[Detection and analysis of intestinal flora diversity in patients with complex anal fistula]

Objective: To explore the possibility that the intestinal flora profile in complex anal fistula patients is different to that of healthy controls. This was assessed by sequencing of 16S rDNA in fecal samples from cohorts representing these populations. Methods: Fecal samples were collected from 30 complex anal fistula patients and 30 matched healthy controls. Patients were included if they met the diagnostic criteria of cryptoglandular anal fistula and had exhibited symptoms for more than 3 months. Complex anal fistula is diagnosed under the following circumstances: if the fistula in question spans 2/3 or more of the diameter of the anal sphincter; if there are more than two external orifices or fistula tracks; or if recurrence is observed after previous anal fistula surgery. Patients were excluded if there were comorbities including inflammatory bowel disease (as assessed by colonoscopy), chronic diarrhea, chronic constipation, diabetes, gastrointestinal malignancies, liver/ kidney dysfunction, or cognitive impairment. Patients whose anal fistulas were caused by Crohn's disease, trauma, special infections (such as actinomycosis and tuberculosis) were also excluded, as were those who had used antibiotics, prebiotics, or probiotics that may affect intestinal microecology in the month prior to the study. Total bacterial genomic DNA was extracted by PCR amplification of the V4 hypervariable region of the 16S rRNA sequences. High-throughput sequencing and data analysis were performed on the Illumina Miseq platform. Finally, operational taxonomic unit (OTU) clustering, alpha diversity and LEfSE data analysis were carried out. The larger the Chao or ACE index is, the higher the species abundance of the microflora is expected to be. Similarly, a smaller value for the Simpson index or a larger value for the Shannon index indicates greater microflora diversity. There was no statistically significant difference in gender, age, body mass index (BMI), drinking history, or smoking history between the two groups (P>0.05), indicating that they were comparable. Results: The α-diversity analysis including ACE, Chao, Shannon and Simpson indexes indicated a richer diversity of intestinal microflora in complex anal fistula patients than in healthy controls. In both patients and controls, OUT cluster analysis demonstrated that 93.4%±32.0% and 87.4%±41.2% of sequences were from Firmicutes and Bacteroidetes spp., respectively. On a genus level, samples from anal fistula patients showed a greater abundance of Prevotella spp. (4.9%±7.4% vs. 0.1%±1.1%, P<0.001), Megamonas (3.9%±8.2% vs. 0.5%±4.2%, P<0.05) and Lachnospira (2.6%±5.7% vs. 0.1%±3.4%, P<0.05), while showing a lesser abundance of Proteobacteria spp. (0.02%±4.2% vs. 9.3%±14.4%, P<0.01), Enterococcus (0.02%±2.3% vs. 9.3%±19.6%, P<0.05), Bacteroides (24.7%±9.9% vs. 29.8%±9.1%, P<0.05) and Klebsiella (0.4%±4.2% vs. 3.9%±7.3%, P<0.05) compared with healthy controls. Intestinal flora diversity in the complex anal fistula group was richer than in controls, as indicated by a higher ACE index (293.30±44.00 vs. 218.75±33.83, t=102.069, P<0.001), a higher Chao index (318.40±41.99 vs. 250.00±46.38, t=77.818, P=0.028), a higher Shannon index (3.36±0.29 vs. 2.43±0.34, t=9.657, P=0.001), and a lower Simpson index (0.103±0.013 vs. 0.131±0.013, t=5.551, P=0.046). LDA effect size analysis suggests that the main strains of Veillonellaceae, Selenemondales and Negativicutes, which all belong to the phylum Firmicutes, have the greatest influence on the above difference (LDA>4). Conclusions: The diversity of intestinal flora in patients with complex anal fistula is greater than in healthy controls, suggesting that these bacteria or their metabolites may be involved in the occurrence and development of anal fistulas.