PROJECT ABSTRACT Persistent bloodstream infections are life-threatening infectious disease emergencies posing significant challenges to effective treatment. Such infections occur when a pathogen is susceptible to an anti-infective agent in vitro but is not cleared from the bloodstream in vivo when that anti-infective agent is used appropriately. As a result, anti-infective usage increases, accelerating alarming increases in anti-infective resistance. This vicious cycle of persistence driving anti- infective escalation driving resistance is an NIH high–priority concern. Bloodstream infections caused by Staphylococcus aureus (SA) or Candida albicans (CA) are increasingly common. Of urgent concern, up to 35% of patients with methicillin-resistant SA (MRSA) persistent bacteremia succumb even on gold-standard therapy. Likewise, in patients with hematogenously disseminated candidiasis (HDC), mortality is 39% overall and 47% in those in the intensive care unit, despite appropriate treatment. A disease mystery is central to such infections: the causative pathogen is susceptible to antimicrobials in laboratory testing—but not in the human being. Importantly, persistence reflects a unique type of treatment-refractory infections distinct from classical antibiotic resistance. Rather, persistent MRSA or CA are elusive: they adapt to host immune responses and antibiotic stresses uniquely in vivo and then revert quickly in vitro. Presently, there are few therapeutic options for persistent MRSA or CA bloodstream infections. Hence, there is a critical, unmet need to understand the unique interactions of the human, pathogen and therapeutic factors driving persistence outcomes. Based on our extensive preliminary data, we believe that persistent infections caused by MRSA and CA result from a three-way interaction of the pathogen, host immune response and antimicrobial agent in vivo. We hypothesize that persistent isolates: 1) have specific epigenomes to enable persistence; 2) subvert innate immune programming and memory for immune evasion; 3) evoke non-protective or maladaptive immune responses; and 4) exploit contextual immunity as persistence reservoirs. We further posit that conventional approaches to study this clinically urgent phenomenon are insufficient to understand it. We have developed three independent but synergistic research Projects to overcome these limitations. Each Project brings proven strengths and innovative approaches to bear on Specific Aims that synergize via a systems-based approach supported by outstanding technology, bioinformatics and computational Cores. Here, we will use state-of-the-art technologies to comprehensively analyze the genetics and epigenetics of pathogens and the host immune system in context of antimicrobial therapy in laboratory studies and experimental models of infection. In turn, these data will be analyzed using powerful bioinformatics and computational methods to detect hidden patterns within large complex datasets. By understanding these factors and their interactions, new approaches to identify and treat high risk patients can be developed and applied to improve and save lives. These goals are ideally aligned with priorities of the National Institutes of Health and Centers for Disease Control & Prevention.

PROJECT NARRATIVE Persistent bloodstream infections are life-threatening emergencies that pose significant challenges to effective treatment. A disease mystery is central to these infections: the causative pathogen is susceptible to antimicrobials in laboratory testing—but not in the human being. Persistent bloodstream infections caused by Staphylococcus aureus and Candida albicans are increasingly common, but there are few therapeutic options and patients frequently succumb. In this U19 Center, we will use state-of-the-art technologies in synergistic research to understand the host-pathogen interactions driving persistence. In turn, these data will be analyzed using powerful computational methods to detect hidden patterns within large complex datasets. As a result, new approaches to identify and treat high risk patients can be developed and applied to improve and save lives. These goals are ideally aligned with priorities of the National Institutes of Health and Centers for Disease Control & Prevention.