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Society for Surgery of the Alimentary Tract

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Sara Gaines*1, Ashley Williamson1, Romina Pena3, Richard Jacobson2, Jacob Mozdzen4, John C. Alverdy1, Olga Zaborina1, Neil Hyman1, Jack Gilbert1, Benjamin D. Shogan1
1Surgery, University of Chicago, Chicago, IL; 2Surgery, Rush University, Chicago, IL; 3Surgery, Hospital Clinic of Barcelona, Barcelona, Spain; 4Surgery, Nortre Dame, Notre Dame, IN

Background: Mechanical bowel preparation (MBP) with oral antibiotics has been shown in large clinical datasets to reduce the incidence of anastomotic leak after colorectal resection. We have previously found that collagenase producing bacteria play a key role in the pathogenesis of anastomotic leak. We hypothesize that preoperative bowel prep decreases intestinal colonization with collagenase producing organisms.
Methods: We prospectively enrolled patients undergoing colon resection at a tertiary care academic center. On the day before surgery, all patients were given a MBP with GoLytely and an oral antibiotic prep. All patients completed a survey documenting diet habits, use of antibiotics, smoking, and the use of immunosuppressants. Three stool samples were collected from each patient: stool from home prior to bowel prep, intraoperative stool sample, and a 2 week postoperative stool sample. We analyzed: (1) Microbial collagenase activity quantified by fluorescence produced during degradation of gelatin by the growing microbial population (2) Microbial community analysis by 16S rRNA sequencing to understand how bowel prep influences the entire composition of the bacterial community.
Results: Twenty-five patients undergoing colon or rectal resection were enrolled in the study. Analysis of the entire cohort showed that bowel prep caused a 2-fold decrease in the amount of collagenase producing bacteria (3.27x104 RFU vs 1.56x104 RFU; p=0.01). Samples in the 2-week postoperative period showed return of the colonization of collagenase organisms back to pre-bowel levels (pre-bowel prep 3.27x104 vs postoperative 3.94x104; p>0.05-Figure 1). Subset analysis revealed a similar pattern of microbial collagenase reduction after bowel prep in patients whom had previously been treated with antibiotics, had a high vegetable diet, were on immunosuppressive medications, or were smokers. In obese patients (BMI > 30), bowel prep did not reduce the microbial collagenase activity (3.18x104 vs 3.17x104; p>0.05). 16S rRNA analysis showed that the composition of the community structure was significantly changed by bowel prep only in normal weight patients, whereas the community structure remained the same in obese patients. Interestingly, 2 of the 3 patients that developed anastomotic leak were in this obese cohort.
Conclusions: MBP with oral antibiotics significantly decreases colonization with collagenase producing organisms and alters the composition of the intestinal microbiota in normal weight patients. This may explain the marked effect of bowel prep on anastomotic leak rates consistently demonstrated in large clinical datasets. The lack of an impact in obese patients is intriguing and may explain the higher leak rate commonly reported in this subgroup, highlighting the concept that the optimal strategy to prepare the bowel for surgery may not be "one size fits all."?

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