Brief exposure to pks+ E. coli was also sufficient to cause mutations that lead to changes in growth factor dependence and differentiation in cell culture models.78 Preclinical studies using genetically susceptible mouse models demonstrated that common pks+E. coli strains increased tumor burden compared to non-producing control strains.34,36,79,80 Similarly, compared with an aat mutant, indolimine-producing M. morganii increased gut permeability and exacerbated colon tumor burden in gnotobiotic mice in the context of a mock community of human gut microbes.6 This evidence concerns the gene ARAF and neoplasm.