Dimorphism and biofilm formation are important virulence factors of some opportunistic human pathogenic yeasts. Such species commensally colonize skin or mucosal surfaces generally in yeast form, but under particular circumstances, convert into virulent hyphae and disseminate internal organs or cause mucocutaneous infections. The yeast-to-hypha shape-conversion promotes the development of a biofilm, a thick extracellular matrix with sessile cells within. The biofilm is capable to prevent the penetration of antifungal drugs, rendering the surviving biofilm-resident cells intrinsic sources of recurrent infections. The aim of this study was to evaluate the ability of silver nanoparticles (AgNPs) to attenuate the morphological switch and biofilm formation of several opportunistic pathogenic yeasts and to determine whether this feature depends on the nanoparticle size. AgNPs in three different sizes were prepared by chemical reduction approach and characterized by transmission electron microscopy, ultraviolet–visible spectroscopy and dynamic light scattering. The antifungal activity was evaluated by the microdilution method, the inhibitory capacity on biofilm formation and the biofilm degradation ability of differently sized AgNPs was assessed by viability assay. The morphological state of opportunistic pathogenic yeast cells in monoculture and in co-culture with human keratinocytes in the presence of AgNPs was examined by flow cytometry and scanning electron microscopy. All the three AgNPs inhibited the growth of the examined opportunistic pathogenic yeasts, nevertheless, AgNPs with the smallest diameter exhibited the most prominent toxic activities. AgNPs attenuated the biofilm formation in a nanoparticle size-dependent manner; however, their biofilm destruction capacity was negligible. AgNPs with the smallest size exerted the most significant effect on suppressing the morphological change of pathogens in monoculture as well as in a co-culture with keratinocytes. Our results confirm that AgNPs are capable to hinder yeast-to-hypha morphological conversion and biofilm formation of opportunistic pathogens and this biological effect of AgNPs is size-dependent.

中文翻译：

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银纳米颗粒的尺寸依赖性活性对机会致病酵母的形态转换和生物膜形成的影响。

二态性和生物膜形成是某些机会性人类致病酵母的重要毒力因子。这些物种通常以酵母形式共生地定居在皮肤或粘膜表面，但在特定情况下，会转化为强毒菌丝并散布内部器官或引起粘膜皮肤感染。酵母菌到菌丝的形状转化促进了生物膜的发展，生物膜是一种具有无柄细胞的厚细胞外基质。生物膜能够阻止抗真菌药物的渗透，使存活的生物膜驻留细胞成为反复感染的内在来源。这项研究的目的是评估银纳米颗粒（AgNPs）减弱几种机会致病酵母的形态转换和生物膜形成的能力，并确定该特征是否取决于纳米颗粒的大小。通过化学还原法制备了三种不同大小的AgNP，并通过透射电子显微镜，紫外可见光谱和动态光散射进行了表征。通过微稀释法评估其抗真菌活性，通过生存力分析评估不同大小的AgNP对生物膜形成的抑制能力和生物膜降解能力。通过流式细胞术和扫描电子显微镜检查在存在AgNPs的情况下在单培养和与人角质形成细胞共培养中机会致病性酵母细胞的形态学状态。所有这三种AgNPs均抑制了所检查的机会致病酵母菌的生长，但是，直径最小的AgNPs表现出最突出的毒性活性。AgNPs以纳米颗粒大小依赖性的方式减弱了生物膜的形成。然而，它们的生物膜破坏能力微不足道。在单培养以及与角质形成细胞的共培养中，最小尺寸的AgNP在抑制病原体的形态变化方面发挥了最显着的作用。