Novel Burkholderia -Targeting Lytic Phage Rocko Preferentially Kills Stationary Phase Bacterial Cells

Abstract

Introduction:

Burkholderia cepacia complex (BCC) infections pose a significant risk to people with cystic fibrosis and can result in high mortality rates. High levels of antimicrobial resistance within the BCC have increased interest in using bacteriophages (phages) as alternative therapeutics. However, most currently available BCC-targeting phages are temperate or lysogeny-capable, limiting their therapeutic use.

Methods:

To expand the pool of lytic Burkholderia phages, a phage targeting Burkholderia cenocepacia isolated from lake water was characterised by genome sequencing, electron microscopy, host range analysis, and bacterial killing assays performed at different temperatures.

Results:

The phage, designated as Burkholderia phage vB_BceS_Rocko (φRocko), possessed a 47 kb dsDNA circularly permuted genome and siphovirus morphology. At 37°C, antibacterial activity was modest and limited to actively growing bacterial cells. However, at higher phage densities and reduced temperatures (27°C and 30°C), pronounced bacterial killing was observed, particularly against stationary-phase cells. φRocko also exhibited activity against three additional BCC species, including both clinical and environmental isolates. Turbid plaques were produced by φRocko at cooler temperatures (23°C and 30°C), whereas plaques were largely absent at 37°C. Despite this, no lysogenic activity was detected at any temperature, suggesting that plaque morphology was not associated with lysogeny.

Conclusion:

The discovery of this novel phage adds another option to the limited arsenal of lytic phages active against BCC. Notably, φRocko’s ability to target stationary-phase bacteria may prove useful for therapeutic applications.