Variation in Antibacterial Activity, Thymol and Carvacrol Contents of Wild Populations of Thymus Daenensis Subsp. Daenensis Celak (Report‪)‬

Introduction The genus Thymus L. belongs to the mint family (Lamiaceae), and consists of about 215 species of herbaceous perennials and small shrubs in the world. The Mediterranean region can be described as the center of the genus (Cronquist, 1988; Heywood, 1993; Morales, 2002; Stahl-Biskup and Saez, 2002). Fourteen Thymus species has been reported in Flora Iranica (Jalas, 1982; Stahl-Biskup and Saez, 2002), four of which, T. carmanicus Jalas, T. daenensis Celak subsp. daenensis Celak, T. daenensis Celak subsp. lancifolius (Celak.) Jalas, T. persicus (Roniger ex Reach. F.) and T. trautvetteri Klokov & Desj.-Shost have been known to be endemic (Rechinger, 1982). T. daenensis subsp. daenensis is an endemic subspecies of Iran. This subspecies generally grows in high altitudes in Zagros mountains range (Rahimmalek et al., 2009). The areal parts and volatile constituents of thyme, a perennial dwarf shrub, are used as a medicinal herb. Thymus species are commonly used for herbal tea, flavoring agents (condiment and spice) and medicinal purposes (Stahl-Biskup and Saez, 2002). Infusion and decoction of aerial parts of Thymus species are used to produce a tonic, carminative, digestive, antispasmodic, anti-inflammatory, and expectorant and for the treatment of colds in Iranian traditional medicine (Zargari, 1990; Nickavar et al., 2005; Ghasemi Pirbalouti, 2009). Recent studies have shown that Thymus species have strong antibacterial, antifungal, antiviral, anti-parasites, spasmolytic and antioxidant activates (Rahimmalek et al., 2009b; Jordan et al., 2009). The pervious study showed that essential oil and extract of T. daenensis exhibited antimicrobial activities against Candida albicans (Ghasemi Pirbalouti et al., 2009a), Listeria monocytogenes (Ghasemi Pirbalouti et al., 2009b), Campylobacter jejuni and Campylobacter coli (Ghasemi Pirbalouti et al., 2010a), Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae (Ghasemi Pirbalouti et al., 2010b), Escherichia coli O157:H7 (Ghasemi Pirbalouti et al., 2010c) and Saprolegnia parasitica (Ghasemi Pirbalouti et al., 2009c). The aromatic and medicinal properties of the genus Thymus have made it one of the most popular medicinal plants (Nickavar et al., 2005). It is believed that these activities are to some extent caused by the constituents. Therefore, there is a considerable research interest towards the compositional analysis of Thymus essential oil and extract (Stahl-Biskup and Saez, 2002). It has been reported that essential oil yield and their components in plants is related to genetic (Mohammad Shafie et al., 2009), climate, edaphic, elevation and topography (Pourohit and Vyas, 2004; Rahimmalek et al., 2009a) and genetyp (G), growing conditions (E) and their interaction (G x E) (Basu et al., 2009). Chemical polymorphisms or chemotypes have been reported for many medicinal plants (Mockute et al., 2001; Russell and Southwell 2003; Curado et al., 2006; Mohammad Shafie et al., 2009). Recent findings showed that some of the medicinal plant characteristics can be affected by genetic and ecological factors such as precipitation, temperature, plant competition and nitrogen content in the soil (Letchamo et al., 1995). For example, higher altitude, variation in soil type had profound effect in the spread and amount of volatile constituents of T. serpylloides in Southeastern Spain (Letchamo et al., 1995). However, there are no reports in assessment of major compounds (thymol and carvacrol) of T. daenensis subsp. daenensis essential oil growing in different climatic regions of the country. The aims of this study were (1) to evaluate the antibacterial properties of the extract of wild populations of T. daenensis, grown in various geographical regions of Iran, (2) to determine the variation of thymol and carvacrol contents of different populations, (3) to assess the relationships between variations of thymol and carvacrol contents and the environmental facto