Population Genomics of Legionella longbeachae and Hidden Complexities of Infection Source Attribution.

Rodrigo Bacigalupe,J Ross Fitzgerald,Diane Lindsay,Giles Edwards

doi:10.3201/eid2305.161165

Abstract

Legionella longbeachae is the primary cause of legionellosis in Australasia and Southeast Asia and an emerging pathogen in Europe and the United States; however, our understanding of the population diversity of L. longbeachae from patient and environmental sources is limited. We analyzed the genomes of 64 L. longbeachae isolates, of which 29 were from a cluster of legionellosis cases linked to commercial growing media in Scotland in 2013 and 35 were non–outbreak-associated isolates from Scotland and other countries. We identified extensive genetic diversity across the L. longbeachae species, associated with intraspecies and interspecies gene flow, and a wide geographic distribution of closely related genotypes. Of note, we observed a highly diverse pool of L. longbeachae genotypes within compost samples that precluded the genetic establishment of an infection source. These data represent a view of the genomic diversity of L. longbeachae that will inform strategies for investigating future outbreaks.

Highlights

Legionella longbeachae is the primary cause of legionellosis in Australasia and Southeast Asia and an emerging pathogen in Europe and the United States; our understanding of the population diversity of L. longbeachae from patient and environmental sources is limited
64 of the 70 isolates examined co-segregated within the L. longbeachae–specific clade, 4 isolates clustered with Legionella anisa, and 2 belonged to a separate clade that was distinct from all known Legionella spp. (Figure 1; online Technical Appendix Figures 1, 2)
We provide evidence for extensive recombination and lateral gene transfer among L. longbeachae, including the presence of widely distributed mosaic plasmids that have likely recombined with plasmids from other Legionella spp., suggesting an ecologic overlap or shared habitat

Summary

Introduction

Legionella longbeachae is the primary cause of legionellosis in Australasia and Southeast Asia and an emerging pathogen in Europe and the United States; our understanding of the population diversity of L. longbeachae from patient and environmental sources is limited. We observed a highly diverse pool of L. longbeachae genotypes within compost samples that precluded the genetic establishment of an infection source These data represent a view of the genomic diversity of L. longbeachae that will inform strategies for investigating future outbreaks. To examine the etiology of the 2013 cluster of legionellosis cases in Scotland in the context of L. longbeachae species diversity, we analyzed the genomes of 70 Legionella spp. isolates from 4 countries over 18 years

Methods

Results

Conclusion