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Molecules 2014, 19(3), 2896-2910; doi:10.3390/molecules19032896

Unravelling the Complex Antimicrobial Interactions of Essential Oils — The Case of Thymus vulgaris (Thyme)

1 Department of Pharmaceutical Sciences, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa 2 Department of Pharmacy and Pharmacology, University of Witwatersrand, 7 York Road, Parktown 2193, South Africa
* Author to whom correspondence should be addressed.
Received: 7 February 2014 / Revised: 22 February 2014 / Accepted: 26 February 2014 / Published: 6 March 2014
(This article belongs to the collection Bioactive Compounds)
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Thymus vulgaris has gained tremendous popularity as an ornamental, culinary herb and its use in phytotherapy is well established and supported in the literature. The objective of this study was to explore possible interactions between selected molecules within Thymus vulgaris essential oil (TvEO) to gain a better understanding of how this complex essential oil exerts its antimicrobial activity. Evaluation of the antimicrobial efficacy and interactions were assessed on the essential oil and volatile constituents against various pathogens. Interactions between molecules at various ratios were graphically observed through the construction of isobolograms. Gas chromatography-mass spectrometry (GC-MS) analysis revealed 22 compounds which collectively represent >95% of the oil composition. Based on their minimum inhibitory concentration (MIC) values, they were categorised into weak (≥4 mg mL−1), moderate (2–4 mg mL−1) and noteworthy active (≤2 mg mL−1) compounds. For the combination study, 21% synergistic, 42% additive, 36% indifferent and 1% antagonistic interactions were observed. Most of the interactions were observed between the weak and highly active molecules, and interestingly, no synergistic interaction was observed between the highly active compounds. Synergistic and additive interactions between the strong and weaker antimicrobial constituents present in TvEO enhance the antimicrobial efficacy of this commercially important essential oil.
Keywords: antimicrobial activity; additivity; synergism; essential oil; Thymus vulgaris antimicrobial activity; additivity; synergism; essential oil; Thymus vulgaris
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Ahmad, A.; van Vuuren, S.; Viljoen, A. Unravelling the Complex Antimicrobial Interactions of Essential Oils — The Case of Thymus vulgaris (Thyme). Molecules 2014, 19, 2896-2910.

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