Synergistic Antibacterial Activity and Mechanism of Cinnamaldehyde and Thymol Against Staphylococcus aureus
[Objective]This study was aimed to explore the antibacterial activity and mechanism of the combined action of cinnamaldehyde(CA)and thymol(Thy)on Staphylococcus aureus(S.aureus),develop a novel plant-derived essential oil antibacterial agent,establish a theoretical foundation for the clinical application in preventing and treating mastitis in dairy cows.[Method]In this study,the fractional inhibitory concentration index(FICI)of CA and Thy was determined using the micro-checkerboard dilution method.The time-sterilization curve was further used to verify the synergistic bactericidal ability.The effects of CA and Thy on the bacterial cell membrane structure were studied by observing the membrane integrity,membrane permeability,cell membrane potential,biofilm formation,and alkaline phosphatase(AKP)activity of S.aureus.The effect of CA and Thy on reactive oxygen species(ROS)production was also examined.[Result]CA and Thy demonstrated significant synergistic antibacterial activity,with a FICI between 0.1875 and 0.375.The results of the time-killing test confirmed the synergistic effect of the CA and Thy combination on S.aureus.The cell membrane integrity significantly decreased,the cell membrane permeability significantly increased(P＜0.05),the cell membrane potential depolarized,and the biofilm formation significantly decreased under the synergistic effect of CA and Thy(P＜0.05).The synergistic effect of CA and Thy significantly increased the AKP extravasation of S.aureus(P＜0.05)and significantly increased ROS level(P＜0.05),leading to cell damage and death.[Conclusion]In summary,the synergistic combination of CA and Thy exerted antibacterial activity by inducing cell membrane damage,leading to leakage of cell contents and disruption of intracellular homeostasis.This study provided a reference for the clinical application of the natural plant essential oil antibacterial agents CA and Thy in the treatment of mastitis in dairy cows.
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