Abstract
Spirostachys africana Sond. stem bark is used traditionally for the treatment of diarrhoea and dysentery in Limpopo Province of South Africa. Bioassay-guided fractionation of ethanolic extract from bark of
Spirostachys africana led to the isolation of four known compounds, two triterpenoids, compound
1 [
d-Friedoolean-14-en-oic acid (3-acetyl aleuritolic acid)] and compound
2 (Lupeol), and two diterpenes, compound
3 [
ent-2,6α-dihydroxy-norbeyer-1,4,15-trien-3-one (diosphenol 2)] and compound
4 (
ent-3β-hydroxy-beyer-15-ene-2-one). Isolated compounds were tested for antibacterial activity using micro-dilution method. Compound
1, exhibited minimum inhibitory concentration (MIC) of 50
μg/ml against
Staphylococcus aureus,
Salmonella typhy,
Vibrio cholera,
Escherichia coli and
Shigella dysentery. Compound
2 was not active against all tested microorganisms at 200
μg/ml, which was the highest concentration tested. At this concentration, all four compounds were not active against
Shigella sonnei. Cytotoxicity of ethanol crude extracts and isolated compounds from
Spirostachys africana was determined using the sodium-2,3-bis-[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) assay on Vero cells. Compounds
2 and
3, isolated from
Spirostachys africana, had up to three times higher [50% inhibitory concentration (IC
50 values; 300.9 and 308.9
μg/ml)] than the ethanol crude extracts (102.8
μg/ml) suggesting higher toxicity of the crude extract as compared to these two compounds. In contrast, compounds
1 and
4 were not cytotoxic to Vero cell lines (African green monkey)
in vitro at the concentrations tested (IC
50
>
400
μg/ml). This is the first report on the antibacterial activity and cytotoxicity of purified compounds from
Spirostachys africana.