In an initial experiment using the streptomycin pre-treated C57bl/6 mouse model of colitis we found that mice infected with randomly selected strains of the same phylogroup (ST34 or U288) exhibited similar colonisation level (Supplementary Fig. 4A), induction of Cxcl1 (KC) and Nos-2 (iNOS) (Supplementary Fig. 4B) and intestinal pathology (Supplementary Fig. 4C). This evidence concerns the gene NOS2 and colitis.