Lytic bacteriophage as an adjunct to antibiotic therapy for Pseudomonas aeruginosa lung infection in cystic fibrosis patients
Creators: name: Martin, Isaac
Publisher: name: Imperial College London
Year: 2021

description: Longer lifespan and improved quality of life for patients with cystic fibrosis (CF) have been attributed to, at least in part, advances in treating pulmonary infection in this disease. The acquisition of ubiquitous environmental organisms and the development of inflammation and airway scarring as a result is a major hurdle to improving the lives of patients with CF. This is especially true for Pseudomonas aeruginosa (Pa), the dominant respiratory pathogen in CF patients, due to the development of antibiotic resistance as well as the development of a biofilm mode of growth. The problem posed by this organism has necessitated exploration of novel therapies, including bacteriophage. As phage therapy in the context of CF is unlikely to be used in isolation, the first part of this thesis explores the efficacy of a cocktail of 4 lytic bacteriophages when used as adjunctive therapy to the commonly used antibiotics ceftazidime and tobramycin in high-throughput models of Pa infection. Reduction in both biofilm biomass and cell viability was demonstrated when combining phage with the two antibiotics in a biofilm model of infection across 16 different clinical Pa strains. To interrogate the effect of combination therapy more thoroughly, checkerboard experiments combining phage and ceftazidime or tobramycin individually in both planktonic and biofilm Pa culture were performed. Although there were individual examples of synergy, there were also examples of antagonism. Efficacy of the phage cocktail varied based on Pa strain, type of culture (biofilm vs. planktonic), as well as the antibiotic used. For 3 of the 16 clinical strains used in these experiments, there was an observed conversion to mucoid phenotype on Congo Red agar. As a small pilot study, transcriptomic analysis on 1 of these strains was undertaken and demonstrated upregulation of genes involved in alginate production with phage in both planktonic and biofilm culture, mirroring the phenotypic findings seen. Lastly, bacteriophage sensitivity was tracked over time with the objective of answering questions pertaining to the recruitment of participants to prospective clinical trials involving phage. With the objective of knowing whether recruitment of patients could be based on historical sensitivity to phage, I selected 24 patients with chronic Pa infection and looked at serial isolates over the course of 12 months, performing antibiotic sensitivity testing, plaque assays as well as variable number tandem repeat (VNTR) typing of each isolate. Results showed that even when representing a single Pa strain, there was a high degree of variability in sensitivity to both bacteriophage and antibiotics. There were high rates of sensitivity to bacteriophage – even in multi-drug resistant (MDR) strains -which supports the development of this therapy. However, the observed variability implies that selection of patients in future trials should be on the basis of current, not past, isolate testing. Broadly speaking, my results with relation to the development of bacteriophage therapy in CF lung disease are promising, showing broad efficacy in a large number of clinical Pa strains in both biofilm and planktonic culture, both as adjunctive therapy with use of commonly used anti-Pa antibiotics, and in MDR strains. The variability of results, both across strains, but also in individual strains at different time points, should be taken into consideration as trials with phage are developed.