Isolation and characterisation of bacteriophages infecting Legionella spp.
Legionella spp. are waterborne pathogens that can cause Legionnaires' disease, a potentially fatal acute pneumonia. These pathogens can be resistant to many disinfectants and thermal treatments. Furthermore, detection of Legionella spp. is often difficult. Thus, infections with these organisms can be difficult to both diagnose and treat. Bacteriophages are a potential tool to be exploited to aid in the elimination and detection of Legionella spp. in both the environment and in patients, with bacteriophage based diagnostics and therapeutics already successfully developed for many organisms. However, little is known about the bacteriophages capable of infecting Legionella spp. Thus, with little knowledge available in the literature, the aim of this study was to obtain more information on Legionella spp. bacteriophages using both experimental and bioinformatic approaches. Here, a diverse range of Legionella spp. were collected either through isolation from 262 water and soil samples from natural reservoirs and man-made systems, or obtained from Public Health England. These strains were then characterised, used to isolate bacteriophages from the same 262 samples, and were exposed to prophage-inducing agents to isolate bacteriophages directly from the bacteria themselves. While no bacteriophages were isolated from the samples, virus-like particles were observed following induction of Legionella spp. These particles were not like any currently identified bacteriophages, and warrant further investigation to confirm they are in fact bacteriophages. A bioinformatic approach was conducted in parallel to these investigations. Using this approach, a total of 717 Legionella spp. genomes in the GenBank database were screened for the presence of prophage-like regions. Although putative complete prophage elements were identified in the Legionella spp. genomes, further investigation concluded that these were due to fX-174 contamination that had not been removed by the submitting group before adding their genomes to GenBank. Other elements were discovered, but with little core recognisable bacteriophage genes. These results show that much more fundamental knowledge remains to be understood about Legionella spp. bacteriophages before extensive work is carried with the aim of developing bacteriophage diagnostics and therapeutics for Legionella spp. infections.