Pathogenesis of adherent-invasive <i>Escherichia coli</i> LF82 in human colonic epithelium is characterized by adhesive biofilms, mucus penetration, and contact-dependent cytotoxicity

Adherent-invasive <i>Escherichia coli</i> (AIEC) associated with Crohn's disease (CD) are traditionally defined by the adherence and invasion of epithelial cells and survival in macrophages. However, their interactions with differentiated intestinal epithelia remain largely unexplored. Here, we investigated the pathogenesis of AIEC prototype strain LF82 in polarized human colon carcinoma cells and colonic organoids. While LF82 infection of Caco-2 and T84 cells was characterized by CEACAM6-independent adherence, biofilm formation, inflammation, and contact-mediated cytotoxicity, invasion was comparably low to that of noninvasive <i>E. coli</i> MG1655. An investigation of additional AIEC isolates revealed that biofilm production and cell damage were specific for strain LF82. Infection of human colonoids confirmed biofilm formation, negligible invasion, and cytotoxicity of AIEC LF82. However, bacteria adhered preferentially to the mucus layer and penetrated to the epithelial surface. Our results suggest that LF82 pathogenesis in the human colon is characterized by the formation of adherent biofilms, mucus penetration, and contact-dependent cytotoxicity, which likely contributes to epithelial leakage and inflammation in CD.