Lytic activity by temperate phages of Pseudomonas aeruginosa in long-term cystic fibrosis chronic lung infections.

Chloe E James,Joanne L Fothergill,Craig Winstanley,Emily V Davies,Colin M Beale,Martin J Walshaw,Michael A Brockhurst

doi:10.1038/ismej.2014.223

Abstract

Pseudomonas aeruginosa is the most common bacterial pathogen infecting the lungs of cystic fibrosis (CF) patients. The transmissible Liverpool epidemic strain (LES) harbours multiple inducible prophages (LESϕ2; LESϕ3; LESϕ4; LESϕ5; and LESϕ6), some of which are known to confer a competitive advantage in an in vivo rat model of chronic lung infection. We used quantitative PCR (Q-PCR) to measure the density and dynamics of all five LES phages in the sputa of 10 LES-infected CF patients over a period of 2 years. In all patients, the densities of free-LES phages were positively correlated with the densities of P. aeruginosa, and total free-phage densities consistently exceeded bacterial host densities 10–100-fold. Further, we observed a negative correlation between the phage-to-bacterium ratio and bacterial density, suggesting a role for lysis by temperate phages in regulation of the bacterial population densities. In 9/10 patients, LESϕ2 and LESϕ4 were the most abundant free phages, which reflects the differential in vitro induction properties of the phages. These data indicate that temperate phages of P. aeruginosa retain lytic activity after prolonged periods of chronic infection in the CF lung, and suggest that temperate phage lysis may contribute to regulation of P. aeruginosa density in vivo.

Highlights

Cystic fibrosis (CF) patients are subject to life-long chronic respiratory infections, most commonly with the bacterium Pseudomonas aeruginosa
The levels of free-Liverpool epidemic strain (LES) phages detected in all patients throughout this study suggest an active lytic cycle that may be promoted by the presence of H2O2 or DNA-damaging antibiotics in the CF lung (McGrath et al, 1999; Fothergill et al, 2011)
We observed no effect of patient exacerbation on total free-phage density, this is consistent with previous studies showing that neither fluctuations in P. aeruginosa populations (Mowat et al, 2011), nor in the wider bacterial population (Fodor et al, 2012), show any relationship with the exacerbation period in chronically infected patients, despite the use of high-level intravenous antibiotic therapy

Summary

Introduction

Cystic fibrosis (CF) patients are subject to life-long chronic respiratory infections, most commonly with the bacterium Pseudomonas aeruginosa. Phage DNA copy numbers were quantified culturable phages in 10 sputum samples from 3 LES- from DNA samples (1 ml) in triplicate using a infected patients (CF3, CF4 and CF7).

Results

Conclusion