A work from the Institute of Integrative Biology of Systems (I2SysBio) –a mixed center of the Higher Council for Scientific Research (CSIC) and the University of Valencia (UV)–, in collaboration with the Carlos III Health Institute (ISCIII), has described for the first time how the water network of a building can generate and sustain new variants of the bacterium 'Legionella pneumophila', endowed with a greater ability to persist in the environment and with a higher potential for human infection.
The research, whose results have been published in the journal 'Water Research', reinforces the role of water infrastructures as active scenarios in the evolution of pathogens of importance for public health.
The study focuses on a singular episode of chronic contamination, maintained for about 20 years in the water distribution system of a residential facility. Despite the continued application of usual control strategies, such as hyperchlorination and thermal shocks, along with other intensive actions on the facility itself, the bacterium managed to remain in the circuit.
The variant detected in this network is a new recombinant form, identified by the scientific team, which accounted for more than 80% of the bacterial population present in the system and was the only one found in the disease cases linked to that building.
Through the combination of genomic surveillance, comparative genomics, cellular infection models, and three-dimensional biofilm analysis, the researchers reconstructed the evolutionary process of this variant. The phylogenetic study indicates that the new variant –resulting from the mixing of other pre-existing variants– emerged coinciding with the commissioning of the building, suggesting that the selection and consolidation of this evolutionary line occurred within the water infrastructure of the residential complex.
"Unlike the original variants, which remained confined to minority niches, the new variant showed marked differences, both in its ability to disperse through water - it is more dispersive and less adherent - and in its ability to infect in the laboratory, reproducing more," explains Mireia Coscollá, a researcher at I2SysBio and one of the authors of the article.
"This combination of environmental persistence, efficient dispersion, and greater infection capacity could explain its predominance among clinical isolates linked to the facility," he adds.
Fernando González Camacho, researcher at ISCIII in the National Center for Microbiology, emphasizes that this is a work that integrates two decades of real epidemiological surveillance with tools of genomics, transcriptomics, biofilm modeling, and cellular infection assays.
"We have found a strain that is exclusive to this facility that, through a recombination process, has acquired new capabilities that allow it to persist, redesigns the architecture of the biofilm -the biological layer of the pipes-, creating a three-dimensional matrix that functions as a continuous 'launcher' of bacteria that contaminate the water and can put people at risk," he points out.
Water Infrastructure and Public Health
The authors of the study point out that these findings demonstrate that water systems do not act only as passive reservoirs of Legionella, but as dynamic ecosystems in which environmental pressure, prolonged permanence, and genetic recombination facilitate the emergence of variants better adapted to local conditions.
This process, in which environmental, microbiological, and human exposure factors converge, reinforces the relevance of One Health approaches, by integrating environmental health, human health, and infrastructure management to anticipate risks, optimize water safety plans, and protect the most vulnerable groups.
The research team emphasizes the convenience of implementing long-term genomic surveillance programs in the water systems of buildings, complemented by phenotypic analyses. The combination of these methodologies would allow for the early identification of the emergence of new variants before they compromise control strategies, facility safety, or public health.