**11.4 In vitro effect of essential oils of** *T. broussonetii* **and** *T. maroccanus*

As has been reported in the literature, we considered that an essential oil has bacteriostatic action if the diameter of inhibition is greater than 12 mm (Baudoux, 2001; Sağdac ° 2003) or 15mm (Rossi, 2003). The diameters of inhibition zones obtained with the essential oils of *T. broussonetii* and *T. maroccanus*, from the region of Marrakech (Morocco), are 19 mm and 23 mm respectively. The essential oils acted actively on the growth of *Salmonella sp* responsible for salmonellosis. They have an inhibitory effect on the growth of Salmonella sp.


Table 4**.** Antibacterial activity of the essential oils of *Thymus broussonetii* (T.b.) and *Thymus maroccanus* (T.m.) and from antibiotic expressed by diameter of inhibition zone.

These values are reported as means ± standard deviations of three separate determinations. Disc diameter. 6mm (Romane et al, 2010).

The major activity of essential oils of *Thyme broussonetii* and *Thyme maroccanus* is due to their richness in phenolic compounds (thymol and carvacrol). Most antimicrobial compounds are phenols (carvacrol, thymol, eugenol), followed by alcohol (cineole, linalool ...) and to a lesser extent alkenes (p-cymene, pinene, terpinene ...) (Burt, 2004, Ultee et al., 2002). Indeed, several studies have shown that high antimicrobial power of essential oils of several species of thyme is attributed to their high phenolic compounds (carvacrol and thymol) (Marino et al. 1999; Mirmostafa and Rasool, 2002; Dafer and Ziogas , 2000; Baranauskiene et al. 2003; Di Pasqua et al. 2005; Di Pasqua et al. 2007; Cristan et al., 2007).

Most of the work that had for its object the study of the mechanism of action of phenolic compounds suggests that their main site of action is the bacterial plasma membrane (Shunying et al., 2005). They are able to disintegrate the bacterial cell membrane (Ultee et al., 1999). The membrane loses its structure and becomes more permeable to ions (Lambert et al., 2001). Damages to the cell membrane may also allow the dissipation of pH gradient and decreased membrane potential (Ultee et al., 1999).
