Essential oil composition and antimicrobial interactions of understudied tea tree species

• The monthly essential oil composition for a year is reported for selected tea tree species.
• Promising antimicrobial efficacies were evident, with the lowest MIC value of 0.06 mg/ml attained.
• Additive effects predominated when tea tree oils were combined.
• No antagonism was noted in tea tree combinations.

The essential oil composition of three Myrtaceous species (Leptospermum petersonii, Leptospermum scoparium and Kunzea ericoides) belonging to the tea tree group were analysed using gas chromatography coupled to mass spectrometry (GC–MS). The major compounds determined from the mean ± SD of the monthly samples collected for one calendar year in L. petersonii are citronellal (11.4 ± 4.3%), citronellol (17.5 ± 7.1%), neral (19.7 ± 1.6%) and geranial (34.7 ± 3.3%). The major compounds in L. scoparium are eudesma-4(14)-11-diene (11.6 ± 2.4%), α-selinene (10.4 ± 2.3%) and (E)-methyl cinnamate (12.6 ± 3.8%). The major compounds in K. ericoides are α-pinene (37.6 ± 6.3%) and p-cymene (13.5 ± 4.1%). The essential oils show some promising antimicrobial activity against selected micro-organisms when investigated using the minimum inhibitory concentration assay. Highest sensitivities were noted for the Brevibacteria (lowest MIC value of 0.06 mg/ml), a genus associated with foot odour. When the different essential oils were combined in various ratios and tested against Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans, a predominantly additive effect was noted.