Abstract:
BACKGROUND: The aim of this study was to evaluate the antimicrobial activity and the cytotoxicity of the ethanol
crude extract, fractions and isolated compounds from the twigs of Eriosema robustum, a plant used for the
treatment of coughs and skin diseases.
METHODS: Column chromatographic and spectroscopic techniques were used to isolate and identify eight
compounds, robusflavones A (1) and B (2), orostachyscerebroside A (3), stigmasterol (4), 1-O-heptatriacontanoyl
glycerol (5), eicosanoic acid (6), 3-O-β-D-glucopyranoside of sitosterol (7) and 6-prenylpinocembrin (8), from
E. robustum. A two-fold serial microdilution method was used to determine the minimum inhibitory concentration
(MIC) against fungi and bacteria, and the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide reduction
assay was used to evaluate the cytotoxicity.
RESULTS: Fraction B had significant antimicrobial activity against Aspergillus fumigatus and Cryptoccocus neoformans
(MIC 0.08 mg/ml), whilst the crude extract and fraction A had moderate activity against A. fumigatus and
Candida albicans (MIC 0.16 mg/ml). Fraction A however had excellent activity against Staphylococcus aureus (MIC
0.02 mg/ml), Enterococcus faecalis and Escherichia coli (MIC 0.04 mg/ml). The crude extract had significant activity
against S. aureus, E. faecalis and E. coli. Fraction B had good activity against E. faecalis and E. coli (MIC 0.08 mg/ml).
All the isolated compounds had a relatively weak antimicrobial activity. An MIC of 65 μg/ml was obtained with
robusflavones A (1) and B (2) against C. albicans and A. fumigatus, orostachyscerebroside A (3) against A. fumigatus,
and robusflavone B (2) against C. neoformans. Compound 8 had the best activity against bacteria (average MIC
55 μg/ml). The 3 fractions and isolated compounds had LC50 values between 13.20 to > 100 μg/ml against Vero
cells yielding selectivity indices between 0.01 and 1.58.
CONCLUSION: The isolated compounds generally had a much lower activity than expected based on the activity of
the fractions from which they were isolated. This may be the result of synergism between different compounds in
the complex extracts or fractions. The results support the traditional use of E. robustum to treat infections. The
crude extract had a good activity and low preparation cost, and may be useful in topical applications to combat
microbial infections.
