Abstract
The antimicrobial activity of 35 indigenous South African Helichrysum species was determined against six microorganisms. Seven of the 36 chloroform:methanol (1:1) extracts (leaf and stem extracts for all plants and an additional flower extract for H. rugulosum) exhibited minimum inhibitory concentration (MIC) values lower than 0.1 mg/ml against Bacillus cereus and/or Staphylococcus aureus. The in vitro cytotoxicity [against transformed human kidney epithelial (Graham) cells, MCF-7 breast adenocarcinoma and SF-268 glioblastoma cells] of these extracts was also determined at a concentration of 0.1 mg/ml using the sulforhodamine B (SRB) assay. For seven species less than 25% growth was observed for the Graham and MCF-7 cell lines at the test concentration.
Highlights
Helichrysum species are often used to treat conditions associated with infections of the skin and the respiratory and gastro-intestinal tracts
The IC50 value of 172.01 μg/ml reported in the cytotoxicity assay was lower than the minimum inhibitory concentration (MIC) values (313 μg/ml) reported for seven of the screened microorganisms, indicating that cell growth may be inhibited at the concentrations required to inhibit pathogen growth
H. foetidum is used to treat festering sores while H. nudifolium is often used as wound dressing (Lourens et al, 2008 and references therein)
Summary
Helichrysum species are often used to treat conditions associated with infections of the skin and the respiratory and gastro-intestinal tracts. There are several reports on the antimicrobial activities of Helichrysum extracts, comparative toxicity values are often not available (Drewes and van Vuuren, 2008; Drewes et al, 2006; Lourens et al, 2004; Mathekga and Meyer, 1998). In a study by Van Vuuren et al (2006), the antimicrobial activity of an acetone extract of H. cymosum was determined against ten pathogens and toxicity determined against transformed human kidney epithelial cells. Heyman and Meyer (2009) investigated the cytotoxicity of 12 Helichrysum species and reported IC50 values ranging from b3.125 μg/ ml to 277 μg/ml, while a dichloromethane extract of H. nudifolium roots caused total growth inhibition of three cancer cell lines at concentrations below 34 μg/ml (Fouche et al, 2008). An aqueous extract of H. aureonitens did not exhibit any cytotoxic effects at a concentration as high as 8.44 mg/ml against HF cells (Meyer et al, 1996)
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