Fungicidal and inhibitory efficacy of cinnamon and lemongrass essential oils on Candida albicans biofilm established on acrylic resin: An in vitro study

Abstract

Statement of problem: It is unclear whether cinnamon and lemongrass essential oils can effectively reduce the Candida-biofilm frequently formed on dental devices made from heat-polymerized polymethyl methacrylate (PMMA) resin that contributes to the development of mild oropharyngeal as well as life-threatening candidiasis in patients wearing the devices. Purpose: The purpose of this in vitro study was to determine the efficacy of cinnamon and lemongrass essential oils in eradicating Candida albicans biofilm on heat-polymerized PMMA specimens and to determine whether they retard the formation of fungal biofilm. Material and methods: The antifungal effect of cinnamon and lemongrass essential oils was determined by using agar disk diffusion and broth microdilution methods to obtain minimum inhibitory concentrations. The mature C albicans biofilm (48 hours) was pre-established on PMMA specimens before being individually treated with various concentrations (½, 1, 2, 4, 8, 16 times minimum inhibitory concentration) of each tested oil for different exposure times (1, 2, 4, 8, and 24 hours). In another experiment, fungal biofilm was established on the PMMA specimens that were primed individually with various concentrations of the tested oils for different times. The 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT)-reduction assay was used to quantitate biofilm viability in both experiments. Statistical analysis was performed by using the 1-sample Kolmogorov-Smirnov test and 2-way ANOVA followed by the Tukey multiple comparison test (α=.05). Results: Minimum inhibitory concentration values of cinnamon and lemongrass essential oils against planktonic C albicans were 0.1 μL/mL (0.01% v/v) and 0.4 μL/mL (0.04% v/v). At 8 times the minimum inhibitory concentration, cinnamon oil (0.8 μL/mL or 0.08% v/v) and lemongrass oil (3.2 μL/mL or 0.32% v/v) eradicated the pre-established fungal biofilm by 99.0% in an exposure time of 1 hour. In contrast, high concentrations of 8 and 16 times the minimum inhibitory concentration of cinnamon oil (0.8 μL/mL or 0.08% v/v) and lemongrass oil (6.4 μL/mL or 0.64% v/v) coated on PMMA specimens for 24 hours were only able to inhibit the formation of fungal biofilm by approximately 70.0%. Conclusions: Cinnamon and lemongrass essential oils can eliminate pre-established C albicans biofilm and restrain the formation of fungal biofilm on heat-polymerized PMMA specimens. Both effects of the tested essential oils depended on dose and exposure or priming time.