Abstract :
[en] The most abundant bifidobacteria found in breastfed infant feces are able to metabolize human milk oligosaccharides (HMO), by cleaving the α-glycosidic bonds of fucoses and sialic acids, as well as the β-glycosidic bonds in the HMO core. The whey obtained from cow’s milk contains complex oligosaccharides, also called bovine milk oligosaccharides (BMO), especially 3’-sialyllactose (3’SL). BMO are structurally very similar to HMO and share some common properties. Because they are of bovine origin, Bifidobacterium crudilactis FR/62/b/3 and Bifidobacterium mongoliense FR/49/f/2, two bifidobacterial strains isolated from a raw cow’s milk cheese, could encode the enzymes necessary to digest them. In addition, the fermentation of carbohydrates by bifidobacteria could produce some metabolites able to modulate the virulence of intestinal pathogens. Because in vivo experimentations are difficult and limited by obvious ethical reasons, some in vitro digestive models have been developed. Among all models, the simulator of the human intestinal microbial ecosystem (SHIME®) represents all parts of digestive tract and seems particularly adapted to evaluate the interactions between the pre/probiotics and the microbiota of young children.
This research was divided into three main axes:
-Ability of B. crudilactis FR/62/b/3 and B. mongoliense FR/49/f/2 to metabolize BMO (genome analysis: study 2; BMO fermentation: studies 1 and 2).
-Virulence gene expression analysis of intestinal pathogens after contact with cell-free spent media (CFSM; containing potential antivirulent metabolites) obtained from BMO fermentation by B. crudilactis FR/62/b/3 and B. mongoliense FR/49/f/2 (studies 1 and 2).
-Challenges in a toddler SHIME® model inoculated with prebiotic (3’SL), probiotic (B. crudilactis FR/62/b/3), synbiotic (3’SL+B. crudilactis FR/62/b/3) and CFSM (metabolites): impact on the microbiota (study 3).
Genome analysis revealed that B. mongoliense DSM 21395 has a more sophisticated enzymatic pathway for BMO digestion compared to B. crudilactis LMG 23609. B. crudilactis FR/62/b/3 and B. mongoliense FR/49/f/2 were able to grow on media supplemented with BMO or 3’SL as the main source of carbohydrates. The CFSM issued from the fermentation of 3’SL by these two bifidobacteria significantly down-regulated the virulence gene expression of enterohaemorrhagic Escherichia coli (EHEC) O157:H7 and Salmonella enterica serotype Typhimurium, respectively. Those obtained from fermentation of BMO (in whey) by B. mongoliense FR/49/f/2 significantly down-regulated the virulence gene expression of EHEC O157:H7. Finally, the synbiotic combination of 3’SL and B. crudilactis FR/62/b/3 tested in the toddler SHIME® model, in which specific bacterial populations proper to each colon are developed, tended to a bifidogenic effect.
In conclusion, the glycobiome of B. mongoliense DSM 21395 seemed more adapted to BMO digestion to that of B. crudilactis DSM 23609. However, the synbiotic combination of 3’SL and B. crudilactis FR/62/b/3 led to interesting in vitro results by decreasing the virulence gene expression of intestinal pathogens and by having a bifidogenic effect on the microbiota implemented in the gastrointestinal system. In addition, the toddler SHIME® model developed in this work shares both infant and adult microbiota properties and seems appropriate to study the interactions between the pre/probiotics and the microbiota of young children.
