Consistent with previous studies using intestinal contents and faecal samples from CF mice and CF human faecal samples18,19,45, our results revealed that both CFTR-null and F508del-mutant mice had increased abundance of the opportunistic pro-inflammatory taxa Escherichia/Escherichia coli within the small intestinal mucosa, particularly the ileum. This evidence concerns the gene CFTR and cystic fibrosis.