Investigation of the biological activities of Siphonochilus aethiopicus and the effect of seasonal senescence

Abstract

Siphonochilus aethiopicus (Schweinf.) B.L. Burtt (Zingiberaceae), commonly known as wild ginger, is one of the most important and threatened medicinal plants in South Africa. A study of the pharmacological properties of S. aethiopicus and the effect of seasonal senescence on antibacterial and anti-inflammatory properties was undertaken. Water, ethanol and ethyl acetate extracts were prepared from the leaves, rhizomes and roots of S. aethiopicus plants. The extracts were tested in a variety of pharmacological assays. Results for the general screening showed antibacterial and anti-inflammatory activity. Some cytotoxicity was observed with the aqueous extracts of the rhizome. However, no significant activity against the herpes simplex virus types 1 and 2, the influenza A virus, and in the anthelmintic, antischistosomal and biochemical induction assays were observed. In the microdilution antibacterial assay, no inhibitory activity against the test bacteria was detected with the aqueous extracts. The ethanol and ethyl acetate extracts tested showed greater antibacterial activity at minimal inhibitory concentrations ranging from 0.78 to 3.13 mg ml − 1 against the Gram-positive bacteria ( Bacillus subtilis , Staphylococcus aureus ) than the Gram-negative bacteria ( Escherichia coli , Klebsiella pneumoniae ). Little difference was observed between the ethanol and ethyl acetate extracts, or between the different plant parts. Ethanol extracts were prepared from the different plant parts before and after seasonal senescence, and tested for antibacterial and anti-inflammatory activity. There appeared to be a loss of antibacterial activity in the leaves with senescence, concomitant with an increase of activity in the alpha-roots. In the cyclooxygenase-1 assay, the aqueous extracts showed no significant prostaglandin synthesis inhibition. For the ethanol and ethyl acetate extracts, the leaves showed the highest levels of activity at a concentration of 250 ng ml −1 per test solution, in both the cyclooxygenase-1 and −2 assays. Some differences in the levels of anti-inflammatory activity in the roots following senescence were also observed. There was a slight loss of activity as a result of drying the rhizome material prior to extraction. This suggests that fresh rhizome material may be more effective for medicinal use, although it should be noted that the aqueous rhizome extracts displayed moderately high levels of cytotoxicity, and may require further investigation.