In vitro Antimicrobial, Cytotoxic and Radical Scavenging Activities and Chemical Constituents of the Endemic Thymus laevigatus (Vahl)

The leaves of Thymus laevigatus (Vahl), Lamiaceae (Labiatae), an endemic species of Yemen, are traditionally used in the treatment of various disorders including stomach and respiratory system. In a first biological and chemical study of this endemic species we investigated antimicrobial, cytotoxic and antioxidant activities of different extracts of the leaves of this plant. The preliminary phytochemical screening of extracts composition was performed by TLC while the composition of the essential oil was determined by GC-MS. Twelve constituents were detected from the essential oil, which constituted 99.6 % of the total amount. The major constituents of the oil were: carvacrol (84.3 %), p-cymene (4.1 %) p-mentha-1, 4-diene (4.0 %) and trans-anethole (3.6%). The main active components were identified by TLC as carvacrol and anethole for dichloromethane extract and as non-volatile phenols and flavonoids for the methanol extract. The methanol, dichloromethane and aqueous extracts were tested for their antimicrobial activities against five bacteria strains and six human pathogenic fungi. Both methanol and dichloromethane showed strong activities against most human pathogenic strains. In the contrast,  methanol extract showed broader and stronger antibacterial activities than the dichloromethane extract, especially against the Gram-negative bacterium  Pseudomonas aeruginosa. The methanol extract showed the same strong radical scavenging activity in the DPPH assay (14.9mg/ml), when compared to the standard antioxidant, ascorbic acid. In contrast, the cytotoxic activity of the methanol against FL cells, a human amniotic epithelial cell line, was only moderate (IC50 298, 8 mg/ml). On the contrary, the water extract did not show any biological activity. Results presented here suggest that the essential oil and extracts ofThymus laevigatus possess strong antimicrobial and antioxidant properties, and therefore, they can be used as a natural preservative ingredient in food and/or pharmaceutical industry