Abstract: Objective To investigate the effect of Enterococcus faecium QH06 on TNBS-induced ulcerative colitis (UC) in rats and explore the mechanisms in light of intestinal flora and intestinal immunity. Methods Thirty-six male Wistar rats were randomized equally into control group, UC model group, and E.faecium QH06 intervention group. The rats in the latter two groups were subjected to colonic enema with 5% TNBS/ethanol to induce UC, followed by treatment with intragastric administration of distilled water or E.faecium QH06 at the dose of 0.21 g/kg. After 14 days of treatment, the rats were examined for colon pathologies with HE staining. The mRNA and protein expression levels of IL-4, IL-10, IL-12, and IFN-γ in the colon tissues were detected using RT-qPCR and ELISA, and the expression of TLR2 protein was detected with immunohistochemistry and ELISA. Illumina Miseq platform was used for sequencing analysis of the intestinal flora of the rats with bioinformatics analysis. The correlations of the parameters of the intestinal flora with the expression levels of TLR2 and cytokines were analyzed. Results The rats with TNBS- induced UC showed obvious weight loss (P<0.01) and severe colon tissue injury with high pathological scores (P<0.01). The protein expression levels of IFN-γ, IL-12, and TLR2 (P<0.01) and the mRNA expression levels of IFN-γ, IL-12 and IL-10 (P<0.05) were significantly increased in the colon tissues of the rats with UC. Illumina Miseq sequence analysis showed that in UC rats, the Shannon index (P<0.05) ACE (P<0.01)and Chao (P<0.05) index for the diversity of intestinal flora both decreased with a significantly increased abundance of Enterobacteriaceae (P<0.01) and a lowered abundance of Burkholderiaceae (P<0.05). Compared with the UC rats, the rats treated with E.faecium QH06 showed obvious body weight gain (P< 0.05), lessened colon injuries, lowered pathological score of the colon tissue (P<0.05), decreased protein expressions of IFN-γ, IL-12, and TLR2 and mRNA expressions of IFN-γ and IL-12 (P<0.01 or 0.05), and increased protein expressions of IL-4 (P<0.05). The Shannon index ACE (P<0.05) and Chao (P<0.05) index of intestinal microflora were significantly increased, the abundance of Enterobacteriaceae was lowered and that of Burkholderiaceae and Rikenellaceae was increased in E.faecium QH06- treated rats (P< 0.01 or 0.05). Correlation analysis showed that IFN-γ was positively correlated with the abundance of Enterobacteriaceae, and IFN-γ was negatively correlated with the abundance of Prevotellaceae, Desulfovibrionaceae, norank_o_Mollicutes_RF39 and Clostridiales_vadinBB60_group; TLR2 was negatively correlated with Clostridiales_vadinBB60_group, norank_o_Mollicutes_RF39 and Prevotellaceae. Conclusion E.faecium QH06 can alleviate TNBS-induced colonic mucosal injury in rats, and its effect is mediated possibly by increasing the abundance of SCFA-producing bacteria such as Prevotellaceae and inhibiting abnormal immune responses mediated by TLR2.

Key words: Enterococcus faecium; ulcerative colitis; intestinal flora; Toll-like receptor 2; cytokines