The impact of human milk oligosaccharides and galacto-oligosaccharides on the growth of early life pathogenic gut bacteria.

Antibiotics are widely used to prevent and treat early life gut infections, but their aberrant use has raised global concerns about antibiotic resistance. As breastfed infants have fewer intestinal infections than formula-fed infants, this stimulated scientific interest in the anti-pathogenic properties of breastmilk, specifically human milk oligosaccharides (HMOs). HMOs are non-digestible sugars that support infant gut microbiome development, immune maturation, and protection against pathogens. However, to determine how specific HMO structures differentially affect microbial growth and pathogen susceptibility investigating individual HMOs is essential. This study therefore evaluates the effects of single-structure HMOs and galacto-oligosaccharides (GOS) on the growth of key early-life gut pathogens, Escherichia coli, Salmonella enterica, Yersinia enterocolitica, and Clostridium perfringens. The strongest pathogen inhibitory effects of HMOs were further assessed by colony forming unit enumeration and tested across variable media to confirm oligosaccharide-specific efficacy. Oligosaccharide screening revealed clear differences in bacterial growth, with S. enterica most strongly inhibited and C. perfringens exhibiting growth stimulation. Among the tested oligosaccharides, 3'-galactosyllactose and GOS showed the most pronounced growth-inhibitory effects against Escherichia coli, Salmonella enterica, Yersinia enterocolitica. Salt concentration and nutrient richness further modulated oligosaccharide activity, highlighting the multifactorial nature of their antibacterial potential. Overall, our findings show that oligosaccharides display structure-specific and environment-dependent effects on bacterial growth, indicating that their antimicrobial activity is shaped by oligosaccharide structure, bacterial species, and growth environment.