Antibacterial activity of leaf essential oil and its constituents from Cinnamomum longepaniculatum

Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Salmonella enteritidis CMCC (B) 50041, were used in the antibacterial tests of Cinnamomum longepaniculatum leaf essential oil and its five chemical constituents. The effect of 1, 8-cineole on the ultrastructural structure of the bacteria (S. aureus and E. coli) was also investigated by transmission electron microscopy. The C. longepaniculatum leaf essential oil and the five chemical constituents showed variable levels of inhibition. Their MIC ( minimum inhibitory concentration ) and MBC (minimal bacteriocidal concentration) values were all in the range of 0.781 µL/mL~6.25 µL/mL and 0.781 µL/mL~12.5 µL/mL respectively except γ-terpinene. The MIC values of γ-terpinene against E. coli and S. aureus were all higher than 50 µL/mL, but the MIC and MBC values of γ-terpinene against S. enteritidis was only 3.125 µL/mL. Among them, α-terpineol possessed the best antibacterial activity. Under the transmission electron microscope, cell size of treated E. coli decreased, cell wall and cell membrane ruptured, and nucleoplasm was reduced and gathered onto the side. After the S. aureus was treated with 1, 8-cineole, the cell size and shape were damaged and nucleus cytoplasm was concentrated or reduced or agglomerated on the side. These results suggest that C. longepaniculatum leaf essential oil and its constituents have excellent antibacterial activities, the antibacterial mechanism of 1, 8-cineole against E. coli and S. aureus might attributable to its hydrophobicity.