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Mabona, U., Viljoen, A.M., Shikanga, E., Marston, A., Van Vuuren, S.F. 2013. Antimicrobial activity of southern African medicinal plants with dermatological relevance: From an ethnopharmcological screening approach, to combination studies and the isolation of a bioactive compound. Journal of Ethnopharmacology 148: 45-55.
Ethnopharmacological relevance: Guided by ethnobotanical data, this paper explores theantimicrobial efficacies of southern African medicinal plants used to treat skin ailments.
Aim of the study: To investigate the antimicrobial properties of southern African medicinalplants against dermatologically relevant pathogens. The study also aimed at providing ascientific rationale for the traditional use of plant combinations to treat skin diseases and theisolation of the bioactive compound from the most active species, Aristea ecklonii (Iridaceae).
Materials and methods: Organic and aqueous extracts (132) were prepared from 47 plantspecies and screened for antimicrobial properties using the micro-titre plate dilution method.Four different plant combinations were investigated for interactive properties and the sum ofthe fractional inhibitory concentration (Ʃ FIC) calculated. Isobolograms were used to furtherinvestigate the antimicrobial interactive properties of Pentanisia prunelloides combined withElephantorrhiza elephantina at varied ratios. A bioactivity-guided fractionation process wasadopted to fractionate the organic leaf extract of Aristea ecklonii.
Results: Many plants demonstrated notable broad-spectrum activities (MIC values ≤ 1.00mg/ml) against the tested pathogens. The organic extract of Elephantorrhiza elephantina, aplant reportedly used to treat acne vulgaris, demonstrated noteworthy antimicrobial activity(MIC value of 0.05 mg/ml) against Propionibacterium acnes. Similarly, Diospyros mespiliformis reported for its traditional use to treat ringworm, also displayed noteworthyantimicrobial activity against Trichophyton mentagrophytes (MIC 0.10 mg/ml) andMicrosporum canis (MIC 0.50 mg/ml). The aqueous root extracts of Pentanisia prunelloides combined (1:1) with Elephantorrhiza elephantina displayed synergistic interactions (Ʃ FICvalues 0.31-0.38) against some test organisms. Fractionation of Aristea ecklonii resulted inthe isolation of the known bioactive compound, plumbagin, displaying noteworthy antimicrobial activity (MIC range between 2.00-16.00 μg/ml).
Conclusion: Most of the plant extracts demonstrated pathogen specific antimicrobial effectswith a few exhibiting broad-spectrum activities. These give some validation to their reportedtraditional uses. Synergistic interactions noted for Pentanisia prunelloides combined with Elephantorrhiza elephantina validate an enhanced antimicrobial effect when used incombination. Noteworthy antimicrobial activities (MIC range between 2.00-16.00 μg/ml)were observed for plumbagin isolated from Aristea ecklonii.