Moroccan J. Biol. 1(2004) EUGENOL INDUCES DAMAGE OF BACTERIAL AND FUNGAL ENVELOPE S. Bennis 1 , F. Chami 1 , N. Chami 1 , K. Rhayour 1 , A. Tantaoui-Elaraki 2 , A. Remmal 1* 1 Faculté des Sciences, Laboratoire de Biotechnologie BP 1796 Atlas Fez, Morocco 2 Sup Agro, 22 rue le Câtelet Belvédère, Casablanca, Morocco. *Corresponding author: Phone +21261532398, Fax +21255732981, E-mail adnaneremmal@hotmail.com Abstract. Eugenol, the phenolic major component of clove essential oil, was used in this study to elucidate its antimicrobial mechanism against the yeast; Saccharomyces cerevisiae, gram positive bacteria; Bacillus subtilis and gram negative bacteria; Escherichia coli. For all organisms tested, the treatment with this phenolic major component reduced the cellular viability by inducing the release of substances absorbing at 260 nm. This supposes that cell lethality was a consequence of cellular lysis. In addition, scanning electron microscopy analysis revealed that the envelope of all treated cells by eugenol was significantly damaged. Key words: Eugenol, S. cerevisiae, B. subtilis, E. coli, Mechanism of action. Introduction The antimicrobial activity of essential oils (EO) has been widely described in several studies [1, 9, 10, 11]. This activity of EO is mainly due to their high content in phenolic derivatives [7, 18, 20, 22]. In the present work, we sought to elucidate the antimicrobial mechanism of eugenol; the phenolic major component of clove essential oil on Saccharomyces cerevisiae, Bacillus subtilis and Escherichia coli, in order to determine how these component act on the cell envelope of yeast and bacteria cells. In this respect, the antimicrobial activity of eugenol was investigated using two approaches: 260 nm absorbing of released cytosolic compounds coupled with cellular mortality and scanning electron microscope (SEM). Material and methods Microorganisms S. cerevisiae strain (SB36–85) was isolated from Baker’s yeast in our laboratory and identified using standard yeast determination procedures [12]. E. coli strain (APL 87/1) was isolated from a hen affected by collibacillosis. It was identified at the Avian Pathology laboratory of the Institut Agronomique et Vétérinaire Hassan II, Rabat- Morocco. B. subtilis strain (APL 87/35) was isolated from poultry meat in the same laboratory. Culture media Glucose-YNB (0.67 % yeast nitrogen base and 0.5 % glucose) was used for yeast culture. M9 medium [14] was used for bacterial culture. The washing medium used was Phosphate Buffer Saline PBS (8 g/l NaCl; 0.2 g/l KCl; 1.13 g/l Na 2 HPO 4 2 H 2 O and 0.2 g/l KH 2 PO 4 ). Preparation of washed yeast and bacteria cells S. cerevisiae cells were grown in 200 ml glucose YNB for 18 h on a shaker at 30°C. The cell cultures were washed twice in PBS by centrifugation 10 min at 12000 x g at 4°C. The bacteria were grown overnight at 37°C in 200 ml under aeration in minimal medium M9 with initial pH 7.2-7.4. The cells were 33