Surface-functionalized Bifidobacterium bifidum alleviates Clostridioides difficile infection by coordinating host immune modulation and gut microbiota restoration^☆

Clostridioides difficile infection (CDI) is a major ecological disruption of the gut ecosystem, characterized by loss of colonization resistance, persistent inflammatory feedback and incomplete microbial recovery. Meta-analysis of clinical cohorts identified Bifidobacterium depletion as a conserved feature of CDI-associated dysbiosis, suggesting that restoring this genus may promote recovery from CDI. Comparative in vitro assays identified B. bifidum as the most protective strain. This effect was not attributable to direct inhibition of C. difficile growth, but instead was associated with strong adhesion to intestinal mucus and epithelial cells and direct competition for epithelial attachment sites. However, B. bifidum alone was insufficient to counteract host inflammation and showed limited survival during gastrointestinal transit. To address these constraints, we integrated B. bifidum with β-hydroxybutyrate (BHB) to mitigate inflammation-associated habitat filtering and applied an outer hyaluronic-acid (HA) coating to protect B. bifidum viability and confer preferential targeting to the colon and inflamed mucosa. This sequential strategy, termed BB@PCB-HA, markedly alleviated inflammation and restored epithelial barrier integrity, microbial community structure and metabolic function in both CDI and recurrent CDI mouse models. These findings advance probiotic therapy from strain supplementation to programmable functionalized microecological intervention, providing a new paradigm for treating CDI and other gastrointestinal diseases.