Inhibition of biofilm- and hyphal- development, two virulent features of Candida albicans by secondary metabolites of an endophytic fungus Alternaria tenuissima having broad spectrum antifungal potential

摘要

Fungal resistance against frequently used antifungal medicines used for invasive candidiasis and other fungal infections is directing scientist for searching and developing novel antifungal drugs. An endophytic fungal strain Alternaria tenuissima OE7 has been isolated from leaves of Ocimum tenuiflorum L. which showed antifungal activity against numbers of human pathogenic fungi including Trichophyton rubrum, Microsporum gypseum, Aspergillus parasiticus, A. flavus, A. fumigates, Candida albicans and C. tropicalis. Thermostable, non-proteinacious antifungal metabolites produced zones of inhibition against all pathogenic fungi tested. The ethyl acetate extract of the cell free supernatant was found inhibitory to the radial growth and conidial germination of T. rubrum and M. gypseum. It also showed cidal mode of action against C. albicans at a concentration of 1.0 mg/ml. Most interestingly, inhibition of biofilm formation and hyphal development of C. albicans were observed upon treatment with EA fraction at comparatively lower concentrations (100-500 mu g/ml). Release of intracellular contents from treated cells of Candida and scanning electron microscopic observation suggested cellular disruptions by antifungal metabolites. Checkerboard study revealed synergy between EA fraction of OE7 (150 mu g/ml) and fluconazole (30 mu g/ml) with Sigma FIC of 0.45. Two active fractions viz. band 'C' and band 'G' derived after thin layer chromatographic analysis showed inhibitory activity against C. albicans with MIC values of 80 mu g/ml and 130 mu g/ml respectively. GC-MS analysis suggested presence of numbers of compounds in each active fraction. Overall observations attest the prospective role of the isolate OE7 as a potent candidate for the production of antifungal metabolites against human pathogenic fungi.