ARAF and colorectal neoplasm: For example, to reveal the significance of the microbiota in promoting carcinogenesis, human Escherichia coli pks (polyketide synthase) pathogenicity strains, either pks+ or Δpks E. coli (containing and with deleted pks, respectively), were treated with the pro-carcinogen azoxymethane (AOM) to induce colorectal tumors.