Abstract
Silver nanoparticles (AgNPs) were synthesized extracellularly using a bacterium Cuprividus sp., which was isolated from urban soil and assumed be heavy metal resistant. The successful synthesis of nano size (10-50 nm) spherical crystalline particles was shown by microscopic, diffractometric and spectroscopic analyses. Further, the FTIR spectrum of the AgNPs indicated the presence of amides, which supports the previously suggested enzymatic mechanism of the extracellular reduction of silver ions to atomic silver nanoparticles. The antibacterial properties of the synthesized AgNPs were studied with two assays. The disk diffusion assay indicated the antibacterial activity of the AgNPs against the growth of four human clinical pathogenic bacteria, namely Stenotrophomonas pavanii, Aeromonas enteropelogenes, Proteus mirabilis, and Enterobacter xiangfangensis. The first two were inhibited significantly more than the latter two. The crystal violet assay revealed the strong biofilm inhibition efficacy of the AgNPs with no significant differences between the pathogenic species. The efficacy of the AgNPs against the four pathogens varied. This indicates a need to use several pathogens in nano biomedical studies, and a need to search nanoparticles with high efficiency against a broad spectrum of pathogens. (C) 2019 Elsevier B.V. All rights reserved.