Light-mediated antifungal activity of Echinacea extracts

This study demonstrated that plant extracts containing acetylenic isobutyla mides and polyacetylenes, previously reported as occurring in Echinacea, ha ve phototoxic antimicrobial activity against fungi, including clinically re levant pathogenic fungi. Results show that hexane extracts of Echinacea var iably inhibit growth of yeast strains of Saccharomyces cerevisiae, Candida shehata, C. kefyr, C. albicans, C. steatulytica and C. tropicalis under nea r UV irradiation (phototoxicity) and to a lower extent without irradiation (conventional antifungal activity). The presence of polyacetylenes and alky lamides in extracts of different organs was confirmed in Echinacea purpurea by HPLC in agreement with previously reported data in the literature, and was related to phototoxic activity. Two representative pure compounds, unde ca-2E,4Z-diene-8,10-diynoic acid isobutylamide and dodeca-2E,4E,8Z,10E/Z-te traenoic acid isobutylamide, were isolated from Echinacea purpurea root ext racts, and compared in a disk assay (5 mu g/disk) with the highly conjugate d trideca-1-ene-3,5,7,9,10-pentayne (previously isolated in our laboratory and found here in E. purpurea). Significant phototoxicity was demonstrated by pure trideca-1-ene-3,5,7,9,10-pentayne, while only minor phototoxicity w as induced by the other two acetylenic compounds. Phototoxic activity of Ec hinacea spp. is primarily attributed to the ketoalkenes and ketoalkynes abu ndantly present in the roots.