Although studies have shown thatexpression of matrix metalloproteinase 9 is associated with IBD, the influence ofMMP-9 expression on gut microbial community dynamics has not been studied invivo. This work demonstrates that, in a model of bacterial-induced colitis,the particular microbial community of MMP-9−/− micecontributes to reduced levels of C. rodentium preventing a reduction in themicrobial diversity associated with infection [21]. This evidence concerns the gene MMP9 and infection.