Impact of dietary chitosan on host immune response and gut microbiome composition in a Listeria monocytogenes high-fat diet murine infection model

Chitosan is a dietary polymer with known metabolic and immunomodulatory properties. We investigated the impact of chitosan on Listeria monocytogenes pathogenesis using in vitro assays and a high-fat diet (HFD) murine infection model. In vitro, chitosan downregulated L. monocytogenes virulence gene expression without affecting bacterial growth or macrophage immune responses. In vivo, chitosan reduced HFD-induced weight gain, enhanced expression of Il-10, and altered gut microbiota composition, impacting Clostridium, Bifidobacterium, and Faecalibaculum species prior to infection. However, chitosan did not alter progression of L. monocytogenes infection or prevent pathogen-driven microbiota disruption, which included reduction in overall diversity and increases in Escherichia, Enterococcus, and Phocaeicola. While dietary chitosan modulated host weight gain, immunity and microbiota composition, it did not enhance resistance to infection in this model. These findings provide insights into the role of chitosan as a potential dietary modulator in the context of host–pathogen–microbiota interactions and support further investigation.