Publication details, including instructions for authors and subscription information:ABSTRACT: The influence of the number of bacterial cells inoculated and the emulsifying agent used to disperse essential oils (EO) into the culture media on the measurement of the antibacterial activity of EO in an agar medium was determined. The results showed that EO (oregano, thyme and clove) were most effective as antimicrobial agents when the bacterial load was low. Minimum inhibitory concentrations (MICs) were found to vary as a function of the emulsifylng agent used. However, MICs obtained by dispersing EOs into 0.2% agar solution without the use of solvents and detergents were greatly reduced compared to when they were used. This demonstrates the fact that solvents and detergents often used in antimicrobial studies significantly decrease the antibacterial activity of EO.

The mechanism of the antimicrobial action of oregano (Ot-iganum compacturn) and clove essential oils was studied simultaneously with two phenolic components, namely thymol and eugenol. Escherichia coli and Bacillus subtilis were used as Gram negative and Gram positive bacterial models, respectively. The oils as well as their major components were capable of inducing cell lysis. Bacteria lysis was shown by the release of substances absorbing at 260 nm. For E. coZi, the results were similar to those obtained with polymyxin B. Scanning electronic microscope observations revealed that both cell wall and membrane of the treated bacteria were significantly damaged.

Aims:  This study aims to bring some information about the mechanism of the fungicidal action of thymol and eugenol; phenolic major components of thyme and clove essential oils respectively. Saccharomyces cerevisiae was used as yeast model. Methods and Results:  Treatment of yeast cells with these components led to their lysis as shown by the release of substances absorbing at 260 nm. In addition, scanning electron microscope observations revealed that the surface of the treated cells was significantly damaged. Conclusions:  Antifungal activity of thymol and eugenol involve alteration of both membrane and cell wall of the yeast. Significance and Impact of the Study:  This work is a preliminary contribution aiming to develop a new generation of efficient and natural antifungal agents.

The antimicrobial properties of volatile aromatic oils have been recognized since antiquity. Oregano and clove oils have been shown to possess a broad spectrum of antimicrobial activity. In this paper, the fungicidal action of these two essential oils was studied on the yeast model Saccharomyces cerevisiae. Yeast cell lysis was shown by the release of substances absorbing at 260 nm. In addition, scanning electron microscopy analyses revealed that the surface of treated cells by oregano and clove oils was significantly damaged.

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