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.

The Micro-atmosphere method of Kellner and Kober was modified and used to study antifungal properties of six essential oils that have different chemical compositions (three chemotypes from mugwort, Artemisia herba alba, one from thyme, Thymus capitatus, one from rosemary, Romarinus officinalis and one from Eucalyptus, Eucalyptus globulus). They were tested against 39 mold strains (13 from the genus Penicillium, nine from Aspergillus and 17 others). The essential oil from thyme was the most effective, suscessively followed by those from mugwort, rosemary and eucalyptus. The strains studied were classified into three groups: sensitive, intermediate and resistant.

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During the 2003 and 2004 olive oil production campaigns in Morocco, 136 samples from spoiled olive and olive cake were analyzed and 285 strains were isolated in pure culture. Strains included 167 mesophilic strains belonging to ten genera: Penicillium, Aspergillus, Geotrichum, Mucor, Rhizopus, Trichoderma, Alternaria, Acremonium, Humicola, Ulocladium as well as 118 thermophilic strains isolated in 2003 and 2004, mainly belonging to six species: Aspergillus fumigatus, Paecilomyces variotii, Mucor pusillus, Thermomyces lanuginosus, Humicola grisea, and Thermoascus aurantiacus. Penicillium and Aspergillus, respectively, 32.3 and 26.9% of total isolates represented the majority of mesophilic fungi isolated. When considering total strains (including thermotolerant strains) Aspergillus were the predominant strains isolated; follow-up studies on mycotoxins therefore focused primarily on aflatoxins (AFs) and ochratoxin A (OTA) from the latter strains. All isolated Aspergillus flavus strains (9) and Aspergillus niger strains (36) were studied in order to evaluate their capacity to produce AFs and OTA, respectively, when grown on starch-based culture media. Seven of the nine tested A. flavus strains isolated from olive and olive cake produced AF B1 at concentrations between 48 and 95 microg/kg of dry rice weight. As for the A. niger strains, 27 of the 36 strains produced OTA.