Silver nanoparticles (Ag-NPs) possess excellent antibacterial properties and are considered to be an alternative material for treating antibiotic-resistant bacteria. The present study was aimed at enhancing the antibacterial efficiency of Ag-NPs using visible laser light against Escherichia coli and Staphylococcus aureus in vitro. Four concentrations of Ag-NPs (12.5, 25, 50, and 100 μg/ml), synthesized by the chemical reduction method, were utilized to conduct the antibacterial activity of prepared Ag-NPs. The antibacterial efficiencies of photoactivated Ag-NPs against both bacteria were determined by survival assay after exposure to laser irradiation. The mechanism of interactions between Ag-NPs and the bacterial cell membranes was then evaluated via scanning electron microscopy (SEM) and reactive oxygen species analysis to study the cytotoxic action of photoactivated Ag-NPs against both bacterial species. Results showed that the laser-activated Ag-NP treatment reduced the surviving population to 14% of the control in the E. coli population, while the survival in the S. aureus population was reduced to 28% of the control upon 10 min exposure time at the concentration of 50 μg/ml. However, S. aureus showed lower sensitivity after photoactivation compared to E. coli. Moreover, the effects depended on the concentration of Ag-NPs and exposure time to laser light. SEM images of treated bacterial cells indicated that substantial morphological changes occurred in cell membranes after treatment. The results suggested that Ag-NPs in the presence of visible light exhibit strong antibacterial activity which could be used to inactivate harmful and pathogenic microorganisms.

中文翻译：

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使用蓝色激光增强银纳米颗粒对革兰氏阳性和革兰氏阴性细菌的抗菌效率

银纳米粒子 (Ag-NPs) 具有优异的抗菌性能，被认为是治疗耐抗生素细菌的替代材料。本研究旨在利用可见激光在体外提高 Ag-NPs 对大肠杆菌和金黄色葡萄球菌的抗菌效率。通过化学还原法合成的四种浓度的 Ag-NPs（12.5、25、50 和 100 μg/ml）被用来进行制备的 Ag-NPs 的抗菌活性。暴露于激光照射后，通过存活测定确定光活化的 Ag-NPs 对两种细菌的​​抗菌效率。然后通过扫描电子显微镜 (SEM) 和活性氧分析评估 Ag-NPs 与细菌细胞膜之间相互作用的机制，以研究光活化的 Ag-NPs 对两种细菌的​​细胞毒性作用。结果表明，激光激活的 Ag-NP 处理使大肠杆菌种群中的存活种群减少至对照的 14%，而在 10 分钟暴露时间后，金黄色葡萄球菌种群的存活减少至对照的 28%浓度为 50 μg/ml。然而，与大肠杆菌相比，金黄色葡萄球菌在光活化后表现出较低的敏感性。此外，效果取决于 Ag-NPs 的浓度和激光照射时间。处理过的细菌细胞的 SEM 图像表明处理后细胞膜发生了实质性的形态变化。