JAC Advance Access originally published online on June 20, 2006
Journal of Antimicrobial Chemotherapy 2006 58(3):706-707; doi:10.1093/jac/dkl269
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Correspondence |
In vitro antimycoplasmal activity of Melaleuca alternifolia essential oil
1 Department of Microbiological Sciences and Gynaecological Sciences, University of Catania Via Androne 81, 91524 Catania, Italy 2 Department of Pharmacobiological Sciences, University ‘Magna Grecia’ of Catanzaro Viale Europa, I-88100 Catanzaro, Italy 3 Department of Pharmacobiology, University of Messina Viale Annunziata, 98100 Messina, Italy
*Corresponding author. Tel: +39-095316038; Fax: +39-095312798; E-mail: furneri{at}unict.it
Keywords: tea tree oil , TTO , Mycoplasma , susceptibility tests
Sir,
The essential oil of Melaleuca alternifolia [i.e. tea tree oil (TTO)] has a long history of use as a topical antiseptic and has been used in Australia as an antiseptic since the 1920s. It is currently enjoying resurgent popularity and it is widely available in various formulations suitable for topical use.1
TTO has a wide spectrum of antimicrobial activity against Gram-positive and Gram-negative bacteria, both aerobic and anaerobic, against yeasts and fungi. It is also active against clinically isolated fluconazole-resistant Candida strains. The mechanism of the cytotoxic effect of the TTO against bacteria and yeasts has been reviewed recently.1 In particular, it was demonstrated that the exposure of Escherichia coli, Staphylococcus aureus and Candida albicans to minimum inhibitory and minimum bactericidal/fungicidal concentrations of TTO inhibits respiration and increases the permeability of bacterial cytoplasmic and yeast plasma membranes; in the case of E. coli and S. aureus, TTO also caused potassium ion leakage. The observed differences in the susceptibility of the microorganisms to TTO may be interpreted in terms of variations in the rate of monoterpene penetration through the cell wall and cell membrane structures. The antimicrobial activity of TTO has been principally attributed to terpinen-4-ol.1 Finally, TTO is relatively non-toxic when applied topically, even though cases of allergic contact dermatitis have been reported.2
The objective of the study described here was to determine the in vitro susceptibilities of Mycoplasma pneumoniae, Mycoplasma hominis and Mycoplasma fermentans to TTO.
TTO employed in our experiments was provided by Australian Botanical Products (Hallam, Australia). The oil complied with ISO 4730–1996.3 When analysed by gas chromatography and gas chromatography–mass spectrometry, the oil appeared to be characterized by a high proportion of terpinen-4-ol (36.71%) and 
-terpinene (22.20%), and moderate levels of 1,8-cineole (2.49%), p-cymene (2.52%), 
-terpinene (10.10%) and terpinolene (3.53%).4 Stock solutions of TTO were prepared in fetal calf serum (Biokrom by Bio-Spa, Milan, Italy).
Twenty-five low-passage clinically isolated strains of M. hominis (from vagina, urethra and cervix) and one reference strain (PG 21) of M. hominis, one clinically isolated strain of M. pneumoniae and one reference strain (FH) of M. pneumoniae, four low-passage strains (from vagina) and two reference strains (PG18 and K7) of M. fermentans were investigated. Mycoplasmas were grown in SP-4 broth5 and maintained frozen (–80°C) until used. The presence of arginine in SP-4 broth was avoided for cultivation of M. fermentans; the pH of SP-4 medium was decreased to 6.0 when used with M. hominis.
The MIC was determined by a broth microdilution assay as described previously.6
The MIC was defined as the lowest concentration of the essential oil that inhibited a colour change in the broth by a given strain of mycoplasma at the time when the colour of the control tube changed, that is when the pH of the medium decreased from 7.5 to 7.0 (M. pneumoniae and M. fermentans) or increased from 6.0 to 6.5 (M. hominis). The required incubation times were 24–48 h for M. hominis and M. fermentans and 3–5 days for M. pneumoniae. Further incubations were not carried out. Standard control procedures were done as previously described.6 Moreover, S. aureus ATCC 29213 was included as control; the MIC of the essential oil obtained in Mueller–Hinton broth (Beckton Dickinson & C., Sparks, MD) (MH) was compared with that obtained in SP-4.
The results of the in vitro susceptibility tests are given in Table 1. TTO inhibited mycoplasmas at concentrations from 0.01% to 0.12% (v/v). M. pneumoniae showed MIC values of 0.01% (v/v). M. fermentans, showed MIC90 values of 0.06% (v/v). M. hominis was the least susceptible with MIC90 values of 0.12% (v/v). As regards reproducibility no variations among the results of MIC values were observed in the separate assays. S. aureus retained its susceptibility to TTO in both MH broth and SP-4 broth (MIC 0.12% v/v).
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TTO has broad antimicrobial activity and is incorporated into a diverse range of pharmaceutical and cosmetic products. Therefore, TTO and products containing the oil have been evaluated in vivo for the treatment of superficial fungal infections such as onychomycosis and oral candidiasis, with some favourable clinical outcomes. It is difficult to explain the observed differences of MIC values among mycoplasmas, though differences in the susceptibility might be interpreted in terms of variations in the rate of monoterpene penetration through cell membranes; furthermore, the cytotoxic activity might be impaired by the fact that a more rapid growth accounts for a minor time of contact with cell membranes.1
Appropriate studies are now needed to determine whether this in vitro activity will translate into in vivo activity and also to clarify the mechanism of antimycoplasmal activity, given that mycoplasmas could be an interesting tool in order to characterize the interaction of TTO with bacterial membranes.
Transparency declarations
None to declare.
References
1
Carson CF, Hammer KA, Riley TV. (2006) Melaleuca alternifolia (tea tree) oil: a review of antimicrobial and other medicinal properties. Clin Microbiol Rev 19:50–62.
2 Fritz TM, Burg G, Krasovec M. (2001) Allergic contact dermatitis to cosmetics containing Melaleuca alternifolia (tea tree oil). Ann Dermatol Venereol 128:123–6.[Web of Science][Medline]
3 Shellie R, Marriott P, Zappia G, et al. (2003) Interactive use of linear retention indices on polar and apolar columns with an MS-library for reliable characterisation of Australian tea tree and other Melaleuca sp. oils. J Essent Oil Res 15:305–12.
4 International Organisation for Standardisation. (1996) Essential Oils—Oil of Melaleuca, terpinen-4-ol type (tea tree oil). ISO-4730 (ISO, Geneva, Switzerland).
5 Tully JG, Rose DL, Whitcomb RF, et al. (1979) Enhanced isolation of Mycoplasma pneumoniae from throat washings with a newly-modified culture medium. J Infect Dis 139:478–82.[Web of Science][Medline]
6
Furneri PM, Piperno A, Sajia A, et al. (2004) Antimycoplasmal activity of hydroxytyrosol. Antimicrob Agents Chemother 48:4892–4.
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