###### Abstract  
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. Acanthamoeba polyphaga; Acanthamoeba keratitis (AK); essential oils; _Melaleuca alternifolia_ Cheel (tea tree); _Eucalyptus globulus_ Labill _Academic Editor: [PERSON]_  
11 February  
The main disease caused by _Acanthamoeba_, AK, is a serious, painful eye infection that, if not diagnosed and treated early, can cause corneal perforation and fusion [10]. GAE is a rare but almost always fatal central nervous system infection affecting debilitated or immunocompromised individuals [11], although cases have been reported in apparently healthy patients. This rare central nervous system disease is highly fatal, with a mortality rate greater than 90%, leading to death within 1-2 months of symptom onset due to increased intracranial pressure. Between 1990 and 2020, 75 cases of _Acanthamoeba_ spp. GAE have been described worldwide [12]. Other rare pathological conditions are cutaneous acanthamoebaisis (CA) [13] and _Acanthamoeba_ pneumonia (AP), mainly observed in patients with AIDS and in patients with a low immune response, respectively. From 1990 to 2020, 19 cases of AP or similar lung infections were related to _Acanthamoeba_ spp., mainly in the USA, but similar events have also been observed in Europe and Eastern countries [14]. As previously mentioned, the number of infections caused by _Acanthamoeba_ is very high, resulting in an incidence of 23,561 annual cases, as reported in a recent study that collected data from 20 countries [15]. Risk factors for AK vary between developing and developed countries. In the latter, most AK cases (86%) are related to contact lens use (inadequate disinfection of the lens or insufficient efficacy of the solution), while in developing countries, trauma remains the main risk factor (27%). The current AK treatment protocol consists of topical agents (chlororexiidine, polyhexamethylene, and antifungal drugs); however, due to the ability to form cysts, the biological stage of the pathogen is particularly difficult to treat due to unfavourable environmental conditions and the emergence of drug-resistant parasites; alternative approaches with tolerable side effects are urgently needed. Despite the significant progress that has been made in identifying new therapeutic agents that are active against _Acanthamoeba_ infections [16], to date, there are no highly effective and low-toxicity anti-amoebic drugs available. Recently, in fields including antiparasitics, the interest of researchers has focused on alternative therapeutics from herbal sources. Many natural compounds are widely studied for numerous biological activities, including the ability to antagonize pathogens of public health concern, including protozoan disease agents such as amoebae [17,18].