This study aimed to evaluate the effectiveness of silver nanoparticles–chitosan composites (AgNPs) with different morphologies and particle size distributions against resistant bacteria and biofilm formation. Four different samples were prepared by a two-step procedure using sodium borohydride and ascorbic acid as reducing agents and characterized by UV–Vis absorption spectra, scanning transmission electron microscopy. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the AgNPs were determined according to the Clinical and Laboratory Standards Institute (CLSI) against clinical isolates multidrug-resistant and strains of the American Type Culture Collection (ATCC). An assay was performed to determine the MICs during 20 successive bacteria exposures to AgNPs to investigate whether AgNPs induce tolerance in bacteria. The antibiofilm activities of AgNPs were also evaluated by determining the minimum biofilm inhibitory concentration (MBIC). The spherical AgNPs present diameters ranging from 9.3 to 62.4 nm, and some samples also have rod-, oval-, and triangle-shaped nanoparticles. The MIC and MBC values ranged from 0.8 to 25 μg/mL and 3.1 to 50 μg/mL, respectively. Smaller and spherical AgNPs exhibited the highest activity, but all the AgNPs developed in this study exhibit bactericidal activity. There was no significant MIC increase after 20 passages to the AgNPs. Regarding the antibiofilm activity, MBICs ranged from 12.5 to 50 μg/mL. Again, smaller and spherical nanoparticles presented the best results with phenotypic inhibition of production of slime or exopolysaccharide (EPS) matrix. Thus, it was concluded that AgNPs have a promising potential against resistant bacteria and bacteria that grow on biofilms without inducing tolerance.

本研究旨在评估具有不同形态和粒径分布的银纳米粒子-壳聚糖复合材料 (AgNPs) 对耐药细菌和生物膜形成的有效性。使用硼氢化钠和抗坏血酸作为还原剂，通过两步程序制备四种不同的样品，并通过紫外-可见吸收光谱、扫描透射电子显微镜对其进行表征。AgNPs 的最低抑菌浓度 (MIC) 和最低杀菌浓度 (MBC) 是根据临床和实验室标准研究所 (CLSI) 针对临床分离株耐多药和美国典型培养物保藏中心 (ATCC) 菌株确定的。进行了一项测定以确定 20 次连续细菌暴露于 AgNPs 期间的 MIC，以研究 AgNPs 是否诱导细菌耐受。还通过确定最小生物膜抑制浓度 (MBIC) 来评估 AgNPs 的抗生物膜活性。球形 AgNPs 的直径范围从 9.3 到 62.4 nm，一些样品还具有棒状、椭圆形和三角形的纳米颗粒。MIC 和 MBC 值分别为 0.8 至 25 μg/mL 和 3.1 至 50 μg/mL。较小的球形 AgNPs 表现出最高的活性，但本研究中开发的所有 AgNPs 都表现出杀菌活性。AgNPs 传代 20 次后 MIC 没有显着增加。关于抗生物膜活性，MBIC 的范围为 12.5 至 50 μg/mL。再次，更小和球形的纳米颗粒在抑制粘液或胞外多糖 (EPS) 基质产生的表型上表现出最好的结果。因此，得出的结论是，AgNPs 具有抵抗耐药细菌和在生物膜上生长而不诱导耐受性的细菌的有希望的潜力。