Helichrysum (Asteraceae) belongs to a large genus consisting of approximately 500 species of which 245 are indigenous to South Africa. Species of Helichrysum have been widely used in South Africa by the indigenous population to treat various ailments, including coughs, colds, fever, infections, headache, menstrual pain and in wound dressings. Medicinal uses of the plant are dependent on the local availability of the plant rather than on particular species. This group of plants is extensively utilised throughout South Africa, in traditional medicine and is commonly known as "imphepo”.
It has been postulated that the medicinal properties of this plant is related to the abundance of essential oils that are prevalent within the plant and the actual composition of the plant material. The anti-microbial activity of the essential oils and plant extracts are of interest due to its antiseptic and anti-microbial properties.
Guided by traditional and chemotaxonomic criteria, nine species of Helichrysum were selected. The essential oils were obtained through hydro-distillation and the plant extracts were prepared using acetone and methanol as solvents.
The essential oil composition was determined using GC/MS. The composition was dominated by the presence of monoterpenes such as α-pinene, 1,8 cineole and p-cymene. In the oils of Helichrysum felinum, monoterpenes were largely absent. Its profile consisted of sesquiterpenes in low concentrations with β-caryophyllene dominating.
The anti-microbial activity was determined by disc diffusion assays using the essential oils and the plant extracts, to identify which plant species had anti-microbial activity and the organisms that they were active against. The anti-microbial activity of the most active samples was measured using MIC.
The acetone and methanol extracts as well as the essential oils, exhibited activity against Gram-positive bacteria (S.aureus and B. cereus). Helichrysum dasyanthum exhibited the greatest activity against B.cereus that was confirmed by a 16 mg/ml MIC value in the micro-titre plate assay. The acetone extract of Helichrysum dasyanthum was the only extract that exhibited activity against all 3 of the fungal strains tested against. (Cryptococcus neoformans, 1 mm; Candida albicans, 3 mm; and Alternaria alternate, 2 mm). The essential oil of Helichrysum petiolare and Helichrysum felinum exhibited the most significant activity against the fungal strains in the disc diffusion assay (Candida albicans, 2mm).
It is evident that the anti-microbial activity in the Helichrysum species studied does support the basis for the indigenous use of this plant in traditional medicine for its anti-microbial properties. This study does warrant the need for greater investigation into the benefits of the anti-microbial activity of the Helichrysum species in South Africa.
Principal supervisor: Prof AM Viljoen
Co-supervisor: Dr SF van Vuuren (WITS)