Melaleuca alternifolia Cheel (Tea Tree) and Eucalyptus globulus Labill. Essential Oils’ Effectiveness Against an Acanthamoeba polyphaga Strain Responsible for Human Keratitis

Among free-living amoebae (FLA), Acanthamoeba polyphaga is an important causal agent of Acanthamoeba keratitis (AK), a severe and potentially sight-threatening condition. The present study evaluated the “in vitro” efficiency of Melaleuca alternifolia Cheel (tea tree) (tea tree oil—TTO) and Eucalyptus globulus Labill. (Eucalyptus essential oil—EEO) essential oils against an Acanthamoeba strain isolated from human keratitis. The Minimum Inhibitory Concentration (MIC) of the EOs and the Fractional Inhibitory Concentration (FIC) Index were used to evaluate the decrease in viable cells of Acanthamoeba over time and at different concentrations of EOs, used alone or in association. A relevant amoebicidal effect emerged during the first hours of exposure for both compounds, and TTO was the most effective. The TTO/EEO association clearly indicated a synergistic effect in all tests, and at 2 days post-treatment, no viable A. polyphaga cells were observed at all tested concentrations. In conclusion, the potential therapeutic use of EOs represents a promising therapeutic strategy for the treatment of AK.