Session: Posters:

Nosocomial or hospital-acquired infections (HAIs) are predominant in intensive care unit with the central line bloodstream and ventilator usage, resulting in over 12 million deaths/year globally. Novel antimicrobials that are designed to be effective against HAIs and safer for human use are warranted. We hypothesize that nanomaterials of near-atomic size and positively charged could specifically target bacterial cell wall and adherent fimbriae, serving as the next generation antimicrobial agent. Synthesizing two different sized (5nm vs. 45nm diameter) and surface charged (zeta potential of +41.6mV vs. -30mV) silver nanoparticles (AgNPs) with different surface functionalizations (-NH₂ vs. citrate), we tested their antibacterial efficacies against gram-negative Escherichia coli. Results show that positively charged 5nm NH₂–AgNPs were bactericidal, negatively charged 45nm Citrate–AgNPs were nontoxic, and Ag⁺ ions were bacteriostatic, against E. coli at comparable concentrations (10µg/mL). Differential phenotypic responses in bacteria were observed using FE-SEM with different treatments: cells were shorter and wider with NH₂–AgNPs (0.5µg/mL), and were not statistically different from controls with Citrate–AgNPs (10ug/mL) or Ag⁺ ions (0.5ug/mL) treatment. However, E. coli treated with 10µg/mL Ag⁺ ions demonstrated no cell wall damage with hexagonal honeycomb-shaped phenotype—a discovery that was not previously reported for Ag⁺ ion stress response in E. coli. In contrast, at 10 mins post-exposure, larger particulates (155-157nm in diameter) of AgNPs were observed on E. coli surface upon treatment with10µg/mL positively charged 5nm NH₂–AgNPs, resulting in increased cell wall damage, death and complete population collapse by 72h, suggesting that positively charged 5nm NH₂–AgNPs have higher affinity to bacterial cell surface binding compared to the negatively charged 45nm Citrate–AgNPs. These results are confirmed by FE-SEM coupled with surface EDS elemental mapping. Further, adherent fimbriae were observed with Citrate–AgNPs, whereas NH₂–AgNPs (0.5-10µg/mL) or Ag⁺ ions (only at 10µg/mL) treatment inhibited fimbriae expression. Potent bactericidal effects demonstrated by NH₂–AgNPs and no toxicity of Citrate–AgNPs lend credence to the hypothesis that near-atomic size and positively charged AgNPs could serve as a next-generation antibacterial agent, addressing the rising HAIs and patient health and safety.

Dmitriy Dikin

Appearances