Objective To identify whether gut microbial changes were associated with recurrent oral ulcer (ROU) and to determine possible factors associated with the pathogenesis of ROU.  Methods We performed metagenomic sequencing and detected inflammatory cytokines ［interleukin (IL)-10, IL-22］ using ELISA in faeces. Eight students who frequently suffered from oral ulcers were selected as the experimental group (HR); accordingly, 14 healthy volunteers served as the control group (HN).  Results There were some differences in intestinal microbial community structures and core flora between the HR and the HN. At the phylum level, the abundance of Firmicutes in the HR was higher than that in the HN (P<0.05). At the genus level, the abundance of Escherichia/Shigella and Bifidobacterium in the HN were higher than that in the HR (P<0.05). The abundance of enterococcus in the HR was higher than that in the HN (P<0.05). IL-10 levels in feces were similar in HN and HR, and there was no statistical difference between the two groups (P>0.05). IL-22 level in HR was higher than that in HN, and there was statistical significance between the two groups (P<0.05). Univariate Logistic regression analysis showed that IL-22 was a risk factor for ROU. Multivariate Logistic regression analysis showed that Bifidobacterium abundance may be a protective factor for ROU, IL-22 in faeces may be a risk factor. Conclusion Our results suggest that there is an interaction between IL-22 and the distribution of intestinal flora in the patients with ROU, the occurrence of ROU may be related to the decrease of the abundance of Bifidobacteriumand the increase of IL-22 in the faeces, and IL-22 has a stronger proinflammatory effect than the antiinflammatory effect generated by IL-10 and itself in the occurrence of ROU, but further research will be needed.

Recurrent oral ulcer, Intestinal flora, Interleukin-10, Interleukin-22, High-throughput sequencing, Enzyme linked immunosorbent a ssay, Adult