Whole-Genome Sequencing and Comparative Genome Analysis: a pangenome approach to understand population diversity, antimicrobial resistance, and adaptive mechanisms of bacterial pathogens within the water system of large occupational buildings

The emergence and development of next-generation sequencing technologies (NGS) made the reconstruction of environmental bacterial genomes much accessible and opens new perspectives in microbial ecology studies. NGS technology provide information on organism detection, identity, virulence- and antimicrobial-associated genes, and genetic relatedness with a high degree of discrimination within species. Furthermore, this technology has the potential to provide information about the underlying mechanisms involved in microbial persistence in built environments. Enrichments in accessory genes under specific conditions may represent adaptation to the environment. Many waterborne pathogens colonize and persist in building water systems despite disinfection strategies that aim to mitigate their presence. Here we present the pangenome characterization of Legionella pneumophila from hot water lines of adjacent large occupational buildings. L. pneumophila is a Gram-negative bacterium and is the major causative agent of Legionnaires' disease, in which serogroup 1 has been implicated in most cases associated with built environments. Results show that the water system has been colonized by two sequence types (STs) with evidence for spatial structuring of the population throughout locations and within their respective hot water systems, suggesting that the population is influenced by environmental conditions. Genomic analysis confirmed the presence of the lpeAB genes encoding a macrolide efflux pump, which confers reduced sensitivity to azithromycin. Overall, a pangenome approach provide an ecological insight of the microbial population and the potential risk associated with Legionella.