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Int J Antimicrob Agents. 2008 Aug;32(2):170-3. doi: 10.1016/j.ijantimicag.2008.03.013. Epub 2008 Jun 20.

Frequencies of resistance to Melaleuca alternifolia (tea tree) oil and rifampicin in Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis.

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Discipline of Microbiology and Immunology, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA, Australia.


This study was conducted to determine the frequencies at which single-step mutants resistant to tea tree oil and rifampicin occurred amongst the Gram-positive organisms Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. For tea tree oil, resistance frequencies were very low at <10(-9). Single-step mutants resistant to tea tree oil were undetectable at two times the minimum inhibitory concentration (MIC) for S. aureus RN4220 and derivative mutator strains or at 3 x MIC for the remaining S. aureus strains, including a clinical meticillin-resistant S. aureus isolate. Similarly, no mutants were recovered at 2x MIC for S. epidermidis or at 1x MIC for E. faecalis. Resistance frequencies determined in vitro for rifampicin (8 x MIC) ranged from 10(-7) to 10(-8) for all isolates, with the exception of the S. aureus mutator strains, which had slightly higher frequencies. These data suggest that Gram-positive organisms such as Staphylococcus and Enterococcus spp. have very low frequencies of resistance to tea tree oil.

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