A study published online in Genome Research (www.genome.org) describes new insights into Legionella pneumophila, the bacteria responsible for most cases of Legionnaires' disease.
This report investigates the genetic background of L. pneumophila, provides clues to the evolution and emergence of this pathogen, and describes the identification of a worldwide-distributed epidemic clone.
Legionnaire's disease is characterized by severe pneumonia, afflicting the elderly and individuals with weakened immune responses in particular. While L. pneumophila, a genetically diverse species and one of many Legionella species, is common in natural and drinking water supplies, the majority of Legionnaire's disease cases worldwide (approximately 84%) are caused by a single serogroup, L. pneumophila Sg1. Recent work has suggested that even though Sg1 is responsible for most clinical cases, this serogroup accounts for only about 30% of environmental Legionella.
As the prevalence of Sg1 in Legionnaire's disease cases does not appear to be a result of environmental predominance, the frequent occurrence of Sg1 in disease is likely due to higher virulence. In this study, researchers led by Dr. Carmen Buchrieser of the Institut Pasteur conducted a comparative genomics analysis to gain insight into the basis for the higher virulence of Sg1. To compare Sg1 and other Legionella isolates, the researchers constructed DNA-arrays containing genes known to be variable in L. pneumophila strains, including a set of known and potential virulence genes. “We screened the gene content of 217 L. pneumophila strains and 32 other Legionella (non- pneumophila) strains that were isolated from humans and the environment,” describes Buchrieser. “We discovered core virulence- and eukaryotic-like genes are highly conserved, indicating strong selection pressures for their preservation.”