Correlation between oral microbiome and inflammatory bowel disease (IBD). The oral bacteria can induce the development of IBD via several mechanisms: (1) Destruction of the intestinal epithelial barrier: P. gingivalis and K. pneumoniae can downregulate the expressions of tjp-1 and occludin. (2) Release of pro-inflammatory cytokines: F. nucleatum and K.pneumoniae can induce stimulate the pro-inflammatory cytokine LPS. (3) Disruption of the host immune system and induction of immune escape: F. nucleatum and Candida imbalance the Th1/Th17 which induce inflammatory reactions. (4) Migration to the gut and activation of the inflammasome in colonic mononuclear phagocytes: K. pneumoniae and F. nucleatum can migrate to the gut and activate the inflammasome in immune cells, leading to intestinal inflammation. Outer-membrane vesicles (OMV), Toll-like receptor 4 (TLR4), myeloid differentiation protein-2 (MD2), Helper T 17 cell (Th17 cell), Cluster of differentiation 4+ T cell (CD4+ T cell), Helper T 1 cell (Th1 cell), Limited Power Supply (LPS), Nitric Oxide (NO), Phosphoinositide 3-Kinase (PI3K), Cyclooxygenase-2 (COX2), Interleukin-18 (IL-18), Interleukin-17 (IL-17), Interleukin-23 (IL-23), Jumonji domain-containing protein-3 (JMJD3), Signal transducer and activator of transcription (STAT3), Peroxisome proliferator-activated receptorγ (PPARγ), Interferon-γ (IFN-γ).