The Rutaceae is an aromatic family of plants confined to the Fynbos biome in South Africa. This family is represented by a number of genera e.g. Agathosma, Adenandra, Coleonema, Vepris etc. all containing a number of species which have been used for centuries in traditional healing. Although many of these species have been used for centuries in local healing rites the biological activity and phytochemistry are poorly recorded. Guided by both traditional use and chemotaxonomic criteria fourteen species were selected and collected from the wild. The leaves were hydrodistilled to extract the essential oils. The chemotypic variation was recorded by gas chromatography analysis (GC) and GC coupled to mass spectrometry. The oils were then subjected to antimicrobial activity against 8 bacteria and 4 fungi. The essential oil composition varied quantitatively and qualitatively within and between populations. The results from the disc diffusion assay revealed that the essential oil from all the plants were active against all organisms except Pseudomonas aeruginosa and Aspergillus niger. Coleonema pulchellum (A) was the most active in terms of the zones of inhibition observed, particularly for that of Enterococcus faecalis. Minimum inhibitory concentrations (MIC) were performed on the seven most active sample specimens. None of the essential oils showed a clear MIC for Escherichia coli. MIC values for Staphylococcus aereus ranged from 8 mg/ml for Coleonema pulchellum (A) to 32 mg/ml for Acmadenia sheilae. The results for Enterococcus faecalis were more promising across the seven samples tested. All except Adenandra villosa and Coleonema calicynum had MICs of 8 mg/ml. It was decided to explore whether there were any differences in the MIC values with different solvents as a base to explore solubility. In this case acetone and dimethylsulfoxide acid (DMSO) were used separately. The MICs for the acetone solvent method compared to the DMSO solvent method, differed substantially with the exception of Escherichia coli.
In conclusion, the chemical profiles varied substantially within and between the species and the oils had a moderate to poor level of activity.
Principal supervisor: Prof AM Viljoen
Co-supervisor: Dr SF van Vuuren (WITS)