ABSTRACT The overall goal of this proposal is to develop a novel therapy for the treatment of burn wound infections caused by the opportunistic Gram-negative pathogen Pseudomonas aeruginosa (Paer), a leading cause of burn wound infections.Paer colonizes 14 to 33% of burn wounds within 14 days after hospital admission. Paer infections are difficult to treat due to intrinsic antibiotic resistance, its propensity to adopt the biofilm mode of growth within burn wounds, and the prevalence of strains that are resistant to several antibiotics. In fact, Paer strains that are resistant to all anti-pseudomonal antibiotics except the antibiotic of last resort, colistin, have been identified, prompting the CDC to designate Paer as a “Serious Threat” pathogen. To address the need for innovative therapies to treat Paer burn wound infections, we propose to evaluate a novel class of small molecules that inhibit the type 3 secretion system (T3SS), the major virulence factor utilized by Paer to establish infections and to disseminate in the host. In previous research, we have discovered and chemically optimized the phenoxyacetamides (PhAs), a series of potent, small molecule inhibitors of the Paer T3SS. As the result of extensive chemical optimization of this series, we have identified five distinct compounds that are potent inhibitors of T3SS activity in vitro, are drug-like, and are efficacious as single agents against Paer in an immunocompetent murine pneumonia model, decreasing bacterial load in the lungs by >1 log10 CFU, and significantly decreasing dissemination to the liver by >1 log10 CFU. Our strategy for achieving the overall goal of this proposal is to obtain proof-of-principle data demonstrating that the in vivo validated PhA T3SS inhibitors are efficacious against Paer burn wound infections using in vitro and in vivo burn wound infection models. Compounds that meet the milestones for in vivo efficacy will be developed further as novel therapy for burn wound infections in a follow-on Phase II proposal. To achieve the goal of this proposal, we will complete the following specific aims: Aim 1. Prioritize in vivo validated T3SS inhibitors using an in vitro burn wound model (MBX, years 1 and 2); Aim 2. Evaluate 2 prioritized T3SS inhibitors in the murine thermal injury infection model (MGH, years 1 and 2).