Genomic investigation of Legionella pneumophila

Legionella pneumophila is a waterborne pathogen responsible for outbreaks of Legionnaires' disease. We investigated a facility with recurrent outbreaks over two decades, where a single recombinant strain, ST3043, became dominant. Combining genomic, transcriptomic, and phenotypic approaches, we demonstrate that ST3043 emerged from a horizontal gene transfer event between two co-circulating strains and acquired a 225 kb genomic fragment approximately 25 years ago