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

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 mu g Ag/mL in E. coli. Further, adherent fimbriae were expressed with Citrate-AgNPs (0.5-10 mu g/mL), whereas NH2-AgNPs (0.5-10 mu g/mL) or Ag+ ions (only at 10 mu g/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.

Automated summary

The highly positively charged 5 nm amino-functionalized silver nanoparticles exhibited strong bactericidal effects, while the highly negatively charged 45 nm citrate-functionalized silver nanoparticles were non-toxic. Moreover, the positively charged nanoparticles inhibited the expression of adherent fimbriae and showed no toxicity to human cells.