Colonization of larval zebrafish ( Danio rerio ) with adherent-invasive Escherichia coli prevents recovery of the intestinal mucosa from drug-induced enterocolitis

Abstract

ABSTRACT Inflammatory bowel disease (IBD) is a broad term for a range of chronic intestinal disorders, including Crohn’s disease and ulcerative colitis. The global prevalence of IBD is rising, with over one million patients affected in the United States alone. Adherent-invasive Escherichia coli (AIEC) is a pathobiont frequently found in IBD biopsies. AIEC adhere to and invade epithelial cells, and can survive inside phagocytes in vitro . However, how AIEC contribute to IBD in vivo remains unclear. Here, we established a larval zebrafish ( Danio rerio ) model to study the interplay between pre-existing intestinal inflammation and AIEC colonization of the gut. We used the pro-inflammatory drug dextran sulfate sodium (DSS) to induce intestinal inflammation. This was followed by food-borne infection of larvae with AIEC using the protozoan Paramecium caudatum , a natural prey, as a vehicle. We show that AIEC more robustly colonize the zebrafish gut and are cleared slower than non-pathogenic E. coli . In addition, DSS-induced enterocolitis increases bacterial burden and decreases bacterial clearance in the larval gut. We benchmark our model against existing rodent models using two mutants deficient in the known AIEC virulence factors FimH and IbeA, which have virulence defects in both rodent and the larval zebrafish model. Finally, we show that AIEC colonization exacerbates DSS-induced enterocolitis and prevents recovery from inflammation-induced damage. In conclusion, we established a high-throughput, genetically tractable model to study AIEC-host interactions in the context of pre-existing inflammation. IMPORTANCE Although inflammatory bowel diseases are on the rise, what factors influence IBD risk and severity, and the underlying mechanisms remain to be fully understood. Although host genetics, microbiome, and environmental factors have all been shown to correlate with the development of IBD, cause and effect are difficult to disentangle in this context. For example, AIEC is a known pathobiont found in IBD patients, but it remains unclear if gut inflammation during IBD facilitates colonization with AIEC, or if AIEC colonization makes the host more susceptible to pro-inflammatory stimuli. It is critical to understand the mechanisms that contribute to AIEC infections in a susceptible host in order to develop successful therapeutics. Here, we show that the larval zebrafish model recapitulates key features of AIEC infections in other animal models and can be utilized to address these gaps in knowledge.