This study was performed to evaluate the minimum inhibitory concentration (MIC) of some essential oils against pathogenic bacteria strains in aquaculture. This in vitro trial was carried out by a micro dilution assay using liquid cultures in 96-well microplates. Eleven (11) essential oils were screened against three pathogenic bacteria including Aeromonas salmonicida salmonicida , Vibrio harveyi , Flavobacterium psychrophylum . Regulatory issue, environmental concerns and chemistry expertise were considered for the selection of screened ingredients.
Results showed that synthetic cinnamaldehyde (62.5-125 mg. L-1), synthetic thymol (62.5-125 mg. L-1 ) and natural oregano essential oil (125-250 mg. L-1) had the lowest MIC against these three strains followed by natural tea tree and eucalyptus essential oils. From all strains tested, A. salmonicida salmonicida is less sensitive to active phytogenics except for synthetic thymol and cinnamaldehyde and natural oregano EO. Moreover, these three active phytogenics showed the highest antibacterial activity against all studied strains. From all active phytogenics, natural lemon and pine EOs revealed the lowest a ntibacterial activity with the highest MIC against three bacterial strains (4000-16000 mg. L-1) . Natural tea tree, lavender, eucalyptus, garlic and caraway Eos showed relative inhibition activity following bacteria strains. Overall, phenolic and aldehyde compounds tested were the most antibacterial against these three strains.
From these preliminary data, it might be interesting to combin e relevant active ingredients for further in vitro and potentially in vivo trials against the se pathogenic bacteria strains.