Abstract :
[en] Introduction
Complex oligosaccharides from human milk (HMO) promote growth of bifidobacteria improving health children [1]. Whey, a by-product of dairy-industry, contents complex oligosaccharides (BMO) similar to HMO, which are mainly represented in colostrum by 3’-sialyllactose (3’SL) [2]. Bifidobacterium mongoliense, a species of bovine origin, encodes for β galactosidases and α-glucosidases and could therefore be able to metabolise those BMO [3]. Fermentation products from bifidobacteria can produce antivirulent activity against intestinal pathogenic bacteria and modulations of virulence genes expression by metabolites from culture between 3’SL and B. crudilactis, another bifidobacteria from bovine origin, have been highlighted [3]. This study focused on capacity of B. mongoliense to metabolise BMO, more particularly 3’SL, and on potential antivirulent effect of cell-free spent media (CFSM) against virulence gene expression of pathogenic bacteria.
Material and methods
B. mongoliense FR/49/F/2 isolated from cow raw milk cheese, was grown on media supplemented with glucose (MG), whey rich in BMO (MWh) and 3’SL (M3’SL), as sole source of carbon. A media without carbohydrate (MwG) was used as a control. The CFSM were harvested by centrifugation of cells culture, freeze-drying and 10 fold concentration. Next, their effects were tested against virulence gene expression of Escherichia coli 0157:H7 ATCC 43890 (ler, fliC, luxS, stx1 and qseA genes) and Salmonella Typhimurium ATCC 14028 (hil, ssrB2 and sopD genes) using RT-qPCR.
Results
B. mongoliense was able to grow in presence of whey (8.3 ± 1.0 log cfu/ml) and 3’SL (6.7 ± 0.3 log cfu/ml). For E. coli 0157:H7, CFSM from MwG resulted to under-expressions of fliC, luxS and stx1 genes (-15.8, -9.5, -2.3, respectively) while CFSM from MG showed over-expressions of ler, luxS and stx1 genes (+5.3, +2.2, +2.5, respectively). CFSM from MWh caused an under-expression of all the tested genes ler, fliC, luxS, stx1 and qseaA (-2.2, -5.3, -2.4, -2.5 and -4.8, respectively). CFSM from M3’SL led to under-expression of fliC gene (-5.2) and a slight over-expression of luxS gene (+2.0). For S. Typhimurium, CFSM from MwG induced an up-regulation of sopD gene (+2.8). CFSM from MG up-regulated hil, ssrB2 and sopD (+11.6, + 37.2, +42.5, respectively) and CFSM from MWh up-regulated hil and sopD genes (+ 3.4 and +2.9, respectively). Only CFSM from M3’SL down-regulated hil and sopD genes (-2.2 and -4.2, respectively).
Discussion
Because its genome encodes the enzymatic machinery to use BMO (β galactosidases and α-glucosidases), B. mongoliense presented a good potential growth on BMO [2]. Also, their fermentation presented an interesting effect against E. coli O157:H7 virulence genes expression, effect not observed against S. Typhimurium. However, metabolites from 3’SL fermentation could have a positive impact on S. Typhimurium virulence, effect observed only on E. coli O157:H7 fliC gene expression. Produced metabolites differed in function of culture media nutrients and a same CFSM influenced differently the 2 tested pathogens. BMO combined with B. mongoliense could be an interesting synbiotic to maintain or restore the intestinal health of young children. These effects observed in vitro will be further investigated regarding the exact nature of the active molecules.
