Antibacterial Activity and Mechanism of Self-Assembly Spermidine-Capped Carbon Dots against Staphylococcus aureus

This paper investigated the antibacterial mechanism of spermidine-capped carbon dots (S-PCDs) against Staphylococcus aureus. The results showed that there were a large number of amino groups on the surface of S-PCDs and they had a high positive charge (+47.06 mV), which could be adsorbed on the negatively charged bacterial surface through electrostatic interaction and changed the permeability of the bacterial cell membrane. The extracellular protein and nucleic acid contents of S. aureus treated with S-PCDs were 5.4 and 1.2 times higher than those of the control group, respectively. The surface folds and defects of the bacterial cell membrane, and the leakage of cell contents were observed using SEM and TEM. The expression of metabolic oxidation regulatory genes dmpI, narJ and narK was upregulated and the intracellular ROS generation was induced, causing bacterial oxidative stress and eventually bacterial death. S-PCDs can effectively inhibit biofilm formation and had low cytotoxicity. The S-PCD treatment successfully inhibited microbial reproduction when pasteurized milk was stored at 25 °C and 4 °C. These results provide important insights into the antimicrobial mechanism of S-PCDs and lay the foundation for their application in the food field as a potentially novel bacteriostatic nanomaterial.