ABSTRACT: Multi-drug resistant bacteria are not effectively managed with current treatments, making it a serious global problem. Therefore, there is an essential need for finding new antimicrobial agents. In this regard, silver nanoparticles (Ag-NPs) have been projected as a new generation of antimicrobial agents. Ag-NPs were biomediated by Egyptian Streptomyces roseolus for the first time, which was molecularly identified using 16S rRNA sequencing under accession no. MT071505. Biosynthesized Ag-NPs were characterized using UV-Vis spectroscopy, XRD, TEM, FTIR, and DLS. FTIR analysis confirmed the presence of different bioactive functional groups, such as N-H, C-H, C-O-C, C-NH2, and C=O acting as bioreducing/stabilizing agents for Ag-NPs. Ag-NPs exhibited antimicrobial activity against some multi-drug resistant Gram-positive and Gram-negative pathogens. MBC of Ag-NPs against Listeria monocytogenes and Klebsiella pneumonia were 0.195 and 0.048 mg/mL, respectively, with a tolerance level of 2 confirming its biocidal effect. SEM imaging of Ag-NPs-treated L. monocytogenes and K. pneumonia showed shrunk destroyed cells after 6 h of treatment. Biosynthesized Ag-NPs exhibited IC50 of < 0.3 and 8.21 mg/mL, on normal Human Skin Fibroblast, and Blood Lymphocytes, respectively. IC50 values were significantly higher than its MBC values, with no harmful cytotoxic effect, thus can be safely applied at its biocidal concentration. For biosafety purposes, the genotoxicity of biosynthesized Ag-NPs was assessed using Comet assay for the first time on Blood Lymphocytes, with zero-tail and 100% head intensity indicating non-genotoxic effect. An ecofriendly biomediated synthesis of Ag-NPs was described with easy scale-up, non-toxic by-products, so, it can be recommended as a powerful-safe antimicrobial agent.
