In vitro antifungal evaluation and studies on mode of action of eight selected species from the Argentine flora.

Twenty nine extracts belonging to eight species of the Argentine flora reported as antifungal in folk medicine, were assayed for antifungal properties by using the agar dilution method, against a panel of yeasts, filamentous fungi as well as dermatophytes. Nine extracts belonging to six species, exhibited a broad spectrum of activity against Microsporum cants, Microsporum gypseum, Trichophyton mentagrophytes, Trichophyton rubrum and Epidermophyton floccosum, with MICs ranging from 25 to 900 μg/ml. A dichloromethanis extract of Polygonum ferrugineum was the most active extract with MICs from 25-50 μg/ml. To gain an insight into the mode of action of the active extracts they were evaluated for their inhibitory activities toward the fungal cell wall, using the whole cell Neurospora crassa hyphal growth inhibition agar diffusion assay. A hazy zone around the paper disk strongly suggested that the dichloromethane extracts from aerial parts of Polygonum punctatum, Polygonum ferrugineum and the bark of Luehea divaricata acted by inhibiting polymer synthesis or assembly of the cell wall. The clear zone of inhibition produced by the dichloromethane and methanol antifungal extracts of Xanthium spinosum could be ascribed to the fact that these extracts have another effect on fungal cells in addition to inhibition of cell walls.