PROJECT SUMMARY/ABSTRACT Surgical site infection (SSI) is a major public health problem with devastating perioperative outcomes, affecting as many as 1 in 20 patients undergoing instrumented spine surgery. Procedures such as spinal fusion comprise the largest overall category of US spending on surgical care and are frequently performed for patients with pain or disability arising from a wide range of musculoskeletal conditions, such as congenital or degenerative disease, trauma, and neoplastic disorders. However, SSI rates in instrumented spine surgery are among the highest of any procedure involving a clean skin incision and they have not substantially decreased in decades. The development of more effective strategies for SSI prevention in spine surgery is significantly limited by a lack of fundamental understanding about the origins of causative bacteria, the basic pathogenesis of spinal wound infection, the microbiome of the back, and the role of antimicrobial resistance to surgical prophylaxis. We recently demonstrated that the microbiologic causes of spine SSI may vary by operative level and patient sex, and that most infections are resistant to the surgical antibiotic prophylaxis administered. The objectives of this K23 proposal are to build upon this foundation through training in translational microbiome sciences and by prospectively characterizing the role of the patient microbiome in spine SSI. The central hypothesis is that most spine SSIs arise from strains colonizing the patient prior to surgery (rather than acquired in the hospital environment) and that clinically actionable features of the preoperative patient microbiome strongly influence individual, modifiable risk. The long-term objective of this work is to use novel bacterial genomic techniques and large clinical datasets to identify the fundamental mechanisms by which spinal wound infection occurs, enabling the development of more effective prevention strategies. The specific aims of this proposal are to: 1) define preoperative bacterial genetic features of Staphylococcus aureus associated with spine SSI, allowing development of improved screening and decolonization measures, 2) identify sources of endogenous gram-negative spine SSI and associated resistance to surgical antibiotic prophylaxis, enabling prevention strategies for this important class of infection that may disproportionately affect specific groups (e.g., women undergoing lumbosacral procedures), and 3) determine clinical risk factors for resistance to surgical antibiotic prophylaxis in spine surgery to inform tailored approaches to selection of antibiotic prophylaxis in spine surgery for diverse patient populations. These research activities are closely aligned with my career development plans. Through the team of expert mentors assembled from anesthesiology, surgery, and molecular microbiology, I will receive training in cutting-edge translational microbiome research and career development toward independence...