Adaptation of adherent-invasive E. coli to gut environment: Impact on flagellum expression and bacterial colonization ability

ABSTRACT

The pathogenesis of Crohn's disease (CD) is multifactorial and involves genetic susceptibility, environmental triggers and intestinal microbiota. Adherent-invasive Escherichia coli (AIEC) are flagellated bacteria more prevalent in CD patients than in healthy subjects and promote chronic intestinal inflammation. We aim at deciphering the role of flagella and flagellin modulation by intestinal conditions. AIEC flagellum expression is required for optimal adhesion to and invasion of intestinal epithelial cells. Interestingly, differential flagellin regulation was observed between commensal E. coli (HS) and AIEC (LF82) strains: flagellum expression by AIEC bacteria, in contrast to that of commensal E. coli, is enhanced under intestinal conditions (the presence of bile acids and mucins). Flagella are involved in the ability of the AIEC LF82 strain to cross a mucus layer in vitro and in vivo, conferring a selective advantage in penetrating the mucus layer and reaching the epithelial surface. In a CEABAC10 mouse model, a non-motile mutant (LF82-ΔfliC) exhibits reduced colonization that is restored by a dextran sodium sulfate treatment that alters mucus layer integrity. Moreover, a mutant that continuously secretes flagellin (LF82-ΔflgM) triggers a stronger inflammatory response than the wild-type strain, and the mutant's ability to colonize the CEABAC10 mouse model is decreased. Overexpression of flagellin in bacteria in contact with epithelial cells can be detrimental to their virulence by inducing acute inflammation that enhances AIEC clearance. AIEC pathobionts must finely modulate flagellum expression during the infection process, taking advantage of their specific virulence gene regulation to improve their adaptability and flexibility within the gut environment.

Competing interests

None.

Acknowledgments

We thank Dr Abdelkrim Alloui for animal care (Animal facilities, Clermont-Ferrand, France), and Maëva Meynier and Melissa Chervy for experimental help. We also thank the Imagerie Confocale Clermont-Ferrand (ICCF) platform (Université d'Auvergne, Clermont-Ferrand, France) for electron microscopy.

Ethics statement

Animal protocols were approved by the committee for ethical issues, CEMEA Auvergne (Permit Number: CEMEAA, 2015032716314007), and all animals were used in accordance with the European Community Directive in the care and use of animals (86/609/CEE) Animal experiments performed at Georgia State University were under institutionally-approved protocols, Institutional Animal Care and Use Committee, IACUC #A14033.

Additional information

Funding

This study was supported by the Ministère de la Recherche et de la Technologie, Inserm (U1071), INRA (USC-2018) and by grants from the Association F. Aupetit (AFA), from Région Auvergne (Nouveau Chercheur), from ANR in the frame of JCJC Nutribiote (N. Barnich).