UC San Diego

Bacteriophages are viruses of bacteria that are among the leading alternative antimicrobials for treatment of the multidrug resistant (MDR) and opportunistic pathogen Pseudomonas aeruginosa. Although phage therapy is now generally considered safe, access to the treatment remains limited and its efficacy remains unproven. The goal of this dissertation is to develop innovative phage processes and intravenous treatment regimens to combat MDR P. aeruginosa. In the third chapter, I evaluate how to select phages to combat P. aeruginosa and study the interactions between different phage strains during combination treatment. In two-phage cocktail treatment, I found that mixing phages with inequal activities diminishes initial treatment potency. Sequential treatment with the same phages improved potency but generated unique patterns of resistance. This study provides new insight on how to formulate and administer phage combinations based on the infectivity of each phage to its bacterial host. In the fourth chapter, I develop and optimize the standardized production of phages by introducing cross-flow filtration to improve the removal of endotoxin from phage preparations. The simultaneous washing and concentration of phage particles was found to improve endotoxin removal across multiple Gram-negative species. Leveraging the kinetics of each phage, the accumulation of phage-resistant bioburden could then be reduced in an improved purification process. In the fifth chapter, I validate the targeting and replication of clinical phages during the treatment of patients infected by multidrug resistant P. aeruginosa. Phages suitable for therapy were determined by screening across a multi-infection isolate library. The efficacy of clinical phage treatments were then validated using a combination of microbiological and metagenomic markers of failure or success. In conclusion, this thesis provides insights into current barriers for phage therapy. Identifying and characterizing individual phage properties will have important implications on how to treat and reduce the mortality of MDR P. aeruginosa infections.