Exploring the effects of silver nanoparticles on the bacterial microbiota composition of normal human skin

Here, we report a pilot study to investigate the skin microbiome impacts of a 7-day repeated topical exposure to green synthetized bio-AgNPs (Gly-AgNPs), chemically synthetized chem-AgNPs (TSC-AgNPs and PVP-AgNPs) or vehicle control on healthy adult subjects with normal skin (n = 12). Microbiome analysis of swabs collected from the AgNPs exposed forearm skin areas using 16S rRNA gene amplicon sequencing revealed no significant difference in the number of species observed, the bacterial richness (Chao1), and diversity (Shannon) indexes upon exposure to any AgNPs samples. Notably, the two chem-AgNPs treatment groups were significantly different (p < 0.01) in the intergroup weighted Unifrac distance compared with the controls, which was not observed on the bio-AgNP treatment group. Furthermore, taxonomic analysis of the dominant bacteria of flora demonstrates that the relative abundance of opportunistic pathogenic species in any AgNPs exposed groups showed no significant difference. Compared with Gly-AgNPs (bio-AgNPs), transient bacteria Lawsonella were enriched after exposure to TSC-AgNPs (chem-AgNPs), and significant differences were detected in glycolipid metabolism (p < 0.05) and monobactam biosynthesis (p < 0.05) pathways by KEGG analysis. Overall, our data demonstrate that a short-term topical exposure to bio-AgNPs or chem-AgNPs did not significantly alter the bacterial composition and diversity of the core skin microflora while TSC-AgNPs induced changes of the transient bacteria and metabolic profiles which warrants further investigation.