Tea tree oil: the science behind the antimicrobial hype 

The Lancet. Vol 358. October 13, 2001

Pim Allen

With a major VRE (vancomycin- resistant enterococcus) outbreak involving 77 people and leading to the partial closure of Royal Perth Hospital's intensive-care unit, interest in alternatives to antibiotics was strong at "2001: A Microbial Odyssey" (Perth, Australia; Oct 1-5), hosted by the Australian Society for Microbiology .

"We need to look for novel approaches to antimicrobial agents", said Christine Carson (University of Western Australia, Perth). "Tea tree oil [TTO] has been widely used in the community for 80 years and is active against many microorganisms, including haemolytic streptococci, bacteroides, coliforms, and fungi at minimal inhibitory concentrations of 0.25-1.0% v/v. But there has been insufficient in-vitro, in-vivo, or safety information, leading to understandable medical caution."

"A pilot study of 30 MRSA [meticillin-resistant Staphylococcus aureus] carriers comparing routine mupirocin nasal ointment and triclosan skin wash with TTO ointment and wash, showed one third were completely cleared by TTO but only 13% by conventional treatment", said Carson  ( Hosp Infect 2000; 46: 236-37). "Westmead Hospital, Sydney is now running a trial with 180 patients which should be completed soon."

Tea tree oil: a new antimicrobial agent?

In a randomised, placebo controlled pilot study of TTO in the treatment of herpes cold sores, Carson found the oil assisted healing to a similar degree as topical 5% acyclovir ( Antimicrob Chemother 2001; 48: 450) "But we still need to know more about its microbicidal mechanisms", she said.

The oil has about 100 components but seven terpenes and their related alcohols constituted 80-90% of the who1e oi1. "We've shown cell counts fall from 1010 to 104 over 2 h if Staphylococcus aureus is incubated with terpinen-4-oil at its minimum inhibitory concentration, but the cells are not lysed", Carson added. "Cell electron microscopy after 10 min incubation shows marked morphological changes, particularly the formation of mesosomes."

In a complementary presentation, Kate Hammer (a1so from University of Western Austra1ia) described how several TTO constituents affect Candida albicans. After incubating cells with minimum inhibitory concentrations of TTO or its components, Hammer measured the 1eakage of 260 nm absorption materials-chiefly nucleic acids and DNA-and the uptake of the membrane-impermeable dye methylene blue. Within 30 min, significant leaks deve1oped. "Terpenes are lipophilic and partition into the phospholipid 1ayer of cell membranes, disrupting normal structure and function", Hammer commented.

Pim Allen