The widespread use of silver nanoparticles (AgNPs) has prompted studies on different species and at various trophic levels, however, little is known about possible toxicological impacts on their corresponding microbiota. Here the effects of AgNPs on a defined bacterial community established from the collected stool of a healthy donor have been investigated. The anaerobic consortium was exposed to several concentrations (0–200 mg/L) of AgNPs (capped; 10 nm) for 48 h. Nanosilver had a negative impact on the bacterial community as evidenced by a significant reduction (~ 22%) in culture-generated gas production at the two highest AgNP concentrations compared to controls, as well as significant (p< 0.05) changes in fatty acid methyl ester profiles even at the lowest concentration. DNA analysis confirmed these observations showing a shift in the community structure as demonstrated by cluster analysis of PCR-denaturing gradient gel electrophoresis (DGGE) profiles, as well by phylogenetic distributions obtained from 454 pyrotag 16S rRNA gene sequencing. The bacterial assemblage was significantly (p< 0.01) different in the AgNP-treatment groups compared to controls. As expected, ionic silver (AgCl; 25-200 mg/L) was also antibacterial, as shown by all four assessment methods, but its effects were distinct from the AgNP-mediated changes. Thus, nano size-dependent impacts were evident. Taken together, these experiments suggest that AgNP ingestion, either deliberate or inadvertent, could have negative consequences on our intestinal microbiota. human donor [15] that holds promise as a simplified, defined proxy for a healthy gut microbial ecosystem, allowing experimental control and reproducibility [16].

In the fruitfly, Drosophila melanogaster, experimental dietary exposure to AgNPs resulted in the increased midgut abundance of Gram positive genera, chiefly Lactobacillus, at the expense of Gram negative genera such as Sphingdomonas and Rhizobiales, relative to untreated or Ag microparticle-treated controls [17]. This shift in the midgut community was correlated with a reduction in developmental success. To our knowledge, however, the impact of AgNPs on the human intestinal microbiota has not yet been reported. Although it is possible that some human ingestion of AgNPs might occur subsequent to aquatic or soil contamination, we suspect that it is more likely that exposure would be a consequence of the deliberate addition of nanosilver to cosmetics, foods and beverages, in water purifiers, as well as the consumption of silver as an alternative medicine [1, 18, 19]. Here we have modeled such exposure by using “RePOOPulate” as a simplified representation of the human gut microbiota in batch anaerobic fermentation. Polyvinylpyrrolidone (PVP) capped AgNPs were used, as well as ionic silver controls, and across a range of exposure concentrations. We hypothesized that both ionic silver and nanosilver could perturb this microbial community and that there would be a nanosize-dependent impact. We further postulated that if the effect on gut bacteria was significant, then toxicity