Are silver nanoparticles better than triclosan as a daily antimicrobial? Answers from the perspectives of gut microbiome disruption and pathogenicity

As an alternative to triclosan (TCS), the widespread use of silver nanoparticles (AgNPs) in daily products shows genuine potential. However, information regarding whether AgNPs are substantially better than TCS in their potential disruption of the gut microbiome and health effects is lacking. Using a simulator of the human intestinal microbial ecosystem (SHIME), we systemically compared the effects of TCS and AgNPs (at 1 μg/L and 30 μg/L) on the human gut microbiome in terms of changes in gut homeostasis, microbial community structure, antibiotic resistance profiles and abundances of opportunistic pathogens. Generally, TCS exerted more severe effects than AgNPs on gut disturbances (i.e., decreased production of short-chain fatty acids, increased contents of ammonium and total bile acids, and increased β-glucosidase activities) in a dose-dependent manner, whereas no clear dose effect was observed for the AgNP treatment because of potential nanoparticle transformation. The more serious effect of TCS than AgNPs on the microbiota composition was indicated by the dynamic increase in the Firmicutes/Bacteroidetes ratio determined using 16S rDNA sequencing. Metagenomic analyses revealed a more pronounced effect of TCS than AgNPs on the selection and dissemination of multiple resistance genes to antibiotics, TCS, and even Ag via the enrichment of genes encoding efflux pumps and mobile genetic elements. Consequently, the overgrowth of opportunistic pathogens was observed upon TCS exposure due to an imbalanced microbiome, in contrast to a slight increase in the abundance of some beneficial bacteria (i.e., Bifidobacterium) induced by the AgNP treatment. In conclusion, from the perspective of effects on gut health, AgNPs may prevail over TCS to some extent. However, the stress and potential selection of Ag resistance indicates the need for targeted surveillance of AgNP commercialization for daily use.