Planta Med 2009; 75(11): 1231-1236
DOI: 10.1055/s-0029-1185541
Pharmacology
Original Paper
© Georg Thieme Verlag KG Stuttgart · New York

Additive Antmicrobial Effects of the Active Components of the Essential Oil of Thymus vulgaris – Chemotype Carvacrol

Felix Iten1 , Reinhard Saller1 , Gudrun Abel2 , Jürgen Reichling3
  • 1Institute of Complementary Medicine, University Hospital Zurich, Zurich, Switzerland
  • 2Bionorica AG, The Phytoneering Company, Neumarkt/Opf., Germany
  • 3Institute of Pharmacy and Molecular Biotechnology, Department of Biology, University of Heidelberg, Heidelberg, Germany
Further Information

Publication History

received January 28, 2009 revised February 17, 2009

accepted February 28, 2009

Publication Date:
03 April 2009 (online)

Abstract

Herbal remedies are multicomponent mixtures by their nature as well as by pharmaceutical definition. Being a multicomponent mixture is not only a crucial property of herbal remedies, it also represents a precondition for interactions such as synergism or antagonism. Until now, only a few phytomedicines are accurately described concerning the interactions of their active components. The aim of this study was to search for interactions within such a naturally given multi-component mixture and to discuss the pharmaceutical and clinical impacts. The thyme oil chosen for the examination belongs to the essential oils with the most pronounced antimicrobial activity. Antibiotic activity of thyme oil and single active components were tested against six different strains of microorganisms. The checkerboard assay was used to search for interactions. The time-kill assay was used to verify the observed effects and to get information about the temporal resolution of the antimicrobial activity. The degree of the detected interactions corresponded with the demarcating FICI measure of 0.5, which separates the additive from the over-additive (synergistic) effects. Therefore, the observed effect was called a “borderline case of synergism” or, respectively, “partial synergism”. Partial synergism was observed only in the presence of Klebsiella pneumoniae. Additive antimicrobial activity was observed for the combination of the two monosubstances carvacrol plus linalool and thymol plus linalool as well as with the combination of the two essential oils of the carvacrol and linalool chemotypes. An increase of the carvacrol oil concentration from one to two times the MIC resulted in a considerable acceleration of the kill-rate. Thyme oil is composed of several different components that show antimicrobial activity (at least: carvacrol, thymol and linalool). The antimicrobial activity of thyme oil is partly based on additive effects, which might especially enhance the rapidity of the antimicrobial action. In addition, a mixture of several active ingredients that varies in its composition from year to year and from lot to lot as is the case with herbal remedies may be more stable concerning the antimicrobial activity than mixtures containing just a single active component.

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Felix Iten

Institute of Complementary Medicine
University Hospital Zurich

Rämistrasse 100

8091 Zurich

Switzerland

Phone: + 41 4 42 55 24 29

Fax: + 41 4 42 55 43 94

Email: felix.iten@usz.ch