Summary of the key findings as reported in the paper by Mansoori Moghadam et al. The CGD genetic background in combination with a specific pathogen-free (standard laboratory) microbiota or a healthy genetic background with a wildling microbiota both lead to abnormalities of colonic phagocytes and low-grade inflammation but no overt colitis. However, the combination of the CGD genetic background and wildling microbiota leads to severe spontaneous colitis with translocation of bacterial species and distant granuloma formation.