Abstract
The Liverpool Epidemic Strain (LES) is a polylysogenic, transmissible strain of Pseudomonas aeruginosa, capable of superinfecting existing P. aeruginosa respiratory infections in individuals with cystic fibrosis (CF). The LES phages are highly active in the CF lung and may have a role in the competitiveness of the LES in vivo. In this study, we tested this by competing isogenic PAO1 strains that differed only by the presence or absence of LES prophages in a rat model of chronic lung infection. Lysogens invaded phage-susceptible populations, both in head-to-head competition and when invading from rare, in the spatially structured, heterogeneous lung environment. Appreciable densities of free phages in lung tissue confirmed active phage lysis in vivo. Moreover, we observed lysogenic conversion of the phage-susceptible competitor. These results suggest that temperate phages may have an important role in the competitiveness of the LES in chronic lung infection by acting as anti-competitor weapons.
Highlights
To test whether temperate phages increase competitive fitness during lung infection, we performed competition experiments between lysogenic and non-lysogenic strains of P. aeruginosa in a rat model of chronic lung infection (Winstanley et al, 2009)
Initial in vitro experiments suggested that the triple lysogen (PAO1φtriple ) was more invasive than any of the constituent single lysogens (Supplementary Figure S1), PAO1φtriple was selected for use in the in vivo experiments
Competitors were embedded in agar beads in PAO1 LES-Phage Lysogens (PLPLs) to PAO1φ − ratios of 1:5 or 1:1, to model invasion-from-rare and head-tohead competition, respectively
Summary
To test whether temperate phages increase competitive fitness during lung infection, we performed competition experiments between lysogenic and non-lysogenic strains of P. aeruginosa in a rat model of chronic lung infection (Winstanley et al, 2009). The densities of each competitor in the lungs were quantified (Supplementary Table S2) and the selection rate constant (rij) was calculated as described previously (Lenski et al, 1991). Phage-mediated invasion by lysogens can be ness of lysogens against phage-susceptible populations in limited by lysogenic conversion of the originally chronic lung infection.
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