Fungicidal activity of thymol and carvacrol by disrupting ergosterol biosynthesis and membrane integrity against Candida

Abstract

Natural isopropyl cresols have been reported to have antifungal activity. This work is an attempt to examine thymol and carvacrol against 111 fluconazole-sensitive and -resistant Candida isolates. Insight into the mechanism of action was elucidated by flow cytometric analysis, confocal imaging and ergosterol biosynthesis studies. The susceptibility tests for the test compounds were carried out in terms of minimum inhibitory concentrations (MICs), disc diffusion assays and time-kill curves against all Candida isolates by employing standard protocols. Propidium iodide (PI) cell sorting has been investigated by flow cytometric analysis and confocal imaging. Haemolytic activity on human erythrocytes was studied to exclude the possibility of further associated cytotoxicity. Both compounds were found to be effective to varying extents against all isolates, including the resistant strains. In contrast to the fungistatic nature of fluconazole, our compounds were found to exhibit fungicidal nature. Significant impairment of ergosterol biosynthesis was pronouncedly induced by the test entities. Negligible cytoxicity was observed for the same compounds. Furthermore, it was observed that the positional difference of the hydroxyl group in carvacrol slightly changes its antifungal activity. Carvacrol and thymol show strong fungicidal effect against all of the Candida isolates. The mechanisms of action of these natural isopropyl cresols appear to originate from the inhibition of ergosterol biosynthesis and the disruption of membrane integrity.

Synthesis, Antimicrobial Activity and in silico Studies on Thymol Esters

“…[11][12][13][14][15][16] The mode of action of thymol against yeast and fungi has been sparsely investigated, though certain studies point to interactions with the cell envelope and intracellular targets. [16][17][18][19] Thymyl derivatives are well represented in Asteraceae plants, particularly within tribes Senecioneae, Eupatorieae, Inuleae and Helenieae. In some Inula, Doronicum and Pulicaria species, thymyl derivatives rather than sesquiterpenoids are the major root constituents.…”

“…Keeping in view diverse pharmacological activities of thymol [7][8][9][10][11][12][13][14][15][16][17][18][19] and preliminary results on bioactivity of thymyl derivatives 4,5,22,25,[28][29][30]33 we have set the aim of our study. By making a single modification of a phenolic functionality in thymol we have obtained a series of ester compounds (3a-t), performed their structural characterization, in vitro antimicrobial testing and in silico calculation of physico-chemical, pharmacokinetic and toxicological properties.…”

Application of essential oils as natural cosmetic preservatives

“…It has been found that some EOs exhibit the highest potential against Candida species [31,32] and aspergillus sp. [32,33].…”

Reversing Antifungal Drug Resistance using Natural Plant Products

“…Several of these plant products have significant antimicrobial properties [2,13,14]. Thymol and carvacrol are two potent antifungal agents found abundantly in essential oils of plants like thyme and organo [15]. They have excellent antifungal properties with low MIC values and negligible cytotoxicity.…”

“…These results were in concurrence with the observed changes in the accumulation and efflux of R6G and Hoescht 33342 dyes by Candida cells treated with thymol and carvacrol. Although some results show upregulation of these genes in the presence of thymol [20][21][22], we can say that these natural antifungals may not specifically impair expression of the transporters but their fungicidal activity may include inhibition of the plasma membrane proton efflux pump and disruption of membrane integrity [13,15]. Inhibition of drug efflux pumps using natural plant products seems to be excellent strategy for overcoming or rather reversing drug resistance in pathogenic fungal species.…”