Comparison of the cidal activity of tea tree oil and terpinen-4-ol against clinical bacterial skin isolates and human fibroblast cells

Aims: The aim of this study was to compare both the antimicrobial activity of terpinen‐4‐ol and tea tree oil (TTO) against clinical skin isolates of meticillin‐resistant Staphylococcus aureus (MRSA) and coagulase‐negative staphylococci (CoNS) and their toxicity against human fibroblast cells. Methods and Results: Antimicrobial activity was compared by using broth microdilution and quantitative in vitro time‐kill test methods. Terpinen‐4‐ol exhibited significantly greater bacteriostatic and bactericidal activity, as measured by minimum inhibitory and bactericidal concentrations, respectively, than TTO against both MRSA and CoNS isolates. Although not statistically significant, time‐kill studies also clearly showed that terpinen‐4‐ol exhibited greater antimicrobial activity than TTO. Comparison of the toxicity of terpinen‐4‐ol and TTO against human fibroblasts revealed that neither agent, at the concentrations tested, were toxic over the 24‐h test period. Conclusions: Terpinen‐4‐ol is a more potent antibacterial agent against MRSA and CoNS isolates than TTO with neither agent exhibiting toxicity to fibroblast cells at the concentrations tested. Significance and Impact of the Study: Terpinen‐4‐ol should be considered for inclusion as a single agent in products formulated for topical treatment of MRSA infection. However, further work would initially be required to ensure that resistance would not develop with the use of terpinen‐4‐ol as a single agent.