engleski

Essential oils of selected Thymus species wild- growing in Croatia: chemical composition and antibacterial activity

The genus Thymus (Lamiaceae) is notewory for the numerous plants biosynthesizing remarkable amount of volatile compounds. Present study aimed to evaluate chemical composition and antibacterial activity of essential oils from five selected Thymus species originated from Croatia (T. longicaulis C. Presl, T. praecox Opiz subsp. polytrichus (A. Kern. ex Borbás) Jalas, T. pulegioides L., T. serpyllum L. subsp. serpyllum and T. striatus Vahl), in comparison with T. vulgaris L. The extraction yields (V/m) of essential oils isolated by hydrodestilation from aerial parts of investigated species were in the range 0.2- 1.7%. According to GC-MS analysis 95 different components were identified, representing 87.6- 99.7% of the total oil content. Thymol (43%), p-cymene (18%) and γ-terpinene (11%) were the most abundant compounds of essential oil of T. longicaulis. The main component of T. pulegioides essential oil was carvacrol (39%) while 1, 8-cineole (37%) was found to be the major compound of the essential oil of T. serpyllum subsp. serpyllum. The essential oils of mountain species T. praecox subsp. polytrichus and T. striatus were rich in sesquiterpenes, with germacrene-D-4-ol (12% and 12%) and β-caryophyllene (10% and 12%) as predominant compounds. The multivariate analysis of the essential oil constituents from the selected Thymus species indicated that the greatest similarity to the thyme oil, thymol type which is officially recognized in European Pharmacopoeia, was presented by T. longicaulis. In vitro antibacterial activity of the essential oils against Gram-positive and Gram- negative bacterial strains (S. aureus, E. faecalis and E. coli) was determined using the microdilution method. E. coli showed the highest susceptibility to all tested essential oils, while E. faecalis was the most resistant. MIC values for E. coli and S. aureus ranged from 0.5 mg/mL to 2 mg/mL, while the MIC value for E. faecalis was 4 mg/mL. Our study showed that, in addition to the phenolic compounds (thymol and carvacrol) well-known as strong antimicrobial agents, sesquiterpenes also contribute to the antibacterial activity of the selected Thymus species.

Thymus spp. ; essential oil ; antibacterial effect

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