Antibacterial mechanism of thymol to methicillin-resistant Staphylococcus aureus

Objective  To investigate the antibacterial mechanism of thymol to methicillin-resistant Staphylococcus aureus(MRSA), and provide a reliable theoretical basis for the exploitation of high efficient and low toxic anti-MRSA medicine.

Method  The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of thymol to MRSA standard strain USA300 were determined via microbroth dilution method and colony counting method. Bacterium solution conductivity and DNA amount were detected to investigate the effect of thymol on USA300 cell membrane. SDS-PAGE was used to detect the effect of thymol on USA300 soluble protein synthesis. The ultra structure of USA300 cell treated by thymol was observed through transmission electron microscope. The effect of thymol on USA300 biofilm formation was investigated via crystal violet staining method.

Result  Thymol had definite inhibitory activity on USA300, both MIC and MBC of thymol to USA300 were 256 mg·L^–1. Compared with the control group, after treating the strain with 512 mg·L^–1 thymol for 1 h, the conductivity of bacterium solution was improved by 18.08%±1.80%, and DNA exosmosis amount increased by (123.40±8.06) mg·L^–1; after treating for 24 h, the soluble protein content of USA300 was reduced 68.20%±0.15%. Thymol destroyed cytoderm and cytomembrane of USA300, disturbed its normal binary fission, and inhibited biofilm formation at subinhibitory concentration.

Conclusion  Thymol can inhibit bacterium growth by changing its cytomembrane permeability and disturbing protein synthesis and normal binary fission, and depress biofilm formation at subinhibitory concentration in the premise of not affecting bacterium growth. Thymol has the potential of developing as anti-MRSA medicine.