Silver nanoparticle enhanced silver ion stress response inEscherichia coliK12

Abstract

This study investigated the dissolution-based toxicity mechanism for silver nanoparticles to Escherichia coli K12. The silver nanoparticles, synthesised in the vapour phase, are effective anti-bacterial agents against the Gram-negative bacterium, E. coli K12. The nanoparticles associate with the bacterial cell wall, appearing to interact with the outer and inner membranes, and then dissolve to release Ag(+) into the cell and affect a transcriptional response. The dissolution of these nanoparticles in a modified LB medium was measured by inductively coupled plasma mass spectrometry (ICP-MS) and has been shown to follow a simple first-order dissolution process proportional to the decreasing surface area of the nanoparticles. However, the resulting solution phase concentration of Ag(+), demonstrated by the ICP-MS data, is not sufficient to cause the observed effects, including inhibition of bacterial growth and the differential expression of Cu(+) stress response genes. These data indicate that dissolution at the cell membrane is the primary mechanism of action of silver nanoparticles, and the Ag(+) concentration released into the bulk solution phase has only limited anti-bacterial efficacy.

Repeated dose (28-day) administration of silver nanoparticles of varied size and coating does not significantly alter the indigenous murine gut microbiome

“…Thus, despite having in vitro antimicrobial properties (Morrill et al, 2013, McQuillan et al, 2012, McQuillan and Shaw, 2014, Ivask et al, 2014), ingested AgNPs do not appear to have a similar effect on the gut microbiome as do broad-spectrum antibiotics (Theriot et al, 2014, Theriot et al, 2011, Bassis et al, 2014). This finding is significant in assessing the potential for antimicrobial effects of ingested silver nanoparticles at exposure levels likely to be encountered in consumer products and dietary additives.…”

“…Most in vitro experimental evidence suggests that dissolution and local silver ion concentration play a significant role in the antimicrobial activity of AgNP (McQuillan et al, 2012, McQuillan and Shaw, 2014, Behra et al, 2013), although some aspects are not entirely explained by Ag ion availability (McQuillan and Shaw, 2014, Ivask et al, 2014). Assuming that antimicrobial effects of silver are dependent on direct interaction with gut microbes (Volker et al, 2013, Behra et al, 2013), particles present in higher luminal concentrations in the distal gut, which is the site of maximal bacterial concentration, may be more likely to have antimicrobial effects.…”

Quantifying the total ionic release from nanoparticles after particle-cell contact

“…It results in great uncertainty when exploring the mechanisms underlying the microbial toxicity of NPs. For example, numerous studies have found that solvated Ag þ from silver NPs (Ag NPs) into the soluble phase during toxicity assays were too low to explain the observed antibacterial effects (Gunawan et al, 2009;Jin et al, 2010;McQuillan et al, 2012;Sotiriou and Pratsinis, 2010). However, Wang et al (2013) found it possible to underestimate the Ag þ releasing during exposure, making it difficult to discern whether Ag NPs exerted particlespecific toxicity.…”

Effects of particle size and coating on toxicologic parameters, fecal elimination kinetics and tissue distribution of acutely ingested silver nanoparticles in a mouse model

“…Antibiotics can have adverse effects on intestinal health by eliminating normal intestinal microbes (Antonopoulos et al, 2009). Silver is known to have antimicrobial properties (McQuillan et al, 2012; Morrill et al, 2013). It is unknown whether concurrent AgNP ingestion will enhance antimicrobial effects of a typically well-tolerated antibiotic dose, causing potential adverse effects due to disruption of normal gastrointestinal microbes (e.g.…”