THE SEARCH FOR OPTIMALLY BIOACTIVE AUSTRALIAN TEA TREE OIL
Antimicrobial activity of tea tree oil was determined using the disc diffusion assay.
Terpinen-4-ol,
-terpineol and 1,8-cineole were found to have greater mobility through agar than hydrocarbon congeners in agar plate zone-of-inhibition measurements.
Minimum inhibitory concentrations were measured using an agar plate dilution method where a range of oil concentrations in agar were tested against S. aureus, E. coli, P. aeruginosa, C. albicans and A. niger.

This method was used to show that concentrations of 1,8-cineole in excess of the upper limit specified in the Australian Standard are not inhibitory. At concentrations up to 30% cineole appears to be synergistic. Antimicrobial activity decreased only when terpinen-4-ol levels fell below 30%, the minimum limit specified in the standard. Preliminary results also indicated that (+) and (-)-terpinen-4-ol are equally bioactive.
Southwell, I.A., Hayes, A.J., Markham, J. and Leach, D.N. (1993). THE SEARCH FOR OPTIMALLY BIOACTIVE AUSTRALIAN TEA TREE OIL. Acta Hortic. 344, 256-265
DOI: 10.17660/ActaHortic.1993.344.30
https://doi.org/10.17660/ActaHortic.1993.344.30
DOI: 10.17660/ActaHortic.1993.344.30
https://doi.org/10.17660/ActaHortic.1993.344.30
Melaleuca, Myrtaceae, essential oil, anti-microbial, zone-of-inhibition, minimum inhibitory concentration