Impact of 3’-sialyllactose and Bifidobacterium crudilactis on infant feces microbial composition and virulence modulation of Escherichia coli O157:H7, using the SHIME® gastrointestinal model

Bifidobacterium crudilactis, a bacterial species from bovine origin, growths on bovine milk
oligosaccharides (BMO). Cell free spent media (CFSM) from B. crudilactis and
3’-sialyllactose (3’SL), a major BMO, modulated Escherichia coli O157:H7 virulence gene
expressiona. In this study, the SHIME® gastrointestinal model was inoculated with 4 different
treatments: 3’SL (ttm1), B. crudilactis (ttm2), 3’SL and B. crudilactis (ttm3) and CFSM from
3’SL and B. crudilactis culture (ttm4). In each section of the colon, samples were collected
and analysed for short chain fatty acid (SCFA) concentration using HPLC, microbial
populations using 16S rDNA metagenetic analysis and correlated with E. coli O157:H7
virulence gene expression. The results showed that SCFA levels were stable during the
experiments. 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. Ttm4 and ttm2 induced mainly a down-regulation of virulence
genes: fliC in DC with ttm4, and luxS, stx1, qseA in AC, DC or TC with ttm2. Ttm1 also
showed a down-regulation of fliC in DC, similar to the one observed with ttm4, but this was
associated with an up-regulation of fliC and stx1 in AC or TC. Finally, ttm3 showed slight upregulation
of ler, fliC and qseA in AC. These results show that ttm4 and ttm2 might have a
positive effect against virulence expression of E. coli O157:H7. However, this trend has to be
validated with the further replicates on the SHIME® system.