Antidermatophyte activity of medicago extracts and contained saponins and their structure-activity relationships

Saponin-rich extracts of Medicago sativa L. have been shown to display antifungal activity against a range of common fungibut only a few individual saponins have been tested against dermatophytes. Total saponins were separately obtained from roots and aerial parts of Medicago sativa, M. murex, M. arabica and M. hybrida. Nineteen saponins and three parent triterpenoids, were tested against three dermatophytic fungi Microsporum gypseum, Trichophyton interdigitale and T. tonsurans using mircowell plate serial dilution assay to determine the Minimum Inhibitory Concentration (MIC). Miconazole was used as a positive control. T. tonsurans appeared to be the most sensitive of the dermatophytes to the active compounds. Aglycones showed less antifungal effect than the glycosides, which displayed a range of activities. Monodesmosidic glycosides of medicagenic acid were the most active compounds, especially the 3-O-beta-D-glucopyranoside, which displayed MIC less than 0.09mm against all three fungi, although those of hederagenin and zanhic acid also showed weak activity (MIC 3.3mm against two fungal species). Bidesmosidic saponins had weaker activity than monodesmosidic ones. This corresponds to activity of these and similar compounds against other fungal species but this is the first comprehensive report of activity of Medicago saponins against dermatophytes.