Dietary fibre counters the oncogenic potential of colibactin-producing Escherichia coli in colorectal cancer.

Diet, microbiome, inflammation and host genetics have been linked to colorectal cancer development; however, it is not clear whether and how these factors interact to promote carcinogenesis. Here we used Il10 mice colonized with bacteria previously associated with colorectal cancer: enterotoxigenic Bacteroides fragilis, Helicobacter hepaticus or colibactin-producing (polyketide synthase-positive (pks)) Escherichia coli and fed either a low-carbohydrate (LC) diet deficient in soluble fibre, a high-fat and high-sugar diet, or a normal chow diet. Colonic polyposis was increased in mice colonized with pks E. coli and fed the LC diet. Mechanistically, mucosal inflammation was increased in the LC-diet-fed mice, leading to diminished colonic PPAR-γ signalling and increased luminal nitrate levels. This promoted both pks E. coli growth and colibactin-induced DNA damage. PPAR-γ agonists or supplementation with dietary soluble fibre in the form of inulin reverted inflammatory and polyposis phenotypes. The pks E. coli also induced more polyps in mismatch-repair-deficient mice by inducing a senescence-associated secretory phenotype. Moreover, oncogenic effects were further potentiated by inflammatory triggers in the mismatch-repair-deficient model. These data reveal that diet and host genetics influence the oncogenic potential of a common bacterium.