Abstract
Colonization resistance is a fundamental host defense mechanism that relies on the synergistic interaction between the gut microbiota and the host immune system to prevent enteric pathogen colonization and infection. This review synthesizes current knowledge of the multifaceted mechanisms governing colonization resistance against intestinal pathogens. We examine how commensal microbes directly suppress pathogens through niche and nutrient competition, contact-dependent inhibition, and the production of antimicrobial compounds and metabolites. From the host perspective, we outline the essential roles of gut barriers, innate and adaptive immunity, and antimicrobial peptides in maintaining microbiota homeostasis while selectively restricting pathogen expansion. We also emphasize the role of IL-22 signaling and its regulation of epithelial glycosylation, which modulates nutrient availability and shapes microbial competitiveness. Finally, we discuss key challenges and future research directions in colonization resistance and related translational research, with the goal of informing novel strategies to prevent and treat intestinal infections and inflammatory diseases.