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Projekt Druckansicht

Analyse der Ökologie und Virulenz von Legionella spp. Populationen von Süßwassersystemen in Deutschland, Palästina und Israel - Phase 2

Fachliche Zuordnung Hydrogeologie, Hydrologie, Limnologie, Siedlungswasserwirtschaft, Wasserchemie, Integrierte Wasserressourcen-Bewirtschaftung
Mikrobielle Ökologie und Angewandte Mikrobiologie
Förderung Förderung von 2011 bis 2018
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 202422244
 
Erstellungsjahr 2018

Zusammenfassung der Projektergebnisse

The overall objective of this project was to advance current knowledge on the ecology of Legionella populations in man-made freshwater systems, the environmental factors affecting their occurrence, virulence potential and infectivity and to understand their transmission to humans. The overall research strategy to achieve this objective was to sample bacteria from Drinking Water Supply Systems (DWSS) in the three countries from relevant habitats, i. e. bulk water and biofilm of the surfaces of the DWSS. In parallel, clinical material (sputum and BAL) was obtained from the same geographical areas. Both types of samples were subjected to molecular and conventional microbiological analyses to determine the abundances of Legionella species with emphasis on L. pneumophila and its clonal structure. The DWSS of the city of Braunschweig, Germany, was analysed for its Legionella species composition. These analyses comprised the whole supply chain including raw water, treatment process and large-scale storage, and a seasonal study of finished drinking water sampled monthly from cold and hot tap water. Treatment of raw water had a major impact on Legionella species by reducing their diversity and abundances. During the seasonal cycle L. pneumophila was only observed at low relative abundances (<1%) in cold tap water. The first surprise was that in hot drinking water (50°C to 58°C) L. pneumophila was present during all seasons at high relative abundances (8% to 40%). This thermophilic Legionella community, including L. pneumophila, was able to grow in the hot water above 50°C. Such thermophilic Legionella populations are of general relevance for drinking water management and public health. For an understanding of the environmental factors, other than temperature, the abundances of L. pneumophila were compared with a set of chemical parameters determined in parallel for the related bulk water. Correlation analyses with these parameters indicated a decrease of L. pneumophila abundance for water and biofilm with increasing magnesium concentrations above 30 mg/l, most relevant in Palestine. From studies across the three countries, it could be concluded that different environmental factors influenced the abundances of Legionella species and genotypes of L. pneumophila due to the specific conditions and the differences of the DWSS. Detailed molecular analyses of the occurrence of specific genotypes of L. pneumophila indicated that a specific genotype cooccurred with high Legionella counts determined by conventional plate counts on agar medium. This finding pointed towards the need for high-resolution molecular analyses able to identify individual clones of L. pneumophila in DWSS. To this end, advanced molecular methods, such as genus(Legionella)-specific Next Generation Sequencing (NGS) and Nested PCR Sequence-Based Typing (NPSBT), were developed and applied to DNA obtained from environmental and clinical samples. These advanced molecular approaches enabled us to understand the relationship between Legionella infections and the environment by the analysis of clinical samples from pneumonia patients in comparison with related samples or isolates from the environment. Here, sputum from patients in Israel and Palestine were compared with the respective environmental material. The sputum samples that were Legionella-positive were inhabited by aquatic bacteria that have been observed in association with amoeba, indicating that amoeba might have transferred Legionella from the drinking water together with its bacterial microbiome. This was the second surprise in our project to demonstrate the co-occurrence of major bacterial commensals and pathogens in sputum with respect to the presence of Legionella. These observations lead to the hypothesis that Legionella infections are supported by co-infections with other potentially pathogenic bacteria co-transferred by the amoeba. The molecular findings were complemented by experimental studies of the virulence of relevant isolates indicating that the pathogenicity is clone dependent. Our findings and the developed high-resolution molecular diagnostic methodologies provide new surveillance tools for Legionella infections and can help improve the management of DWSS in the three countries. The International publications and press releases by the HZI solicited a substantial response in the German media and guaranteed the dissemination of the project’s results to the informed and general public.

Projektbezogene Publikationen (Auswahl)

 
 

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