Seasonal variations in gut microbiota and disease course in patients with inflammatory bowel disease

Environmental factors are associated with onset and course of inflammatory bowel disease (IBD). Our previous study by about 1,100 IBD patients revealed half of the patients experienced seasonal exacerbation of disease. We investigated the seasonality of fecal microbiota composition of IBD patients.

Fecal samples were consecutively collected in each season from IBD outpatients and healthy controls between November 2015 and April 2019. Participants who were treated with full elemental diet or antibiotics within 6 months or had ostomates were excluded. Bacterial profiles were analyzed by 16S rRNA sequencing, and the changes between the diseases and seasons were compared.

A total of 188 fecal samples were analyzed from 47 participants comprising 19 Crohn's disease (CD) patients, 20 ulcerative colitis (UC) patients, and 8 healthy controls (HC). In CD patients, the phylum Actinobacteria and TM7 were both significantly more abundant in autumn than in spring and winter, but not in UC patients and HC. Moreover, the genera Actinomyces, a member of Actinobacteria, and c_TM7-3;o_;f_;g_ (TM7-3), that of TM7, were significantly more abundant in autumn than in spring, and the abundance of Actinomyces was significantly correlated with that of TM7-3 throughout the year in CD patients, but not in UC patients and HC. CD patients with high abundance of TM7-3 in the autumn required significantly fewer therapeutic intervention than those without seasonal fluctuation.

Oral commensals Actinomyces and its symbiont TM7-3 were correlatively fluctuated in the feces of CD patients by season, which could affect the disease course.