Objectives: There is increasing demand to develop antifungals to combat Madurella mycetomatis which has been recently added to the list of Neglected Tropical Diseases (NTDs) by the 69th World Health Assembly in May 2016 as one of the most neglected and aggressive fungal infections. Despite the number of the knowledge gaps associated with M. mycetomatis, the treatment remains the most challenging due to the resistance of this fungus almost to all currently available chemotherapeutic options. Therefore, there is an urgent need for novel approaches to overcome the resistance, biofilm formation and virulence associated with this stubborn fungus. To confront these challenges a systematic approach involving the screening of the essential oils (EOs) of a dozen taxonomically diverse medicinal plants belonging to six botanical families including: Burseraceae, Cyperaceae Euphorbiaceae Lamiaceae, Myrtaceae, and Poaceae coupled with hyphenated analysis by GC/MS was attempted. 

Methods: Dried plants (200 gram) of different morphological parts were subjected to hydrodistillation and their EOs were analyzed by gas chromatography-mass spectrometry (GC-MS). Each of these EOs was screened for their in vitro antifungal activity against ten M. mycetomatis employing an already established XTT assay.1. 
Itraconazole was used as positive control. The efficacy and toxicity of each of the oils was tested in vivo on Galleria mellonella larvae and monitored for 10 days. The results were subjected to analysis by the principle component analysis (PCA).   

Results: Ten out of 13 tested oils exhibited antifungal activity against M. mycetomatis isolates at MIC range (0.125-0.0039 %v/v) (Table 1).The EOs of Commiphora myrrh, Croton zambesicus, Cymbopogon citratus, and Commiphora erythraea exhibited the lowest MIC50 values when tested on the isolates of M. mycetomatis, whilst the EOs of Melaleuca alternifolia. Eucalyptus camaldulensis, and Mentha spicata showed the highest MIC50 values. Other EOs showed moderate antifungal activity in tested isolates. GC-MS analysis resulted in the identification of diverse monoterpenes and sesquiterpenrs associated with antifungal activity.  The results were subjected to chemometric analysis. The in vivo results consolidated the in vivo findings.  

Conclusion: Essential oils considered as potential sources of novel compounds acting in vitro as natural antifungal agents.

References:  Ahmed, A.O. et al. Antimicrobial Agents and Chemotherapy, 48 (7), 2742-46, 2004.  


Metabolomic approach to tap the potential of essential oils against Madurella mycetomatis – one of the most neglected fungal infections