Antimicrobial activity and composition of essential oils from Thymus mastichina L. collected in Beira Interior (Portugal)

Thymus mastichina L. is an endemic plant of the Iberian Peninsula and it is widely spread in Portugal. In this work we evaluated the antimicrobial activity of the essential oil from T. mastichina against genital microorganisms. The aerial parts of at least ten wild plants were collected, during flowering phase, from two different places in Portugal (Pinhel and Vale do Tejo). Essential oils were extracted by hydrodistilation for 2h, using a Clevenger-type apparatus and analyzed by GC-FID and GC-MS. The identities of the oils essentials components were established from their GC retention indices, relative to C7-C25 n-alkanes, and by comparison computer matching with the Wiley mass spectra library, and whenever possible, by co-injection with standards available at the laboratory. The main components were 1,8-cineol; linalool; α-terpineol; β-pinene; carvacrol; α-pinene.The antimicrobial activity against Candida spp. S. aureus, S. agalactea and S. epidermidis was studied, by determination of minimum inhibitory concentrations (MIC) and minimum lethal concentration (MLC), according to the CLSI macro method and respectively. The essential oils were able to inhibit all microorganisms tested, being C. albicans the most susceptible species, probably due to the inhibition of germ tube formation. However, the results show a lower profile than other antimicrobial chemotypes in the literature. This clearly demonstrates the contribution of the chemical composition of essential oil in its bioactivity. Thus, the production of plants grown under controlled conditions, specific for the production of selected essential oils chemotypes is vital to ensure its bioactivity.

Keywords: Thymus mastichina L; essentials oils; antimicrobial activity; 1,8-cineol