PROJECT SUMMARY Infections due to antibiotic resistant organisms (ARO) are a major threat to public health worldwide and a significant cause of healthcare-associated infections (HAI). AROs are especially threatening to immunocompromised patients in intensive care units (ICUs), where a weakened immune system combined with cancer chemotherapy and antibiotic exposures results in increased risk for HAIs due to AROs. A potential source of ARO transmission is the hospital environment. AROs can survive on objects and surfaces in the ICU for prolonged time intervals, resulting in fixed reservoirs for ongoing ARO transmission to vulnerable patients. To create and optimize infection prevention strategies, it is crucial to understand the link between the hospital environment and HAIs, and to optimize environmental hygiene intervention strategies to prevent HAIs due to AROs. To characterize the environmental areas with the greatest ARO burden in the ICU, our group cultured, identified, and created a biospecimen repository of 1,109 potential AROs from collected from ICU surfaces, patient fecal samples, and clinical bloodstream infection (BSI) isolates from patients admitted to the bone marrow transplant (BMT) ICU. Our preliminary selective microbiologic culture techniques and whole genome sequencing (WGS) data indicate that there is a genetic link between AROs isolated from sink drains and clinical BSI isolates. This raises the hypothesis that AROs in sink drains are being transferred between the ICU environment and patients (or vice-versa), and that the environment may be a reservoir for ARO transmission. Based on these preliminary data, our goal is to define the link between AROs found in the ICU environment and patients with HAIs, and to design and test interventions to reduce the burden of AROs in the ICU environment. In this project, we will utilize antimicrobial susceptibility testing and WGS to longitudinally determine the presence and transmission of AROs across the hospital environment, and determine the genetic link between these strains to those causing BSIs in patients in a BMT ICU. Further, we will implement and measure the impact of a bleach and hydrogen peroxide-based environmental hygiene intervention on the concentration of AROs present in ICU sink drains. Completion of these specific aims will allow us to extensively characterize the transmission dynamics of AROs across environmental surfaces and patients, and to evaluate an environmental hygiene intervention that focuses on sink surfaces and drains.