Escherichia coli isolates from inflammatory bowel diseases patientssurvive in macrophages and activate NLRP3 inflammasome

Abstract

Crohn’s disease (CD) is a multifactorial pathology associated with the presence of adherent-invasiveEscherichia coli (AIEC) and NLRP3 polymorphic variants. The presence of intracellular E. coli in otherintestinal pathologies (OIP) and the role of NLRP3-inflammasome in the immune response activated bythese bacteria have not been investigated. In this study, we sought to characterize intracellular strainsisolated from patients with CD, ulcerative colitis (UC) and OIP, and analyze NLRP3-inflammasome rolein the immune response and bactericidal activity induced in macrophages exposed to invasive bacteria.For this, intracellular E. coli isolation from ileal biopsies, using gentamicin-protection assay, revealeda prevalence and CFU/biopsy of E. coli higher in biopsies from CD, UC and OIP patients than in con-trols. To characterize bacterial isolates, pulsed-field gel electrophoresis (PFGE) patterns, virulence genes,serogroup and phylogenetic group were analyzed. We found out that bacteria isolated from a given patientwere closely related and shared virulence factors; however, strains from different patients were geneti-cally heterogeneous. AIEC characteristics in isolated strains, such as invasive and replicative properties,were assessed in epithelial cells and macrophages, respectively. Some strains from CD and UC demon-strated AIEC properties, but not strains from OIP. Furthermore, the role of NLRP3 in pro-inflammatorycytokines production and bacterial elimination was determined in macrophages. E. coli strains inducedIL-1 through NLRP3-dependent mechanism; however, their elimination by macrophages was indepen-dent of NLRP3. Invasiveness of intracellular E. coli strains into the intestinal mucosa and IL-1 productionmay contribute to CD and UC pathogenesis.