Antibacterial Mechanism of Cinnamon Essential Oil Vapor Fumigation against Staphylococcus aureus
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Abstract:
The antibacterial function of the vapor-phase of the essential oil from Cinnamomum cassia (EOL) against Staphylococcus aureus (S. aureus) and the underlying mechanisms were investigated. Gas phase fumigation was used in the experiments to examine the antibacterial mechanism of gas-phase cinnamon essential oils by TEM, conductivity test, FT-IR spectroscopy, fluorescence spectroscopy and other methods were used to characterize the change of cellular membrane after treated by essential oil through gas phase fumigation method. The results showed that EOL had significant vapor-phase antibacterial activity with a MIC and MBC against S. aureus being 0.25 μL/mL and 0.5 μL/mL, respectively. TEM observations showed that the cell membrane of S. aureus was damaged and dissolved after being fumigated by Cinnamomum essential oil, and the cells shrank, causing the contents to leak out. The conductivity experiments further confirmed that the cell membrane permeability of S. aureus was improved, and apositive correlation between nucleic acid leakage and the changes in the concentration of essential oil was found by measuring OD260. The FT-IR and fluorescence spectra showed the changes in protein conformation of S. aureus caused by the treatment with cinnamon essential oil. On the analysis of the amide I band, it was speculated that the secondary structure of bacterial proteins became more disordered in the process of fumigation. Based on the changes in fluorescence intensity and spectralpeak position, one could speculate that the bacterial proteins had changed after the cinnamon essential oil fumigation, leading to more exposed chromophores. Accordingly, the possible antibacterial mechanism of cinnamon essential oil fumigation against S. aureus was related to the changes in the cell membrane permeability and morphology, and secondary and tertiary structures of bacterial proteins.
