Synbiotic intervention with <i>Bifidobacterium bifidum</i> and prebiotics reduces enterohemorrhagic <i>Escherichia coli</i> colonization

This study evaluated the protective effect of combining Bifidobacterium bifidum with the prebiotics inulin and isomalto-oligosaccharides against enterohemorrhagic Escherichia coli infection and investigated the underlying mechanisms, using an integrated strategy of in vitro screening followed by in vivo validation. Among ten prebiotics screened, IMO and inulin were identified as optimal for promoting B. bifidum proliferation and acetate production (>2.5-fold), with IMO further enhancing bacterial adhesion to Caco-2 cells (four-fold). In a murine infection model, B. bifidum alone reduced total intestinal EHEC colonization, whereas inulin alone was ineffective. The combination of IMO and B. bifidum markedly suppressed EHEC colonization, particularly in the colon (five-fold reduction), while inulin provided no added benefit. Although fecal acetate levels were elevated in synbiotic groups, no linear correlation with EHEC clearance was observed, suggesting that protection may rely on mechanisms other than bulk acetate production-such as localized metabolite delivery or microbial ecological interactions. These findings demonstrate that an IMO-based synbiotic can effectively limit EHEC colonization through multifactorial modulation of the gut ecosystem. The presented strategy offers a rational framework for designing synbiotics to prevent foodborne infections.