Background: There is an increasing report of bacterial resistance to antibiotics in the world. Also side effects of chemical food preservatives suspected to be carcinogenic have drawn attention towards application of herbal medicine and natural substitutions. In this study, antibacterial activities of essential oils from four medicinal plants and chemical compositions of essential oils from Thymus (T.) eriocalyx and T. persicus of Lorestan were examined.

Materials and Methods: Flowers and leaves from T. persicus, T. eriocalyx, Crocus sativus and Gundelia tolurntortel L. were collected freshly. Essential oils were prepared in Clevenger apparatus and analyzed by GC/MS. Antibacterial activities were examined by disk diffusion and broth microdillution technique, using standard (ATCC) gram positive and negative bacteria and standard (Muller Hinton agar and broth or Isosensitest agar) media in order to determine Minimum Inhibitory (MIC) or Bactericidal (MBC) concentration.

Results: Twenty seven compounds in essential oils from T. Eriocalyx and fifteen in T. persicus were identified. The major compounds were Thymol and Crvacrol which constitute %66 and % 7.5 respectively in essential oils from T. erocalyx and %10 and %25 in T. persicus. Strong antibacterial activities were observed against both gram positive and negative bacteria including S. aureous and P. aeroginosa by T. eriocalyx and T. persicus. Essential oils from T. persicus produced MIC =MBC= 10 /ml against P. aeroginosa which is significant. Essential oils of leaves from Gundela tourntorel and Crocus sativus showed antibacterial activities against some gram positive bacteria.