Preparation of copper sulfate/natamycin/carboxymethylcellulose/agar film for synergistic antibacterial application in fruit via causing cuproptosis of Escherichia coli O157: H7

This study has investigated cuproptosis caused by copper sulfate (CuSO4) in Escherichia coli O157: H7 and its mechanism. Meanwhile, the mechanism of CuSO4 combined with natamycin (Nata) against E. coli O157: H7 planktonic and biofilm cells were also investigated. Finally, we prepared an agar-based film, researched its properties, and used it for packaging cherry tomatoes and purple kale. The results indicated that CuSO4 could cause cuproptosis in E. coli O157: H7 and lead the genes related to Fe-S cluster protein (hyfA, sufB, xdhC, and narY) to down-regulate and cuproptosis-related proteins to change. Then, CuSO4 combined with Nata could synergistically decrease E. coli O157: H7 bacterial counts in planktonic condition and biofilm by synergistically affecting the membrane potential, cytoplasm leakage, permeability of outer membrane and inner membrane. After that, CuSO4 and Nata could change the mechanical properties, color and optical characteristics of agarbased film, and decrease the water vapor permeability and oxygen permeability value. Finally, CuSO4@Nata@Carboxymethylcellulose@Agar film effectively lowered the counts of E. coli O157: H7 in cherry tomatoes and purple kale during the storage.