Whole-Genome Mapping as a Novel High-Resolution Typing Tool for Legionella pneumophila

Abstract

Legionellais the causative agent for Legionnaires' disease (LD) and is responsible for several large outbreaks in the world. More than 90% of LD cases are caused byLegionella pneumophila, and studies on the origin and transmission routes of this pathogen rely on adequate molecular characterization of isolates. Current typing ofL. pneumophilamainly depends on sequence-based typing (SBT). However, studies have shown that in some outbreak situations, SBT does not have sufficient discriminatory power to distinguish between related and nonrelatedL. pneumophilaisolates. In this study, we used a novel high-resolution typing technique, called whole-genome mapping (WGM), to differentiate between epidemiologically related and nonrelatedL. pneumophilaisolates. Assessment of the method by various validation experiments showed highly reproducible results, and WGM was able to confirm two well-documented DutchL. pneumophilaoutbreaks. Comparison of whole-genome maps of the two outbreaks together with WGMs of epidemiologically nonrelatedL. pneumophilaisolates showed major differences between the maps, and WGM yielded a higher discriminatory power than SBT. In conclusion, WGM can be a valuable alternative to perform outbreak investigations ofL. pneumophilain real time since the turnaround time from culture to comparison of theL. pneumophilamaps is less than 24 h.