Optmization of culture media for Bifidobacterium bifidum and Bifidobacterium crudilactis and study of the antimicrobial effect of culture supernatants

Complex oligosaccharides from human milk (HMO) contribute to infant health. Bifidobacteriumbifidum mainly found in breast-fed infant microbiota has all the enzymatic machinery for degradation of HMO. On the other hand, whey is rich in complex bovin milk oligosaccharides (BMO) very similar to HMO, including 3’-sialyllactose (3’SL). They are very likely to be metabolised by B. bifidum too, but also by B. crudilactis, a bovine origin strain. Fermentation of HMO or BMO by bifidobacteria can result in production of metabolites modulating virulence expression of several pathogenic bacteria.
Two strains of bifidobacteria were used in this study: B. bifidum, isolated from breastfed infant feces and B. crudilactis, isolated from bovine raw milk. The ability of those strains to metabolise culture media enriched in glucose, whey and 3’SL has been assessed. Then, the obtained culture supernatant has been tested against virulence genes expression of E. coli O157:H7.

Both strains were able to grow in presence of BMO and 3’SL. B. crudilactis presented the best growth on all media. All culture supernatants obtained after supplementation with 3’SL resulted in significant under-expression of genes ler and qseA. The trend of genes stxB2 and luxS was also toward a down-regulation.
BMO combined to some bovine or human origin bifidobacteria strains could be interesting synbiotics to maintain or restore the intestinal health of young children. These effects observed in vitro require further investigations to ensure repeatability in humans and to identify the exact nature of molecules obtained from fermentation media by B. bifidum and B. crudilactis.