Deciphering the implications of Escherichia coli in inflammatory bowel disease: from symbiont to pathogen

Inflammatory bowel disease (IBD) is a chronic inflammatory condition resulting from complex interactions between the immune system, genetic predisposition, and the gut microbiota. In this context, Escherichia coli (E. coli) plays a dual role in the human gut, ranging from harmless commensal strains to pathobionts capable of promoting intestinal inflammation. A growing body of evidence suggests that specific E. coli pathotypes, such as adherent-invasive E. coli (AIEC) and diffusely adherent E. coli (DAEC), contribute to the development and progression of IBD. This narrative review critically examines the microbiological, immunological, and clinical evidence supporting the role of E. coli in IBD, with particular emphasis on mechanisms of mucosal colonization, host-microbe interactions, and persistence within the inflamed intestinal environment. Furthermore, the lack of a standardized operational definition and the limited reproducibility of the AIEC phenotype are addressed, as well as uncertainty about the role played by E. coli as a primary initiator of the disease or as an opportunistic amplifier of intestinal inflammation, and the varying strength of evidence supporting associations with Crohn's disease versus ulcerative colitis. Diagnostic implications, antimicrobial resistance, and therapeutic aspects are addressed as downstream and context-dependent consequences of E. coli-host interactions, with relevance for disease management and therapeutic response in patients with established IBD. By integrating data from experimental models, clinical studies, and translational research, the review identifies areas of consensus, ongoing controversy, and major knowledge gaps in IBD pathophysiology and clinical practice.