Investigation of the antimicrobial effects of carvacrol in clinical Candida isolates and imaging by immunoelectron microscopic method

Abstract

Candida species can cause superficial and systemic disease and their biofilms have become an important problem for both hospital-acquired and device-associated infections. The efficacy of many antifungal agents are limited by their cytotoxicity and increasing rate of drug-resistant. In last years, the antimicrobial and antibiofilm activity of some natural products such as essential oils have drawn attention. Carvacrol [2-methyl-5-(1-methylethyl)phenol] is one of the phenolic components of thyme and have strong antimicrobial activity. Thus far, limited reports have discussed the antimicrobial effects of carvacrol on clinical Candida strains. In our study, it was aimed to investigate the effects of carvacrol on clinical Candida isolates by microbiological and transmission electronmicroscopic methods and to investigate the effects of carvacrol on the fungal cell wall by immunoelectron microscopic method using the hyphal wall protein Hwp1 protein. In this study, 24 clinical isolates and 1 reference strain (C. albicans ATCC 14053) were used. The minimum inhibitory concentration (MIC) of carvacrol was determined using the broth microdilution method. MIC results showed a MIC ⩽ 0.031% (vol/vol) for all isolates tested. For transmission electron microscopic studies, isolates were also exposured to the carvacrol at concentration of 1⁄2 MIC for 48 hours and results were compared with the control. According to our results, carvacrol showed high antifungal potential with very low MIC values on Candida isolates. Electron microscopically, no growth was observed at the MIC value and the higher concentrations; cellular damage was also determined at sub MIC concentrations. It has been shown that carvacrol causes irreversible damage to cells. We observed that carvacrol did not increase cell growth or hyphal growth at all studied concentrations. The immunogold labeling results were used to observe the effect of carvacrol on the cell wall. Although immune labeling was greatly reduced in carvacrol treated cells, the presence of Hwp1 protein was also observed in the scattered cytoplasm. Usage of carvacrol in the topical treatment of Candida infections with further study it was determined that a potentially promising drug and detailed studies on the subject are needed.