In order to test whether the worsened disease outcome following infectious gastroenteritis was directly linked to expansion of AIEC in the gut, we colonized mice with an AIEC ΔPI-6 mutant that is sensitive to killing by defensins, cathelicidins, and by the antimicrobial activity of the monokine MIG/CXCL9 [34], and tested whether this peptide-sensitive mutant could expand in the post-infectious period following gastroenteritis. This evidence concerns the gene CXCL9 and gastroenteritis.