Toxicity Assessment of Nano-ZnO Exposure on the Human Intestinal Microbiome, Metabolic Functions, and Resistome Using an In Vitro Colon Simulator

Nano-ZnO, as a commonly used nanomaterial, has been found in drinking water, food, and medicine; therefore, it poses potential health risks via the digestion system. However, little is known about the toxicity of nano-ZnO on the human intestinal microbiome, which plays critical roles in human health. This study comprehensively investigated the impact of nano-ZnO on the human gut microbiome, metabolic functions, and resistome using an in vitro colon simulator. Nano-ZnO induced concentration-dependent decreases in the production of short-chain fatty acids (SCFAs). Metagenomic analysis revealed that nano-ZnO not only led to dose-dependent shifts in the composition and diversity of the gut microbiota but also changed the key functional pathways of the gut microbiome. Although the diversity of the gut microbiota basically recovered after stopping exposure to nano-ZnO, SCFAs still showed a concentration-dependent decrease. Furthermore, although a medium concentration of nano-ZnO (2.5 mg/L) reduced the abundance of many antibiotic resistance genes (ARGs) by inhibiting the growth of related host bacteria, a low concentration of nano-ZnO (0.1 mg/L) greatly enriched the abundance of tetracycline resistance genes. Our findings provide evidence that nano-ZnO can impact the diversity, metabolism, and functional pathways of the human gut microbiome, as well as the gut resistome, highlighting the potential health effects of nanoparticles.