Structural Diversity of Human Milk Oligosaccharides Mediates Bifidobacterium bifidum-Induced Adhesion to Intestinal Epithelial Cells

Human milk oligosaccharides (HMOs) delivered via breastfeeding stimulate Bifidobacterium proliferation in the infant gut, where bacterial adhesion is critical for colonization. This study screened HMOs-utilizing Bifidobacterium strains from infant fecal microbiota and investigated their adhesion mechanisms. In vitro fermentation with lacto-N-triose II (LNT II), 2′-fucosyllactose (2′-FL), and 3′-sialyllactose (3′-SL) showed that 2′-FL significantly increased butyric acid production and suppressed harmful bacteria in two week-old infants. Three Bifidobacterium bifidum strains (B-63, B-67, and B-82) capable of HMOs utilization were identified, carrying conserved HMO-digestion gene clusters including key GH13 and GH20 glycoside hydrolases. Then, the effects of LNT II, 2′-FL, and 3′-SL treatments on adhesion capacity of three B. bifidum strains to Caco-2 intestinal epithelial cells were investigated, and results demonstrated that 2′-FL significantly upregulated hyaluronan synthase 2 (HAS2) and MUC2 expression in strains B-63 and B-67. Furthermore, addition of 2′-FL to fucosyl-inhibited cells selectively upregulated HAS1 protein expression, demonstrating that 2′-FL-mediated fucosylation promotes intestinal epithelial cell adhesion.