Metaplasia Enables Stomach Colonization by Fusobacterium animalis

Infection with Helicobacter pylori is the major risk factor for gastric cancer worldwide; yet the exact mechanisms behind this link remain unclear. H. pylori-associated tissue changes often disrupt the gastric microbiome, enabling secondary gastric colonization by oral bacteria. Among these secondary colonizers, Fusobacterium species have documented associations with several gastrointestinal cancers. We found that both F. animalis and F. nucleatum invade cultured human gastric adenocarcinoma cells, but F. animalis exhibited higher adherence and invasion, and hypoxic conditions promoted higher bacterial survival. Both adherence and invasion were inhibited by exogenous GalNAc, a glycan commonly observed in membrane glycoproteins of adenocarcinoma cells, and a target of the fusobacterial adhesin Fap2. Using a mouse model of gastric metaplasia, we found that F. animalis colonized gastric tissue only after metaplasia onset, growing in multispecies biofilms in the mucus layer, while F. nucleatum colonized neither healthy nor metaplastic gastric tissue. Metaplasia led to upregulation of Gal-GalNAc in the stomach, and reduced gastric acidity allowed higher F. animalis loads in this model. By contrast, inflammation and the presence of H. pylori did not significantly influence stomach colonization by F. animalis. Overall, our data support a model in which H. pylori-induced metaplasia makes the stomach susceptible to secondary infection by another cancer-associated microbe, F. animalis.