Exploring the Adhesion Potential of Bifidobacterium bifidum Strains Isolated from Infant Feces

Bifidobacteria capable of metabolizing human milk oligosaccharides (HMOs) regulate microbial balance and enhance immune defenses, yet their adhesive properties and pathogen-inhibitory capacity remain understudied. We examined auto-aggregation, surface hydrophobicity, adhesion, and pathogen antagonism in 12 HMO-metabolizing bifidobacterial strains isolated from infant feces, using Bifidobacterium longum subsp. infantis ATCC 15697 (BI_15697) and M63 (BI_M63) as reference strains. Bifidobacterium bifidum BB_Y10 and BB_Y22 exhibited the highest auto-aggregation, hydrophobicity, and adhesion. Adhesion assays using Caco-2 cells and mucin, combined with scanning electron microscopy (SEM) for qualitative morphological observation, revealed distinct surface characteristics among the strains. These morphological differences may be associated with, but do not directly establish, the observed variability in adhesion capacity. Surface-associated molecules, including surface layer proteins (SLPs), extracellular polysaccharides (EPS), and lipoteichoic acid (LTA), differentially contributed to adhesion across the strains. BB_Y10 and BB_Y22 demonstrated strong adhesive capacity and enhanced pathogen antagonism in competitive, exclusion, and displacement assays in vitro, suggesting their potential to inhibit pathogen colonization in future in vivo studies and identifying them as promising probiotic candidates for further development.