Essential oil composition and antibacterial activity of Thymus caramanicus at different phenological stages

Thymus species are well known as medicinal plants because of their biological and pharmacological properties. Thymus caramanicus is an endemic species grown in Iran. Variation in the quantity and quality of the essential oil of wild population of T. caramanicus at different phenological stages including vegetative, floral budding, flowering and seed set are reported. The oils of air-dried samples were obtained by hydrodistillation. The yields of oils (w/w%) at different stages were in the order of: flowering (2.5%), floral budding (2.1%), seed set (2.0%) and vegetative (1.9%). The oils were analyzed by GC and GC–MS. In total 37, 37, 29 and 35 components were identified and quantified in vegetative, floral budding, full flowering and seed set, representing 99.3, 98.6, 99.2 and 97.8% of the oil, respectively. Carvacrol was the major compound in all samples. The ranges of major constituents were as follow: carvacrol (58.9–68.9%), p-cymene (3.0–8.9%), γ-terpinene (4.3–8.0%), thymol (2.4–6.0%) and borneol (2.3–4.0%). Antibacterial activity of the oils and their main compounds were tested against seven Gram-positive and Gram-negative bacteria by disc diffusion method and determining their minimum inhibitory concentration (MIC) values. The inhibition zones (IZ) and MIC values for bacterial strains, which were sensitive to the essential oil of T. caramanicus, were in the range of 15–36 mm and 0.5–15.0 mg/ml, respectively. The oils of various phenological stages showed high activity against all tested bacteria, of which Bacillus subtilis and Pseudomonas aeruginosa were the most sensitive and resistant strains, respectively. Thus, they represent an inexpensive source of natural antibacterial substances that exhibited potential for use in pathogenic systems.