title: Interactions between components of the essential oil of Melaleuca alternifolia.
abstract: OBJECTIVE
  This study compared the antimicrobial activity of Melaleuca alternifolia (tea tree) oil with that of some of its components, both individually and in two-component combinations.
  
  
  RESULTS
  Minimum inhibitory concentration and time-kill assays revealed that terpinen-4-ol, the principal active component of tea tree oil, was more active on its own than when present in tea tree oil. Combinations of terpinen-4-ol and either gamma-terpinene or p-cymene produced similar activities to tea tree oil. Concentration-dependent reductions in terpinen-4-ol activity and solubility also occurred in the presence of gamma-terpinene.
  
  
  CONCLUSIONS
  Non-oxygenated terpenes in tea tree oil appear to reduce terpinen-4-ol efficacy by lowering its aqueous solubility.
  
  
  CONCLUSIONS
  These findings explain why tea tree oil can be less active in vitro than terpinen-4-ol alone and further suggest that the presence of a non-aqueous phase in tea tree oil formulations may limit the microbial availability of its active components.
authors.affiliation: Centre for Biostructural and Biomolecular Research, University of Western Sydney, Hawkesbury, New South Wales, Australia. s.cox@uws.edu.au
authors.forename: S D
authors.initials: SD
authors.lastname: Cox
authors.forename: C M
authors.initials: CM
authors.lastname: Mann
authors.forename: J L
authors.initials: JL
authors.lastname: Markham
mesh_terms: D000891:Anti-Infective Agents, Local / Q000737:chemistry / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects; D000081005:Cyclohexane Monoterpenes; D004926:Escherichia coli / Q000187:drug effects; D041743:Herb-Drug Interactions; D019684:Magnoliopsida / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D039821:Monoterpenes; D009822:Oils, Volatile / Q000737:chemistry / Q000494:pharmacology; D010938:Plant Oils / Q000737:chemistry / Q000494:pharmacology*; D010946:Plants, Medicinal / Q000737:chemistry*; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D012995:Solubility; D013211:Staphylococcus aureus / Q000187:drug effects; D013662:Tea / Q000737:chemistry; D013729:Terpenes / Q000737:chemistry; D014197:Trees / Q000737:chemistry
chemical_list: D000891:Anti-Infective Agents, Local; D000081005:Cyclohexane Monoterpenes; D039821:Monoterpenes; D009822:Oils, Volatile; D010938:Plant Oils; D013662:Tea; D013729:Terpenes; C018669:gamma-terpinene; C034019:terpinenol-4