ARAF and colitis: In vivo studies used colitis-susceptible interleukin-10-deficient mice under germ-free condition, and when they were associated with either pks-positive E. coli or pks-negative E. coli, together with azoxymethane, the group of mice receiving pks-positive E. coli showed significantly greater increase in colon tumor occurrence and invasiveness compared to the other group, while the severity of colitis was similar between the two groups [8].