Biogenic Silver Nanoparticles Processed Twice Using 8M Urea Exhibit Superior Antibacterial and Antifungal Activity to Commercial Chemically Synthesized Counterparts

Biogenic silver nanoparticles (b-AgNPs) were produced extracellularly using a cell lysate of genetically modified Escherichia coli and subdivided into three groups. Each group received a different treatment to determine which one best removed residual cell lysate material. The first group was treated twice using only water (water ×2), the second using 8M urea once (8M urea ×1), and the third using 8M urea twice (8M urea ×2). Subsequently, each group was assessed for its ability to inhibit the growth of six bacterial and two fungal pathogens. Testing was accomplished using the minimum inhibitory concentration (MIC) method. Commercially produced c-AgNPs were included for comparison. In all cases, the b-AgNPs (8M urea ×2) demonstrated the greatest inhibition of microbe growth. Conversely, the commercial AgNPs failed to show any growth inhibition at 10 µg/mL the highest concentration tested. The greater antibacterial activity of the b-AgNPs (8M urea ×2) over both b-AgNPs (8M urea ×1) and b-AgNPs (water ×2) is thought to be due to a larger degree of biofunctionalization (coating) occurring during the two sequential 8M urea treatments.