In vitro assays have shown that Australian tea trea oil (TTO) reveals a high antibacterial effect on a great number of Gram-positive and Gram-negative bacteria. Despite its in vitro data on bacterial activity, however, only few is known about the antibacterial mode of action of TTO.
We analysed the antibacterial effect of TTO against the Gram-positive bacterium Staphylococcus aureus because this germ is very sensitve to low concentrations of this essential oil. In a first investigation we studied the antibacterial effect of TTO on cell ultrastructures (e.g., cytoplasm, cytoplasmic membrane, cell wall) by electron microscopic and biochemical methods.
At sub-MIC (minimum inhibitory concentration) of 0.12 % TTO lamellar-like membrane structures were seen in the cytoplasm on electron microscopic studies. In the presence of 0.25 % TTO (MIC) cell division was inhibited completely, and condensed, filamentous, electrondense material in the cytoplasm was seen. Lamellar-like membrane structures, as seen in the sub-MIC of 0.12 % TTO in the cytoplasm, were no longer visible.
On the other hand, the integrity of the cytoplasmic membrane as well as the cell wall of Staphylococcus aureus seems not to be affected by TTO since no leakage of the bacterium cell was observed after oil treatment.
It is supposed that the mode of action of TTO on Staphylococcus aureus is similar to that of membrane-active disinfectants, such as phenol derivatives, and chlorhexidine.
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