Differential infection properties of three inducible prophages from an epidemic strain of Pseudomonas aeruginosa

Background: Pseudomonas aeruginosa is the most common bacterial pathogen infecting the lungs of patients withcystic fibrosis (CF). The Liverpool Epidemic Strain (LES) is transmissible, capable of superseding other P. aeruginosapopulations and is associated with increased morbidity. Previously, multiple inducible prophages have been foundto coexist in the LES chromosome and to constitute a major component of the accessory genome not found inother sequenced P. aerugionosa strains. LES phages confer a competitive advantage in a rat model of chroniclung infection and may, therefore underpin LES prevalence. Here the infective properties of three LES phageswere characterised.Results: This study focuses on three of the five active prophages (LESφ2, LESφ3 and LESφ4) that are members ofthe Siphoviridae. All were induced from LESB58 by norfloxacin. Lytic production of LESφ2 was considerably higherthan that of LESφ3 and LESφ4. Each phage was capable of both lytic and lysogenic infection of the susceptibleP. aeruginosa host, PAO1, producing phage-specific plaque morphologies. In the PAO1 host background, the LESφ2prophage conferred immunity against LESφ3 infection and reduced susceptibility to LESφ4 infection. Eachprophage was less stable in the PAO1 chromosome with substantially higher rates of spontaneous phageproduction than when residing in the native LESB58 host. We show that LES phages are capable of horizontal genetransfer by infecting P. aeruginosa strains from different sources and that type IV pili are required for infection by allthree phages.Conclusions: Multiple inducible prophages with diverse infection properties have been maintained in the LESgenome. Our data suggest that LESφ2 is more sensitive to induction into the lytic cycle or has a more efficientreplicative cycle than the other LES phages