Five nanometer size highly positive silver nanoparticles are bactericidal targeting cell wall and adherent fimbriae...

To tackle growing antibiotic resistance (AR) and hospital-acquired infections (HAIs), novel antimicrobials are warranted that are effective against HAIs and safer for human use. We hypothesize that small 5 nm size positively charged nanoparticles could specifically target bacterial cell wall and adherent fimbriae expression, serving as the next generation antibacterial agent. Herein we show highly positively charged, 5 nm amino-functionalized silver nanoparticles (NH₂-AgNPs) were bactericidal; highly negatively charged, 45 nm citrate-functionalized AgNPs (Citrate-AgNPs) were nontoxic; and Ag⁺ ions were bacteriostatic forming honeycomb-like potentially resistant phenotype, at 10 µg Ag/mL in E. coli. Further, adherent fimbriae were expressed with Citrate-AgNPs (0.5-10 µg/mL), whereas NH₂-AgNPs (0.5-10 µg/mL) or Ag⁺ ions (only at 10 µg/mL) inhibited fimbriae expression. Our results also showed no lipid peroxidation in human lung epithelial and dermal fibroblast cells upon NH₂-AgNPs treatments, suggesting NH₂-AgNPs as a biocompatible antibacterial candidate. Potent bactericidal effects demonstrated by biocompatible NH₂-AgNPs and the lack of toxicity of Citrate-AgNPs lend credence to the hypothesis that small size, positively charged AgNPs may serve as a next-generation antibacterial agent, potentially addressing the rising HAIs and patient health and safety.