The high frequency of resistance of pathogenic bacteria and fungi to commercial antimicrobial agents has become an alarming public health threat. We report a versatile option for antimicrobial therapy, through recycling metal pollutants, using Ag/Ag2O nanoparticles (NPs) naturally synthesized by dead biomass of the yeast Rhodotorula mucilaginosa (R. mucilaginosa), a nano-biosorbent isolated from the wastewater of a mine in the Amazon region. In in vitro assays, the Ag/Ag2O NPs exhibited promissing antimicrobial activity against Gram-positive Methicillin-resistant Staphylococcus aureus (MRSA) and Gramnegative multidrug-resistant (MDR) Escherichia coli (E. coli) strains, and against the yeast Cryptococcus neoformans (C. neoformans), as demonstrated by the disc diffusion method, minimum inhibitory concentration (MIC), minimal bactericide concentration (MBC) and minimum fungicidal concentration (MFC). The atomic force microscopy (AFM) revealed complete destruction of the microorganisms by the Ag/Ag2O NPs. The toxicity assays of the Ag/Ag2O NPs in mammalian cells demonstrated reduced cytotoxicity, an important characteristic in biomedical application. The Ag/Ag2O NPs synthesized by the nanobiosorbent R. mucilaginosa exerts a potent inhibitory effect on microorganisms and is safe for eukaryotic cells, providing a possible application to nanomedicine and, at the same time, recycling polluting material.