Andrew Marston

Antimicrobial activity of southern African medicinal plants with dermatological relevance: From an ethnopharmacological screening approach, to combination studies and the isolation of a bioactive compound.

ETHNOPHARMACOLOGICAL RELEVANCE Ethnobotanical reports on more than 100 southern African medicinal plants with dermatological relevance have been highlighted, yet there is still limited scientific data to support claims for their antimicrobial effectiveness against skin pathogens. Guided by ethnobotanical data, this paper explores the antimicrobial efficacies of southern African medicinal plants used to treat skin ailments. AIM OF THE STUDY To investigate the antimicrobial properties of southern African medicinal plants against dermatologically relevant pathogens. The study also aimed at providing a scientific rationale for the traditional use of plant combinations to treat skin diseases and the isolation of the bio-active compound from the most active species, Aristea ecklonii (Iridaceae). MATERIALS AND METHODS Organic and aqueous extracts (132) were prepared from 47 plant species and screened for antimicrobial properties against dermatologically relevant pathogens using the micro-titre plate dilution method. Four different plant combinations were investigated for interactive properties and the sum of the fractional inhibitory concentration (ƩFIC) calculated. Isobolograms were used to further investigate the antimicrobial interactive properties of Pentanisia prunelloides combined with Elephantorrhiza elephantina at varied ratios. A bioactivity-guided fractionation process was adopted to fractionate the organic leaf extract of Aristea ecklonii. RESULTS Plants demonstrating notable broad-spectrum activities (MIC values ≤1.00mg/ml) against the tested pathogens included extracts from Aristea ecklonii, Chenopodium ambrosioides, Diospyros mespiliformis, Elephantorrhiza elephantina, Eucalyptus camaldulensis, Gunnera perpensa, Harpephyllum caffrum, Hypericum perforatum, Melianthus comosus, Terminalia sericea and Warburgia salutaris. The organic extract of Elephantorrhiza elephantina, a plant reportedly used to treat acne vulgaris, demonstrated noteworthy antimicrobial activity (MIC value of 0.05mg/ml) against Propionibacterium acnes. Similarly, Diospyros mespiliformis reported for its traditional use to treat ringworm, also displayed noteworthy antimicrobial activity against Trichophyton mentagrophytes (MIC 0.10mg/ml) and Microsporum canis (MIC 0.50mg/ml). The aqueous root extracts of Pentanisia prunelloides combined (1:1) with Elephantorrhiza elephantina displayed synergistic interactions (ƩFIC values 0.31-0.38) against Staphylococcus aureus, gentamycin-methicillin resistant Staphylococcus aureus, Staphylococcus epidermidis and Candida albicans. Fractionation of Aristea ecklonii resulted in the isolation of the known bio-active compound, plumbagin, displaying noteworthy antimicrobial activity (MIC range between 2.00μg/ml and 16.00μg/ml). CONCLUSION Most of the plant extracts demonstrated pathogen specific antimicrobial effects with a few exhibiting broad-spectrum activities. Positive antimicrobial effects noted for plants such as Elephantorrhiza elephantina and Diospyros mespiliformis used for acne vulgaris and ringworm infections, respectively, give some validation to their reported traditiona l uses. Synergistic interactions noted for Pentanisia prunelloides combined with Elephantorrhiza elephantina validate an enhanced antimicrobial effect when used in combination. Noteworthy antimicrobial activities (MIC range between 2.00μg/ml and 16.00μg/ml) were observed for plumbagin isolated from Aristea ecklonii.

Biologische und chemische Screening-Methoden für Pflanzenextrakte

Biologisches und chemisches Screening gehort heute zu den taglich verwendeten Routinearbeiten des Phytochemikers bei der Suche nach neuen bioaktiven Naturstoffen. Das folgende Kapitel beschreibt das einfache und schnelle biologische Screening von Extrakten und daraus isolierten Reinsubstanzen. Beispiele sind DC-Bioautographie und HPLC-online-Bioassay zur Auffindung von antimikrobiell, antimykotisch und antioxidativ wirkenden Naturstoffen sowie zur Entdeckung von Radikalfangern und neuen Enzyminhibitoren. Zum Nachweis von Pflanzeninhaltsstoffen sowie zur Trennung von komplexen Naturstoffgemischen in Extrakten werden heute in erster Linie chromatographische Methoden in Kombination mit spektrometrischen [Massenspektrometrie(MS)] bzw. spektroskopischen [UV-Dioden-Array-Detektion, Kernresonanzspektroskopie (NMR)] Methoden verwendet. Die am meisten verwendeten Kopplungen der HPLC (LC) mit UV, MS und NMR werden naher beschrieben und anhand neuer Beispiele aus der Naturstoffforschung erlautert.