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Molecular diversity and high virulence of Legionella pneumophila strains isolated from biofilms developed within a warm spring of a thermal spa

Zineddine Chaabna1, Françoise Forey2, Monique Reyrolle2, Sophie Jarraud23, Danièle Atlan4, Dominique Fontvieille1 and Christophe Gilbert4*

Author affiliations

1 UMR CARRTEL, Université de Savoie-INRA, Le Bourget du Lac, F-73376, France

2 Centre de Biologie et Pathologie Est, Centre National de Référence des Légionelles, Bron, F-69677, France

3 Université Lyon, INSERM U851, Université Lyon 1, Lyon, F-69008, France

4 Université de Lyon, CNRS UMR 5240, Université Lyon1, Villeurbanne, F-69622, France

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Citation and License

BMC Microbiology 2013, 13:17  doi:10.1186/1471-2180-13-17

Published: 28 January 2013



Several cases of legionellosis have been diagnosed in the same French thermal spa in 1986, 1994 and 1997. L. pneumophila serogroup 1 (Lp1) strains have been isolated from several patients, but the source of contamination was not identified despite the presence of different Lp1 in water samples of the three natural springs feeding the spa at this period.


Our strategy was to investigate L. pneumophila (Lp) strains from natural biofilms developed in a sulphur-rich warm spring of this contaminated site. Biofilm analysis revealed the presence of three Lp serogroups (Lp1, Lp10 and Lp12). Surprisingly, Lp10 and Lp12 were not reported in the previous described studies from water samples. Besides, the new seven Lp1 we isolated exhibit a high molecular diversity and have been differentiated in five classes according to their DNA genome patterns obtained by PFGE and mip sequences. It must be noted that these DNA patterns are original and unknown in databases. Interestingly, the 27 Lp environmental strains we isolated display a higher cytotoxicity and virulence towards the amoeba Acanthamoeba castellanii than those of known Lp1 epidemic strains.


The characteristics of Legionella pneumophila Lp1 strains isolated from the warm spring are in agreement with their presence in biofilms and their probable long-term persistence in this ecosystem.

Legionella pneumophila; Biofilms; Warm spring; Biodiversity; Virulence