title: Tolerance of Pseudomonas aeruginosa to Melaleuca alternifolia (tea tree) oil is associated with the outer membrane and energy-dependent cellular processes.
abstract: OBJECTIVE
  The essential oil of Melaleuca alternifolia (tea tree oil) and its components have antimicrobial activity against a wide range of Gram-positive and Gram-negative bacteria, fungi and viruses. The mechanism(s) by which Pseudomonas aeruginosa NCTC 10662 maintains a decreased susceptibility to tea tree oil and components was investigated.
  
  
  RESULTS
  Ethylene diamine tetraacetic acid enhanced the antimicrobial activity of tea tree oil and terpinen-4-ol against stationary phase P. aeruginosa while polymyxin B nonapeptide enhanced the activity of tea tree oil and gamma-terpinene. Pre-treatment with the protonophore carbonyl cyanide m-chlorophenylhydrazone increased the susceptibility of exponential phase cells to sub-inhibitory concentrations of tea tree oil, terpinen-4-ol and gamma-terpinene, indicating that intrinsic tolerance to tea tree oil and components is substantially energy dependent.
  
  
  CONCLUSIONS
  Increased tolerance to tea tree oil in P. aeruginosa is directly related to the barrier and energy functions of the outer membrane, and may involve efflux systems.
authors.affiliation: Microbiology Discipline (M502), School of Biomedical and Chemical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009. chelsea@cyllene.uwa.edu.au
authors.forename: Chelsea J
authors.initials: CJ
authors.lastname: Longbottom
authors.forename: Christine F
authors.initials: CF
authors.lastname: Carson
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Hammer
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Mee
authors.forename: Thomas V
authors.initials: TV
authors.lastname: Riley
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology; D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects* / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D004492:Edetic Acid / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects*; D008854:Microscopy, Electron; D011112:Polymyxin B / Q000031:analogs & derivatives* / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000648:ultrastructure; D020947:Tea Tree Oil / Q000494:pharmacology*; D013997:Time Factors; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D000890:Anti-Infective Agents; D000891:Anti-Infective Agents, Local; D001425:Bacterial Outer Membrane Proteins; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D020947:Tea Tree Oil; C038934:polymyxin B nonapeptide; D004492:Edetic Acid; D011112:Polymyxin B