Antifungal activity of spider venom-derived peptide lycosin-I against Candida tropicalis

Candida species are a major cause of human mucosal and deep tissue fungal infections, but few antifungal treatments are available. Here, we showed that lycosin-I, a peptide isolated from venom of the spider Lycosa singoriensis, acted as a potent antifungal inhibitor against Candida species. The MIC50 values of lycosin-I reached 8 μg/mL to treat fluconazole-susceptible and fluconazole-resistant C. tropicalis isolates. Time-kill kinetics assays revealed that after a 2-hour exposure, lycosin-I reduced colony-forming units/mL in fluconazole-susceptible and fluconazole-resistant C. tropicalis isolates approximately 70%. Furthermore, salinity tolerance assays suggested that even in the presence of Mg2+, lycosin-I maintained its potent antifungal ability at a high concentration. When the concentration of lycosin-I was increased from 1 × MIC to 8 × MIC, a significant decrease of the biofilm metabolic activity was observed in both fluconazole-susceptible and fluconazole-resistant C. tropicalis isolates. Moreover, the biofilm inhibitory concentration 50 (BIC50) and the biofilm eradicating concentration 50 (BEC50) were approximately 32 μg/mL and 128 μg/mL, respectively. Confocal laser scanning microscopy showed the localization of CY5-labeled lycosin-I mainly in the cell cytoplasm, and lycosin-I was likely to be localized in the cytoplasm after its transportation across the cell wall and membrane. Overall, our work shows that lycosin-I is a potent antifungal agent with a high efficacy, a high salinity tolerance, and potent anti-biofilm properties.