Combinatorial Antimicrobial Effects of Imidazolium-Based Ionic Liquids and Antifungals on Model Fungal Organisms

Ionic Liquids (IL) are a unique class of molten salts, with specific formulations exhibiting antimicrobial properties. Several recent studies have highlighted the ability of ILs to form micelles, permeabilize the plasma membrane, and destabilize cellular structure, ultimately initiating cell death. Moreover, while these membrane-destabilizing properties are cytotoxic to most cellular organisms at high concentrations, their membrane destabilization capability at lower concentrations may lead to improvements in drug delivery for combinatorial therapies against specific microbes. Work presented in this study aimed to identify a synergistic relationship between ILs, 1-n-Hexyl-3-methylimidazolium chloride (HMIM[Cl]) and 1-Methyl-3-n-octylimidazolium chloride (OMIM[Cl]), and antifungal drugs (AF), Clotrimazole, Ketoconazole, Fluconazole, and Itraconazole, with the hypothesis that in a combinatory setting there should be improved AF efficacy against model fungal organisms: S. boulardii, S. cerevisiae, S. pombe, and C. albicans. Several complementary assays were used to identify the combined effects of IL + AF treatment, including Kirby-Bauer tests and minimum inhibitory concentrations (MIC) assays to establish antimicrobial effects, and flow cytometry to evaluate cell wall permeability. Finally, we demonstrate that at low concentrations, the ILs tested in this study are capable of improving the effectiveness of current antifungal compounds at concentrations not cytotoxic to human cells.