Intestinal flora alterations in patients with ulcerative colitis and their association with inflammation

Ulcerative colitis (UC), which is a type of inflammatory bowel disease, is a chronic intestinal disorder of multifactorial etiology. Numerous studies have indicated an association between UC and intestinal bacteria. However, a limited number of studies regarding the expression of interleukin-17 (IL-17) and interleukin-23 (IL-23) in association with intestinal bacteria have been performed. The aim of the current study was to investigate the gut microbiota alterations in patients with UC, at a number of taxonomic levels, and their relationship with intestinal inflammation by analyzing the protein expression of IL-17 and IL-23. Specimens were collected from 10 healthy controls and 16 patients with UC. A histological examination was performed in colonic tissues, IL-17 and IL-23 protein expression was detected by immunohistochemistry, fecal samples were sequenced using 16S rDNA sequencing and bioinformatics analysis was performed. The UC group exhibited an increased histological score (P<0.01) and upregulated IL-17 and IL-23 expression (P<0.01). At the order level, the bacterial diversity of the UC group was decreased. beta-diversity analyses, including principal component analysis, principal coordinate analysis and non-metric multidimensional scaling, demonstrated that the two groups of samples were separated into two taxonomic categories, as distinct variations were observed in the analysis of group differences (P=0.001). Regarding the differences in species composition between the groups, Enterococcus was indicated to be the species with the greatest difference in abundance compared with the healthy control group (P<0.01), followed by Lactobacillus (P<0.05), Escherichia-Shigella (P<0.05), Bifidobacterium and Bacteroides. In addition, the average optical density of IL-17 was positively correlated with the histological score (rho=0.669; P=0.035), Enterococcus (r=0.843; P<0.001), Lactobacillus (r=0.737; P=0.001), Bifidobacterium (r=0.773; P<0.001) and Escherichia-Shigella (r=0.663; P=0.005), and the average optical density of IL-23 was positively correlated with the histological score (rho=0.733; P=0.016), Enterococcus (r=0.771; P<0.001), Lactobacillus (r=0.566; P=0.022), Bifidobacterium (r=0.517; P=0.041) and Escherichia-Shigella (r=0.613; P=0.012). The results of the present study indicated that the intestinal microbiota of patients with UC differed from that of healthy controls at multiple taxonomic levels. The alterations of the intestinal microflora were closely associated with the degree of inflammation. The IL-23/IL-17 axis, as a key factor in the development of UC, maybe associated with the alterations of intestinal microflora. The interaction between intestinal microflora and the IL-23/IL-17 axis may serve an important role in the pathogenesis of UC.