Observations with rapid micro-colony assay to screen antifungal activity of Origanum vulgare L., Zostera marina L. and Centaurea ensiformis P.H. Davis extracts

Currently, synthetic antifungal drugs are the main option to treat fungal pathogens e.g. Candida albicans C.P. Robin in humans. In turn, fungal pathogens generate resistance upon clinical treatments. Moreoever, human pathogen Aspergillus fumigatus Fresenius isolates were suggested to generate resistance to azole antifungal drugs due to the exposure to control plant fungal diseases in the field conditions. Thus, antifungal agents derived from natural products have vital importance for sustainable control of fungal infections. Plants accumulate plethora of antimicrobial compounds e.g. alkaloids, iridoids, flavonoids and lignans which could target the different sites e.g. cell wall formation and protein biosynthesis in fungi. Alternative antifungal agent screening methods should be assayed for faster and sound detection. Previously, the micro-colony method i.e. the measurement of the early fungal development using microscopy was developed to screen dose response in the filamentous fungal species Fusicladium effusum Winter. The micro-colony assay was tested to detect dose response in Candida albicans (ATCC 10231), A. fumigatus, Fusarium oxysporum Schlecht. emend. Snyder&Hansen on Origanum vulgare L. (Lamiaceae), Zostera marina L. (Zosteraceae) and Centaurea ensiformis P.H. Davis (Asteraceae) extracts and reference fungicide flucanozole. The O. vulgare essential oil was toxic in all testing concentrations, but Z. marina methanol extracts were ineffective. C. ensiformis methanol extract showed slight growth inhibition on C. albicans and A. fumigatus. This method provides a dose response in 24 hours. Additionally, method could be used to evaluate topical treatments, pigmentation and filament morphology in fungi.

Keywords: Antifungal drugs, natural products, Candida albicans, Aspergillus fumigatus, Fusarium oxysporum, dose response in fungi, rapid detection, Centaurea spp., Centaurea ensiformis, Zostera marina

Acknowledgement: Authors thank Assoc. Prof. Dr. Sibel Konyalıoğlu for the utilization of the microscopy facility.