Susceptibility of Candida spp. to An Antimicrobial Decapeptide

Objectives: We demonstrated that a decapeptide KSL, KKVVFKVKFK, and its analog KSL-W, KKVVFWVKFK, exhibited a broad range of antibacterial activity (Concannon et al., 2003; Na et al., 2007). However, their antifungal activity has remained undetermined. In this study we examined the peptide KSL-W for its antifungal activity in comparison with other antifungal agents such as Amphotericin B and Histatin 5 (His-5) under different test conditions. Methods: Antifungal activities of KSL-W and Amphotericin B were first measured by minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) using broth microdilution assay on eight different species of Candida in 50% and 100% RPMI 1640. Susceptibility to His-5 was also tested on two species of Candida. For comparing the growth inhibitory activity of KSL-W and His-5 under different salt concentrations, a killing assay for obtaining 50% inhibition (IC₅₀) was used. The salt concentrations tested included low, medium, and high concentrations of potassium phosphate buffer (PPB) pH 7.0. We are also investigating the effects of using saliva as a test condition in determining the effectiveness of KSL-W. Results: For the eight species of Candida, MICs and MFCs in 100% RPMI 1640 ranged from 9.5 to 76.4 µM for KSL-W, and 0.54 to 17.3 µM for Amphotericin B. For His-5 treated C. albicans and Candida glabrata, the MICs and MFCs in 100% RPMI 1640 were over 165 µM. Similar assays performed in 50% RPMI 1640 gave the same results for Amphotericin B and His-5. However, the MICs and MFCs for KSL-W were on average 2 dilutions lower. While the IC₅₀ of C. albicans for KSL-W was not greatly affected by the high salt concentrations, the IC₅₀ of His-5 was significantly affected by the high salt. Conclusion: KSL-W may be a good candidate antifungal agent.