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

Human milk oligosaccharides (HMOs) delivered via breastfeeding stimulate <i>Bifidobacterium</i> proliferation in the infant gut, where bacterial adhesion is critical for colonization. This study screened HMOs-utilizing <i>Bifidobacterium</i> strains from infant fecal microbiota and investigated their adhesion mechanisms. <i>In vitro</i> fermentation with lacto-<i>N</i>-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 <i>Bifidobacterium bifidum</i> 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 <i>B. bifidum</i> 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.