Abstract: The antibacterial effects of the volatile oils extracted with absolute ethanol from lemon flowers (Citrus limon), tea tree leaves (Melaleuca alternifolia) and spearmint leaves (Mentha spicata L.) against Escherichia coli, Staphylococcus aureus, Salmonellas enteritidis and Listeria monocytogenes were investigated in this study, and their active ingredients were identified by gas chromatography-mass spectrometry (GC-MS). Meanwhile, the antibacterial mechanism was evaluated by determining the electric conductivity of bacterial suspensions and observing bacterial cells by scanning electron spectroscopy (SEM). The active ingredients were identified as cinene (65.50%) in lemon oil, 1,8-cineole (48.67%) in tea tree oil, and cinene (16.33%) and L(-)-carvone (35.67%) in spearmint oil. Among these, spearmint oil and its L(-)-carvone had the broadest antibacterial spectrum and strongest antibacterial activity. SEM examination showed that the bacterial cells were crumpled and ruptured after active ingredient treatment, demonstrating these substances could effectively suppress bacterial growth and reproduction by changing cell membrane permeability.

Key words: antibacterial effect, Escherichia coli, Staphylococcus aureus, Salmonellas enteritidis, scanning electron microscope (SEM), gas chromatography-mass spectrometry (GC-MS)