Abstract: The chemical composition of essential oil isolated from the whole plant of Dendranthema indicum var. aromaticum was investigated by gas chromatography-mass spectrometry (GC-MS), and its antimicrobial activity was evaluated against 4 bacterial strains by filter paper agar diffusion and constant dilution methods. Meanwhile, the antimicrobial mechanism was explored by transmission electron microscopy (TEM) and sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that 149 components were detected in the essential oil and 63 compounds were identified. The major compounds included terpenes (13.99%), alcohols (25.82%), and aldehydes and ketones (3.69%). The essential oil had obvious inhibitory effect on all four tested species of bacteria with an inhibitory ring diameter of 8.15—10.90 mm. Its inhibitory activity against Gram-positive bacteria was much higher than against Gram-negative bacteria. TEM and SDS-PAGE analyses revealed that the antimicrobial mechanism may be achieved by damaging bacterial cell walls, causing deformed bacterial cells and reduced protein content until the cells are broken into pieces.

Key words: Dendranthema indicum var. aromaticum, essential oil, gas chromatography-mass spectrometry(GC-MS) , antibacterial mechanism