Dietary κ-carrageenan facilitates gut microbiota-mediated intestinal inflammation

Background: After nearly half a century, the inflammatory effects of carrageenan (CGN), a ubiquitous food additive, remain controversial. Little is known about its impact on the gut microbiota and intestinal homeostasis.Results: Mice fed κ-CGN showed no significant inflammatory symptoms, but showed altered colonic microbiota composition, thereby decreasing bacteria-derived short-chain fatty acids (SCFAs) and increased penetrability of the mucus layer. In mice administered the pathogenic bacterium Citrobacter rodentium, inflammation and mucosal damage were further aggravated in the presence of κ-CGN. Mucus layer defects and altered SCFA levels could be reproduced by fecal transplantation from κ-CGN-fed mice, but not from germ-free κ-CGN-fed mice. These symptoms could be partially repaired by administering the probiotics Bifidobacterium longum NCC-2705 and Faecalibacterium prausnitzii.Conclusions: We report a novel evidence that κ-CGN may not be directly inflammatory, but creates an environment that favors inflammation by perturbation of gut microbiota composition and then facilitates expansion of pathogens, which may be partially reversed by the introduction of probiotics.