Polygonatum sibiricum Extract Inactivates Cronobacter sakazakii Isolated from Powdered Infant Formula

This study aimed to investigate the antibacterial activity and mechanism of Polygonum sibiricum extract (PSE) against Cronobacter sakazakii (C. sakazakii) isolated from powdered infant formula (PIF). The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and growth curves were measured to evaluate the antibacterial effects. The antibacterial mechanism was elucidated by revealing the changes in cell membrane potential, intracellular reactive oxygen species (ROS) level, cell membrane permeability, protein and nucleic acid leakage, and cell morphology of C. sakazakii. The antibacterial effects of PSE against C. sakazakii in biofilm on stainless steel and in PIF were further analyzed. The results showed that the MIC and MBC of PSE against C. sakazakii were 4 mg/mL and 8 mg/mL, respectively. The growth of C. sakazakii can be completely inhibited by two MIC of PSE. Cell membrane depolarization, increased and then decreased intracellular ROS content, significantly increased cell membrane permeability (p < 0.05), more leakage of intracellular protein and nucleic acid, and severely damaged cell morphology were found in C. sakazakii after treatment with PSE. Furthermore, PSE can significantly reduce the viable bacteria count of C. sakazakii in biofilm on stainless steel and in PIF (p < 0.05). These findings suggest that PSE has the potential to serve as a natural antibacterial agent to reduce contamination by C. sakazakii in PIF.