Antibacterial characteristics of oregano essential oil and its mechanisms against Escherichia coli O157:H7

The present study aimed to investigate the antimicrobial property of oregano essential oil (OEO). The results showed that OEO exhibited antibacterial activity against Escherichia coli O157:H7 with the minimum inhibition concentration (MIC) of 0.156 mu L/mL. Obvious changes in the morphology and microstructure of E. coli O157:H7 cells were observed after OEO treatment at 2 x MIC. After being treated with OEO at 2 x MIC for 6 h, the extracellular nucleic acids and proteins concentrations increased by 9.75- and 6.42-fold (p < 0.05), respectively, indicating the membrane permeabilization of E. coli O157:H7 cells. Exposure of the cells to OEO (1/4 x MIC-2 x MIC) resulted in an increase in DiBAC(4)(3) fluorescence intensity, indicating the membrane potential depolarization of E. coli O157:H7 cells. OEO also caused significant increases in the intracellular levels of reactive oxygen species in E. coli O157:H7 cells. The results suggest that OEO exerts bactericidal effect via causing damages to cell structures, permeabilizing cellular membranes, inducing depolarization of membrane potential and oxidative stress. Accordingly, OEO can be considered as a natural antibacterial agent with potential application in the food industry.