Composition and in vitro antimicrobial activity of the essential oil of Thymus herba-barona Loisel growing wild in Sardinia

Two samples of the essential oils from Thymus berba-barona Loisel (Labiatae) of Sardinian origin were chemically characterized and their antimicrobial activity evaluated, in comparison with T. vulgaris and T. serpyllum oils, on the basis of their minimum inhibitory concentrations (M.I.C.s) and of the contact times required to totally inhibit development of microorganisms. GC and GC/MS analysis showed that the main components of essential oils of T. berba-barbona were carvacrol (75.4% and 73.0%), borneol (3.6% and 6.4%) and p-cymene (3.9% and 3.3%), while the percentage of thymol was very low (1.0% and 0.7%). Results of the antimicrobial investigation demonstrated that both oils possessed similar and relevant microbicidial activities, especially against Gram+ bacteria (M.I.C.s range 0.125-0.500 mg/mL) and mycetes (M.I.C.s 0.125-0.500 mg/mL). At inhibitory concentrations, times required to kill microbial inocula (5-10 min) are comparable with those of chlorhexidine gluconate, an antiseptic with a broad range of antimicrobial activities. The strong activity of T. berba-barona oils is very probably due to the presence of carvacrol, which was found from our screenings to exhibit a similar antimicrobial activity. Our findings provide for a rationale basis of a possible utilization of this oil in fields requiring safe and cheap compounds with antiseptic and preservative properties, such as cosmetic, pharmaceutical and food industries.