Dysbiosis of gut microbiota during fecal stream diversion in patients with colorectal cancer.

Background: The effect of fecal stream diversion on the gut microbiota is still uncertain. The present study was designed to assess the effect of fecal stream diversion on the composition of the gut microbiota in patients with colorectal cancer. We included patients undergoing left-sided colorectal cancer surgery with (ileostomy group) or without (control group) diverting ileostomy. Fecal samples were collected from 10 patients in each group before surgery (t₁) and after ileostomy repair in the ileostomy group and 6-12 months after the initial surgery in the control group (t₂). The fecal microbiota was assessed using 16S rRNA sequencing, and changes in the composition of the fecal microbiota were compared between the two groups.

Results: Alpha diversity analysis revealed that the complexity of fecal microbiota decreased between t₁ and t₂ only in the ileostomy group. Beta diversity analysis also showed dissimilarity between t₁ and t₂ only in the ileostomy group. The composition of the microbiota was similar between the two groups at t₁. However, at t₂, the ileostomy group had lower proportion of beneficial bacteria (Lachnospiraceae, 3.8% vs. 29.9%, p < 0.001; Ruminococcaceae, 0.6% vs. 18.4%, p < 0.001; Blautia, 0.1% vs. 9.1%, p < 0.001; Faecalibacterium, 0.2% vs. 7.5%, p < 0.001) and a higher proportion of harmful bacteria (Proteobacteria, 17.9% vs. 5.1%, p = 0.006; Clostridium, 16.2% vs. 1.1%, p = 0.013; Streptococcus, 17.7% vs. 1.6%, p = 0.002) than the control group.

Conclusions: Fecal stream diversion was closely associated with less diversity and dysbiosis of the gut microbiota.