Pharmacological and antimicrobial studies on different tea-tree oils (Melaleuca alternifolia, Leptospermum scoparium or Manuka and Kunzea ericoides or Kanuka), originating in Australia and New Zealand

Three different species of Myrtaceae growing in Australia and New Zealand a re known as 'Tea-tree': the Australian Tea tree (Melaleuca alternifolia), t he New Zealand Manuka (Leptospermum scoparium) and Kanuka (Kunzea ericoides ). All three essential oils are used by aromatherapists, although only Mela leuca has been tested for toxicity, and its antimicrobial effects studied, The pharmacology and antimicrobial activity of the three 'tea-tree' oils wa s determined using guinea-pig ileum, skeletal muscle (chick biventer muscle and the rat phrenic nerve diaphragm) and also rat uterus in vitro. Differe nces were shown between the three essential oils in their action on smooth muscle: Manuka had a spasmolytic action, while Kanuka and Melaleuca had an initial spasmogenic action. Using the diaphragm, Manuka and Melaleuca decre ased the tension and caused a delayed contracture; Kanuka had no activity a t the same concentration, The action on chick biventer muscle was, however, similar for all three oils, as was the action on the uterus, where they ca used a decrease in the force of the spontaneous contractions. The latter ac tion suggests caution in the use of these essential oils during childbirth, as cessation of contractions could put the baby, and mother, at risk. The comparative antimicrobial activity showed greater differences between diffe rent samples of Manuka and Kanuka than Melaleuca samples, The antifungal ac tivity of Kanuka was inversely proportional to its strong antibacterial act ivity, whilst Manuka displayed a stronger antifungal effect, though not as potent as Melaleuca, The antioxidant activity of Manuka samples was more co nsistent than that of Kanuka, while Melaleuca showed no activity. The varia bility in the Manuka and Kanuka essential oils suggests caution in their us age, as does the fact that the oils have not been tested for toxicity.