Antifungal Effects of Silybum marianum Extract Individually and in Combination with Fluconazole on Clinical Candida Isolates in Northern Iran

    Candidiasis is a spectrum of opportunistic fungal diseases. The resistance of Candida to antibiotics is unfortunately increasing. Silybum marianum, which belongs to the Asteraceae family, is a wild plant growing in most parts of Iran. The present study was conducted to investigate the effect of Silybum marianum extract, both individually and in combination with fluconazole, on the growth of drug-resistant clinical Candida isolates. Candida species isolated from 85 patients suspected of Candidisis was identified and cultured on CHROMagar Candida and API 20CAUX system. The test of susceptibility to fluconazole was performed using broth microdilution. The minimum inhibitory concentration (MIC) of Silybum marianum extract and its antagonistic effects were determined using the microdilution assay. The highest resistance to fluconazole was reported in Candida glabrata (81.8%) and Candida albicans (72.9%). Variations in the MIC of the aqueous extract of Silybum marianum in a range of 4096 - 8 μL/mL showed that 77.8% of C. glabrata isolates and 88.6% of C. albicans isolates were resistant to fluconazole, and did not grow at a concentration of 2048 μL/mL; nevertheless, in the case of Silybum marianum extracts in combination with fluconazole, 89% of C. glabreta and 94.3% of C. albicans isolates were resistant to fluconazole, and stopped growing at concentrations of at least 128 μL/mL (P < 0.01). The aqueous extract of Silybum marianum seeds found to present proper inhibitory effects on clinical fluconazole-resistant Candida isolates at high concentrations. Silybum marianum extract in combination with fluconazole was found to have a more potent in-vitro activity than the extract and drug individually.