The Presence of Staphylococcus and Pseudomonas in the Breast Microbiome of Post-Mastectomy Expander Infection Patients and the Impact of Prophylactic Antibiotics

INTRODUCTION: Post-mastectomy implant infections have been cited ranging from 2-28%, with Staphylococcus and Pseudomonas as the usual culprits.¹⁻³ Individuals each have a unique microbiome, or composition of internal microorganisms, that impacts their response to the external environment,⁴ but its role in breast infections is unknown. Often by the time of operative washout, clinical culture data is negative due to antibiotics. However, microbiome analysis of the breast would still show a signal and potentially before fulminant clinical infection. In a pilot study using 16s rRNA sequencing, we explore the breast microbiome in post-mastectomy tissue expander infection patients and the implications of prophylactic antibiotics. METHODS: We designed a two-arm randomized-controlled trial for mastectomy patients undergoing two-stage implant-based reconstruction. Patients were randomized to 7 days of prophylactic post-operative antibiotics (Cohort A), versus only 24 hours of Cefazolin (Cohort B) at the time of surgery. Post-operatively the peri-prosthetic space was sampled via expander aspiration or drain output at 3 weeks. Microbial analysis was performed with 16S rRNA microbiome sequencing. The relative abundance percentages of pseudomonas and staphylococcus in each sample were recorded. Culture data was collected at the time of operative explantation. RESULTS: Of the 39 enrolled patients, 19 patients (32 breasts) were in Cohort A and 20 (32 breasts) were in Cohort B. Expander removal due to infection was required in 7 breasts (22%) of Cohort A, compared to 5 breasts (15.6%) of cohort B (p=0.200). Of the 12 tissue expanders that were removed, 10 were the cancerous breast, while 2 were prophylactic. Negative cultures at the time of explant were seen in 3 of Cohort A (42%) compared to 1 (20%) in Cohort B (p=0.408). Of those that had positive cultures, Staphylococcus was present in 7(88%) compared with Pseudomonas in 2 (12%). The main cultured organism at time of explant was already abundantly present on the prior aspirate microbiome data in 50% of Cohort A compared to 100% of Cohort B explants (p=0.079). Mean time from mastectomy to second aspiration was 22.3 vs 21.2 days (p=0.860). Mean relative abundance of staphylococcus at this visit was 16.1% in Cohort A compared to 37.1% in Cohort B (p=0.356). Pseudomonas was 29.3% in A vs 17.3% in B (p=0.852). Time from mastectomy to explant was 92 days (cohort A) vs 63 days (Cohort B) p=0.426. Mean time from last aspiration to explantation was 70 days in Cohort A, compared to 42 days in Cohort B (p=0.432). CONCLUSION: Prophylactic oral antibiotics did not significantly alter infection rates in post-mastectomy patients, however infections in this cohort had more negative operative cultures, delayed time to explantation, and lower correlation with aspirate microbiome data. Larger cohort samples are necessary to continue studying these variations but this may reflect changes to the balance of the microbiome seen with prolonged antibiotics, and provides novel insight into the larger impact of antibiotics in effacing potential markers for implant infections. References: 1. Yamin F, Nouri A, McAuliffe P, et al. Routine Postoperative Antibiotics After Tissue Expander Placement Postmastectomy Does Not Improve Outcome. Ann Plast Surg. 07 01 2021;87(1s Suppl 1):S28-S30. doi:10.1097/SAP.0000000000002826 2. Phillips BT, Fourman MS, Bishawi M, et al. Are Prophylactic Postoperative Antibiotics Necessary for Immediate Breast Reconstruction? Results of a Prospective Randomized Clinical Trial. J Am Coll Surg. 06 2016;222(6):1116-24. doi:10.1016/j.jamcollsurg.2016.02.018 3. Banuelos J, Abu-Ghname A, Asaad M, Vyas K, Sohail MR, Sharaf B. Microbiology of Implant-Based Breast Reconstruction Infections: A Systematic Review. Ann Plast Surg. Aug 2020;85(2):194-201. doi:10.1097/SAP.0000000000001974 4. Meng S, Chen B, Yang J, et al. Study of Microbiomes in Aseptically Collected Samples of Human Breast Tissue Using Needle Biopsy and the Potential Role of. Front Oncol. 2018;8:318. doi:10.3389/fonc.2018.00318