Metabolites from media supplemented with 3’-sialyllactose and fermented by bifidobacteria have an antivirulent effect against intestinal pathogens

Complex oligosaccharides from human milk (HMO) promote growth of Bifidobacterium bifidum. Oligosaccharides from cow milk (BMO), similar to HMO, are mainly represented in colostrum by 3’-sialyllactose (3’SL). Bifidobacterium crudilactis, a species from bovine origin and encoding for β galactosidases and α-glucosidases, could be able to metabolise them. Also, fermentation products could have antivirulent activity against intestinal pathogens. This study focused on capacity of bifidobacteria to metabolise 3’SL and on potential antivirulent effect of cell-free spent media (CFSM) against pathogenic bacteria.
B. bifidum BBA1 and B. crudilactis FR/62/B/3 isolated respectively from breastfed children feces and cow raw milk cheese were grown on media supplemented with 3’SL as sole source of carbon. Next, CFSM effects were tested against virulence gene expression using ler and hilA promoter activity of luminescent constructs of Escherichia coli 0157:H7 ATCC 43888 and Salmonella Typhimurium SA 941256, respectively. The effect was confirmed on wild type strains of E. coli O157:H7 ATCC 43890 and S. Typhimurium ATCC 14028 using RT-qPCR.
Both strains were able to grow in presence of 3’SL. CFSM resulted in under-expression of hilA and ler genes for the luminescent constructs and in under-expression of ler (ratios of -15.4 and -8.1) and qseA (ratios of -2.1 and -3.1) genes for the wild type strain of E. coli O157:H7. No effect was observed with S. Typhimurium.
Little is known about CFSM metabolites and they have to be isolated and identified. The potential synbiotic effect between 3’SL and bifidobacteria will be tested using the Shime®, a human gastrointestinal model.