause of zoonotic streptococcosis in fish. Food conservation is based on an intermittent search for foods with a high nutritional quality and microbial stability and it has been reached by the control of the growth / survival of spoiling and pathogen foodborne microorganisms. Based on several reports, fish streptococcosis is currently considered as one of the main limiting factors in the aquaculture industry, due to the significant economic losses (annually more than $150 million) that these infections cause in different cultured fresh and seawater fish species worldwide. The sensitivity of S. iniae to antibacterial activity of the essential oils was determined using well diffusion assays and paper disc diffusion method. The ranges of minimum inhibitory concentration (MIC) of the oils and extracts were 3.9–250 and 7.8- 500 µg/ml and the ranges of minimum bactericidal concentration (MBC) values for the oils and extracts were found to be in the range of 7.8-250 and 15.6-500 µg/ml, respectively. The essential oils exhibited antibacterial activity against S. iniae. The essential oil of rosemary showed the strongest antimicrobial activity.