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

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Summary

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 >105-fold reduction against all four test organisms within a 1-min contact time. The AHSW achieved a ≥105-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 >104-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 >104-fold reduction in E. coli and A. baumannii cell numbers, respectively, and the AHR achieved a >4log10 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.

Introduction

Morbidity and mortality due to life-threatening hospital-acquired infections remains a significant problem in health care today. The major mode of infection transmission is still thought to be hand carriage of pathogens from staff to patient, and from patient to patient.1, 2, 3 Despite clear evidence that appropriate handwashing and skin antisepsis play a major role in reducing the spread of infections in hospital settings,2, 4, 5 compliance with hand-hygiene practices is still unacceptably low.3, 6, 7 Most soaps and detergents can be damaging to the skin when applied routinely during handwashing, leading to a change in microbial flora, an increase in bacterial shedding and thus an increased risk of transmission of micro-organisms.1, 8

The essential oil of Melaleuca alternifolia [tea tree oil (TTO)] has been used medicinally for about 80 years.9 TTO has broad-spectrum antimicrobial9 and anti-inflammatory10, 11 activity in vitro. Hammer et al.12 showed that transient skin organisms were more susceptible to TTO than commensal organisms. This finding supports the use of TTO-containing handwash products since the normal skin flora represents one of the natural defences against colonization by pathogenic organisms.13 Other reports have suggested that the repeated use of TTO-containing hand wash does not lead to the dermatological problems associated with some formulations,14 and this finding might be used to encourage healthcare staff's compliance with handwashing. Although the antibacterial activity of TTO has been well established in vitro,11, 15, 16, 17, 18, 19 TTO has not yet been assessed using European standard methods that are now widely accepted for the evaluation of disinfectant and antiseptic efficacy. In this study, we assessed the activity of TTO and TTO-containing formulations according to two European standard suspension methods, EN 127620 and prEN 12054.21

Section snippets

Micro-organisms

Staphylococcus aureus (ATCC 25923), Acinetobacter baumannii (NCTC 7844), Escherichia coli K12 (NCTC 10538) and Pseudomonas aeruginosa (NCTC 6749) stock cultures were made on tryptone soya agar (TSA; Oxoid, Basingstoke, Hampshire, UK) plates, stored at 4 °C and renewed once a week.

Working cultures of bacteria

Subcultures on to further TSA plates were prepared from the stock cultures and incubated for 18–24 h at 37 °C. From this second subculture, a third subculture was produced in the same way. As recommended by European

Antibacterial activity and efficacy of the neutralizer

As shown in Table I, the neutralizer did not reduce the concentration of bacterial cells significantly (P>0.05). The neutralizing solutions quenched the antiseptics effectively (P>0.05) at the concentrations tested (Table II).

Antibacterial activity of the TTO-containing antiseptics

According to the European standard method used, the products under test had to achieve log10 reduction in bacterial cell numbers of at least after a 1- or 5-min contact time. Products that complied with the European standard are listed in Table III. After a 1-min contact

Discussion

Handwashing is one of the most important measures to reduce the transmission of infection in hospital settings.24 However, compliance with hand-hygiene guidelines is low6, 7 and this can be partly attributed to the fact that most recommended handwash agents available in healthcare settings are irritant to the skin when used repetitively.25 The efficacy of TTO has been demonstrated in vitro and its incorporation into skin products does not appear to cause the dermatological problems commonly

Acknowledgements

This work was supported by a grant from the Rural Industries Research and Development Corporation, Canberra, Australia (UWA-72A).

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