Pathogenic biofilms have been associated with
persistent infections due to their high resistance to
antimicrobial agents, while commensal biofilms often fortify the host's immune system. Hence, controlling biofilm formation of both pathogenic bacteria and commensal bacteria is important in bacterium-related diseases. We investigated the effect of plant
flavonoids on biofilm formation of enterohemorrhagic Escherichia coli O157:H7. The
antioxidant phloretin, which is abundant in apples, markedly reduced E. coli O157:H7 biofilm formation without affecting the growth of planktonic cells, while
phloretin did not harm commensal E. coli K-12 biofilms. Also,
phloretin reduced E. coli O157:H7 attachment to human colon epithelial cells. Global transcriptome analyses revealed that
phloretin repressed toxin genes (hlyE and stx(2)), autoinducer-2 importer genes (lsrACDBF), curli genes (csgA and csgB), and dozens of prophage genes in E. coli O157:H7 biofilm cells. Electron microscopy confirmed that
phloretin reduced fimbria production in E. coli O157:H7. Also,
phloretin suppressed the
tumor necrosis factor alpha-induced inflammatory response in vitro using human colonic epithelial cells. Moreover, in the rat model of
colitis induced by trinitrobenzene
sulfonic acid (TNBS),
phloretin significantly ameliorated colon
inflammation and
body weight loss. Taken together, our results suggest that the
antioxidant phloretin also acts as an inhibitor of E. coli O157:H7 biofilm formation as well as an
anti-inflammatory agent in
inflammatory bowel diseases without harming beneficial commensal E. coli biofilms.