Antimicrobial activity of essential oils and extracts of rosinweed (Silphium trifoliatum and Silphium integrifolium) plants used by the American Indians

This paper presents a comparison of the chemical composition and biological activity of the volatile fraction (essential oil solution) of rhizomes of two plant species, Silphium trifoliatum L. and Silphium integrifolium Michx., and the respective soft ethanol and chloroform extracts; 51 components were identified in the extracts and oils (the main constituents of the oils were modhephene, alpha-isocomene, allo-aromadendr-9-ene, 7 alpha-H-silphiperfol-5-ene, 7 beta-H-silphiperfol-5-ene and germacrene D). The studied initial essential oil solutions contained 336 mg/ml (S. trifoliatum) and 406 mg/ml (S. integrifolium) of volatile substances. The soft extracts contained between 15.84 mg/ml (ethanol extract, S. trifoliatum) and 35.65 mg/ml (ethanol extract, S. integrifolium) of substances identified with GC-MS. Additionally, the analysed soft extracts contained flavonoids, o-dihydroxyphenoles and glycoside-bonded triterpenic acids (oleanolic and ursolic acid). Antimicrobial tests were performed on two bacterial reference strains (Staphylococcus aureus and Escherichia coli) and two fungal reference strains (Candida albicans and Malassezia pachydermatis). The highest level of activity was displayed by essential oils, i.e. fractions rich in volatile components. Copyright (C) 2008 John Wiley & Sons, Ltd.