Antibacterial properties and mechanism of biopolymer-based films functionalized by CuO/ZnO nanoparticles against Escherichia coli and Staphylococcus aureus

Highlights: • Nanocomposite film are fabricated by incorporating CuONPs/ZnONPs into SA/CS matrix. • Packaging properties of SA/CS film are improved by incorporation of CuONPs/ZnONPs. • SA-CS@CuO/ZnO film inhibits growth of bacteria and regulates their gene expression. • SA-CS@CuO/ZnO film regulates cellular antioxidant pathway of E. coli and S. aureus. • SA-CS@CuO/ZnO film affects bacterial gene guiding repair of cell membranes and DNA. In this study, the nanocomposite film (SA-CS@CuO/ZnO) composed of sodium alginate (SA) and chitosan (CS) functionalized by copper oxide nanoparticles (CuONPs) and zinc oxide nanoparticles (ZnONPs) was fabricated, then its antibacterial mechanisms against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were systematically investigated. When the contents of CuONPs and ZnONPs reached 1.5 % (w/w) and 0.5 % (w/w), respectively, the SA-CS@CuO/ZnO exhibited great mechanical, barrier, and optical properties. Moreover, the incorporation of ZnONPs enhanced the photocatalytic ability of SA-CS@CuO/ZnO, producing a high level of reactive oxygen species under light irradiation. Further, antibacterial results showed that SA-CS@CuO/ZnO treatment inhibited the growth of E. coli and S. aureus higher than 60 % in the dark and exceeded 90 % under light irradiation. This was also manifested in the incompleteness of bacterial cell structure, accompanied by unstable cellular redox balance and DNA disruption. The functions of differentially expressed genes screened by transcriptome analysis were mainly involved in membrane transport, cell wall and membrane synthesis, cellular antioxidant defense system, cell membrane and DNA repair system. The changes in bacterial transcriptional regulation reflected the disturbance in the physiological activities and loss of cell integrity, leading to damage of bacterial cells or death.