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Open Access Highly Accessed Research article

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

Chloe E James1*, Joanne L Fothergill1, Hannah Kalwij1, Amanda J Hall1, Jennifer Cottell1, Michael A Brockhurst2 and Craig Winstanley1

Author Affiliations

1 Institute of Infection and Global Health, University of Liverpool, 8 West Derby Street, Liverpool, L69 7BE, UK

2 Department of Biology, University of York, York, YO10 5DD, UK

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BMC Microbiology 2012, 12:216  doi:10.1186/1471-2180-12-216

Published: 21 September 2012

Abstract

Background

Pseudomonas aeruginosa is the most common bacterial pathogen infecting the lungs of patients with cystic fibrosis (CF). The Liverpool Epidemic Strain (LES) is transmissible, capable of superseding other P. aeruginosa populations and is associated with increased morbidity. Previously, multiple inducible prophages have been found to coexist in the LES chromosome and to constitute a major component of the accessory genome not found in other sequenced P. aerugionosa strains. LES phages confer a competitive advantage in a rat model of chronic lung infection and may, therefore underpin LES prevalence. Here the infective properties of three LES phages were characterised.

Results

This study focuses on three of the five active prophages (LESφ2, LESφ3 and LESφ4) that are members of the Siphoviridae. All were induced from LESB58 by norfloxacin. Lytic production of LESφ2 was considerably higher than that of LESφ3 and LESφ4. Each phage was capable of both lytic and lysogenic infection of the susceptible P. aeruginosa host, PAO1, producing phage-specific plaque morphologies. In the PAO1 host background, the LESφ2 prophage conferred immunity against LESφ3 infection and reduced susceptibility to LESφ4 infection. Each prophage was less stable in the PAO1 chromosome with substantially higher rates of spontaneous phage production than when residing in the native LESB58 host. We show that LES phages are capable of horizontal gene transfer by infecting P. aeruginosa strains from different sources and that type IV pili are required for infection by all three phages.

Conclusions

Multiple inducible prophages with diverse infection properties have been maintained in the LES genome. Our data suggest that LESφ2 is more sensitive to induction into the lytic cycle or has a more efficient replicative cycle than the other LES phages.

Keywords:
Pseudomonas aeruginosa; Prophage induction; Bacteriophage infection; Cystic fibrosis; Host range; Type IV pili