The dynamics and mechanism of the antimicrobial activity of tea tree oil against bacteria and fungi
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Tea tree oil (TTO) is a yellow liquid extracted from Melaleuca alternifolia. Although the antimicrobial activity of TTO has been known for a long time, its specific antimicrobial effects and mechanism underlying these remain poorly characterized. The present study investigated the chemical composition of TTO and the dynamics and mechanism of its antimicrobial activities in two bacterial and two fungal strains. Gas chromatography–mass spectrometry analysis identified alkenes and alcohols as the main constituents of TTO. Terpinen-4-ol was the most abundant individual component, accounting for approximately 23 % of the TTO. Poisoned food technique assessment showed that the minimum inhibitory concentrations of TTO for bacterial strains (Escherichia coli and Staphylococcus aureus) and fungal strains (Candida albicans and Aspergillus niger) were 1.08 and 2.17 mg/mL, respectively. Antimicrobial dynamic curves showed that with increasing concentrations of TTO, the rate of cell killing and the duration of growth lag phase increased correspondingly. These data indicated that TTO produced concentration and time-dependent antimicrobial effects. The minimum bactericidal and fungicidal concentrations of TTO were 2.17, 4.34, and 4.34 against E. coli, S. aureus, and C. albicans, respectively. However, A. niger conidia were not completely eradicated, even after 3 days in the presence of 17.34 mg/mL TTO. Transmission electron microscopy images indicated that TTO penetrated the cell wall and cytoplasmic membrane of all the tested bacterial and fungal strains. TTO may also penetrate fungal organelle membrane. These findings indicated that TTO maybe exerts its antimicrobial effects by compromising the cell membrane, resulting in loss of the cytoplasm and organelle damage, which ultimate leads to cell death.
KeywordsTea tree oil Escherichia coli Staphylococcus aureus Candida albicans Aspergillus niger
We thank all partners and laboratory members for their kind help. We are obliged to the anonymous reviewers of Applied Microbiology and Biotechnology for their constructive comments.
Compliance with ethical standards
The authors gratefully acknowledge the support of the Nature Science of Foundation of China (No. 31500113), Guangdong Provincial Nature Science of Foundation (No. 2016A030313800), Guangdong Provincial Science and Technology Project (No. 2013B010102014), and Guangzhou Municipal Science and Technology Research Project (No. 201607020020).
Conflict of interest
The authors declare that they have no conflict of interests.
This paper is our original work. It has not been submitted elsewhere, and it is not under consideration in any other journal. This article does not contain any studies with human participants or animals performed by any of the authors. All the authors have seen the manuscript and approved its submission to applied microbiology and biotechnology.
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