Dietary iron attenuates Clostridioides difficile infection via modulating intestinal immune response and gut microbiota

Clostridioides difficile (C. difficile) causes antibiotic-associated diarrhea. Susceptibility to C. difficile infection (CDI) is largely affected by the gut microbiota, which in turn is influenced by diet. However, the mechanism underlying the interplay between diet and the gut microbiota that regulates host susceptibility to CDI remains unclear. To investigate the effects of a high-iron diet on the intestinal immune response, microbiota, and metabolism in mice infected with C. difficile, we explored the specific role of the unique gut microbiota and metabolites on CDI. A mouse model of CDI was constructed with or without high dietary iron treatment. High dietary iron (400 mg/kg ferrous sulfate) alleviated CDI by decreasing the pathogenicity of C. difficile and altering host intestinal neutrophil recruitment. The effect of high iron levels on the gut microbiota was analyzed by 16S rRNA gene sequencing, and the role of gut microbiota was confirmed by fecal microbiota transplantation (FMT). Furthermore, E. coli AVS0501, enriched in the gut microbiota of iron-treated CDI mice, was found to have prophylactic and therapeutic effects on CDI. Moreover, the production of L-proline and tauroursodeoxycholic acid (TUDCA) in CDI mice treated with high dietary iron directly determines the colonization and toxin production of C. difficile, and in turn, regulates the intestinal neutrophil response. In summary, high dietary iron alleviates C. difficile induced enteritis by regulating gut microbiota. Overall, the interplay between dietary iron and gut microbiota maintains gut homeostasis in CDI and determines the severity of CDI, suggesting that high dietary iron may be an important determinant of disease control.