Sessile Legionella pneumophila is able to grow on surfaces and generate structured monospecies biofilms

Abstract

Currently, models for studying Legionella pneumophila biofilm formation rely on multi-species biofilms with low reproducibility or on growth in rich medium, where planktonic growth is unavoidable. The present study describes a new medium adapted to the growth of L. pneumophila monospecies biofilms in vitro. A microplate model was used to test several media. After incubation for 6 days in a specific biofilm broth not supporting planktonic growth, biofilms consisted of 5.36 ± 0.40 log (cfu cm⁻²) or 5.34 ± 0.33 log (gu cm⁻²). The adhered population remained stable for up to 3 weeks after initial inoculation. In situ confocal microscope observations revealed a typical biofilm structure, comprising cell clusters ranging up to ∼300 μm in height. This model is adapted to growing monospecies L. pneumophila biofilms that are structurally different from biofilms formed in a rich medium. High reproducibility and the absence of other microbial species make this model useful for studying genes involved in biofilm formation.

Keywords:

• Legionella pneumophila
• biofilm
• sessile growth
• confocal microscopy

Acknowledgements

Sophie Pécastaings is grateful for grants received from the French Association for Thermal Spa Treatments Research (Association Française pour la Recherche Thermale, AFReTh) and the General Council of Les Landes. The authors also express their gratitude to the Regional Council of Midi-Pyrénées and to Genesystems (Bruz, France), for providing a GeneExtract and a GeneDiscCycler device and appropriate reagents for q-PCR analyses. In addition, the authors would like to thank C. Pouzet, Y. Martinez and A. Jauneau from the Microscopy Platform, and the Institut Fédératif de Recherche 40 of CNRS (National Center of Scientific Research) for microscopic analyses.