We detected genes necessary to metabolize sialic acids, including N-acetylneuraminic acid (Neu5Ac) including neuB (N-acetylneuraminate synthase [EC 2.5.1.56]) and mnaA (UDP-N-acetylglucosamine 2-epimerase [EC 5.1.3.14]) in each of the B. fragilis MAGs isolated from pouchitis patients. Here, NANS is linked to pouchitis.