title: The Molecular Mechanisms of the Antibacterial Effect of Picosecond Laser Generated Silver Nanoparticles and Their Toxicity to Human Cells.
abstract: Silver nanoparticles (Ag NPs) are known to have antibacterial properties. They are commonly produced by chemical synthesis which involves the use of harmful reducing agents. Contras, the laser technique is able to generate high-purity Ag NPs in water with specified surface charge characteristics. In the past, the molecular mechanisms contributing to the bactericidal effects of Ag NPs have been investigated extensively, but little is known of the antibacterial and toxic effects and mechanisms involved in laser-generated Ag NPs. In the current study Ag NPs were generated by picosecond laser ablation. Their antibacterial activity was determined on the gram-negative bacteria E. coli and Pseudomonas aeruginosa, and the gram positive bacteria Staphylococcus aureus including the methicillin resistant strain MRSA. Results showed that the laser generated Ag NPs exhibited strong dose-dependent antibacterial activity against all the three bacterial strains tested. Using E.coli as a model system, the laser Ag NPs treatment induced significantly high levels of reactive oxygen species (ROS). These ROS did not include detectable hydroxyl radicals, suggesting for the first time the selective ROS induction in bacterial cells by laser generated Ag NPs. The increased ROS was accompanied by significantly reduced cellular glutathione, and increased lipid peroxidation and permeability, suggesting ROS related bacterial cell damage. The laser generated Ag NPs exhibited low toxicity (within 72 hours) to five types of human cells although a weak significant decrease in cell survival was observed for endothelial cells and the lung cells. We conclude that picosecond laser generated Ag NPs have a broad spectrum of antibacterial effects against microbes including MRSA with minimal human cell toxicity. The oxidative stress is likely the key mechanism underlying the bactericidal effect, which leads to lipid peroxidation, depletion of glutathione, DNA damages and eventual disintegration of the cell membrane.
authors: Faculty of Medical and Human Science, the University of Manchester, Manchester, M13 9PL, United Kingdom.
authors: Peri
authors: P
authors: Korshed
authors: Laser Processing Research Centre, School of Mechanical, Aerospace and Civil Engineering, the University of Manchester, Manchester, M60 IQD, United Kingdom.
authors: Lin
authors: L
authors: Li
authors: Corrosion and Protection Centre, the Mill, School of Materials, The University of Manchester, Manchester, M13 9PL, United Kingdom.
authors: Zhu
authors: Z
authors: Liu
authors: Faculty of Medical and Human Science, the University of Manchester, Manchester, M13 9PL, United Kingdom.
authors: Tao
authors: T
authors: Wang
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007834:Lasers; D053768:Metal Nanoparticles / Q000737:chemistry*; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D012834:Silver / Q000737:chemistry / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects; D013499:Surface Properties
chemical_list: D000900:Anti-Bacterial Agents; D017382:Reactive Oxygen Species; D012834:Silver