Antimicrobial activity and mechanism of action of olive oil polyphenols extract against Cronobacter sakazakii

This study was conducted to analyze the antimicrobial activity of olive oil polyphenols extract (OOPE) against Cronobacter sakazakii. The antimicrobial effect was evaluated by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values, and survival of bacteria after treatments with OOPE in sterile normal saline (NS) and Luria-Bertani (LB) broth. The changes in intracellular ATP concentration, cell membrane potential, content of bacterial protein, and cell morphology were analyzed to reveal possible mechanism of action. The results showed that the MICs and MBCs of OOPE against C. sakazakii strains ranged from 0.625 to 1.25 mg/mL, and 1.25-2.50 mg/mL, respectively. Approximately 8 log CFU/mL of C. sakazakii was completely inactivated after a treatment with 1 MIC of OOPE in NS at 37 °C for 3 h, and in LB broth at 37 °C for 10 h. The mechanism of action of OOPE against C.sakazakii was associated with reduction of intracellular ATP concentrations, cell membranes depolarization, leakage of cytoplasm, decrease of bacterial protein content and leakage of cytoplasm. Therefore, our findings provided a theoretical possibility that OOPE can be used as a natural food preservative or bactericide to reduce the food safety problems caused by C. sakazakii strains in food industries as well as food processing environments.