Biological activity of 16 South African plants with potential efficacy against dermatophytes

Dermatophytosis caused by Microsporum canis is one of the most frequent skin diseases in animals and humans. Few antifungal agents are available and against some of them there is emergence of drug resistance. There is urgent need for new therapeutic agents and medicinal plants represent a good source for such agents. The aim of this study is to investigate South African plants used in ethnopharmacology as well as other related plant species that could be used to combat dermatophytosis. The minimum inhibitory activity of acetone leaf extracts of 16 South African plant species was determined using a serial microdilution method [1]. The diversity of antifungal compounds was determined by bioautography [2]. The activity against Aspergillus fumigatus, A. niger, Candida albicans, Cryptococcus neoformans, Microsporum canis and M. gypseum were determined. The cytotoxicity of the extracts was determined by measuring the viability of Vero African Green monkey kidney cells and bovine dermal cells using the MTT assay. In addition, the antioxidant activity of extracts was also determined by DPPH and ABTS radical scavenging assays. The crude extracts had antifungal activity with MICs that varied from 65 – 2080 µg/mL. The cytotoxicity LC₅₀ ranged from 90 – 670 µg/mL for Vero cells and 90 – 500 µg/mL for the bovine dermal cells. The IC₅₀ using the DPPH and the ABTS scavenging activity assay varied from 100 – 3390 µg/mL and 220 – 1440 µg/mL respectively. Bioautography showed several active compounds for nine of the investigated plants. The crude extracts of Terminalia gazensis and Leucosidea sericea had high activity and were fractionated for further evaluation. Hexane and chloroform fractions had good activity (MIC = 32 µg/mL). The polar fractions (ethyl acetate, butanol and water) had moderate activity against dermatophytes. These preliminary investigations highlight the potential of these two plants, and further studies are required in order to identify the active compounds.

Acknowledgements: The EUROSA project (Erasmus Mundus Action 2 Partnerships scholarship programme, funded by the European Commission) for making the collaboration between the University of Bologna and the University of Pretoria possible.

Keywords: Plant extracts, antifungal activity, cytotoxicity, antioxidant activity, Leucosidea sericea, Terminalia gazensis, dermatophytes.

References:

[1] Eloff JN. A sensitive and quick microplate method to determine the minimal inhibitory concentration of plant extracts for bacteria. Planta Med 1998; 64: 711 – 714

[2] Masoko P, Eloff JN. The diversity of antifungal compounds of six South African Terminalia species (Combretaceae) determined by bioautography. Afr J Biotechnol 2005; 4: 1425 – 1431