EP209 - Variations in Gut Microbiome Recovery Following Colorectal Surgery

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Purpose/Background: The intestinal microbiota is proposed to impact outcomes after colorectal surgery, including anastomotic leak and postoperative infection. It has been shown that surgical bowel preparation (SBP), the combination of mechanical bowel preparation (MBP) and oral antibiotics, alters microbiota composition, persisting through the postoperative period. However, the effect of underlying pathology and type of surgery combined with SBP remains unclear. This study aimed to evaluate these factors on gut microbiota composition in three cohorts: patients undergoing colonoscopy (MBP), non-resectional colorectal surgery (SBP), and resectional colorectal surgery (SBP + partial colectomy) for cancer or diverticulitis.

Methods/Interventions: Fecal samples were assessed for microbiota composition from three cohorts: patients who underwent colonoscopy (n = 30), non-resectional surgery (n = 25), or resectional surgery (n = 26). Microbial composition was characterized using 16S rRNA sequencing at 5 timepoints: baseline (before SBP/MBP), intraoperatively, and postoperative day (POD) 10, 30, and 180.

Results/Outcomes: Microbial diversity, measured by Shannon indices, decreased significantly in both surgical cohorts from baseline to POD30, recovering by POD180. On POD10, colonoscopy patients had significantly higher diversity than non-resectional and resectional patients (Shannon index: 3.55 ± 0.65, 2.73 ± 0.93, 2.70 ± 1.21; Kruskal-Wallis, P = 0.002, 0.006), which was maintained to POD180 (3.78 ± 0.41; P = 0.011, 0.005). No significant differences in diversity were noted between the two surgical groups.

Significant differences in the relative abundance of several genera were observed between cohorts at the same timepoints. Intraoperatively, Faecalibacterium was more abundant in the colonoscopy group compared to the resectional group (K = 89.7, P < 0.0001; Figure 1A). In contrast, Streptococcus was more abundant in the non-resectional cohort than in colonoscopy patients (K = 59.3, P < 0.0001; Figure 1B).

At POD10, the colonoscopy group had lower levels of Enterococcus compared to non-resectional patients (K = 74.3, P = 0.0001), while the resectional cohort had higher relative abundances of both Streptococcus and Enterococcus compared to the colonoscopy group (K=59.3, 74.3, P=0.0001, 0.003; Figure 1B).

At POD30, the colonoscopy group exhibited lower Enterococcus levels than non-resectional patients (K = 74.3, P = 0.0005, Figure 1B). Compared to the resectional group at POD30, the colonoscopy cohort carried greater abundance of Faecalibacterium (Figure 1A), while the resectional group had significantly higher levels of Enterococcus (K = 89.7, 69.2, 74.3, P < 0.0001, < 0.0001, 0.001; Figure 1B).

In a subgroup analysis of surgical indication, patients with diverticulitis had lower Shannon indices and greater relative abundance of Streptococcus and Enterococcus compared to those with cancer (P=0.001, 0.002).

Conclusion/Discussion: While post-MBP/SBP microbial diversity generally recovers across all cohorts over time, patients who undergo SBP exhibit prolonged alterations in key bacterial genera, particularly Streptococcus and Enterococcus, with the most pronounced changes in those undergoing surgical resection. SBP contributes to sustained dysbiosis and influences microbial repopulation, more pronounced in those with diverticulitis. These findings highlight the need for future studies focused on strategies to reintroduce beneficial microbiota postoperatively to optimize outcomes.