Validating the traditional use of medicinal plants in Maputaland to treat skin diseases
Medicinal plants are widely used as a source of primary health care by the rural inhabitants of northern Maputaland, KwaZulu-Natal, South Africa. A recent (2013) ethnobotanical study conducted specifically in four rural communities of Maputaland (Mabibi, Mbazwana, Mseleni and Tshongwe) revealed that lay people use plants individually and in combinations to treat various skin diseases. Based on the extensive use and lack of scientific evidence, the current study established the scientific validity of the documented plants by investigating their antimicrobial effects (individually and combinations) against dermatological relevant pathogens. The chemical profiles of the most antimicrobial active plants and the chemical compounds capable of permeating the skin were also investigated. Aqueous and organic (1:1 dichloromethane-methanol) extracts were prepared from plants collected from Maputaland. Antimicrobial screening (micro-titre plate dilution assay) was performed on bacteria and fungi known to cause skin infections. Efficacy of the plants used in combinations was evaluated using the sum of Fractional Inhibitory Concentration (ΣFIC). The combinations that displayed mostly synergistic interactions when combined in equal ratios were studied further in varied ratio studies to determine possible interactions when combined in various mixtures. Qualitative chemical analysis of the most active plant extracts (aqueous and organic extracts) was performed using phytochemical screening tests, UV-Vis spectrometry and a reverse-phase High Performance Liquid Chromatography (RP-HPLC). The permeation of compounds through the skin was investigated in vitro on intact porcine skin using the ILC07 automated system and qualitatively analysed through RP-HPLC prior and after the permeation assay. When investigated individually, all the organic extracts proved to be active (MIC<1.00 mg/ml) on at least four of the 12 test pathogens. Other plant species such as Anonna senegalensis, Elephantorrhiza elephantina, Garcinia livingstonei, Kigelia africana, Ozoroa engleri, Parinari capensis subsp. capensis, Schotia brachypetala, Sclerocarya birrea, Syzygium cordatum, Terminalia sericea, and Zanthoxylum capense demonstrated broad-spectrum activities giving the mean MIC values<1.00 mg/ml. The organic extract of G. livingstonei was found to be the most antimicrobial active extract displaying a mean MIC of 0.27 mg/ml. It was worth noting that plants such as A. senegalensis, O. Engleri and P. capensis subsp. capensis investigated for the first time against skin pathogens demonstrated broad-spectrum antimicrobial effects. The efficacy of the aqueous extracts was mostly moderate with 66% of the extracts exhibiting pathogen specific noteworthy effects (MIC<1.00 mg/ml). Staphylococcus aureus proved to be the least susceptible pathogen while T. mentagrophytes was the most susceptible with 98% of organic extracts displaying noteworthy effects. When the ΣFICs of plants combined in equal ratios was calculated, the combinations were found to display synergistic (27%), additive (31%), non-interactive (25%) and antagonistic (17%) interactions. The most synergistic effect was observed for the organic extract combination of Hypoxis hemerocallidea and Solanum rigescens against Staphylococcus epidermidis giving the ΣFIC value of 0.04. In varied ratio studies, the combinations combined in various mixtures mostly displayed additive interactions. The organic extract combination of H. hemerocallidea and S. rigescens displayed synergistic interaction regardless of the ratios when tested against S. epidermidis. All the antimicrobially active topically applied plants (aqueous and organic extracts) phytochemically analyzed possessed anthraquinones, flavonoids, tannins and saponins. The UV-Vis spectra of all the tested extracts gave an initial absorption peak at 212-218 nm which might be characteristic of saponins. These compounds were detected in all the extracts. The second absorption maxima occurred between 250-268 for all the extracts and may confirm the presence of flavonoids that are usually absorbed between a range of 250 and 300 nm. From the in vitro permeation assay, it was observed that several compounds present in the crude extracts were able to diffuse across intact porcine skin. Both aqueous and organic extracts of K. africana proved to have more compounds capable of permeating the skin than the other tested extracts. Overall, more than 80% of plants tested displayed a correlation between antimicrobial efficacy and the diseases they were reported to treat. Interesting antimicrobial effects were also noted from the plant combinations. Some compounds present in the extracts are capable of permeating the intact skin in vitro. Thus, the current investigation supported the ethnobotanical claims of the documented plants.
A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the degree of Master of Science October, 2015