Funded by: FWF – Austrian Science Fund
Project Nr: P24535-B22
The bacterium Legionella is able to survive and grow in man-made aquatic environments, especially in warm water systems and cooling towers. They can cause severe infection of the lungs, the so called Legionnaire´s disease, and a milder flue like disease Pontiac Fever. In the European Union, about 6000 cases of Legionnaires Disease are notified per year, but it is estimated that the true incidence rate is 10 to 20 × higher.
Their central survival strategy is the intracellular multiplication in environmental protozoa, particularly amoebae. However, legionellae, specifically Legionella pneumophila, can also infect the human lungs and replicate within alveolar macrophages.
The standard detection method of Legionella up to date is cultivation on microbiological media. Under adverse environmental conditions, like chlorine or heat treatment of the water systems, these bacteria can enter a viable but non-culturable (VBNC) state as a survival mechanism and become undetectable by standard methods. There is a lot of evidence, that from the VBNC state, these cells can get resuscitated by replication in amoebae. However, the potential of VBNC legionellae to infect humans was only studied superficially so far.
Therefore, in this project we take a detailed look on the VBNC state of various Legionella species in response to different stressors (nutrient scarcity, heat, disinfectants) in combination with tests for the infectivity in amoeba and macrophages. We want to significantly expand the knowledge on the health relevance of this potentially important life form of Legionella bacteria.
To achieve these aims, we are establishing different procedures to push culturable cells into the VBNC state and monitor them in terms of viability and virulence. Second, we are building up standardized amoeba models and a human macrophage assay to monitor the infectivity of VBNC cells under various conditions. Third, we establish an immuno-magnetic separation method to isolate Legionella populations from environmental samples, including VBNC cells. It is our final aim to use the established infectivity assays also to characterize directly (without cultivation steps) the isolated environmental cells in terms of their health relevance.
Collaborators from our Center:
Julia Walochnik, Institute of Specific Prophylaxis and Tropical Medicine
Regina Sommer, Head of Water Hygiene Unit
Hannes Stockinger, Head of Institute, Head of Center
Anna Repic, PostDoc at the Molecular Immunology Research Unit
Christian Lück, Technical University Dresden, Legionella Reference Center Germany
Alexander Indra, AGES Vienna, Legionella Reference Center Austria
Publications derived from the project:
KIRSCHNER A (2016) Determination of viable legionellae in engineered water systems: Do we find what we are looking for? Water Research, doi: 10.1016/j.watres.2016.02.016
DIETERSDORFER E, CERVERO-ARAGÓ S, SOMMER R, KIRSCHNER AKT, WALOCHNIK J (2016) Optimized methods for L. pneumophila release from its Acanthamoeba hosts. BMC Microbiology, in press
Pictures from the project: Left: Amoeba cell full with L. pneumophila, middle: lysed amoeba cell, only L. pneumophila visible, right: L. pneumophila microcolony