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

OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Non-antibiotic therapies for infectious diseases

The emergence of multiple antibiotic resistant organisms in the general community is a potentially serious threat to public health. The emergence of antibiotic resistance has not yet prompted a radical revision of antibiotic utilisation. Instead it has prompted the development of additional antibiotics. Unfortunately, this does not relieve the underlying selection pressure that drives the development of resistance. A paradigm shift in the treatment of infectious disease is necessary to prevent antibiotics becoming obsolete and, where appropriate, alternatives to antibiotics ought to be considered. There are already several non-antibiotic approaches to the treatment and prevention of infection including probiotics, phages and phytomedicines. There is some evidence that probiotics such as Lactobacillus spp. or Saccharomyces boulardii are useful in the prevention and treatment of diarrhoea, including Clostridium difficile-associated diarrhoea that can be difficult to treat and recurs frequently. Bacteriophages have received renewed attention for the control of both staphylococcal and gastrointestinal infections. Phytomedicines that have been utilised in the treatment of infections include artesunate for malaria, tea tree oil for skin infections, honey for wound infections, mastic gum for Helicobacter pylori gastric ulcers and cranberry juice for urinary tract infections. Many infections may prove amenable to safe and effective treatment with non-antibiotics.

Susceptibility of oral bacteria to Melaleuca alternifolia (tea tree) oil in vitro

The in vitro activity of Melaleuca alternifolia (tea tree) oil against 161 isolates of oral bacteria from 15 genera was determined. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) ranged from 0.003 to 2.0% (v/v). MIC90 values were 1.0% (v/v) for Actinomyces spp., Lactobacillus spp., Streptococcus mitis and Streptococcus sanguis, and 0.1% (v/v) for Prevotella spp. Isolates of Porphyromonas, Prevotella and Veillonella had the lowest MICs and MBCs, and isolates of Streptococcus, Fusobacterium and Lactobacillus had the highest. Time kill studies with Streptococcus mutans and Lactobacillus rhamnosus showed that treatment with > or = 0.5% tea tree oil caused decreases in viability of >3 log colony forming units/ml after only 30 s, and viable organisms were not detected after 5 min. These studies indicate that a range of oral bacteria are susceptible to tea tree oil, suggesting that tea tree oil may be of use in oral healthcare products and in the maintenance of oral hygiene.

Antifungal activity of the components of Melaleuca alternifolia (tea tree) oil

AIMS

To investigate the in vitro antifungal activity of the components of Melaleuca alternifolia (tea tree) oil.

METHODS AND RESULTS

Activity was investigated by broth microdilution and macrodilution, and time kill methods. Components showing the most activity, with minimum inhibitory concentrations and minimum fungicidal concentrations of < or =0.25%, were terpinen-4-ol, alpha-terpineol, linalool, alpha-pinene and beta-pinene, followed by 1,8-cineole. The remaining components showed slightly less activity and had values ranging from 0.5 to 2%, with the exception of beta-myrcene which showed no detectable activity. Susceptibility data generated for several of the least water-soluble components were two or more dilutions lower by macrodilution, compared with microdilution.

CONCLUSIONS

All tea tree oil components, except beta-myrcene, had antifungal activity. The lack of activity reported for some components by microdilution may be due to these components becoming absorbed into the polystyrene of the microtitre tray. This indicates that plastics are unsuitable as assay vessels for tests with these or similar components.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has identified that most components of tea tree oil have activity against a range of fungi. However, the measurement of antifungal activity may be significantly influenced by the test method.

In vitro activity of Melaleuca alternifolia (tea tree) oil against dermatophytes and other filamentous fungi

The in vitro activity of Melaleuca alternifolia (tea tree) oil against dermatophytes (n = 106) and filamentous fungi (n = 78) was determined. Tea tree oil MICs for all fungi ranged from 0.004% to 0.25% and minimum fungicidal concentrations (MFCs) ranged from <0.03% to 8.0%. Time-kill experiments with 1-4 x MFC demonstrated that three of the four test organisms were still detected after 8 h of treatment, but not after 24 h. Comparison of the susceptibility to tea tree oil of germinated and non-germinated Aspergillus niger conidia showed germinated conidia to be more susceptible than non-germinated conidia. These data demonstrate that tea tree oil has both inhibitory and fungicidal activity.

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.

Safety, efficacy and provenance of tea tree (Melaleuca alternifolia) oil

The identity, sources and composition of tea tree (Melaleuca alternifolia) oil are discussed, and earlier errors in the literature indicated. Reports of both therapeutic and allergenic effects are reviewed.

The water-soluble components of the essential oil of Melaleuca alternifolia (tea tree oil) suppress the production of superoxide by human monocytes, but not neutrophils, activated in vitro

OBJECTIVE

To evaluate the regulatory properties of the essential oil of Melaleuca alternifolia (tea tree oil) on the production of oxygen derived reactive species by human peripheral blood leukocytes activated in vitro.

MATERIALS AND METHODS

The ability of tea tree oil to reduce superoxide production by neutrophils and monocytes stimulated with N-formyl-methionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) was examined.

RESULTS

The water-soluble fraction of tea tree oil had no significant effect on agonist-stimulated superoxide production by neutrophils, but significantly and dose-dependently suppressed agonist-stimulated superoxide production by monocytes. This suppression was not due to cell death. Chemical analysis identified the water-soluble components to be terpinen-4-ol, alpha-terpineol and 1,8-cineole. When examined individually, terpinen-4-ol significantly suppressed fMLP- and LPS- but not PMA-stimulated superoxide production; alpha-terpineol significantly suppressed fMLP-, LPS- and PMA-stimulated superoxide production; 1,8-cineole was without effect.

CONCLUSION

Tea tree oil components suppress the production of superoxide by monocytes, but not neutrophils, suggesting the potential for selective regulation of cell types by these components during inflammation.

Tea tree oil as an alternative topical decolonization agent for methicillin-resistant Staphylococcus aureus

The combination of a 4% tea tree oil nasal ointment and 5% tea tree oil body wash was compared with a standard 2% mupirocin nasal ointment and triclosan body wash for the eradication of methicillin-resistant Staphylococcus aureus carriage. The tea tree oil combination appeared to perform better than the standard combination, although the difference was not statistically significant due to the small number of patients.

Terpinen-4-ol, the main component of the essential oil of Melaleuca alternifolia (tea tree oil), suppresses inflammatory mediator production by activated human monocytes

OBJECTIVE AND DESIGN

To evaluate potential antiinflammatory properties of tea tree oil, the essential oil steam distilled from the Australian native plant, Melaleuca alternifolia.

MATERIAL AND METHODS

The ability of tea tree oil to reduce the production in vitro of tumour necrosis factor-alpha (TNFalpha), interleukin (IL)-1beta, IL-8, IL-10 and prostaglandin E2 (PGE2) by lipopolysaccharide (LPS)-activated human peripheral blood monocytes was examined.

RESULTS

Tea tree oil emulsified by sonication in a glass tube into culture medium containing 10% fetal calf serum (FCS) was toxic for monocytes at a concentration of 0.016% v/v. However, the water soluble components of tea tree oil at concentrations equivalent to 0.125% significantly suppressed LPS-induced production of TNFalpha, IL-1beta and IL-10 (by approximately 50%) and PGE2 (by approximately 30%) after 40 h. Gas chromatography/mass spectrometry identified terpinen-4-ol (42 %), a-terpineol (3 %) and 1,8-cineole (2%, respectively, of tea tree oil) as the water soluble components of tea tree oil. When these components were examined individually, only terpinen-4-ol suppressed the production after 40 h of TNFalpha, IL-1beta, IL-8, IL-10 and PGE2 by LPS-activated monocytes.

CONCLUSION

The water-soluble components of tea tree oil can suppress pro-inflammatory mediator production by activated human monocytes.

Melaleuca alternifolia (tea tree) oil inhibits germ tube formation by Candida albicans

The effect of tea tree oil (TTO) on the formation of germ tubes by Candida albicans was examined. Two isolates were tested for germ tube formation (GTF) in the presence of TTO concentrations (% v/v) ranging from 0.25% (1/2 minimum inhibitory concentration [MIC]) to 0.004% (1/128 MIC). GTF at 4 h in the presence of 0.004 and 0.008% (both isolates) and 0.016% (one isolate) TTO did not differ significantly (P > 0.05) from controls. At all other concentrations at 4 h, GTF differed significantly from controls (P < 0.01). A further eight isolates were tested for GTF in the presence of 0.031% TTO, and at 4h the mean GTF for all 10 isolates ranged 10.0-68.5%. Two isolates were examined for their ability to form germ tubes after 1 h of pre-exposure to several concentrations of TTO, prior to induction of germ tubes in horse serum. Cells pre-exposed to 0.125 and 0.25% TTO formed significantly fewer germ tubes than control cells at 1 h (P < 0.05), but only those cells pre-exposed to 0.25% differed significantly from control cells at later time points (P < 0.01). GTF by C. albicans is affected by the presence of, or pre-exposure to, sub-inhibitory concentrations of TTO. This may have therapeutic implications.

Prevalence of delayed hypersensitivity to the European standard series in a self-selected population

There are limited reports of the prevalence of positive reactions in healthy adults to patch tests with standard allergens; there are no recent comprehensive studies from Australia. Healthy adult volunteers (n = 219) from the Western Australian community were patch tested using the European standard series of allergens. Seventy-seven (35%) reacted to at least one allergen, positive patch tests being most prevalent to nickel sulfate (20%), potassium dichromate (9%), cobalt chloride (6%) and fragrance mix (4%). Prevalence of positive patch tests to nickel and chromate was higher than that reported for another healthy population, which may stem from self-selection of volunteers or geographical differences, including extent of exposure to allergens.

In vitro activities of ketoconazole, econazole, miconazole, and Melaleuca alternifolia (tea tree) oil against Malassezia species

The in vitro activities of ketoconazole, econazole, miconazole, and tea tree oil against 54 Malassezia isolates were determined by agar and broth dilution methods. Ketoconazole was more active than both econazole and miconazole, which showed very similar activities. M. furfur was the least susceptible species. M. sympodialis, M. slooffiae, M. globosa, and M. obtusa showed similar susceptibilities to the four agents.

Antimicrobial activity of essential oils and other plant extracts

The antimicrobial activity of plant oils and extracts has been recognized for many years. However, few investigations have compared large numbers of oils and extracts using methods that are directly comparable. In the present study, 52 plant oils and extracts were investigated for activity against Acinetobacter baumanii, Aeromonas veronii biogroup sobria, Candida albicans, Enterococcus faecalis, Escherichia col, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica serotype typhimurium, Serratia marcescens and Staphylococcus aureus, using an agar dilution method. Lemongrass, oregano and bay inhibited all organisms at concentrations of < or = 2.0% (v/v). Six oils did not inhibit any organisms at the highest concentration, which was 2.0% (v/v) oil for apricot kernel, evening primrose, macadamia, pumpkin, sage and sweet almond. Variable activity was recorded for the remaining oils. Twenty of the plant oils and extracts were investigated, using a broth microdilution method, for activity against C. albicans, Staph. aureus and E. coli. The lowest minimum inhibitory concentrations were 0.03% (v/v) thyme oil against C. albicans and E. coli and 0.008% (v/v) vetiver oil against Staph. aureus. These results support the notion that plant essential oils and extracts may have a role as pharmaceuticals and preservatives.

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.

In-vitro activity of essential oils, in particular Melaleuca alternifolia (tea tree) oil and tea tree oil products, against Candida spp

The in-vitro activity of a range of essential oils, including tea tree oil, against the yeast candida was examined. Of the 24 essential oils tested by the agar dilution method against Candida albicans ATCC 10231, three did not inhibit C. albicans at the highest concentration tested, which was 2.0% (v/v) oil. Sandalwood oil had the lowest MIC, inhibiting C. albicans at 0.06%. Melaleuca alternifolia (tea tree) oil was investigated for activity against 81 C. albicans isolates and 33 non-albicans Candida isolates. By the broth microdilution method, the minimum concentration of oil inhibiting 90% of isolates for both C. albicans and non-albicans Candida species was 0.25% (v/v). The minimum concentration of oil killing 90% of isolates was 0.25% for C. albicans and 0.5% for non-albicans Candida species. Fifty-seven Candida isolates were tested for sensitivity to tea tree oil by the agar dilution method; the minimum concentration of oil inhibiting 90% of isolates was 0.5%. Tests on three intra-vaginal tea tree oil products showed these products to have MICs and minimum fungicidal concentrations comparable to those of non-formulated tea tree oil, indicating that the tea tree oil contained in these products has retained its anticandidal activity. These data indicate that some essential oils are active against Candida spp., suggesting that they may be useful in the topical treatment of superficial candida infections.

In vitro susceptibility of Malassezia furfur to the essential oil of Melaleuca alternifolia

The susceptibility of 64 Malassezia furfur isolates to Melaleuca alternifolia oil was determined. The minimum inhibitory concentration for 90% of isolates was 0.25% by agar dilution and 0.12% by broth dilution. These data indicate that tea tree oil may be useful in the treatment of skin conditions involving M. furfur.

Susceptibility of transient and commensal skin flora to the essential oil of Melaleuca alternifolia (tea tree oil)

OBJECTIVES

The purpose of this study was to determine the susceptibility of a range of transient and commensal skin flora to the essential oil of Melaleuca alternifolia, or tea tree.

METHODS

A modified broth microdilution method was used. Polyoxyethylene sorbitan mono-oleate detergent was added to the test medium to enhance solubility of the tea tree oil.

RESULTS

Serratia marcescens had the lowest minimum inhibitory concentration (MIC90) of 0.25%. The highest MIC90 was 3% for Pseudomonas aeruginosa. The lowest minimum bactericidal concentration (MBC90) was 0.25% for S. marcescens and Klebsiella pneumoniae, whereas the highest was 8% for Staphylococcus capitis.

CONCLUSIONS

S. aureus and most of the gram-negative bacteria tested were more susceptible to tea tree oil than the coagulase-negative staphylococci and micrococci. These results suggest that tea tree oil may be useful in removing transient skin flora while suppressing but maintaining resident flora.

Antimicrobial activity of the major components of the essential oil of Melaleuca alternifolia

Tea tree oil, or the essential oil of Melaleuca alternifolia, is becoming increasingly popular as a naturally occurring antimicrobial agent. The antimicrobial activity of eight components of tea tree oil was evaluated using disc diffusion and broth microdilution methods. Attempts were also made to overcome methodological problems encountered with testing compounds which have limited solubility in aqueous media. After assessing media with and without solubilizing agents, the disc diffusion method was used to determine the susceptibility of a range of micro-organisms to 1,8-cineole, 1-terpinen-4-ol, rho-cymene, linalool, alpha-terpinene, gamma-terpinene, alpha-terpineol and terpinolene. While the disc diffusion method lacked reproducibility, it was considered useful as a procedure for screening for antimicrobial activity. Terpinen-4-ol was active against all the test organisms while rho-cymene demonstrated no antimicrobial activity. Linalool and alpha-terpineol were active against all organisms with the exception of Pseudomonas aeruginosa. Minimum inhibitory and minimum cidal concentrations of each component against Candida albicans, Escherichia coli and Staphylococcus aureus were determined using a broth microdilution method. Modifications to this method overcame solubility and turbidity problems associated with the oil components and allowed the antimicrobial activity of each of the components to be quantified reproducibly. There was reasonable agreement between minimum inhibitory concentrations and zones of inhibition. These results may have significant implications for the future development of tea tree oil as an antimicrobial agent.

Susceptibility of methicillin-resistant Staphylococcus aureus to the essential oil of Melaleuca alternifolia

All 66 isolates of Staphylococcus aureus tested were susceptible to the essential oil of Melaleuca alternifolia, or tea tree oil, in disc diffusion and modified broth microdilution methods. Of the isolates tested, 64 were methicillin-resistant S. aureus (MRSA) and 33 were mupirocin-resistant. The MIC and MBC for 60 Australian isolates were 0.25% and 0.50%, respectively. Comparable results were obtained by co-workers in Britain using similar methods. These in-vitro results suggest tea tree oil may be useful in the treatment of MRSA carriage.