Chemical composition and antimicrobial activities of essential oil and its components from Lebanese Origanum syriacum L.

The chemical composition of essential oils isolated by hydrodistillation from the aerial parts of cultivated and wild Origanum syriacum were analyzed by gas chromatograph (GC) and GC/mass spectrometry (GC/MS). Regardless of growing habitat, both oils were characterized as carvacrol/γ-terpinene chemotypes. High in vitro antimicrobial activities of essential oil were attributed to the high content of phenolic derivative such as carvacrol. Total inhibition of fungal growth was achieved at 0.25–0.50 μL/mL of essential oil. Bacteria on the other hand, were slightly more susceptible to the essential oil with minimal inhibitory concentration (MIC) ranging from 0.15 μL/mL to 0.50 μL/mL. Carvacrol and thymol were the most detrimental compounds towards both bacterial and fungal microorganisms with inhibition concentration at 50% (IC50) ranging between 0.01 and 0.18 μL/mL for bacteria and with total inhibition of fungal growth at a range of concentrations between 0.25 and 0.75 μL/mL. Antimicrobial activities of α-terpinene, p-cymene and β-caryophyllene were comparable with the activities of crude oil extract against almost all microorganisms. p-cymene, however, stimulated mycelial growth of Metarhizium anisopliae.