Article By Genelle Weule
Published in ABC Science, 12 March 2013
Tea tree oil has become a bathroom cabinet staple, but there is no evidence the ubiquitous oil can contribute to antibiotic resistance, say researchers.
The researchers, led by Dr Christine Carson from the University of Western Australia, investigated previous reports that suggested exposure to low levels of tea tree oil may contribute to the development of antibiotic resistance.
Their findings are published in the International Journal of Antimicrobial Agents.
“The balance of evidence seems to suggest you can’t make bacteria resistant to tea tree oil and you can’t make bacteria more resistant to antibiotics by exposing them to tea tree oil,” says Carson.
Therapeutic concentrations containing 5 per cent tea tree oil, an aromatic oil extracted from the Australian native plant Melaleuca alternifloria, have been shown to have broad spectrum anti-bacterial properties in laboratory studies.
But the presence of many personal care and cosmetic products on the market, which contain up to 2 per cent tea tree oil, has led to concerns of resistance not only to tea tree oil itself, but also to other antibiotics.
“[Tea tree oil] is available in many over the counter and supermarket products like soaps, detergents, deodorants, washing powders, disinfectants and things that you can apply to wounds where tea tree oil may or may not be the active ingredient but it’s still in there in low concentrations,” says Carson.
“Sometimes when you use compounds that kill bacteria you can accidentally increase their resistance to other unrelated antibiotics.
“But we’re confident that using tea tree oil doesn’t jeopardise the workings of current antibiotics,” she says.
To test the previous research findings, Carson and colleagues exposed 30 strains of staphylococcus bacteria that cause common skin diseases to tea tree oil. One of the strains was also used in the previous studies.
To replicate the previous studies, the bacteria was exposed to a concentration containing 0.25 per cent tea tree oil.
“When we put our organisms, one of which was the same as theirs, into 0.25 per cent tea tree oil they all died,” says Carson.
The researchers then reduced their concentrations to 0.075 per cent.
“We exposed bacteria to low levels of tea tree oil for three days, then we tested their susceptibility to antibiotics and it was essentially the same,” says Carson.
Carson says it is possible, but unlikely, that other strains not tested could demonstrate resistance.
“The idea that exposing bacteria to some kind of agents can make them less susceptible to others is a very well-accepted phenomenon in microbiology.”
“So the possibility remains, but we would consider it very low.”
The research was funded by a grant from the Australian Government’s Rural Industries Research and Development Corporation and two tea tree oil manufacturers.