ABSTRACT Multidrug resistant organisms (MDROs) are bacteria that have become resistant to more than one antimicrobial agent. Intestinal MDROs constitute a major threat to public health because they are increasingly difficult to treat and result in increased costs, morbidity, and mortality when they spread outside of the gut. Clostridium difficile shares many of the same characteristics as MDROs and along with MDROs has been labeled by the Centers for Disease Control and Prevention as a national priority. No group suffers more from these intestinal MDROs than nursing home residents. The perfect storm of a vulnerable group of frail older adults living in close communities, with increased morbidity and mortality from bacterial infections, and corresponding high rates of MDRO colonization emphasize the importance of the nursing home as a priority setting for studies to reduce MRDO burden. The intestinal microbiome may be a key factor as it influences both the likelihood of de novo colonization and whether colonization results in disease. In this proposal we will: 1) determine carriage rates of key MDROs in nursing homes communities using novel rapid strain-specific technology (molecular inversion probes); 2) assess the dissemination of pathogenic organisms; 3) determine in vivo/vitro how an aging microbiome can induce intestinal inflammation, thus promoting MDRO colonization; and 4) determining the extent to which both microbial dysbiosis and immunosenescence increases the risk of MDRO colonization, infection, and worsening frailty. We hypothesize that environmental and clinical factors (e.g., medication) characteristic of the NH settings contribute to and shape a dysbiotic microbiome that favors an increased risk of MDRO colonization. We further hypothesize the extent of microbial dysbiosis will be the major contributor of MDRO colonization, thus providing a novel target to combat pathogen prevalence within the NH environment. Specifically, in Aim 1 we will develop and implement a cultivation-free, high-throughput, low-cost approach to provide deep strain-level resolution of MDROs and accelerate epidemiological studies of infectious diseases. Further we will derive a microbiome-based predictive tool, the NH-MDI, to assess individual risk of MDRO colonization. Aim 2 will determine the mechanisms by which the microbiome can influence epithelial homeostasis, thus providing a colonic microenvironment supportive of MDRO colonization. Aim 3 will include analysis of stool and blood samples from a prospective nursing home cohort in order to determine the relative contribution of aging microbiome dysbiosis to markers of immunosenescence for increased risk of MDRO colonization as well as risk of worsening frailty. Further, we will determine the extent that dysbiosis and immunosenescence correlates with risk of future infection over 18 months of follow-up. Defining these crucial parameters will provide the basis for development of novel microbiome therapeutics...