Comparative Analysis of Mucosa-Associated and Luminal Gut Microbiota in Pediatric Ulcerative Colitis

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 adults, 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 19 pediatric UC and 19 non-IBD patients. The community structure of MAM inferred by 16S metagenomic analysis was similar throughout the colon regardless of disease type. 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 bacterial groups of upper digestive tract or environmental origin were more abundant in MAM. Monitoring key bacterial markers in MAM, which include <i>Lactobacillus</i> and <i>Enterococcus</i> or <i>Faecalibacterium</i> and <i>Blautia</i> as increased or reduced members in pediatric UC, respectively, might be useful for evaluation of patient prognosis.