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Summary The bactericidal lectin RegIIIβ is inducibly produced by intestinal epithelial cells as a defense against infection by enteropathogens. In the gut lumen, RegIIIβ kills not only certain enteropathogens, but also some commensal bacteria; thus, RegIIIβ is also thought to be an innate immune effector shaping microbiota composition and establishing intestinal homeostasis. Using the streptomycin mouse model for Salmonella colitis, we show that RegIIIβ can promote sustained gut colonization of Salmonella Typhimurium and prolong enteropathy. RegIIIβ expression was associated with suppression of Bacteroides spp. in the gut lumen, prolonged disease-associated alterations in colonic metabolism, and reduced luminal vitamin B6 levels. Supplementation with Bacteroides spp. or vitamin B6 accelerated pathogen clearance from the gut and remission of enteropathy. Our findings indicate that interventions at the level of RegIIIβ and supplementation with Bacteroides spp. or vitamin B6 might open new avenues for therapeutic intervention in the context of Salmonella colitis. [ABSTRACT FROM AUTHOR]