509. <i>Pseudomonas aeruginosa</i>-specific CRISPR-Cas3 bacteriophage cocktail developed to treat respiratory and bloodstream infections

Abstract Background New strategies are needed to combat infections due to multidrug-resistant (MDR) Pseudomonas aeruginosa. Bacteriophage therapy offers an effective, pathogen-specific, microbiome-sparing treatment with an orthogonal mechanism of action to that of small-molecule antibiotics. Here we describe the development and characterization of the P. aeruginosa-targeting 6-phage cocktail LBP-PA01. Methods High-throughput automated methods were used to isolate and characterize wild-type phages. Proprietary Locus-developed software was used to predict the most efficacious combinations of bacteriophages. Selected phages were engineered to express CRISPR-Cas3, and phages were combined into an optimal cocktail and subjected to in vitro antibacterial activity characterization including assessments of bacteriophage and cocktail host range by liquid growth curve assay and by plaque assay, bactericidal activity in the presence of mucin matrices using EpiAirwayTM human airway epithelium tissues, biofilm degradation and inhibition. In vivo efficacy was tested in immuno- compentent mouse models of lower respiratory tract infection with LBP-PA01 administered intranasally and intravenously as well as in a rat model of blood stream infection with intravenous administration. Results &amp;gt;2800 individual bacteriophage were discovered through high throughput methods. Cocktail prediction and optimization resulted in the final combination of 6 unique bacteriophage, LBP-PA01, which was tested against 570 diverse contemporary P. aeruginosa clinical isolates from patients with respiratory or bloodstream infections. The cocktail showed a host range of 97.3% and efficacy against biofilms and in the presence of mucin. In mouse models of acute lower respiratory tract infection and disseminating pulmonary infection and a rat model of bloodstream infection, LBP-PA01 produced multiple log reductions in CFU levels relative to vehicle treatment and superiority to standard-of-care antibiotics. Conclusion Based on the in vitro and mouse model data, LBP-PA01 is a strong candidate for advancement into the clinic for treatment for P. aeruginosa infections. Disclosures All Authors: No reported disclosures