In vitro activity of antimicrobial agents against Pseudomonas tolaasii, pathogen of cultivated button mushroom

In vitro antibacterial activity tests of seven biofungicides (Ekstrasol, Bisolbisan, Bisolbifit, Serenade, Sonata, Timorex, F-Stop) and two disinfectants (colloidal silver alone and in combination with hydrogen peroxide) against the Pseudomonas tolaasii strain (NS3B6) were carried out by the disc-diffusion, broth microdilution and broth macrodilution method. Biofungicides tested in this study did not exhibit any antimicrobial activity in neither one of the methods used. Disc diffusion method revealed high sensitivity of the tested P. tolaasii strain to Ecocute based on colloidal silver and hydrogen peroxide. Both microdilution and macrodilution methods identified the same MICs and MBCs of Ecocute (0.19 mg/L) for P. tolaasii strain. MICs and MBCs values of silver alone were much higher (10 mg/L) compared to silver in combination with hydrogen peroxide.

Evaluation of double-decker traps for emerald ash borer (Coleoptera: Buprestidae)

Improved detection tools are needed for the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), an invasive forest insect from Asia that has killed millions of ash (Fraxinus spp.) trees in North America since its discovery in Michigan in 2002. We evaluated attraction of adult A. planipennis to artificial traps incorporating visual (e.g., height, color, silhouette) and olfactory cues (e.g., host volatiles) at field sites in Michigan. We developed a double-decker trap consisting of a 3-m-tall polyvinyl pipe with two purple prisms attached near the top. In 2006, we compared A. planipennis attraction to double-decker traps baited with various combinations of manuka oil (containing sesquiterpenes present in ash bark), a blend of four ash leaf volatiles (leaf blend), and a rough texture to simulate bark. Significantly more A. planipennis were captured per trap when traps without the rough texture were baited with the leaf blend and manuka oil lures than on traps with texture and manuka oil but no leaf blend. In 2007, we also tested single prism traps set 1.5 m above ground and tower traps, similar to double-decker traps but 6 m tall. Double-decker traps baited with the leaf blend and manuka oil, with or without the addition of ash leaf and bark extracts, captured significantly more A. planipennis than similarly baited single prism traps, tower traps, or unbaited double-decker traps. A baited double-decker trap captured A. planipennis at a field site that was not previously known to be infested, representing the first detection event using artificial traps and lures. In 2008, we compared purple or green double-decker traps, single prisms suspended 3-5 m above ground in the ash canopy (canopy traps), and large flat purple traps (billboard traps). Significantly more A. planipennis were captured in purple versus green traps, baited traps versus unbaited traps, and double-decker versus canopy traps, whereas billboard traps were intermediate. At sites with very low A. planipennis densities, more A. planipennis were captured on baited double-decker traps than on other traps and a higher percentage of the baited double-decker traps captured beetles than any other trap design. In all 3 yr, peak A. planipennis activity occurred during late June to mid-July, corresponding to 800-1200 growing degree-days base 10 degrees C (DD10). Nearly all (95%) beetles were captured by the end of July at approximately 1400 DD10.

MRSA colonisation (eradicating colonisation in people without active/invasive infection)

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) has a gene that makes it resistant to methicillin as well as to other beta-lactam antibiotics, including flucloxacillin, beta-lactam/beta-lactamase inhibitor combinations, cephalosporins, and carbapenems. MRSA can be part of the normal body flora (colonisation), especially in the nose, but it can cause infection. Until recently, MRSA has primarily been a problem associated with exposure to the healthcare system, especially in people with prolonged hospital admissions, with underlying disease, or after antibiotic use. In many countries worldwide, a preponderance of S aureus bloodstream isolates are resistant to methicillin.

METHODS AND OUTCOMES

We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatment for MRSA nasal or extra-nasal colonisation? We searched: Medline, Embase, The Cochrane Library, and other important databases up to January 2010 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

RESULTS

We found 9 systematic reviews, RCTs, or observational studies that met our inclusion criteria.

CONCLUSIONS

In this systematic review we present information relating to the effectiveness and safety of the following interventions: antiseptic body washes, chlorhexidine-neomycin nasal cream, mupirocin nasal ointment, systemic antimicrobials, tea tree oil preparations, and other topical antimicrobials.

Antimicrobial activity of two essential oils

The aim of the study was to evaluate the antimicrobial activity of essential oils in vitro for possible application to reduce the content of microorganisms in the air of animal houses. The essential oils of Cymbopogon citrarus L. and Malaleuca alternifolia L. were screened against bacteria Staphylococcus aureus, Enterococcus faecium, Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis and yeast Candida albicans. The minimal inhibitory concentration of the active essential oils was tested using broth dilution assay. The essential oils concentrations ranged from 0.1-50.0%. The combined effects of essential oils were tested for Malaleuca alternifolia L. and Cymbopogon citrarus L. concentrations ranged from 0.005-50.0%. The oils showed a wide spectrum of antibacterial activity. Concentrations of 0.1-0.5% of Cymbopogon citrarus L. and Malaleuca alternifolia L. reduced total microorganisms count of Proteus mirabilis and Candida albicans. High antibacterial activity was also revealed for Cymbopogon citrarus L. with bactericidal concentrations of 0.8% for Escherichia coli, 5.0% for Enterococcus faecium, 5.0% for Pseudomonas aeruginosa and 8.0% for Staphylococcus aureus. Bactericidal concentrations of Malaleuca alternifolia L. were 5.0% for Pseudomonas aeruginosa and Enterococcus faecium, and 8.0% for Staphylococcus aureus. The essential oils of Cymbopogon citrarus and Malaleuca alternifolia may be a promising alternative of air disinfection in animal houses.

Essential oils as biopreservatives: different methods for the technological application in lettuce leaves

Investigations were carried out to assess the efficiency of 3 essential oils, clove, tea tree, and rosemary, as natural preservatives during the postharvest of lettuce leaves. The effect of different concentration (1 and 0.5 MIC) of plant essential oils applied in 3 forms (spray, immersion, and capsules) was studied on lettuce leaves. The evolution of different microbial populations was evaluated during refrigerated storage. The application forms of the biopreservatives were shown to be an important factor in determining the effectiveness of the essential oils. Clove and tea tree essential oils at 1 MIC and applied embedded in lactose capsules presented a significant inhibition on mesophilic, psicrotrophic, and coliforms populations, while rosemary in none of the 3 technological applications forms exerted inhibitory effect on all microbial populations evaluated. Essential oils (at 0.5 MIC) applied by spray, immersion, and embedded in lactose capsules exerted lower inhibitory effects, with respect to 1 MIC, on the different microbial populations present on lettuce leaves. At the end of the storage (7 d), lettuce samples treated with tea tree, clove, and rosemary (at 1 and 0.5 MIC) by spray were the only organoleptically acceptable. It is concluded that clove and tea tree essential oils can control different microbial population present in lettuce. Practical Application: The exploration of naturally occurring antimicrobials in food preservation receives increasing attention due to consumer awareness of natural food products. Biopreservatives are useful in extending the shelf life of foods, reducing or eliminating pathogenic bacteria and increasing overall quality of food products. The effectiveness of essential oil application in foods is the result of factor associations such as applications forms, concentration applied, the way of action, storage temperatures. The application methods (spray, immersion, and embedded in lactose capsules) and the concentration of essential oils have been shown to be important factors in determining the effectiveness of these biopreservatives. The oil concentrations required to produce a certain level of inhibition in actual foods could be questionable due to the organoleptic impact. However, these novel natural preservatives in combination with other factors in obstacle technologies are an alternative to control the pathogen growth minimizing undesirable changes in organoleptic characteristics.

Synergism and postantibiotic effect of tobramycin and Melaleuca alternifolia (tea tree) oil against Staphylococcus aureus and Escherichia coli

The application of antimicrobial combinations may address the rising resistance to established classes of both systemic and topical agents and their clinical relevance is related to the presence of a significant postantibiotic effect (PAE). We investigated the effectiveness in vitro of the association between tobramycin and tea tree oil (TTO) against Gram-positive and Gram-negative bacteria. The minimal inhibitory concentrations, the bacterial killing and the PAE of tobramycin and TTO were determined both singly and in combination against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213. A synergistic interaction was observed against both strains tested: the mean PAEs were 1.3 and 1.7h for tobramycin against E. coli and S. aureus respectively, 10.8h for tobramycin and TTO (0.05%) against E. coli, 10.4h and 17.4h against S. aureus for tobramycin and TTO (0.25 and 0.50%, respectively). Longer PASMEs were observed with S. aureus after TTO/tobramycin exposure. In vitro interactions can improve the antimicrobial effectiveness of the antibiotic and may contribute for the development of novel topical agents for the treatment of skin lesions including conjunctiva and respiratory infections by inhalation.

The inhibition of Candida species by selected essential oils and their synergism with amphotericin B

In this work we highlight a possible synergistic anti-Candida effect between Melaleuca alternifolia, Origanum vulgare and Pelargonium graveolens essential oils and the antifungal compound Amphotericin B. The antifungal activity was assessed using the agar dilution method in eleven Candida strains. The results obtained indicate the occurrence of a synergistic interaction between the essential oils under study and Amphotericin B. P. graveolens essential oil appeared to be the most effective, inhibiting all the Candida species evaluated by this study.

Antibacterial effect of tea-tree oil on methicillin-resistant Staphylococcus aureus biofilm formation of the tympanostomy tube: an in vitro study

The antibacterial effects of tea-tree oil against the formation of methicillin-resistant Staphylococcus aureus (MRSA) biofilm on the surface of the tympanostomy tubes was evaluated.

MATERIALS AND METHODS

Silicone tympanostomy tubes were pretreated with normal saline for 12 hours, the control group (n=4), with 100% tea-tree oil, experimental group A (n=3), or with 50% tea-tree oil, experimental group B (n=3). All the tubes were incubated in a MRSA solution for 2 days and then processed for evaluation using scanning electron microscopy.

RESULTS

The development of the biofilm mode of growth of MRSA was observed in the saline-treated control group. In contrast, only focal biofilms were present on the tube surface in experimental group A and considerable reduction of biofilm with destruction of the MRSA cells was shown in experimental group B.

CONCLUSION

From these results, the antimicrobial effect of tea-tree oil against biofilm formation on tympanostomy tubes in vitro has been verified.

In vitro antifungal activity of the tea tree (Melaleuca alternifolia) essential oil and its major components against plant pathogens

AIMS

The aim of this study was to examine the effect of Melaleuca alternifolia essential oil (TTO) and its principal components on four cereal-pathogenic fungi.

METHODS AND RESULTS

The antimycotic properties of TTO and of terpinen-4-ol, gamma-terpinen and 1,8-cineole (eucalyptol) were evaluated in vitro on Fusarium graminearum, Fusarium culmorum and Pyrenophora graminea. Moreover, barley leaves infected with Blumeria graminis were treated with whole TTO. All the tested fungi were susceptible to TTO and its components.

CONCLUSIONS

TTO exerted a wide spectrum of antimycotic activity. Single TTO purified components were more active than the whole oil in reducing in vitro growth of fungal mycelium and, among the tested compounds, terpinen-4-ol was the most effective.

SIGNIFICANCE AND IMPACT OF THE STUDY

TTO and its components can be considered potential alternative natural fungicides.

The effect of tea tree oil and antifungal agents on a reporter for yeast cell integrity signalling

Cell integrity in Saccharomyces cerevisiae is ensured by a rigid cell wall whose synthesis is controlled by a highly conserved MAP kinase signal transduction cascade. Stress at the cell surface is detected by a set of sensors and ultimately transmitted through this cascade to the transcription factor Rlm1, which governs expression of many genes encoding enzymes of cell wall biosynthesis. We here report on a number of versatile reporter constructs which link activation of a hybrid, Rlm1-lexA, by the MAP kinase Mpk1/Slt2 to the expression of the bacterial lacZ gene. This system was adapted to automated microwell screening and shown to be activated by a number of compounds inhibiting cell wall biosynthesis or interfering with plasma membrane function. In addition, we tested tea tree oil and two of its purified constituents (alpha-terpineol, terpinen-4-ol) for their effects on growth and on cell integrity signalling using such reporter strains. Tea tree oil was found to inhibit growth of wild-type and slg1/wsc1 mutant cells at a threshold of approximately 0.1% v/v, with the purified compounds acting already at half these concentrations. A mid2 deletion displayed hyper-resistance. Tea tree oil also induces the signalling pathway in a dose-dependent manner.

The influence of essential oils on the process of wound healing: a review of the current evidence

This paper reports on a literature review of evidence on the influence of essential oils on wound healing and their potential application in clinical practice. It focuses mainly on tea tree, lavender, chamomile, thyme and ocimum oils.

In vitro susceptibility of Madurella mycetomatis, prime agent of Madura foot, to tea tree oil and artemisinin

OBJECTIVES

Eumycetoma caused by Madurella mycetomatis is treated with surgery and high doses of itraconazole and ketoconazole. These agents are toxic, and new therapies are required.

METHODS

MICs were determined for artemisinin and tea tree oil, two natural herbal compounds.

RESULTS

Artemisinin was not active against M. mycetomatis, but tea tree oil did inhibit its growth. Since tea tree oil's prime component easily penetrates the skin, tea tree oil could be a useful agent in the treatment of eumycetoma.

CONCLUSIONS

Tea tree oil is active in vitro against M. mycetomatis.

Mechanisms involved in the anti-inflammatory action of inhaled tea tree oil in mice

Tea tree oil (TTO) is well known as an antimicrobial and immunomodulatory agent. In the present study we confirmed the anti-inflammatory properties of TTO and investigated the involvement of the hypothalamic-pituitary-adrenal (HPA) axis in the immunomodulatory action of TTO administered by inhalation. Sexually mature, 6-8-week-old, C(57)BI(10) x CBA/H (F(1)) male mice were used. One group of animals was injected intra-peritoneally (ip) with Zymosan to elicit peritoneal inflammation and was then submitted to four sessions of TTO inhalation (15 mins each). Some of the mice were simultaneously injected ip with Antalarmin, a CRH-1 receptor antagonist, to block HPA axis functions. Twenty-four hours after the injections the mice were killed by CO(2) asphyxia, and peritoneal leukocytes (PTLs) were isolated and counted. Levels of reactive oxygen species (ROS) and cyclooxygenase (COX) activity in PTLs were assessed by fluorimetric and colorimetric assays, respectively. The results obtained show that sessions of TTO inhalation exert a strong anti-inflammatory influence on the immune system stimulated by Zymosan injection, while having no influence on PTL number, ROS level, and COX activity in mice without inflammation. The HPA axis was shown to mediate the anti-inflammatory effect of TTO; Antalarmin abolished the influence of inhaled TTO on PTL number and their ROS production in mice with experimental peritonitis, but it had no effect on these parameters in mice without inflammation.

Prepubertal gynecomastia linked to lavender and tea tree oils

Most cases of male prepubertal gynecomastia are classified as idiopathic. We investigated possible causes of gynecomastia in three prepubertal boys who were otherwise healthy and had normal serum concentrations of endogenous steroids. In all three boys, gynecomastia coincided with the topical application of products that contained lavender and tea tree oils. Gynecomastia resolved in each patient shortly after the use of products containing these oils was discontinued. Furthermore, studies in human cell lines indicated that the two oils had estrogenic and antiandrogenic activities. We conclude that repeated topical exposure to lavender and tea tree oils probably caused prepubertal gynecomastia in these boys.

The vapor activity of oregano, perilla, tea tree, lavender, clove, and geranium oils against a Trichophyton mentagrophytes in a closed box

The vapor activity of six essential oils against a Trichophyton mentagrophytes was examined using a closed box. The antifungal activity was determined from colony size, which was correlated with the inoculum size. As judged from the minimum inhibitory dose and the minimum fungicidal dose determined after vapor exposure for 24 h, the vapor activity of the six essential oils was ranked in the following order: oregano > clove, perilla > geranium, lavender, tea tree. The vapors of oregano, perilla, tea tree, and lavender oils killed the mycelia by short exposure, for 3 h, but the vapors of clove and geranium oils were only active after overnight exposure. The vapor of oregano and other oils induced lysis of the mycelia. Morphological examination by scanning electron microscope (SEM) revealed that the cell membrane and cell wall were damaged in a dose- and time-dependent manner by the action of oregano vapor, causing rupture and peeling of the cell wall, with small bulges coming from the cell membrane. The vapor activity increased after 24 h, but mycelial accumulation of the active oil constituents was maximized around 15 h, and then decreased in parallel with the decrease of vapor concentration. This suggested that the active constituent accumulated on the fungal cells around 15 h caused irreversible damage, which eventually led to cellular death.

In vitro activity of lysostaphin, mupirocin, and tea tree oil against clinical methicillin-resistant Staphylococcus aureus

Colonization of methicillin-resistant Staphylococcus aureus (MRSA) commonly leads to infection by the same strain. We examined the activity of lysostaphin, mupirocin, and tea tree oil against clinical MRSA (n = 98) isolates. MIC(50) (range) were as follows: lysostaphin, 0.125 mg/L (0.125-0.25); mupirocin, 0.5 mg/L (0.19-1024); tea tree oil, 1024 mg/L (512-2048). High- and low-level mupirocin resistance was noted in 9.2% of our MRSA isolates. Time kill results indicate MRSA activity at 24 h was lysostaphin = gentamicin = vancomycin (P <or= .001) > mupirocin > tea tree oil (P >or= .05). Checkerboard testing indicated a synergistic relationship between lysostaphin and mupirocin in combination with gentamicin. Antagonism was observed with the combination of vancomycin and tea tree oil; time kill studies confirmed this result. Decolonization options are limited and resistance to mupirocin exists. Lysostaphin and tea tree oil may offer additional therapeutic options for the decolonization of MRSA where current treatment alternatives are limited.

In vivo activity of terpinen-4-ol, the main bioactive component of Melaleuca alternifolia Cheel (tea tree) oil against azole-susceptible and -resistant human pathogenic Candida species

BACKGROUND

Recent investigations on the antifungal properties of essential oil of Melaleuca alternifolia Cheel (Tea Tree Oil, TTO) have been performed with reference to the treatment of vaginal candidiasis. However, there is a lack of in vivo data supporting in vitro results, especially regarding the antifungal properties of TTO constituents. Thus, the aim of our study was to investigate the in vitro and the in vivo anti-Candida activity of two critical bioactive constituents of TTO, terpinen-4-ol and 1,8-cineole.

METHODS

Oophorectomized, pseudoestrus rats under estrogen treatment were used for experimental vaginal infection with azole (fluconazole, itraconazole) -susceptible or -resistant strains of C. albicans. All these strains were preliminarily tested for in vitro susceptibility to TTO, terpinen-4-ol and 1,8-cineole for their antifungal properties, using a modification of the CLSI (formerly NCCLS) reference M27-A2 broth micro-dilution method.

RESULTS

In vitro minimal inhibitory concentrations (MIC90) values were 0.06% (volume/volume) for terpinen-4-ol and 4% (volume/volume) for 1,8-cineole, regardless of susceptibility or resistance of the strains to fluconazole and itraconazole. Fungicidal concentrations of terpinen-4-ol were equivalent to the candidastatic activity. In the rat vaginal infection model, terpinen-4-ol was as active as TTO in accelerating clearance from the vagina of all Candida strains examined.

CONCLUSION

Our data suggest that terpinen-4-ol is a likely mediator of the in vitro and in vivo activity of TTO. This is the first in vivo demonstration that terpinen-4-ol could control C. albicans vaginal infections. The purified compound holds promise for the treatment of vaginal candidiasis, and particularly the azole-resistant forms.

In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive Staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms

The susceptibility of Staphylococcus aureus [meticillin-resistant (MRSA) and meticillin-sensitive (MSSA)] and coagulase-negative staphylococci (CoNS), which respectively form part of the transient and commensal skin flora, to tea-tree oil (TTO) was compared using broth microdilution and quantitative in vitro time–kill test methods. MRSA and MSSA isolates were significantly less susceptible than CoNS isolates, as measured by both MIC and minimum bactericidal concentration. A significant decrease in the mean viable count of all isolates in comparison with the control was seen at each time interval in time–kill assays. However, the only significant difference in the overall mean log10 reduction in viable count between the groups of isolates was between CoNS and MSSA at 3 h, with CoNS isolates demonstrating a significantly lower mean reduction. To provide a better simulation of in vivo conditions on the skin, where bacteria are reported to grow as microcolonies encased in glycocalyx, the bactericidal activity of TTO against isolates grown as biofilms was also compared. Biofilms formed by MSSA and MRSA isolates were completely eradicated following exposure to 5 % TTO for 1 h. In contrast, of the biofilms formed by the nine CoNS isolates tested, only five were completely killed, although a reduction in viable count was apparent for the other four isolates. These results suggest that TTO exerts a greater bactericidal activity against biofilm-grown MRSA and MSSA isolates than against some biofilm-grown CoNS isolates.

Interaction of tea tree oil with model and cellular membranes

Tea tree oil (TTO) is the essential oil steam-distilled from Melaleuca alternifolia, a species of northern New South Wales, Australia. It exhibits a broad-spectrum antimicrobial activity and an antifungal activity. Only recently has TTO been shown to inhibit the in vitro growth of multidrug resistant (MDR) human melanoma cells. It has been suggested that the effect of TTO on tumor cells could be mediated by its interaction with the plasma membrane, most likely by inducing a reorganization of lipid architecture. In this paper we report biophysical and structural results obtained using simplified planar model membranes (Langmuir films) mimicking lipid "rafts". We also used flow cytometry analysis (FCA) and freeze-fracturing transmission electron microscopy to investigate the effects of TTO on actual MDR melanoma cell membranes. Thermodynamic (compression isotherms and adsorption kinetics) and structural (Brewster angle microscopy) investigation of the lipid monolayers clearly indicates that TTO interacts preferentially with the less ordered DPPC "sea" and that it does not alter the more ordered lipid "rafts". Structural observations, performed by freeze fracturing, confirm that TTO interacts with the MDR melanoma cell plasma membrane. Moreover, experiments performed by FCA demonstrate that TTO does not interfere with the function of the MDR drug transporter P-gp. We therefore propose that the effect exerted on MDR melanoma cells is mediated by the interaction with the fluid DPPC phase, rather than with the more organized "rafts" and that this interaction preferentially influences the ATP-independent antiapoptotic activity of P-gp likely localized outside "rafts".

Natural Oils Affect the Human Skin Integrity and the Percutaneous Penetration of Benzoic Acid Dose-Dependently

Natural oils are extensively used in cosmetics and as treatment for a growing number of more or less specific ailments. Skin irritation and cases of allergy have repeatedly been described in the literature following exposure to these oils. The present study evaluated the extent to which three natural oils (eucalyptus oil, tea tree oil, peppermint oil) would affect the skin integrity and the percutaneous penetration of benzoic acid when applied topically in relevant concentrations. An experimental in vitro model using static diffusion cells mounted with human breast or abdominal skin was applied. The three natural oils decreased the skin integrity dose-dependently. Concomitant dermal exposure to low concentrations of peppermint oil reduced the percutaneous penetration of benzoic acid. The present study lends support to the notion that low concentrations of peppermint oil may act protective against percutaneous penetration of some chemicals, whereas higher concentrations may decrease the integrity of the dermal barrier.

Susceptibility of pseudomonads to Melaleuca alternifolia (tea tree) oil and components

OBJECTIVES

Thirty isolates of Pseudomonas aeruginosa, 15 isolates of Pseudomonas putida and 11 isolates of Pseudomonas fluorescens were tested for susceptibility to tea tree oil (TTO), the essential oil of Melaleuca alternifolia, and the components terpinen-4-ol, alpha-terpineol, cineole, gamma-terpinene and rho-cymene.

METHODS

MICs were determined by broth microdilution in Mueller-Hinton medium supplemented with 0.002% (v/v) Tween 80.

RESULTS

The MIC90 of TTO for all isolates tested was 4% (v/v) or less. Susceptibility to components tested varied between species.

CONCLUSIONS

Pseudomonas spp. are susceptible to TTO and some of its components although they are less susceptible than many other bacteria tested previously.

Tea tree oil: in vitro efficacy in otitis externa

Objective: The purpose of this study was to determine the susceptibility of organisms causing otitis externa (OE) to the essential oil of Melaleuca alternifolia, or tea tree oil (TTO).

Methods: Fifty-seven swabs were taken from the ears of 52 patients with OE for culture and sensitivity. A broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of TTO for each organism.

Results: In 51 per cent of the swabs taken, pathogenic organisms were cultured. Of these cultures 71 per cent, both bacteria and yeast, were susceptible to TTO 2 per cent or less. The only organism showing resistance to TTO was Pseudomonas aeruginosa; however 25 per cent of these bacteria were sensitive.

Conclusion: Tea tree oil may have a role to play in the treatment of OE. However, more work needs to be done to enhance the anti-pseudomonal effect and to assess ototoxicity.

Susceptibility to Melaleuca alternifolia (tea tree) oil of yeasts isolated from the mouths of patients with advanced cancer

Yeasts that are resistant to azole antifungal drugs are increasingly isolated from the mouths of cancer patients suffering from oral fungal infections. Tea tree oil is an agent possessing antimicrobial properties that may prove useful in the prevention and management of infections caused by these organisms. In this study, 301 yeasts isolated from the mouths of 199 patients suffering from advanced cancer were examined by an in vitro agar dilution assay for susceptibility to tea tree oil. All of the isolates tested were susceptible, including 41 that were known to be resistant to both fluconazole and itraconazole. Clinical studies of tea tree oil as an agent for the prevention and treatment of oral fungal infections in immunocompromised patients merit consideration.

Melaleuca alternifolia (Tea Tree) oil: a review of antimicrobial and other medicinal properties

Complementary and alternative medicines such as tea tree (melaleuca) oil have become increasingly popular in recent decades. This essential oil has been used for almost 100 years in Australia but is now available worldwide both as neat oil and as an active component in an array of products. The primary uses of tea tree oil have historically capitalized on the antiseptic and anti-inflammatory actions of the oil. This review summarizes recent developments in our understanding of the antimicrobial and anti-inflammatory activities of the oil and its components, as well as clinical efficacy. Specific mechanisms of antimicrobial and anti-inflammatory action are reviewed, and the toxicity of the oil is briefly discussed.