Antibacterial activity and mechanism of clove essential oil against foodborne pathogens

Clove essential oil (CEO) was extracted from dried clove buds using distillation. Gas chromatography-mass spectrometer confirmed eugenol was the main component of CEO. Assays of the minimum inhibitory and minimum bactericidal concentration revealed CEO and eugenol displayed more potent inhibitory effect against Staphylococcus aureus (S. aureus) than against Escherichia coli (E. coli). Crystal violet and MTT assays suggested eugenol could interfere with fresh biofilm formation and reduce the biofilm cellular activities of S. aureus and E. coli. Transmission electron microscopy observations and assays of alkaline phosphatase and intracellular biological macromolecules leakage verified eugenol disrupted the cell wall and cell membrane of S. aureus. After the treatment with eugenol, the production of reactive oxygen species and the activities of three antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase) increased in S. aureus cells, and eventually led to cell apoptosis due to excessive oxidative stress. Meanwhile, the molecular docking model revealed eugenol could combine with enoyl-[acyl-carrier-protein] reductase [NADPH] FabI in a variety of ways. Moreover, eugenol displayed a positive effect on bacterial DNA cleavage, and thereby restrained the proliferation of the bacterium. These results indicated the antibacterial mechanism of eugenol against S. aureus may occur through many pathways.