Toxicity Mechanisms in Escherichia coli Vary for Silver Nanoparticles and Differ from Ionic Silver

Abstract

Silver nanoparticles (Ag NPs) are commonly added to various consumer products and materials to impair bacterial growth. Recent studies suggested that the primary mechanism of antibacterial action of silver nanoparticles is release of silver ion (Ag(+)) and that particle-specific activity of silver nanoparticles is negligible. Here, we used a genome-wide library of Escherichia coli consisting of ∼4000 single gene deletion mutants to elucidate which physiological pathways are involved in how E. coli responds to different Ag NPs. The nanoparticles studied herein varied in both size and surface charge. AgNO3 was used as a control for soluble silver ions. Within a series of differently sized citrate-coated Ag NPs, smaller size resulted in higher Ag ion dissolution and toxicity. Nanoparticles functionalized with cationic, branched polyethylene imine (BPEI) exhibited equal toxicity with AgNO3. When we used a genome-wide approach to investigate the pathways involved in the response of E. coli to different toxicants, we found that only one of the particles (Ag-cit10) exhibited a pattern of response that was statistically similar to that of silver ion. By contrast, the pathways involved in E. coli response to Ag-BPEI particles were more similar to those observed for another cationic nanoparticle that did not contain Ag. Overall, we found that the pathways involved in bacterial responses to Ag nanoparticles are highly dependent on physicochemical properties of the nanoparticles, particularly the surface characteristics. These results have important implications for the regulation and testing of silver nanoparticles.

Evaluation of nano-specific toxicity of zinc oxide, copper oxide, and silver nanoparticles through toxic ratio

“…Typically, metal (oxide) NPs will easily dissolve in culture medium (e.g., LB medium) than in (deionized) water. (Ivask et al 2014a;Li et al 2011). However, the toxic tests reveal that the serious toxic damages are normally detected in (deionized) water rather than in culture medium Li et al 2011;Zhang et al 2016) due to the less bioavailable NPs and/ or released metallic ions.…”

Antibacterial activity of silver nanoparticles: A surface science insight

“…4A) [12]. Recently, Ivask et al [70] used Atomic Force Microscopy to detect Ag NPs at bacterial surface. They showed that positively charged branched polyethylenimine-coated (BPEI) nanoparticles had a much higher affinity toward negatively charged bacteria than commonly used citrate coated (Fig.…”

Different responses of Caco-2 and MCF-7 cells to silver nanoparticles are based on highly similar mechanisms of action

“…However, selection of in vitro models is often arbitrary, as well as the chosen nanoparticles and exposure conditions. Silver nanoparticles (AgNPs) are interesting for a mechanistic evaluation of in vitro tests because their mechanism of action is suggested to depend on both Ag + and NPs (Ivask et al, 2014;Lemire et al, 2013). In suspension, AgNPs have been described to release ions (Kittler et al, 2010), which strongly contribute to the biological activity of AgNPs in vitro and in vivo (Bouwmeester et al, 2011;Foldbjerg et al, 2012;van der Zande et al, 2012).…”