Physical Fields Reverse FeSO4-Induced VBNC State in Listeria Monocytogenes and Facilitate Ferroptosis

Abstract

Non-thermal sterilization methods offer the advantage of preserving the appearance and quality of food while effectively eliminating foodborne pathogens. In this study, three physical field, magnetic field (MF), ultrasound (US), and blue light (BL), were introduced for their efficacy in sterilizing Listeria monocytogenes (L. monocytogenes) viable but non-culturable (VBNC) cells induced by FeSO4. The results showed that magnetic field-assisted FeSO4 (Fe-MF) treatment induced L. monocytogenes cells to form VBNC state, while ultrasound-assisted FeSO4 (Fe-US) treatment reduced the VBNC cell population by 52.63%. In contrast, blue light-assisted FeSO4 (Fe-BL) treatment resulted in a 100% bactericidal effect, achieving 94.73% decrease in cell viability and a 68.2% cell membrane damage rate. The Fe-BL treatment also caused cell wrinkling and secretion aggregation. Additionally, BL treatment alone disrupted cell membrane permeability and induced intracellular protein aggregation. The investigation of the bactericidal mechanism revealed that Fe-BL treatment reversed the VBNC state toward death and promoted the intracellular accumulation of Fe2+, inducing a reactive oxygen species (ROS) burst and lipid peroxidation. Proteomic analysis further identified significant alterations in pathways related to fatty acid metabolism, ribosome biogenesis, intracellular iron homeostasis, and DNA synthesis in Fe-BL treated cells. In conclusion, Fe-BL treatment effectively disrupted VBNC cell membranes, facilitated the entry of ferrous ion entry, and induced Fenton-reaction-mediated ferroptosis. Therefore, this study offers a promising strategy for inactivating VBNC cells.

Keywords: Magnetic field, Ultrasound, Blue light, Synergistic sterilization, FeSO4, ferroptosis