Mina Popovic, Department of Life Science, University of Modena and Reggio Emilia, Modena, Italy
Human milk and its assembled glycome is known to enrich specific bifidobacterial populations in the infant gastrointestinal tract. Inactive alleles of the fucosyltransferase 2 gene (FUT2; termed “secretor” due to its role in the expression of ABO blood types in secretions) are common in many populations. Some bifidobacteria (common infant gut commensals) are known to be able to consume 2’ fucosylated glycans, such as the oligosaccharides found in the breast milk of a secretor (FUT2+) mother. This work aimed to test whether there is a difference in the ability of bifidobacterial isolates from both secretor-fed infants and non-secretor-fed infants to grow on 2’-fucosyllactose (2FL) as sole carbon source. We also compared the representation of bifidobacterial species isolated from feces to that of data obtained using a Bifidobacterial-specific terminal restriction fragment length polymorphism (Bif-TRFLP) method to measure the bifidobacterial species content of fecal samples.
We isolated and characterized bifidobacterial species from a cohort of breast-fed infants. 106 infant fecal samples from the UC Davis Lactation study cohort representing four time points after birth (days 7, 21, 71 and 120) were chosen. Diluted feces were plated on bifidobacterial-selective medium and up to 10 colonies from each sample were isolated and passaged twice using streak-plate technique to ensure purity. These isolates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, MALDI-TOF MS (Biotyper). Bif-TRFLP was also utilized to identify which species were present in the fecal samples, using DNA extracted from feces by the Zymo Fecal Miniprep kit. Ninety-seven unique isolates were tested for growth on 2’-fucosyllactose, including isolates from both secretor- and non-secretor-fed infants. Isolates were cultured in modified MRS media with 3% 2FL, 3% lactose (positive control), and without carbohydrate (negative control). Their growth was monitored by plate reader in anaerobic chamber by measuring optical density at 600 nm.
382 bifidobacterial isolates were obtained from the feces of 38 brest-fed infants, across 78 samples. Isolates were identified by the MALDI Biotyper as B. longum, B. breve, B. pseudocatenulatum, B. catenulatum, B. gallinarium, B. bifidum, B. dentium, and B. angulatum. B. breve isolate relative abundance increased over time in non-secretor-fed infants while B. longum group increased in secretor-fed infants. It was discovered that approximately 25% of secretor fed infant isolates and 7% of non-secretor fed infant isolates were able to consume 2FL as sole carbon source. The species of the fecal isolates were overall representative of the Bif-TRFLP data, with B. breve proportionally overrepresented and B. pseudocatenulatum proportionally underrepresented.
Differences in bifidobacterial population were observed in the feces of secretor-fed and non-secretor-fed infants, in particular in the abundance of B. breve and B. longum. More isolates from secretor-fed infants were able to consume 2’fucosyllactose than isolates from non-secretor-fed infants, reflecting the enrichment of species that can consume the oligosaccharides found in the mother’s milk. There were differences in the relative species abundance identified by the Bif-TRFLP and isolation methods, although isolates were not obtained from all samples.