The Protective Effects of 2'-Fucosyllactose against E. Coli O157 Infection Are Mediated by the Regulation of Gut Microbiota and the Inhibition of Pathogen Adhesion

Abstract

As the richest component in human milk oligosaccharides (HMOs), 2'-fucosyllactose (2'-FL) can reduce the colonization of harmful microbiota in vivo, thus lowering the risk of infection; however, the mechanism for this is still unclear. In this study, a model of Escherichia coli O157 infection in healthy adult mice was established to explore the effect of 2'-FL intervention on E. coli O157 colonization and its protective effects on mice. The results showed that 2'-FL intake reduced E. coli O157 colonization in mice intestine by more than 90% (p < 0.001), and it also reduced intestinal inflammation, increased the content of fecal short-chain fatty acids, and enhanced intestinal barrier function. These beneficial effects were attributed to the increased expression of mucins such as MUC2 (increased by more than 20%, p < 0.001), and inhibition of E. coli O157 cell adhesion (about 30% reduction, p < 0.001), and were associated with the modulation of gut microbiota composition. 2'-FL significantly increased the abundance of Akkermansia, a potential probiotic, which may represent the fundamental means by which 2'-FL enhances the expression of mucin and reduces the colonization of harmful bacteria. The current study may support the use of 2'-FL in the prevention of foodborne pathogen infections in human.

Keywords: 2’-fucosyllactose; Akkermansia; E. coli O157; gut microbiota; reduced colonization.

Figure 1

Escherichia coli O157 colonization and pathological section of ileum. (A) The colonization in ileum; (B) colonization in colon; (C) representative images of ileum tissue sections in the blank (CK) group (HE 100×); (D) representative images of ileum tissue sections in the FL group (HE 100×); (E) representative images of stained ileum tissue sections in the mode control (MC) group (HE 100×). Different letters (a, b) indicate significant differences among groups (p < 0.05).

Figure 2

Relative mRNA levels of inflammatory cytokines and mucins, all normalized to β-actin mRNA expression. (A) Inflammatory cytokines in ileum; (B) inflammatory cytokines in colon; (C) expression of mucin in colon. Different letters (a–c) indicate significant differences of the same factor among groups (p < 0.05).

Figure 3

Relative abundance, diversity, and function prediction of intestinal microbiome in different groups of mice: (A) Phylum level; (B) genus level; (C) dilution curve; (D) PCoA analysis based on operation taxonomic unit (OTU) results; (E) Tax4Fun analysis based on SILVA database.

Figure 4

Correlation analysis of environmental factors. (A) Canonical correspondence analysis (CCA) analysis of microbial population distribution and environmental factors. Environmental factors are marked by arrows. The angle between the arrow line and the sorting axis indicates the correlation between environmental factors and the sorting axis. Environmental factors with a longer arrow had a higher correlation with the distribution of intestinal microbiome. (B) The significance of environmental factors was analyzed by envfit function. r is the determining coefficient of environmental factors on bacterial distribution; the larger the r value, the greater influence this environmental factor has on microbiome distribution. p is the significance level of correlation test. (C) As shown in the Spearman correlation thermogram, there were significant differences in the abundance of bacteria between different environmental factors. The colors range from blue (negative correlation) to red (positive correlation). A significant correlation is indicated by * p < 0.05 and ** p < 0.01.

Figure 5

Total amount of short-chain fatty acids (SCFAs) in feces before and after infection. (A) Before infection; (B) after infection. Levels of different types of SCFAs are reflected. Different letters (a, b) are used to express significant differences between total SCFAs (p < 0.05).

Figure 6

Adhesion rate of E. coli O157 and cell viability under infection. (A) Adhesion rates in each group at different concentrations; (B) cell viability. Significant differences are indicated by different letters (a–c) (p < 0.05).

Figure 7

The mechanism of 2’-FL protection against E. coli O157 infection in the intestine. The tapered arrow indicates a promoting effect, while the flat end indicates an inhibiting effect. Mucoprotein-2, MUC2; short-chain fatty acids, SCFAs; histone deacetylases, HDACs; G protein-coupled receptors, GPRs; nuclear factor kappa-B, NF-κB.