Abstract :
[en] Introduction
Human milk oligosaccharides (HMO) allow growth of beneficial bifidobacteria improving children health [1]. With their structural similarities, bovine milk oligosaccharides (BMO) could be easily metabolised by the same bifidobacteria, as well as Bifidobacterium crudilactis, a species from bovine origin [2; 3]. Also, cell free spent media (CFSM) obtained from culture of B. crudilactis and a major BMO, the 3’-sialyllactose (3’SL), modulated virulence genes expression of Escherichia coli O157:H7 [4].
Material and methods
The gastrointestinal model SHIME® was inoculated with feces from a young child and stabilised for 2 weeks. Four treatments were successively administrated for 1 week, with a restabilisation period of 1 week between each of them: 3’SL (I), B. crudilactis (II), 3’SL and B. crudilactis simultaneously (III) and CFSM from 3’SL and B. crudilactis culture (IV). In each section of the colon, samples have been collected and analysed using HPLC to determine short chain fat acids (SCFA) concentrations. Microbial populations were determined using 16S rDNA metagenetic analysis. Impact of SHIME samples supernatants has been assessed on E. coli O157:H7 virulence genes expression.
Results
The results showed that SCFA levels were stable during the experiments with mainly production of acetate, propionate and butyrate. Metagenetic analysis showed a microbial diversity in transverse (TC) and descending colon (DC) close to feces, dominated by Bacteroides, Prevotella and Fusobacterium, while the ascending colon (AC) showed a different microbial diversity dominated by Veillonella. In addition, treatment II was able to induce an increase of Akkermancia muciniphila.proportions. Treatments II and IV induced mainly a down-regulation of virulence genes: luxS, stx1, qseA in AC, DC or TC, and fliC and qseA in DC, respectively. Treatment 1 also showed a down-regulation of fliC in DC, similar to the one observed with treatment IV, but this was associated with an up-regulation of fliC, stx1 and qseA in AC or TC. Finally, treatment III showed slight upregulation of ler, fliC and qseA in AC. Diversity indices (Chao1, Simpson’s reciprocal index, evenness and PCoA) are currently analysed.
Discussion
Interesting effects have been highlighted after this first run. SCFA allowed controlling the “good health” of the implemented microbiota. Metagenetic analyses offered a more advanced investigation and treatment II seemed to be the most promising because it probably promotes cross-feeding interactions with A. muciniphila. The trends observed with E. coli O157:H7 virulence gene expression have to be validated with the further replicates on the SHIME® system, but these results showed that treatments II and IV might have a positive effect against pathogenicity of this bacteria.
