In vitroantimicrobial effect of various commercial essential oils and their chemical constituents onAeromonas salmonicidasubsp.salmonicida

Aims This study aimed to evaluatein vitroefficacy of essential oils (EOs) and their compounds (EOCs) alone or in combination againstAeromonas salmonicidasubsp.salmonicida,the causative agent of furunculosis in salmonid fish. Methods and Results Antimicrobial activity of 13 EOs and 16 EOCs was investigated for fourA. salmonicidasubsp. salmonicidastrains using broth microdilution. The checkerboard assay was used to evaluate a putative synergy between the most efficient EOs and EOCs against the tested strains. Cinnamon bark, oregano, clove, and thyme oils and their major compounds cinnamaldehyde, eugenol, carvacrol and thymol showed the lower minimum inhibitory concentration and minimum bactericidal concentration values. The association of cinnamaldehyde and eugenol (V/V: 30%/70%) showed a synergistic activity against three tested strains. The combinations of cinnamon with oregano, clove or thyme EOs showed a neutral or additive activity against all the tested strains. Conclusions Cinnamon, oregano, clove and thyme oils and their major phytochemical compounds showed strong activities againstA. salmonicidasubsp.salmonicidastrains. Significance and Impact of the Study To reduce the use of antibiotics in aquaculture, phytochemicals such as cinnamaldehyde and eugenol can be tested alone or in combination inin vivostudies as functional feed alternatives.