Investigation of the antifungal potential of linalool against clinical isolates of fluconazole resistant Trichophyton rubrum

Abstract

The aim of this study was to investigate the activity of the monoterpene linalool against clinical isolates of Trichophyton rubrum. Initially, a sensitivity assay for commercial antifungals with solid disks in diffusion medium was performed. Minimum inhibitory concentration (MIC) of linalool and ketoconazole (positive control) were determined by microdilution in RPMI 1640 medium (CLSI M38-A2). We then evaluated the action of linalool and ketoconazole at different concentrations (1/2MIC, MIC and 2×MIC) on mycelial growth (radial mycelial growth), conidia production and conidia germination using a hemacytometer. The effects on cell membrane (release of intracellular material) were also investigated. Finally, changes in fungal morphology as induced by the test drugs were analyzed. Based on the sensitivity tests, the fungal strains showed resistance to 5-fluorocytosine and fluconazole. The linalool MIC values ranged from 256μg/mL to 512μg/mL, whereas ketoconazole showed values of 4μg/mL to 8μg/mL. For the LM 305 strain, the test drugs showed the following MIC values: linalool 256μg/mL and ketoconazole 8μg/mL. The mycelial growth of T.rubrum LM 305 was inhibited by linalool (2×MIC) and ketoconazole (1/2MIC, MIC, 2×MIC), in 7 days of treatment (P<0.05). The test-drugs also inhibited conidial germination and conidiogenesis (P<0.05). Linalool also caused leakage of intracellular material (P<0.05). Finally, we verified the effectiveness of linalool and ketoconazole to induce micro-morphological changes, forming abnormal, wide, short and crooked hyphae. Based on these results, we conclude that linalool presents as an antifungal agent with anti-Trichophyton rubrum potential, an important dermatophytosis agent.