Sporicidal activity of tea tree oil

Abstract

Due to the lack of antiseptics with sporicidal properties, the activity of tea tree oil (TTO)-containing products was investigated according to the EN 14347 European suspension method. The activity of different concentrations of TTO in 0.001% Tween 80, as well as an alcoholic hygienic skin wash (AHSW) and an alcoholic handrub (AHR), was compared to the sporicidal disinfectants sodium hypochlorite (SH) and hydrogen peroxide (HP), and the antiseptic povidone iodine (PVI). These formulations were assessed after 30, 60 and 120 minutes against two strains of spore-forming bacteria: Bacillus cereus and Bacillus subtilis. The TTO formulated products and PVI did not achieve >4 log10 reduction in spore counts, thus did not meet the European standard requirements. Nevertheless, 5%, 10% and 15% TTO in 0.001% Tween 80 significantly reduced the concentration of bacterial spores when compared with the water control, and were generally more effective than PVI. At a concentration of 15%, TTO was more active than 0.05% SH against spores of both strains after 30 minutes' contact time, while 5% TTO in Tween 80 was generally more active than the AHSW that also contained 5% TTO. These findings emphasise the fact that it is necessary to assess final formulations rather than the active component by itself as excipients may interfere with the activity. The alcohol-containing AHSW and AHR did not demonstrate any sporicidal properties, confirming previous studies showing that alcohol is not sporicidal and suggesting no synergy between TTO and alcohol against spores. Hence these should not be used for hand hygiene or surface decontamination if spores are involved. Further studies should be carried out to investigate the potential sporicidal activity of TTO directly on human skin in vivo with volunteers and/or by using an 'ex vivo' test that uses freshly excised human skin and which would allow testing of any biocide as well as any spore-forming bacterial strain, including pathogens.