Impact of Infant Diet on Human Milk Oligosaccharide Metabolizing Bifidobacteria

Objectives: Human milk oligosaccharides (HMOs) are a major nutritional component of human milk, yet they are not digested by infants.Instead, they are metabolized by specialized gut microorganisms, including many Bifidobacterium species, into byproducts essential for infant growth and development.In this study, we investigated the impact of infant diet (exclusive human milk vs. exclusive formula milk) on the presence and abundance of HMO-metabolizing Bifidobacterium infantis and Bifidobacterium breve in the infant gut.Methods: Microbial genomic DNA was extracted from fecal samples of exclusively human milk-fed or exclusively formulafed three-month-old infants.Probes used in quantitative realtime PCR (qPCR) detected and quantified GH750 and Sia (two genes targeting B. infantis), a region of the 16S rRNA gene specific to B. breve, and another 16s rRNA gene region specific to members of the genus Bifidobacterium.Results: The qPCR experiments showed that human milk-fed infants had a higher abundance of Bifidobacteria spp.than formula-fed infants (Wilcoxon rank sum exact test; n78, p0.005, human milk median (HMM)25.2,IQR31.5, formula median (FM) 6.0, IQR20.5).No significant differences were observed in the mean levels of B. infantis (GH750, Sia), or B. breve (16S rRNA gene) between the two feeding groups.However, human milk-fed infants showed a wider range of abundances for these genes and were more likely to have higher numerical abundances of HMO-metabolizer genes linked to B. infantis (Wilcoxon rank sum test; GH750: n77, p 0.22, HMM0.15,IQR1.7,FM 0.065, IQR1.6;Sia: n99, p0.87,HMM 0.25, IQR0.44,FM 0.21, IQR0.34).Formula-fed infants had more than 3 times higher abundance of B. breve compared to humanmilk-fed infants (Wilcoxon rank sum exact test; B. breve: n78, p0.64,HMM 42.9, IQR10553.3,FM 151.7,IQR1421.5).Conclusions: These findings highlight the role of diet in shaping gut microbial colonization, particularly for HMOmetabolizing Bifidobacterium species.Future studies should focus on the functional contributions of specific HMO metabolizers under different diet conditions, and these findings may help inform infant feeding strategies to support optimal microbial colonization and infant health and development outcomes.