Journal of Nanomedicine & Nanotechnology

Abstract

Superior Antibacterial Activity of Photochemical Synthesized Ag-CNT Composites and their Synergistic Effects in Combination with other Antimicrobial Agents

Xiuli Dong, Youngmi Koo, Yongan Tang, Yeoheung Yun and Liju Yang

Silver nanoparticle-modified multiwalled carbon nanotubes (MWCNTs) nanocomposites (AgCNTs) were synthesized by photochemical reduction method, their antimicrobial effect on both Gram negative and Gram positive bacteria, using E. coli and Bacillus anthracis as model bacteria, respectively, were investigated. The results indicated that AgCNTs exhibited more potent antibacterial effects against both Gram negative and Gram positive bacterium compared to Ag nanoparticles (Ag NPs). The minimal inhibitory concentrations (MICs) of AgCNTs against E. coli cells (0.5 μg/mL) and B. anthracis cells (0.8 μg/mL) was 1/20 times and 1/17.5 of the MICs of Ag NPs against E. coli and B. anthracis, respectively. Further study on the antibacterial effect of combination treatment of AgCNTs with oxidizing antimicrobial agents (NaOCl or H₂O₂) to E. coli cells indicated a partial synergistic or a synergistic effect using the fractional inhibitory concentration (FIC) index test or isololograms. The combination treatment of AgCNTs with a natural peptide, nisin, also exhibited enhanced inhibitory effect on E. coli growth, as significant delays in growth of E. coli cells treated by the combination of 0.2 μg/mL AgCNTs and 4 or 8 μg/mL nisin was observed compared to AgCNTs alone nisin alone treatment. The synergistic or enhanced effect of the combination of AgCNTs with other antimicrobial relied on the combination of different action mechanisms in which AgCNTs played a role to damage cell membrane which allowed easier access for other small antimicrobial molecules to penetrate into cells. Such combination strategy could be broadly applicable to the improvement of existing antimicrobial methods or design/discover new effective antimicrobial agents/methods.