Microflora in Crohn's disease: the emergence of adherent and invasive Escherichia coli

Bovine Milk Derived Exosomes Affect Gut Microbiota of DSS-Induced Colitis Mice

The objective of this study was to investigate the effect of bovine milk derived exosomes (MDEs) on the gut microbiota of Dextran sodium sulfate (DSS)-induced colitis mice. Total of 42 specific pathogen free (SPF) male BALB/c mice (3 weeks old) were randomly assigned to three groups including control group, DSS group (DSS) and bovine milk derived exosome group (Exo), with 7 replicates/cages per treatment and two mice in one cage. 16S rRNA gene sequencing of cecal digesta samples was conducted. DSS significantly decreased the average daily feed intake of mice in DSS and Exo groups (P = 0.03). Shannon index of the DSS group was significantly lower than the control group (P < 0.05) whereas no difference between the control group and Exo group was observed. Administration of MDEs tended to increase the relative abundance of Campylobaterota. Compared to the control group, the relative abundance of Roseburia was significantly decreased in the DSS group (P < 0.05) whereas no difference between the Exo group and control group was observed. MDEs also tended to increase the relative abundance of Lachnospiraceae_UCG_006. In conclusion, oral administration of 10 µL MDEs (1 mg/mL) positively affected gut microbiota of DSS-induced colitis mice. The results of this study provided valuable reference for MDEs application in the prevention and treatment of colitis.

Rifaximin decreases virulence of Crohn's disease-associated Escherichia coli and epithelial inflammatory responses

Escherichia coli with an adherent and invasive pathotype (AIEC) is implicated in the pathogenesis of Crohn's disease (CD). Rifaximin improves symptoms in mild-to-moderate CD. It is unclear if this outcome is due to its effects on bacteria or intestinal epithelial inflammatory responses. We examined the effects of rifaximin on the growth and virulence of CD-associated E. coli and intestinal epithelial inflammatory responses. Seven well-characterized CD-associated E. coli strains (six AIEC, one non-AIEC; four rifaximin-resistant, three sensitive) were evaluated. We assessed the effects of rifaximin on CD-associated E. coli growth, adhesion to, and invasion of epithelial cells, virulence gene expression, motility, and survival in macrophages. Additionally, we determined the effects of rifaximin on intestinal epithelial inflammatory responses. In vitro rifaximin exerted a dose-dependent effect on the growth of sensitive strains but did not affect the growth of resistant strains. Rifaximin reduced adhesion, invasion, virulence gene expression and motility of CD-associated E. coli in a manner that was independent of its antimicrobial effect. Furthermore, rifaximin reduced IL-8 secretion from pregnane X receptor-expressing T84 colonic epithelial cells. The effect of rifaximin on adhesion was largely attributable to its action on bacteria, whereas decreases in invasion and cytokine secretion were due to its effect on the epithelium. In conclusion, our results show that rifaximin interferes with multiple steps implicated in host-AIEC interactions related to CD, including adhesion to, and invasion of epithelial cells, virulence gene expression, motility, and pro-inflammatory cytokine secretion. Further study is required to determine the relationship of these effects to clinical responses in CD patients.

Genes of intestinal Escherichia coli and their relation to the inflammatory activity in patients with ulcerative colitis and Crohn's disease

Escherichia coli gene fimA was the most frequent gene that occurred in the intestine of all investigated groups. All subjects with fimA gene had significantly higher values of tumor necrosis factor alpha (TNF-α) and CRP than those with other E. coli genes. There was also a tendency to increased serum interleukin (IL)-6 levels in patients carrying the fimA gene; however, no relation was observed to serum IL-8 and IL-10. Patients with Crohn's disease had significantly higher IL-6 than those with ulcerative colitis (UC) and controls. The highest levels of TNF-α were detected in the UC group. There were no significant differences in serum IL-8 and IL-10 between all three groups. The presence of E. coli gene fimA in the large bowel of patients with IBD is related to the immunological activity of the disease which may be important from the aspect of therapeutical strategy.

A role for the RNA chaperone Hfq in controlling adherent-invasive Escherichia coli colonization and virulence

Adherent-invasive Escherichia coli (AIEC) has been linked with the onset and perpetuation of inflammatory bowel diseases. The AIEC strain LF82 was originally isolated from an ileal biopsy from a patient with Crohn's disease. The pathogenesis of LF82 results from its abnormal adherence to and subsequent invasion of the intestinal epithelium coupled with its ability to survive phagocytosis by macrophages once it has crossed the intestinal barrier. To gain further insight into AIEC pathogenesis we employed the nematode Caenorhabditis elegans as an in vivo infection model. We demonstrate that AIEC strain LF82 forms a persistent infection in C. elegans, thereby reducing the host lifespan significantly. This host killing phenotype was associated with massive bacterial colonization of the nematode intestine and damage to the intestinal epithelial surface. C. elegans killing was independent of known LF82 virulence determinants but was abolished by deletion of the LF82 hfq gene, which encodes an RNA chaperone involved in mediating posttranscriptional gene regulation by small non-coding RNAs. This finding reveals that important aspects of LF82 pathogenesis are controlled at the posttranscriptional level by riboregulation. The role of Hfq in LF82 virulence was independent of its function in regulating RpoS and RpoE activity. Further, LF82Δhfq mutants were non-motile, impaired in cell invasion and highly sensitive to various chemical stress conditions, reinforcing the multifaceted function of Hfq in mediating bacterial adaptation. This study highlights the usefulness of simple non-mammalian infection systems for the identification and analysis of bacterial virulence factors.