Pathogen resistance to conventional antibiotics has become a serious clinical and public health problem, making the development of an alternative mean a very urgent issue. Recently, biosynthesis of silver nanoparticles (AgNPs) was successfully accomplished in the presence of Eucalyptus citriodora leaf extract as a reducing agent. In this study, the antimicrobial mechanisms of AgNPs against important hospital-acquired pathogens, including Gram-positive, Gram-negative bacteria, and fungi were further assessed. The results indicated that AgNPs could enhance a broad antimicrobial spectrum against drug-resistant organisms, with a range of minimum inhibitory concentration from 0.02 to 0.36 μg/mL. Time-kill assay showed that AgNPs produced bactericidal effects on the microorganisms. AgNPs could significantly reduce biofilm production in pathogens without affecting growth of the pathogens (p < 0.05). AgNPs inhibited cell viability and biofilm formation in a dose-dependent manner. Cell membrane damage in microorganisms resulting from effects of AgNPs was observed. A significant increase in per cent uptake of crystal violet was observed in all isolates treated with AgNPs when compared with the control (p < 0.05). Upon treatment with AgNPs, the surface charge of the reference strains and clinical isolates of pathogens moved towards neutral. The alteration of surface potential after exposure to AgNPs could contribute to membrane disruption and cell viability. Scanning electron microscopy further confirmed morphological cell changes and disrupted the cell membrane. Increasing resistance to AgNPs was not induced by stepwise isolation of the bacteria after 45 passages on Luria-Bertani agar supplemented with AgNPs. Furthermore, AgNPs was not toxic to red blood cells.

中文翻译：

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柠檬桉叶提取物介导的银纳米粒子的生物合成：广泛的抗菌谱和对抗医院获得性病原体的作用机制。

病原体对常规抗生素的耐药性已成为严重的临床和公共卫生问题，这使得替代药物的开发成为非常紧迫的问题。近来，在作为还原剂的柠檬桉叶提取物的存在下，成功地完成了银纳米颗粒（AgNPs）的生物合成。在这项研究中，AgNPs对重要的医院获得性病原体（包括革兰氏阳性，革兰氏阴性细菌和真菌）的抗菌机制进行了进一步评估。结果表明，AgNPs可以增强对耐药菌的广泛抗菌谱，其最小抑菌浓度范围为0.02至0.36μg/ mL。时间杀灭试验表明，AgNPs对微生物产生杀菌作用。AgNPs可以显着减少病原体中生物膜的产生，而不会影响病原体的生长（p <0.05）。AgNP以剂量依赖性方式抑制细胞活力和生物膜形成。观察到由AgNPs的作用导致的微生物细胞膜损伤。与对照相比，在所有用AgNPs处理的菌株中，结晶紫的摄取率均显着增加（p <0.05）。用AgNPs处理后，参考菌株和病原体临床分离株的表面电荷向中性方向移动。暴露于AgNPs后表面电势的变化可能有助于膜破裂和细胞活力。扫描电子显微镜进一步证实了形态学细胞的改变并破坏了细胞膜。在补充了AgNPs的Luria-Bertani琼脂上传代45次后，逐步分离细菌并没有诱导出对AgNPs的抗性增强。而且，AgNP对红细胞没有毒性。