Proteomic Analysis of the Mode of Antibacterial Action of Silver Nanoparticles

Silver nanoparticles (nano-Ag) are potent and broad-spectrum antimicrobial agents. In this study, spherical nano-Ag (average diameter = 9.3 nm) particles were synthesized using a borohydride reduction method and the mode of their antibacterial action against E. coli was investigated by proteomic approaches (2-DE and MS identification), conducted in parallel to analyses involving solutions of Ag+ ions. The proteomic data revealed that a short exposure of E. coli cells to antibacterial concentrations of nano-Ag resulted in an accumulation of envelope protein precursors, indicative of the dissipation of proton motive force. Consistent with these proteomic findings, nano-Ag were shown to destabilize the outer membrane, collapse the plasma membrane potential and deplete the levels of intracellular ATP. The mode of action of nano-Ag was also found to be similar to that of Ag+ ions (e.g., Dibrov, P. et al, Antimicrob. Agents Chemother. 2002, 46, 2668−2670); however, the effective concentrations of nano-Ag and Ag+ ions were at nanomolar and micromolar levels, respectively. Nano-Ag appear to be an efficient physicochemical system conferring antimicrobial silver activities. Keywords: silver nanoparticles • silver ions • antibacterial agents • E. coli • outer membrane proteins • membrane potential • ATP