Investigations to underpin the development of bacteriophages as therapeutic agents to target pseudomonas aeruginosa infections in patients with cystic fibrosis

Pseudomonas aeruginosa is very adept at evolving antimicrobial resistance, which severely reduces the effectiveness of antibiotic treatments available. This contributes to it being the primary cause of morbidity and mortality associated with cystic fibrosis (CF). A new strategy is needed to target P. aeruginosa, a promising approach is bacteriophage (phage) therapy. The aim of this study was to look at developing a phage based therapeutic for airway associated P. aeruginosa infections. This included isolation and characterisation of suitable phages, in vitro and ex vivo testing against clinical P. aeruginosa strains, delivery methods, purification and resistance detection. Seven phages were isolated from commercial and environmental sources. Some of these had suitable host ranges against clinical strains, and were capable of biofilm prevention and degradation. Although these phages were effective in vitro, their efficiency was increased when combined with each other, or the antibiotic tobramycin. Although resistance was observed in these experimental systems, the use of multiple phages reduced resistance development, and resistant strains displayed both a reduction in virulence and an increase in sensitivity to CF antibiotics. Testing with three nebulisers demonstrated these phages could successfully be aerosolised to produce sizes where they would be expected to reach to the lower airways. When aerosolised on to an ex vivo healthy and CF ciliated cell line model, the phages were also able to prevent the establishment of an infection. The purity of the phages was an issue in cell models due to endotoxin contamination; however, various purification methods were developed and tested, with anion-exchange chromatography lowering the levels by three logs, just above the British legal limits. The results from this study demonstrate the potential of a phage based prophylactic against respiratory P. aeruginosa infections. With additional properties that could widen their use against nosocomial infections.