Traditional medicine is widely used as a source of primary healthcare for more than 80% of the population of Swaziland. Traditional healers use various plants and combinations thereof to manage different ailments. In consultation with Swazi traditional healers, fifteen Swazi plants were selected on the basis of their ethnomedical history. These plants were collected from the Manzini region, extracted with dichloromethane/methanol (1:1) and screened for their antimicrobial, antimalarial and anti-oxidant activities and toxicity profiles. Ultra performance liquid chromatography and high performance thin layer chromatography (HPTLC) was performed to determine chemical profiles of the most active plant extracts. These chromatograms revealed the complexity of each plant extract and provided a fingerprint for each species studied.
Antimicrobial activity was determined using the minimum inhibitory concentrations assay against Staphylococcus aureus (ATCC 25923), S. epidermidis (ATCC 2223), Escherichia coli (ATCC 25922), Klebsiella pneumoniae (NCTC 9633) and Candida albicans (ATCC 10231). A number of the plant extracts (51.52%) displayed good antimicrobial activity with MIC values ranging from 0.0013 to 1.00 mg/ml, with S. epidermidis being the most susceptible. The fruit of Ozoroa sphaerocarpa (MIC value = 0.001 mg/ml) and the leaves of Syzygium cordatum (MIC value = 0.04 mg/ml) were the most active against this pathogen. The HPTLC-bioautography results showed a number of compounds within each extract, such as the fruit of O. sphaerocarpa and leaves of S. cordatum; that were responsible for the inhibitory activity against S. epidermidis, which correlated to the MIC results.
Breonadia salicina, S. cordatum and O. sphaerocarpa were reported to be used in combination for the traditional treatment of diarrhoea. A combination study was designed to determine their pharmacological interaction using E. coli as a test pathogen. A synergistic interaction was observed between S. cordatum and O. sphaerocarpa, as well as between S. cordatum and B. salicina. When the three plants were combined in a triple combination, a synergic interaction was observed, which supports the rationale by traditional healers to use these plants in combination for the treatment of diarrhoea.
The DPPH. (2,2-diphenyl-picryl-hydrazil) scavenging activity, ferrous metal chelating activity and inhibition of lipid peroxidation were correlated to the total phenolic and flavonoid content of the plant extracts. D. cinerea (leaves) was the most active free radical scavenger (IC50: 5.89 ± 0.39 µg/ml) as compared to ascorbic acid (IC50: 5.61 ± 1.13 µg/ml). The leaves of S. cordatum and fruit of Z. mucronata had the highest content of phenolics (806.10 ± 42.28 and 536.87 ± 36.76 mg GAE/g extract), respectively; whilst the bark of Terminalia phanerophlebia, fruit of O. sphaerocarpa, bark of S. cordatum, and bark of Trichilia emetica had the highest content of flavonoids in the range of 26.40 to 33.33 mg RE/g extract. An HPTLC method showed a number of compounds which were responsible for the free radical scavenging activity in each plant extract.
Antimalarial activity against the asexual stages of the 3D7 strain of Plasmodium falciparum was determined using the tritiated hypoxanthine incorporation assay. Whilst the toxicity profiles of the extracts were tested on human kidney epithelial cells using the tetrazolium-based MTT viability assay; as well as using the red blood cell lysis assay. Five of the extracts displayed in vitro antimalarial activity with IC50 values less than 20 µg/ml, namely T. phanerophlebia (leaves), Berkheya setifera (stem/root), Priva meyeri (whole plant), T. emetica (leaves) and B. salicina (bark). The five most active extracts did not cause red blood cell lysis at concentrations ten times greater than the IC50 values. Furthermore, these extracts were combined with quinine at different ratios and predominantly produced antagonistic interactions, highlighting the need for extreme caution when used together with clinical antimalarial drugs. The toxicity profile of the plant extracts on human kidney epithelial cells indicated that about 54.54% of the extracts were non-toxic, with IC50 values greater than 100 μg/ml.
In conclusion, this study has reported for the first time on the pharmacological properties of some species such as B. setifera and P. meyeri, which display the potential of Swazi flora in the search for new and novel compounds in therapeutic drug research.
Principal supervisor: Dr RL van Zyl (WITS)
Co-supervisor: Prof AM Viljoen (TUT)