Mechanism and Antibacterial Activity of Cinnamaldehyde against Escherichia coli and Staphylococcus aureus
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Abstract:
The antibacterial activity of cinnamaldehyde against Escherichia coli and Staphylococcus aureus, and the underlying mechanism were evaluated. Antibacterial activity was determined based on the diameter of inhibition zone (DIZ) that was measured by the disc diffusion method, and by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), measured to a series of doubling dilutions. Furthermore, the antibacterial mechanism was explored using scanning electron microscopy, cell membrane permeability and integrity, as well as membrane potential. The DIZ values of E. coli and S. aureus were 21.75 mm and 29.37 mm, respectively. The MIC (0.25 μL/mL) and MBC values (0.5 μL/mL) were the same for both bacteria. Scanning electron microscope images showed that the structure of the bacterial cell was damaged by cinnamaldehyde with consequent morphologxical changes. With increasing concentration of cinnamaldehyde, the relative electric conductivity increased rapidly, indicating that the permeability of the cell membrane was affected by cinnamaldehyde. Furthermore, the multi-fold increase in nucleic acids and proteins in the cell suspension revealed that cinnamaldehyde damaged the integrity of the bacterial membrane, decreased the membrane potential, and affected the metabolic activity, thus inhibiting bacterial growth. Cinnamaldehyde exerts its main effect on the bacterial cell membrane, and is suitable as a natural preservative to inhibit the growth of food-spoilage and pathogenic bacteria, thus extending the shelf life of food.
