Plants used to treat skin diseases in northern Maputaland, South Africa: antimicrobial activity and in vitro permeability studies

Context: Ethnobotanical claims of medicinal plants used in northern Maputaland are limited.Objectives To establish scientific validity for a selection of the plants used in Maputaland to treat skin diseases.Materials and methods: Aqueous and dichloromethane-methanol extracts were prepared from 37 plant species which were collected from four rural communities in Maputaland. Antimicrobial screening was performed on extracts against 12 dermatological relevant pathogens using the micro-titre plate dilution assay. Their combined effect was evaluated by determining the sum of the fractional inhibitory concentrations (sigma FICs). Chemical analysis was undertaken using reverse-phase high-performance liquid chromatography (RP-HPLC) and investigated in vitro across excised intact porcine skin using the ILC07 automated system.Results: The organic extract of Garcinia livingstonei T. Anderson (Clusiaceae) was found to be the most antimicrobially active displaying an average broad-spectrum MIC value of 270g/mL. The combination of Sclerocarya birrea (A. Rich.) Hotsch. (Anacardaceae) with Syzygium cordatum Hochst. ex C. Krauss (Myrtaceae) displayed synergistic effects. The four antimicrobially active organic extracts were found to possess mainly anthraquinones, flavonoids, tannins and saponins. The organic extracts of Kigelia africana (Lam.) Benth. (Bignoniaceae) and S. cordatum were found to have more compounds capable of permeating intact skin after 10min of exposure.Conclusion: More than 80% of the organic extracts tested displayed a correlation between the antimicrobial efficacy and the reported traditional uses of the plants. Furthermore, the traditional use of topically applied plant preparations is validated as some compounds from the active plants are capable of permeating the skin in vitro.