Comparative study of the antifungal activity of some essential oils and their major phenolic components against Aspergillus niger using three different methods

Abstract

This study aimed to evaluate the antimould activity of oregano, thyme, rosemary and clove essential oils and some of their main constituents: eugenol, carvacrol and thymol against Aspergillus niger. This antifungal activity was assessed using broth dilution, disc diffusion and micro atmosphere methods. In both agar diffusion and micro atmosphere tests, all the investigated agents showed no inhibitory effect on Aspergillus niger growth at concentrations lower than 10% (v/v). However, broth dilution test showed the highest sensitivity. Using this method, the minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) values of the tested agents were between 0.025 and 1%. The anti-Aspergillus effect of oregano and thyme oils was more potent than that of clove and rosemary oils. Concerning the phenolic compounds, thymol and carvacrol proved to have better anti-Aspergillus effect than eugenol. Accordingly, we can say that the antifungal efficacy of these agents is better appreciated when they are applied directly into liquid medium than when they are applied as volatiles or diffused in solid medium. Therefore, as these agents are active at low concentrations, they could be used in the formulation of natural preparations, and thereby could be proposed in therapeutic or hygienic contexts.

Key words: Essential oils, thymol, carvacrol, antifungal activity, Aspergillus niger, micro atmosphere, agar diffusion, broth dilution.