Acanthamoeba spp. are the causative agent of Acanthamoeba keratitis and granulomatous amoebic encephalitis (GAE). The current options to treat Acanthamoeba infections have limited success. Silver nanoparticles show antimicrobial effects and enhance the efficacy of their payload at the specific biological targets. Natural folk plants have been widely used for treating diseases as the phytochemicals from several plants have been shown to exhibit amoebicidal effects. Herein, we used natural products of plant or commercial sources including quercetin (QT), kolavenic acid (PGEA) isolated from plant extracts of Polyalthia longifolia var pendula and crude plant methanolic extract of Caesalpinia pulcherrima (CPFLM) as antiacanthamoebic agents. Furthermore, these plant-based materials were conjugated with silver nanoparticles (AgNPs) to determine the effects of the natural compounds and their nanoconjugates against a clinical isolate of A. castellanii from a keratitis patient (ATCC 50492) belonging to the T4 genotype. The compounds were conjugated with AgNPs and characterized by using ultraviolet visible spectrophotometry and atomic force microscopy. Quercetin coated silver nanoparticles (QT-AgNPs) showed characteristic surface plasmon resonance band at 443 nm and the average size distribution was found to be around 45 nm. The natural compounds alone and their nanoconjugates were tested for the viability of amoebae, encystation and excystation activity against A. castellanii. The natural compounds showed significant growth inhibition of A. castellanii while QT-AgNPs specifically exhibited enhanced antiamoebic effects as well as interrupted the encystation and excystation activity of the amoebae. Interestingly, these compounds and nanoconjugates did not exhibit in vitro cytotoxic effects against human cells. Plant-based compounds and extracts could be an interesting strategy in development of alternative therapeutics against Acanthamoeba infections.

中文翻译：

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基于植物的天然产物及其缀合的银纳米颗粒对棘阿米巴棘孢菌的抗厌氧活性（ATCC 50492）。

棘阿米巴属 是棘阿米巴角膜炎和肉芽肿性阿米巴性脑炎（GAE）的病原体。目前治疗棘阿米巴感染的选择取得了有限的成功。银纳米颗粒显示出抗菌作用，并增强了其有效载荷对特定生物靶标的功效。天然民间植物已被广泛用于治疗疾病，因为几种植物的植物化学物质已显示出杀菌作用。在本文中，我们使用了植物或商业来源的天然产物，包括槲皮素（QT），从长寿花植物提取物中分离出的叶绿酸（PGEA）和多叶草（Caesalpinia pulcherrima）的粗植物甲醇提取物（CPFLM）作为抗风血病药物。此外，这些基于植物的材料与银纳米颗粒（AgNP）结合，以确定天然化合物及其纳米结合物对来自属于T4基因型的角膜炎患者的A. castellanii临床分离株的作用（ATCC 50492）。将化合物与AgNPs缀合，并通过紫外可见分光光度法和原子力显微镜进行表征。槲皮素包被的银纳米颗粒（QT-AgNPs）在443 nm处表现出特征性的表面等离振子共振带，并且平均尺寸分​​布约为45 nm。测试了天然化合物及其纳米共轭物对拟南芥的变形虫活力，侵染和兴奋活性。天然化合物显示出对A的显着生长抑制作用。卡斯特氏菌同时QT-AgNPs表现出增强的抗厌氧作用，并中断了变形虫的入侵和兴奋作用。有趣的是，这些化合物和纳米缀合物对人体细胞没有表现出体外细胞毒性作用。基于植物的化合物和提取物可能是开发针对棘阿米巴感染的替代疗法的有趣策略。