Activity Of Tea Tree Oil Research Articles

An evaluation of the mutagenic potential of commercially available tea tree oil in the United Kingdom

Summary An investigation of the in vitro mutagenic potential of a variety of commercially available and widely used tea tree essential oils was performed. The mutagenic potential of tea tree oil ( Melaleuca alternifolia ) was examined using the Histidine Reversion Assay (Ames Test). One of the major components, the monoterpenoid terpinen-4-ol, was also examined to determine if it demonstrated any mutagenic potential. Salmonella typhimurium (TA102, TA100 and TA98) was utilised in the Ames test. Commercially available tea tree oils were tested. Despite a previous report demonstrating a possible mutagenic trend in a single commercially available tea tree product, no mutagenic effect was determined in any of the brands of tea tree oil on any of the strains of Salmonella examined with or without metabolic activation. The same negative results were obtained for the terpinen-4-ol component examined. There was a clear evidence of toxicity of tea tree oil on all Salmonella strains and also by terpinen-4-ol at higher dose levels. It is suggested that terpinen-4-ol may contribute significantly to the widely reported antibacterial activity of tea tree oil.

Assessment of the antibacterial activity of tea tree oil using the European EN 1276 and EN 12054 standard suspension tests

The activity of tea tree oil (TTO) and TTO-containing products was investigated according to the EN 1276 and EN 12054 European suspension methods. The activity of different concentrations of TTO, a hygienic skin wash (HSW), an alcoholic hygienic skin wash (AHSW) and an alcoholic hand rub (AHR) was investigated. These formulations were assessed in perfect conditions with the EN 12054 test, and in perfect conditions as well as in the presence of interfering substances with the EN 1276 test, against Staphylococcus aureus, Acinetobacter baumannii, Escherichia coli and Pseudomonas aeruginosa. With the latter test, the activity of the same formulations without TTO was also assessed as a control. With the EN 1276 test, the AHR achieved a >10(5)-fold reduction against all four test organisms within a 1-min contact time. The AHSW achieved a >or=10(5)-fold reduction against A. baumannii after a 1-min contact time and against S. aureus, E. coli and P. aeruginosa after a 5-min contact time. The efficacy of TTO appeared to be dependent on the formulation and the concentration tested, the concentration of interfering substances and, lastly, the organism tested. Nevertheless, 5% TTO achieved a >10(4)-fold reduction in P. aeruginosa cell numbers after a 5-min contact time in perfect conditions. TTO (5%) in 0.001% Tween 80 was significantly more active against E. coli and P. aeruginosa than against S. aureus and A. baumannii. With the EN 12054 test, after a 1-min contact time, 5% TTO in 0.001% Tween 80 and the AHSW achieved a >10(4)-fold reduction in E. coli and A. baumannii cell numbers, respectively, and the AHR achieved a >4 log10 reduction against all organisms tested. The formulations used in this study are now being tested using a novel ex vivo method as well as the in vivo European standard handwashing method EN 1499.

Tolerance of Pseudomonas aeruginosa to Melaleuca alternifolia (tea tree) oil is associated with the outer membrane and energy-dependent cellular processes.

The essential oil of Melaleuca alternifolia (tea tree oil) and its components have antimicrobial activity against a wide range of Gram-positive and Gram-negative bacteria, fungi and viruses. The mechanism(s) by which Pseudomonas aeruginosa NCTC 10662 maintains a decreased susceptibility to tea tree oil and components was investigated. Ethylene diamine tetraacetic acid enhanced the antimicrobial activity of tea tree oil and terpinen-4-ol against stationary phase P. aeruginosa while polymyxin B nonapeptide enhanced the activity of tea tree oil and gamma-terpinene. Pre-treatment with the protonophore carbonyl cyanide m-chlorophenylhydrazone increased the susceptibility of exponential phase cells to sub-inhibitory concentrations of tea tree oil, terpinen-4-ol and gamma-terpinene, indicating that intrinsic tolerance to tea tree oil and components is substantially energy dependent. Increased tolerance to tea tree oil in P. aeruginosa is directly related to the barrier and energy functions of the outer membrane, and may involve efflux systems.

Antifungal effects of Melaleuca alternifolia (tea tree) oil and its components on Candida albicans, Candida glabrata and Saccharomyces cerevisiae.

The aim of this study was to investigate the mechanism of action of tea tree oil and its components against Candida albicans, Candida glabrata and Saccharomyces cerevisiae. Yeast cells were treated with tea tree oil or components, at one or more concentrations, for up to 6 h. During this time, alterations in permeability were assessed by measuring the leakage of 260 nm absorbing materials and by the uptake of Methylene Blue dye. Membrane fluidity was measured by 1,6-diphenyl-1,3,5-hexatriene fluorescence. The effects of tea tree oil on glucose-induced medium acidification were quantified by measuring the pH of cell suspensions in the presence of both tea tree oil and glucose. The treatment of C. albicans with tea tree oil and components at concentrations of between 0.25 and 1.0% (v/v) altered both permeability and membrane fluidity. Membrane fluidity was also increased when C. albicans was cultured for 24 h with 0.016%-0.06% (v/v) tea tree oil, as compared with control cells. For all three organisms, glucose-induced acidification of the external medium was inhibited in a dose-dependent manner in the presence of 0.2%, 0.3% and 0.4% tea tree oil. Data from this study support the hypothesis that tea tree oil and components exert their antifungal actions by altering membrane properties and compromising membrane-associated functions.

Terpinen-4-ol, the main component of Melaleuca alternifolia (tea tree) oil inhibits the in vitro growth of human melanoma cells.

The search for innovative therapeutic approaches based on the use of new substances is gaining more interest in clinical oncology. In this in vitro study the potential anti-tumoral activity of tea tree oil, distilled from Melaleuca alternifolia, was analyzed against human melanoma M14 WT cells and their drug-resistant counterparts, M14 adriamicin-resistant cells. Both sensitive and resistant cells were grown in the presence of tea tree oil at concentrations ranging from 0.005 to 0.03%. Both the complex oil (tea tree oil) and its main active component terpinen-4-ol were able to induce caspase-dependent apoptosis of melanoma cells and this effect was more evident in the resistant variant cell population. Freeze-fracturing and scanning electron microscopy analyses suggested that the effect of the crude oil and of the terpinen-4-ol was mediated by their interaction with plasma membrane and subsequent reorganization of membrane lipids. In conclusion, tea tree oil and terpinen-4-ol are able to impair the growth of human M14 melanoma cells and appear to be more effective on their resistant variants, which express high levels of P-glycoprotein in the plasma membrane, overcoming resistance to caspase-dependent apoptosis exerted by P-glycoprotein-positive tumor cells.

In vitro and in vivo activity of tea tree oil against azole-susceptible and -resistant human pathogenic yeasts.

A tea tree oil (TTO) preparation of defined chemical composition was studied, using a microbroth method, for its in vitro activity against 115 isolates of Candida albicans, other Candida species and Cryptococcus neoformans. The fungal strains were from HIV-seropositive subjects, or from an established type collection, including reference and quality control strains. Fourteen strains of C. albicans resistant to fluconazole and/or itraconazole were also assessed. The same preparation was also tested in an experimental vaginal infection using fluconazole-itraconazole-susceptible or -resistant strains of C. albicans. TTO was shown to be active in vitro against all tested strains, with MICs ranging from 0.03% (for C. neoformans) to 0.25% (for some strains of C. albicans and other Candida species). Fluconazole- and/or itraconazole-resistant C. albicans isolates had TTO MIC50s and MIC90s of 0.25% and 0.5%, respectively. TTO was highly efficacious in accelerating C. albicans clearance from experimentally infected rat vagina. Three post-challenge doses of TTO (5%) brought about resolution of infection regardless of whether the infecting C. albicans strain was susceptible or resistant to fluconazole. Overall, the use of a reliable animal model of infection has confirmed and extended our data on the therapeutic effectiveness of TTO against fungi, in particular against C. albicans.

Antimicrobial activity of garlic, tea tree oil, and chlorhexidine against oral microorganisms

To compare the antimicrobial activity of tea tree oil, garlic, and chlorhexidine solutions against oral microorganisms. The five-week study consisted of thirty subjects. The first week was considered baseline. All subjects used a control solution (second week), and were randomly divided into the three groups (third week): G1-0.12% chlorhexidine; G2 - 2.5% garlic (Allium sativum, L.); and G3 - 0.2% tea tree oil (Melaleuca alternifolia). Dishes containing blood agar and Mitis Salivarius Bacitracin agar (MSB) were inoculated with the subjects' saliva (collected twice a week). Total microorganisms and mutans streptococci were counted in blood agar and MSB, respectively. Chlorhexidine and garlic groups showed antimicrobial activity against mutans streptococci, but not against other oral microorganisms. The tea tree oil group showed antimicrobial activity against mutans streptococci and other oral microorganisms. Maintenance of reduced levels of microorganisms was observed only for garlic and tea tree oil during the two consecutive weeks (fourth and fifth). Unpleasant taste (chlorhexidine 40%, tea tree oil 30%, garlic 100%), burning sensation (chlorhexidine 40%, tea tree oil 60%, garlic 100%), bad breath (chlorhexidine 40%, tea tree oil 20%, garlic 90%), and nausea (chlorhexidine 0%, tea tree oil 10%, garlic 30%) were reported. Garlic and tea tree oil might be an alternative to chlorhexidine.

Topical antimicrobial therapy with tea tree oil: fact or fantasy

T his paper reviews briefly the evidence that tea tree oil may be suitable as a topical antimicrobial agent. Tea tree oil is the essential oil extracted by steam distillation from the Australian native tree Melaleuca alternifolia. It has a long history of use in Australia, and has emerged as a possible topical antimicrobial because of antimicrobial resistance to conventional agents. The history, production and chemistry of tea tree oil are described. The in vitro antimicrobial activity of tea tree oil has now been reported in numerous papers, and there is good evidence for antibacterial, antifungal and, to a lesser extent, antiviral activity. What is lacking is sufficient numbers of clinical trials to verify this efficacy in vivo. Tea tree oil is only safe to use as a topical agent and although skin sensitivity has been a concern, the evidence for this is not strong. However, long-term usage studies are still required. Based on the published data, tea tree oil may prove to be a very useful topical antimicrobial and there is a role for infection control practitioners in the validation of its use in clinical practice.

Mechanism of action of Melaleuca alternifolia (tea tree) oil on Staphylococcus aureus determined by time-kill, lysis, leakage, and salt tolerance assays and electron microscopy.

The essential oil of Melaleuca alternifolia (tea tree) has broad-spectrum antimicrobial activity. The mechanisms of action of tea tree oil and three of its components, 1,8-cineole, terpinen-4-ol, and alpha-terpineol, against Staphylococcus aureus ATCC 9144 were investigated. Treatment with these agents at their MICs and two times their MICs, particularly treatment with terpinen-4-ol and alpha-terpineol, reduced the viability of S. aureus. None of the agents caused lysis, as determined by measurement of the optical density at 620 nm, although cells became disproportionately sensitive to subsequent autolysis. Loss of 260-nm-absorbing material occurred after treatment with concentrations equivalent to the MIC, particularly after treatment with 1,8-cineole and alpha-terpineol. S. aureus organisms treated with tea tree oil or its components at the MIC or two times the MIC showed a significant loss of tolerance to NaCl. When the agents were tested at one-half the MIC, only 1,8-cineole significantly reduced the tolerance of S. aureus to NaCl. Electron microscopy of terpinen-4-ol-treated cells showed the formation of mesosomes and the loss of cytoplasmic contents. The predisposition to lysis, the loss of 260-nm-absorbing material, the loss of tolerance to NaCl, and the altered morphology seen by electron microscopy all suggest that tea tree oil and its components compromise the cytoplasmic membrane.

Antifungal effect of Australian tea tree oil on Malassezia pachydermatis isolated from canines suffering from cutaneous skin disease.

The lipophilic yeast Malassezia pachydermatis is part of the normal skin flora of most warm-blooded organisms. In a number of surveys it could be demonstrated that this yeast species might be involved in different skin diseases like seborrhoeic dermatitis, especially in dogs and cats. In order to look for an alternative therapeutic agent to the commonly used antimycotic and antiseptic synthetic substances the in vitro activity of Australian tea tree oil, the essential oil of Melaleuca alternifolia, against several strains of Malassezia pachydermatis was examined. All tested strains showed remarkably high susceptibility to tea tree oil. With these results the excellent antibacterial activity of tea tree oil is extended to a new group of fungal pathogens colonizing mainly mammals' skin. During the last ten years there was an increasing popularity of tea tree oil containing human health care products. The presented data open up new horizons for this essential oil as a promising alternative agent for topical use in veterinary medicine as well.

Tea tree oil reduces the swelling associated with the efferent phase of a contact hypersensitivity response.

To examine the anti-inflammatory activities of tea tree oil (TTO) in vivo. Mice were sensitized to a chemical hapten, trinitrochlorobenzene, on their ventral skin and 7 days later challenged (or re-exposed) on their dorsal skin with the same hapten. TTO applied 30 min before or up to 7 h after to the same dorsal site as hapten challenge caused a significant reduction in skin swelling after 24 h. TTO reduced oedema but not the influx of inflammatory cells. This finding was supported by the inability of TTO to suppress TNFalpha-induced E-selectin expression by human umbilical vein endothelial cells. TTO did not suppress irritant- or ultraviolet B-induced oedema. Topical TTO, specifically the TTO components, terpinen-4-ol and alpha-terpineol can regulate the oedema associated with the efferent phase of a contact hypersensitivity response.

Comparison of Microdilution and Disc Diffusion Methods in Assessing the in vitro Activity of Fluconazole and Melaleuca alternifolia (Tea Tree) Oil Against Vaginal Candida Isolates

The in vitro activity of fluconazole and Melaleuca alternifolia (tea tree) oil was evaluated against 99 vaginal Candida strains by the broth microdilution and disc diffusion methods. The microdilution method was performed in accordance with NCCLS-M27A guidelines. An investigational method was used for the disc diffusion test. Fluconazole and tea tree oil minimum inhibitory concentrations (MICs) obtained at 48 h tended to increase 1- to 2-fold or remain the same compared to 24 h readings for most of the isolates tested. C. krusei and C. norvegensis had significantly higher MICs and smaller inhibition zones for fluconazole compared to other species. Tea tree oil MICs were found to be similar, in general, for all Candida spp. tested. The geometric mean MIC of tea tree oil for all isolates was 2.2% (range, 0.25-4%) at 24 h and 3.0% (range, 1-8%) at 48 h. Tea tree oil mean inhibition zone diameter was 24 mm (range,14-42 mm) at 24 h and 15.8 mm (range,10-35 mm) at 48 h. in vitro activity of tea tree oil against fluconazole-resistant Candida strains was of particular interest. The isolates had similar tea tree oil MICs and inhibition zone diameters regardless of their fluconazole susceptibility profile. Tea tree oil MIC ranges (inhibition zone diameter ranges) were 2-4% (12-21 mm) and 2% (35 mm) at 48 h for C. krusei and C. norvegensis, respectively. These results suggest that tea tree oil MICs of the fluconazole-resistant isolates are comparable to those of fluconazole-susceptible isolates. This in vitro finding is promising for potential use of topical tea tree oil formulations in the treatment of candidiasis due to fluconazole-resistant strains.

In Vitro Activity of Tea Tree Oil Against Candida albicans Mycelial Conversion and Other Pathogenic Fungi

The antifungal activity of Melaleuca alternifolia Maiden (Myrtaceae) essential oil against yeasts (Candida spp., Schizosaccharomyces pombe, Debaryomyces hansenii) and dermatophytes (Microsporum spp. and Tricophyton spp.) is reported. We focused on the ability of tea tree oil to inhibit Candida albicans conversion from the yeast to the pathogenic mycelial form. Moreover we carried out broth microdilution test and contact tests to evaluate the killing time. M. alternifolia essential oil inhibited the conversion of C. albicans from yeast to the mycelial form at a concentration of 0.16% (v/v). The minimum inhibitory concentrations (MICs) ranged from 0.12% to 0.50% (v/v) for yeasts and 0.12% to 1% (v/v) for dermatophytes; the cytocidal activity was generally expressed at the same concentration. These results, if considered along with the lipophilic nature of the oil which enables it to penetrate the skin, suggest it may be suitable for topical therapeutic use in the treatment of fungal mucosal and cutaneous infections.

A Comparative Study of the in vitro Antimicrobial Activity of Tea Tree Oils s.l. with Special Reference to the Activity of β-Triketones

The in vitro antibacterial and antifungal activities of Australian tea tree oil, cajuput oil, niaouli oil, kanuka oil and manuka oil as well as of a beta-triketone complex isolated from manuka oil were investigated in a constituent-oriented study. The compositions of the oils were analysed by capillary GLC and GLC-MS. The MICs for sixteen different microorganisms were determined applying the broth dilution method. Australian tea tree oil showed the best overall antimicrobial effect. The best inhibitory effects on Gram-positive bacteria and dermatophytes were achieved with manuka oil due to its beta-triketone content.

Biological activity of Melaleuca alternifolia (tea tree) oil component, terpinen-4-ol, in human myelocytic cell line HL-60

Background: Tea tree oil is an aboriginal Australian traditional medicine for bruises, insect bites, and skin infections. It was redis-covered in the 1920s as a topical antiseptic that is more effective than Phenol. Previous studies have demonstrated its antiseptic qual-ities, but its effects on human white blood cells have never been investigated. Objective: To test the hypothesis that tea tree oil exerts its antiseptic action through white blood cell activation. Methods: Crude oil and the purified “active” component were studied by using a model system that responds to bioactive components by induction of differentiation in white blood cells. Methods used included white blood cell oxidative burst assay (nitroblue tetrazolium [NBT] dye reduction); cell prolif-eration assay (tritiated thymidine incorporation); cell surface differentiation marker assay (flow cytometric quantitation of phycoerythrin-anti-CD 11b binding); cell via-bility assay (trypan blue exclusion); and cellu-lar differentiation enzyme assay (white cell esterase staining). Results: Collectively, five assays that measure differentiation in white blood cells indicated monocytic differentiation after treatment with either crude oil or the purified active component. Both the crude oil and the purified active component, (+:−) terpinene-4-ol, caused a similar type and amount of differentiation. The cul-ture of cells in medium containing serum caused more activation than in medium containing no serum. Conclusion: The antiseptic activity of tea tree oil appears to be due, in part, to white blood cell activation. (J Manipulative Physiol Ther 1999;22:447–53)

Influence of organic matter, cations and surfactants on the antimicrobial activity of Melaleuca alternifolia (tea tree) oil in vitro.

The effect of some potentially interfering substances and conditions on the antimicrobial activity of Melaleuca alternifolia (tea tree) oil was investigated. Agar and broth dilution methods were used to determine minimum inhibitory and cidal concentrations of tea tree oil in the presence and absence of each potentially interfering substance. Activity was determined against Gram-positive and -negative bacteria, and Candida albicans. Minimum inhibitory or cidal concentrations differed from controls by two or more dilutions, for one or more organisms, where Tween-20, Tween-80, skim-milk powder and bovine serum albumin were assessed. These differences were not seen when assays were performed in anaerobic conditions, or in the presence of calcium and magnesium ions. The effect of organic matter on the antimicrobial activity of tea tree oil was also investigated by an organic soil neutralization test. Organisms were exposed to lethal concentrations of tea tree oil ranging from 1-10% (v/v), in the presence of 1-30% (w/v) dry bakers' yeast. After 10 min contact time, viability was determined. At > or = 1%, organic matter compromised the activity of each concentration of tea tree oil against Staphylococcus aureus and C. albicans. At 10% or more, organic matter compromised the activity of each tea tree oil concentration against Pseudomonas aeruginosa. Organic matter affected 1 and 2% tea tree oil, but not 4 and 8%, against Escherichia coli. In conclusion, organic matter and surfactants compromise the antimicrobial activity of tea tree oil, although these effects vary between organisms.

1998 William J. Stickel Bronze Award. Antifungal activity of Melaleuca alternifolia (tea-tree) oil against various pathogenic organisms.

Tea-tree oil (oil of Melaleuca alternifolia) has recently received much attention as a natural remedy for bacterial and fungal infections of the skin and mucosa. As with most naturally occurring agents, claims of effectiveness have been only anecdotal; however, several published studies have recently demonstrated tea-tree oil's antibacterial activity. This study was conducted to determine the activity of tea-tree oil against 58 clinical isolates: Candida albicans (n = 10), Trichophyton rubrum (n = 8), Trichophyton mentagrophytes (n = 9), Trichophyton tonsurans (n = 10), Aspergillus niger (n = 9), Penicillium species (n = 9), Epidermophyton floccosum (n = 2), and Microsporum gypsum (n = 1). Tea-tree oil showed inhibitory activity against all isolates tested except one strain of E floccosum. These in vitro results suggest that tea-tree oil may be useful in the treatment of yeast and fungal mucosal and skin infections.

Antifungal activity of the essential oil of Melaleuca alternifolia (tea tree oil) against pathogenic fungi in vitro.

The in vitro antifungal activity of tea oil, the essential oil of Melaleuca alternifolia, has been evaluated against 26 strains of various dermatophyte species, 54 yeasts, among them 32 strains of Candida albicans and other Candida sp. as well as 22 different Malassezia furfur strains. Minimum inhibitory concentrations (MIC) of tea tree oil were measured by agar dilution technique. Tea tree oil was found to be able to inhibit growth of all clinical fungal isolates. For the investigated dermatophytes MIC values from 1,112.5 to 4,450.0 micrograms/ml with a geometric mean of 1,431.5 micrograms/ml were demonstrated. Both C. albicans strains and the other strains belonging to the genus Candida and Trichosporon appeared to be slightly less susceptible to tea tree oil in vitro. However, their MIC values, which varied from 2,225.0 to 4,450.0 micrograms/ml (geometric mean 4,080 micrograms/ml), indicated moderate susceptibility to the essential oil of M. alternifolia. The lipophilic yeast M. furfur seemed to be most susceptible to tea tree oil. MIC values between 556.2 and 4,450.0 micrograms/ml (geometric mean 1,261.5 micrograms/ml) were found against the tested M. furfur strains. However, when calculated as percentage tea tree oil of the agar, the above-mentioned concentrations correspond to 0.5-0.44% tea tree oil content. These values are far below the usual relatively high therapeutic concentrations of the agent; approximately 5-10% solution or even the concentrated essential oil are used for external treatment. In comparison with tea tree oil, in vitro susceptibility against miconazole, an established topical antifungal, was tested. As expected, very low MIC values for miconazole were found for dermatophytes (geometric mean 0.2 microgram/ml), yeasts (geometric mean 1.0 microgram/ml), and M. furfur (geometric mean 2.34 micrograms/ml). It is suggested that the in vivo effect of tea tree oil ointment in the therapy of fungal infections of the skin and mucous membranes as well as in the treatment of dandruff, a mild form of seborrheic dermatitis, may be at least partly due to an antifungal activity of tea tree oil.

Susceptibility of Propionibacterium acnes to the essential oil of Melaleuca alternifolia

There is little published information about the anti- bacterial activity of tea tree oil, although the oil is subject to an Australian Standard (AS 2782-1985) and is widely avail- able both in Australia and overseas. The Australian Stan- dard sets compositional limits for only two of the components of tea tree oil, terpinen-4-01, reputedly the antibacterial component, and 1,8-cineole, a putative skin irritant (Carson and Riley 1993).

The antimicrobial activity of tea tree oil

The antimicrobial activity of tea tree oil