Review article: bugs, inflammation and mood—a microbiota‐based approach to psychiatric symptoms in inflammatory bowel diseases

Summary Background Psychiatric co‐morbidities including depression and anxiety are common in inflammatory bowel diseases (IBD). Emerging evidence suggests that interactions between the gut microbiota and brain may play a role in the pathogenesis of psychiatric symptoms in IBD. Aim To review the literature on microbiota‐brain‐gut interactions in gut inflammation, psychosocial stress and mental disorders and to discuss the putative mediating role of gut microbiota in the development of psychiatric symptoms or co‐morbidities in IBD. Methods A literature search was conducted on Ovid and Pubmed to select relevant animal and human studies reporting an association between IBD, mental disorders and gut microbiota. Results Gut microbial alterations are frequently reported in subjects with IBD and with mental disorders. Both have been associated with reduced faecal bacterial diversity, decreased taxa within the phylum Firmicutes and increased Gammaproteobacteria. In animal studies, microbial perturbations induce behavioural changes and modulate inflammation in mice. Anxiety‐ and depression‐like behaviours in animals can be transferred via faecal microbiota. In humans, modulation of the gut microbiota with probiotics is associated with behavioural and mood changes. Recent data show correlations in changes of faecal and mucosal microbiota and psychological distress in patients with IBD independent of disease activity. Conclusion Both IBD and mental disorders are associated with gut microbial alterations. Preclinical and preliminary human studies have shown a mediating role of the gut microbiota in intestinal inflammation and anxiety, depression and stress. Targeting the gut microbiota may represent a useful therapeutic approach for the treatment of psychiatric co‐morbidities in IBD.