Limonene synergistically augments fluconazole susceptibility in clinical Candida isolates from cleft lip and palate patients.

Background: Cleft lip and palate (CLP) patients are prone to Candida infections (oral thrush) mainly due to poor oral hygiene, repetitive surgeries, and orthodontic procedures.

Aim: This study was undertaken to evaluate the antifungal efficacy of limonene against clinical Candida isolates from CLP patients.

Materials and methods: The antifungal efficacy of limonene was studied alone and in combination with fluconazole (FLC) against six standards, twenty nine FLC sensitive, and three FLC resistant clinical strains using broth dilution, checkerboard microdilution, agar disk diffusion, growth curves, and spot assays.

Results: This nontoxic monoterpene gave low minimum inhibitory concentration (MIC) values of 300-375 µg/mL and 500-520 µg/mL for FLC susceptible and FLC resistant strains, respectively. It showed synergistic interaction with FLC in all clinical and standard Candida strains (fractional inhibitory concentration (FIC) index ≤0.5).

Conclusion: Significant chemosensitization of FLC was observed even against resistant clinical isolates. Complete suppression of fungal growth was observed when using combinations. Negligible toxicity, easy availability, and potent antifungal properties suggest that limonene and FLC combinations in appropriate doses can make excellent antifungal mouthwashes during CLP treatment pre and post surgery. Impending in vivo studies are needed to validate the present data.