Klebsiella oxytoca at doses of ≥ 1 × 107 CFU/mouse/day or Escherichia coli at doses of ≥ 1 × 108 CFU/mouse/day also caused colitis in mice: they increased the stenosis score, myeloperoxidase activity, IL-1β and IL-6 expression, and the NF-κB+/CD11c+ cell population in the colon while the claudin-1 expression was decreased (Fig. 2f–h, Supplementary Figs. S1 and S2). Here, CLDN1 is linked to colitis.