Given that C. concisus is a Gram-negative flagellated bacterium, in this study, we examined the effects of both oral and enteric C. concisus strains isolated from patients with IBD and controls on intestinal epithelial expression of TLR4 and its co-receptor myeloid differentiation factor (MD)-2, which recognizes LPS found in Gram-negative bacteria, of TLR2, which recognizes bacterial lipoproteins, and of TLR5, which recognizes bacterial flagellin. Here, TLR4 is linked to inflammatory bowel disease.