Inhibitory Activity of Thymol and Carvacrol Against Cronobacter sakazakii

This study was aimed to determine the antimicrobial effects and mechanisms of thymol and carvacrol against C.sakazakii.The minimum inhibitory concentration (MIC) of thymol and carvacrol against C.sakazakii were first determined. Effects of two substances on growth curves, membrane potential, intracellular pH, and intracellular ATP and membrane integrity of C.sakazakii were also measured.Cell morphology changes were observed under field emission scanning electron microscope. The results showed that both thymol and carvactol had a good antimicrobial effect on C. sakazakii, the MICs of thymol and carvacrol against C.sakazakii strains ranged from 0.1 to 0.2 mg/mL.The membrane of cells treated with thymol and carvacrol became hyperpolarized.In addition, thymol and carvacrol of 4MIC caused a decrease in pH_in of C.sakazakii from 5.45 to 4.96 and 4.97, and also made intracellular ATP concentrations reduce from 0.584 to 0.048 and 0.027 μmol/L, respectively.4MIC thymol and carvacrol also caused 85.0% and 88.1% reduction in cell integrity of C.sakazakii.Field emission scanning electron microscopy showed that both thymol and carvacrol could cause more wrinkled surface of the cells, and pores and even cracks in the cell membrane.The research demonstrated that carvacrol and thymol had strong inhibitory effect on C.sakazakii, which was possibly due to cell membrane dysfunction and changes in cellular morphology.However, the antimicrobial effects of these two natural substances showed no significant differences.