Antimicrobial activities of selected essential oils against Fusarium oxysporum isolates and their biofilms

• Ten essential oils were tested for their ability to control biofilm formation by Fusarium.
• Clove and thyme oil as well as citral, eugenol and thymol exhibited the highest antimicrobial activity.
• Clove and thyme oils totally inhibited the biofilm formation on soft contact lenses at 50 μL/L.

Fusarium infections, such as keratitis, are becoming increasingly difficult to control due to the build-up of resistance of fungi towards conventional antibiotics. Resistance is further enhanced by their ability to form fungal biofilms. Poor storage conditions and inadequate cleaning of contact lenses often lead to corneal infections. The solution to problems associated with contamination and resistance to antimicrobials could lie in the discovery of new, affordable, efficacious antimicrobial compounds. The purpose of this study was to evaluate the antifungal and antibiofilm properties of selected essential oils. The plant-based essential oils were evaluated for in vitro antifungal activity against Fusarium spp. using the Toxic Medium Assay (TMA) for preliminary screening. Clove and thyme oils, as well as pure citral, eugenol and thymol at 500 μL/L, exhibited the highest antimicrobial activity against Fusarium isolates. Antibiofilm capacity was investigated using soft contact lenses as substrate, while confocal laser scanning microscopy (CLSM) was used for visual observation of biofilm architecture. Although severe damage to the lens was observed when the essential oils were applied at 500 μL/L, no visible alteration of the contact lenses was detected at 50 μL/L and therefore the antibiofilm property of thyme and clove EOs was evaluated at this concentration. Clove and thyme oils prevented cell attachment, biofilm development and caused total inhibition of biofilm formation on soft contact lenses. The use of diluted clove and thyme oils could therefore be an option to prevent biofilm formation of soft contact lenses.

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