The human mesenteric lymph node microbiome differentiates between Crohn's disease and ulcerative colitis.

Background and Aims: Mesenteric lymph nodes are sites in which translocated bacteria incite and progress immunological responses. For this reason, understanding the microbiome of mesenteric lymph nodes in inflammatory bowel disease is important. The bacterial profile of Crohn's disease mesenteric lymph nodes has been analysed using culture-independent methods in only one previous study. This study aimed to investigate the mesenteric lymph node microbiota from both Crohn's disease and ulcerative colitis patients.

Methods: Mesenteric lymph nodes were collected from Crohn's disease and ulcerative colitis patients undergoing resection. Total DNA was extracted from mesenteric lymph nodes and assessed for the presence of bacterial DNA (16S). All work was completed in a sterile environment using aseptic techniques. Samples positive for 16S DNA underwent next generation sequencing and the identity of bacterial phyla and species were determined.

Results: Crohn's disease mesenteric lymph nodes had a distinctly different microbial profile to that observed in ulcerative colitis. The relative abundance of Firmicutes was greater in nodes from ulcerative colitis patients while Proteobacteria were more abundant in Crohn's disease. Although species diversity was reduced in Crohn's disease mesenteric lymph nodes, they contained greater numbers of less dominant phyla, mainly Fusobacteria.

Conclusion: This study confirms that there are distinct differences between the Crohn's disease and ulcerative colitis mesenteric lymph node microbiomes. Such microbial differences could aid in the diagnosis of Crohn's disease or ulcerative colitis, particular in cases of indeterminate colitis at time of resection, or help explain their mechanisms of development and progression.