Antibacterial activity of oregano (Origanum vulgare) essential oil, carvacrol and thymol against fish pathogenic bacteria isolated from cultured olive flounder (Paralichthys olivaceus)

In aquaculture industry, diseases of microbial origin are responsible for elevated mortality rates and decrease fish production with consequent economic losses worldwide. The crucial bacterial diseases of marine fish in Korea are edwardsiellosis caused by Edwardsiella tarda; streptococcosis caused by Streptococcus iniae, S. parauberis, and Lactococcus garvieae; and vibriosis caused by Vibrio harveyi, V. ichthyoenteri, and Photobacterium damselae, which have recently increased in cultured fish populations (Jee et al., 2014; Kim et al., 2015). They have been identified as the etiological agents responsible for the most common disease outbreaks of olive flounder (Paralichthys olivaceus) aquaculture in Korea (Nho et al., 2009). Antibiotics are widely used to prevent bacterial infections in fish. However, misuse of antibiotics leads to drug resistance and thereby to the reduced efficacy of the drugs (Wei and Wee, 2013). Therefore, it is essential to develop antibacterial treatments that are made from natural substances. Essential oils (EOs) are one kind of natural products which have been used with their aromatic, flavor, bactericidal, preservative and medicinal properties (Burt, 2004).