Investigating The Impact Of Prophylactic Oral Antibiotics On The Gut Microbiome And Infectious Outcomes In Post-mastectomy Implant-based Breast Reconstruction: Pilot Data From A Prospective Randomized-controlled Trial

PURPOSE: Post-mastectomy implant infections rates are high despite prophylactic antibiotics. Individual gut microbiomes have been shown to influence health outcomes in other fields, but not yet in breast reconstruction. In this randomized-controlled trial, we investigate the impact of prophylactic antibiotics on the gut microbiome in post-mastectomy tissue expander patients, and clinical infections. METHODS: Patients with immediate tissue-expander placement were randomized to 7 days Keflex or 24 hours Ancef. Stool was collected preoperatively, and 1 week post operatively. 16srRNA microbiome sequencing was performed for stool samples. Relative abundance of genera and alpha diversity were compared between cohorts, pre- and post-operatively. RESULTS: 19 patients received 7days of antibiotics, and 20 received 24hours. There was a 34.4% infection rate with 7 days, and 15.6% with 24hrs (p=0.083). In the 7day cohort, the relative abundance of stool Flavonifractor (p=0.001), and Collinsella (p=0.002) significantly increased post-operatively, while Eubacterium(p=0.009) and Streptococcus (p=0.01) decreased post-operatively. No significant changes were seen in these genera with 24hrs antibiotics. In the 24hour cohort, Staphylococcus increased post-operatively (p=0.009) while no change was seen with 7days of antibiotics. Post-operative alpha diversity significantly decreased from preoperatively with 7days (p=0.04) and 24hours (p=0.05), though a greater diversity reduction was seen with 7 days. CONCLUSION: Extended antibiotics were associated with significantly different changes to the gut microbiome. Diversity decreased with any antibiotics, but to a greater extent with the longer course. Our study highlights changes to the balance of the gut microbiome with extended antibiotics and is ongoing to evaluate potential correlations with clinical outcomes.