It is generally accepted that human breast milk is the optimal nutrition for infants. This is partly attributed to the microbiota that breast milk encourages. Breast fed infants tend to harbor a high abundance of bifidobacteria while formula fed infants have a more diverse microbiota with clostridia and enteric bacteria in higher abundance. A number of factors present in human milk are responsible for these differences. Recent research and clinical trials indicate that oligosaccharides present in human milk, also known as prebiotics, are the major factor producing this “bifidogenic” effect. Researchers also suggested that the lower buffering capacity of human milk as another factor. However, no research has been reported that tested this premise.
In this study we aim to determine if and to what extent buffering capacity affects infant fecal cultures in vitro. Fresh infant fecal samples collected from seven infants at two different ages were incubated in media with varying buffering capacities (based on NaCHO3). In a subset of cultures, we included a low dose (0.8g/L) of galacto-oligosaccharide (GOS) to determine if a low buffering capacity can enhance the prebiotic effect of GOS. Quantitative PCR (qPCR) assays were employed to measure microbial shifts among treatments, and short chain fatty acids (SCFAs) were measured by gas chromatography. pH of the cultures dropped significantly with decreasing buffering capacity, but there were no significant changes in SCFA production. As determined by qPCR assays, bacterial abundance varied considerably among individuals, yet we did find a significant decrease in the E. coli population with decreasing buffering capacity, irrespective of GOS addition. However, no significant decrease was found in the abundance of Clostridium difficile . The limited amount of substrates available in the cultures might have limited the production of SCFAs and thus the expected decrease in C. difficile and E. coli . Future studies using higher doses of prebiotics are needed to further evaluate the impact of buffering capacities on inhibition of C. difficile and E. coli .