The antibacterial mechanism of carvacrol and thymol against Escherichia coli

Aims: To investigate the antibacterial mechanism of carvacrol and thymol against Escherichia coli. Methods and Results: The time-kill curve results showed that carvacrol and thymol at 200 mg l(-1) could inhibit the growth of E. coli. Flow cytometry and fluorescent dyes were used to explore the effect of two components on membrane permeability and membrane potential. In membrane permeability experiment, the mean fluorescence intensity of cells treated with 200 mg l(-1) carvacrol or thymol were lower than nonexposed cells. The ratio of red to green fluorescence intensity of DiOC(2)(3) reflected the change of membrane potential. Carvacrol and thymol at 200 mg l(-1) caused the ratio of red/green decreasing from 0.42 of control to 0.08 and 0.07, respectively. Conclusions: Carvacrol and thymol had desired antimicrobial effect on E. coli. The antibacterial effects were attributed to their ability to permeabilize and depolarize the cytoplasmic membrane. Significance and Impact of the Study: This study showed the potential use of flow cytometry as a suitable method to investigate the mode of antibacterial action of essential oil components.