A group of French researchers have sequenced the genome of two strains of the bacterium that causes Legionnaires' disease. The work, to be published in the November issue of Nature Genetics compares both the Paris and the Lens strain. The Paris strain is the only known endemic strain so far, accounting for 12.7% of cases of Legionnaires' disease in France and 33% of those in Paris. In contrast, the Lens strain caused an outbreak between November 2003 to January 2004, resulting in 17 deaths in northern France. With the two strains reacting in such different ways, it would suggest that the Lens strain is potentially more virulent in humans.
Legionnaires' disease is the most common cause of atypical pneumonia in hospitalised patients. It is contracted by around 8,000-18,000 people every year in the US and can be fatal if untreated by antibiotics. Genome sequences like this highlight potential targets for new drugs to more effectively combat the pathogen.
Legionella pneumophila lives in freshwater environments and man-made water systems such as air-conditioning units. It is responsible for over 90% of clinical cases of Legionnaires' disease and strikingly, up to 84% of these cases are caused by L. pneumophila serogroup 1, the group from which both the Paris and the Lens strain originate. Carmen Buchrieser and colleagues found that the two genome sequences were very different and that this degree of flexibility may help explain how it can adapt to survive in both aquatic environments and such hostile environments as the human immune system.
The comparison of an endemic and an epidemic strain might provide clues to the particular adaptability and stability of the Paris strain and other strains like it.
Carmen Buchrieser (Pasteur Institute, Paris, France)
Tel: +33 1 45 68 83 72,
Also available online.
(C) Nature Genetics press release.
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