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.

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