Survey of the Antimicrobial Activity of Commercially Available Australian Tea Tree (Melaleuca alternifolia) Essential Oil ProductsIn Vitro

Abstract Melaleuca alternifolia essential oil (tea tree oil) is widely used as an ingredient in skin care products because of its recognized biological activities. The European Scientific Committee on Consumer Products constantly promotes research and collection of data on both skin distribution and systemic exposure to tea tree oil components after the application of topical formulations. This study quantitatively evaluates permeation, skin layer distribution (stratum corneum, epidermis, and dermis), and release into the surrounding environment of bioactive tea tree oil markers (i.e., α-pinene, β-pinene, α-terpinene, 1,8-cineole, γ-terpinene, 4-terpineol, α-terpineol) when a 5% tea tree oil formulation is applied at a finite dosing regimen. Permeation kinetics were studied in vitro on pig ear skin using conventional static glass Franz diffusion cells and cells ad hoc modified to monitor the release of markers into the atmosphere. Formulation, receiving phases, and skin layers were analyzed using a fully automatic and solvent-free method based on headspace solid-phase microextraction/gas chromatography-mass spectrometry. This approach affords, for the first time, to quantify tea tree oil markers in the different skin layers while avoiding using solvents and overcoming the existing methods based on solvent extraction. The skin layers contained less than 1% of each tea tree oil marker in total. Only oxygenated terpenes significantly permeated across the skin, while hydrocarbons were only absorbed at trace level. Substantial amounts of markers were released into the atmosphere.

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Effects of Melaleuca alternifolia (Tea Tree) Essential Oil and the Major Monoterpene Component Terpinen-4-ol on the Development of Single- and Multistep Antibiotic Resistance and Antimicrobial Susceptibility

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.05741-11 ◽

2011 ◽

Vol 56 (2) ◽

pp. 909-915 ◽

Cited By ~ 80

Author(s):

Katherine A. Hammer ◽

Christine F. Carson ◽

Thomas V. Riley

Keyword(s):

Antibiotic Resistance ◽

Essential Oil ◽

Antimicrobial Susceptibility ◽

Single Step ◽

Tea Tree Oil ◽

Melaleuca Alternifolia ◽

Antibiotic Resistant ◽

Content Type ◽

Tea Tree ◽

E Coli

ABSTRACTThis study examined the effect of subinhibitoryMelaleuca alternifolia(tea tree) essential oil on the development of antibiotic resistance inStaphylococcus aureusandEscherichia coli. Frequencies of single-step antibiotic-resistant mutants were determined by inoculating bacteria cultured with or without subinhibitory tea tree oil onto agar containing 2 to 8 times the MIC of each antibiotic and with or without tea tree oil. Whereas most differences in resistance frequencies were relatively minor, the combination of kanamycin and tea tree oil yielded approximately 10-fold fewer resistantE. colimutants than kanamycin alone. The development of multistep antibiotic resistance in the presence of tea tree oil or terpinen-4-ol was examined by culturingS. aureusandE. coliisolates daily with antibiotic alone, antibiotic with tea tree oil, and antibiotic with terpinen-4-ol for 6 days. Median MICs for each antibiotic alone increased 4- to 16-fold by day 6. Subinhibitory tea tree oil or terpinen-4-ol did not greatly alter results, with day 6 median MICs being either the same as or one concentration different from those for antibiotic alone. For tea tree oil and terpinen-4-ol alone, day 6 median MICs had increased 4-fold forS. aureus(n= 18) and 2-fold forE. coli(n= 18) from baseline values. Lastly, few significant changes in antimicrobial susceptibility were seen forS. aureusandS. epidermidisisolates that had been serially subcultured 14 to 22 times with subinhibitory terpinen-4-ol. Overall, these data indicate that tea tree oil and terpinen-4-ol have little impact on the development of antimicrobial resistance and susceptibility.

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