Secondary metabolites from selected endophytic fungi exhibiting synergistic activity with azole drugs against Candida albicans

Abstract

Based on morphological characteristics and nucleotide sequences of the ribosomal RNA gene region, two endophytic fungi obtained from leaf of Artemisia annua L. and Terminalia chebula Retz. were identified as Nodulisporium sp. Aann-134 and Alternaria alternata Tche-153, respectively. The ethylacetate extracts of the culture broths from both fungi significantly exhibited synergistic activity with ketoconazole against Candida albicans. Bioassay-guided fractionation using column chromatographic technique together with analyses of spectroscopic led to the isolation and identification of seven secondary metabolites from Nodulisporium extract; including four resorcinol polyketides, 1'-(2,6-dihydroxyphenyl)butanone, 1'-(2,6-dihydroxyphenyl)-3'-hydroxybutanone, 1'-(2,6-dihydroxy phenyl)ethanone, and a new compound nodulisporin G; two napthalenes 1,8-dimethoxy naphthalene and 1,8-dihydroxynaphthalene; and phenylacetic acid. In addition, three polyketide salicylates including, altenusin, isoochracinic acid, and altenuic acid, as well as a chromone, 2,5-dimethyl-7-hydroxychromone were identified from the fungus Alternaria alternata extract. By employing the disk diffusion method and the chequerboard technique, 1'-(2,6-dihydroxyphenyl)butanone and 1,8-dihydroxynaphthalene exhibited synergistic activity with fluconazole against C. albicans with the fractional inhibitory concentration indices of 0.250 and 0.375, respectively. In the same manner, altenusin, in combination with ketoconazole, fluconazole, or itraconazole, displayed potent synergistic activity against C. albicans with the fractional inhibitory concentration index in the range of 0.078 to 0.188.