Comparative analysis of mucosa-associated and luminal gut microbiota in pediatric ulcerative colitis

Background Inflammatory bowel diseases (IBD), including ulcerative colitis (UC) and Crohn’s disease, are chronic disorders relating to gut microbiota dysbiosis. Despite severe pancolitis being more prevalent in pediatric UC than in adult cases, alterations in the colon mucosa-associated microbiota (MAM) and their association with disease severity remain to be elucidated. The present study aimed to compare the gut microbiota in colon lavage fluids (CLFs) and fecal samples from pediatric UC patients. Results A total of 140 CLFs and 23 fecal samples from 19 each of pediatric UC and non-IBD patients were analyzed. CLFs were collected by aspirating intestinal fluid after washing the colonic mucosa using an endoscope with a waterjet function. Microbiota profiles of each sample were analyzed by 16S rRNA gene amplicon sequencing. The community structure of MAM was similar throughout the colon in both pediatric UC and non-IBD. Bacterial compositions between MAM and feces were significantly different in non-IBD while no difference was observed in pediatric UC, indicating a compromised mucous layer that could not sufficiently separate the MAM and luminal microbiota in UC. In pediatric UC, homogenous distribution of MAM was gradually disordered with increases in disease activity or mucosal inflammation, and the bacterial groups that usually colonize the upper digestive tract or have environmental origin were more abundant in MAM. To potentially distinguish pediatric UC from non-IBD, we identified the key bacterial genera in MAM; they included Lactobacillus , Enterococcus , Blautia , Parabacteroides , Faecalibacterium and Fusobacterium . Conclusion Compared with feces, MAM is more enriched in specific bacterial groups in non-IBD pediatric patients, whereas the feces and MAM microbiota are similar in pediatric UC. Our results indicate that the fecal microbiota reflect the status of MAM in pediatric UC. Monitoring the key fecal bacteria that are specifically increased in MAM depending on disease activity might be useful for evaluation of patient prognosis in pediatric UC. Further studies on MAM are needed to elucidate the contribution of its community structure to the pathophysiology of pediatric UC.