The aim of the present work was to investigate the antibacterial, antibiofilm, and antiquorum sensing activities of phytosynthesized silver nanoparticles (AgNPs) fabricated from Mespilus germanica extract against multidrug‐resistant (MDR) Klebsiella pneumoniae strains. Fifty strains of K. pneumoniae were isolated from various clinical specimens. Biofilm‐forming strains were identified using Congo red agar and polymerase chain reaction (PCR) techniques. Subsequently, the antibacterial activity of phytosynthesized AgNPs on MDR K. pneumoniae strains was investigated by broth microdilution assay and agar well‐diffusion method. Finally (in the last step), the antibiofilm activity of phytosynthesized AgNPs was determined using microtiter plate assay and real‐time PCR (RT‐PCR) methods for the analysis of type 3 fimbriae (mrkA) and quorum‐sensing system (luxS) gene expression. The results of this study showed that the phytosynthesized AgNPs had a spherical nanostructure with the mean size of 17.60 nm. The AgNPs exhibited dose‐dependent antibacterial activity. The results of the microtiter plate and RT‐PCR methods show that AgNPs inhibited the biofilm formation in MDR K. pneumoniae strains, and the expressions of mrkA and luxS genes were downregulated significantly in MDR strains after treatment with a subminimum inhibitory concentration of AgNPs. In conclusion, AgNPs effectively prevent the formation of biofilms and kill bacteria in established biofilms, which suggests that AgNPs might be a promising candidate for the prevention and treatment of biofilm‐related infections caused by MDR K. pneumoniae strains.

中文翻译：

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由德国 Mespilus Germanica 提取物制备的植物合成银纳米粒子的抗菌、抗生物膜和抗群体感应活性对抗肺炎克雷伯菌临床菌株的多药耐药性

本工作的目的是研究由 Mespilus Germanica 提取物制成的植物合成银纳米粒子 (AgNPs) 对多重耐药 (MDR) 肺炎克雷伯菌菌株的抗菌、抗生物膜和抗微生物传感活性。从各种临床标本中分离出 50 株肺炎克雷伯菌。使用刚果红琼脂和聚合酶链反应 (PCR) 技术鉴定生物膜形成菌株。随后，通过肉汤微量稀释法和琼脂井扩散法研究了植物合成的 AgNPs 对 MDR 肺炎克雷伯菌菌株的抗菌活性。最后（在最后一步），使用微量滴定板测定和实时 PCR (RT-PCR) 方法分析 3 型菌毛 (mrkA) 和群体感应系统 (luxS) 基因表达，确定了植物合成的 AgNPs 的抗生物膜活性。这项研究的结果表明，植物合成的 AgNPs 具有球形纳米结构，平均尺寸为 17.60 nm。AgNPs 表现出剂量依赖性抗菌活性。微量滴定板和 RT-PCR 方法的结果表明，AgNPs 抑制了 MDR 肺炎克雷伯菌的生物膜形成，并且在用亚最低抑制浓度的 AgNPs 处理后，MDR 菌株中 mrkA 和 luxS 基因的表达显着下调。总之，AgNPs 有效地防止了生物膜的形成并杀死了已建立的生物膜中的细菌，