Development, evaluation and evolution of bacteriophage cocktails active against clinical Pseudomonas aeruginosa isolated from Cystic Fibrosis patients

Cystic fibrosis (CF) is a genetic disorder in which impaired mucociliary clearance predisposes patients to chronic pulmonary infection with Pseudomonas aeruginosa, a pathogen that is increasingly resistant to conventional antibiotic therapy. Bacteriophage therapy offers a promising alternative, yet its clinical translation requires systematic evaluation of phage activity, rational cocktail design, and understanding of resistance evolution under therapeutic pressure.
The first study characterised phages with bactericidal activity against clinical P. aeruginosa isolates from CF patients. Phages were evaluated for clearance and resistance interactions relative to antibiotics. Experiments examined clearance kinetics, the effect of infection duration on phage efficacy, whereby strains from patients with longer chronic infections displayed greater phage resistance, and the capacity of phages to prevent or disrupt biofilms, highlighting the variable performance of individual phages across physiological contexts.
Building on these findings, the second study used clearance and biofilm inhibition profiles to design a broad-spectrum phage cocktail targeting genetically diverse clinical isolates. Efficacy was assessed across multiplicities of infection (MOI), simulating early empirical administration prior to personalised matching. Results demonstrated that broad spectrum phage cocktails may present a viable first line treatment for infection, allowing time for a more personalised approach to be devised.
The final study examined evolutionary trajectories under single phage and cocktail selection, quantifying the rate, stability, and mechanisms of resistance emergence. Incorporation of sub-inhibitory polymyxin B revealed synergistic killing and altered resistance dynamics, supporting the potential of phage–antibiotic combinations to suppress resistance while maintaining efficacy. Together, these studies demonstrate that phage host range, biofilm physiology, multiplicity of infection, and resistance evolution under selective pressure are critical determinants of phage therapy efficacy, and that rational cocktail design combined with phage–antibiotic synergy offers a promising framework for treating chronic CF infections
By linking mechanistic experimentation with translational design principles, this work contributes to the rational development of durable phage therapies for chronic CF infections. The study is contextualised within the Danish CF treatment model, which employs centralised patient management, intensive longitudinal microbiological surveillance, and early aggressive antimicrobial intervention, providing a uniquely well-characterised framework for studying infection dynamics and therapeutic innovation. It highlights the need for clinically relevant biofilm models, adaptive cocktail formulation, and integration of phages into combinatorial treatment frameworks.