Strain-Level Characterization of Legionella Environmental Isolates via MALDI-TOF-MS

As a waterborne pathogen of increasing concern, techniques for cost-effective and rapid characterization of Legionella are vital. This study examines the development of a Matrix Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF-MS) analysis methodology for this microbe. First, optimal sample preparation methods for the analysis of environmental Legionella isolates via MALDI-TOF-MS were determined. These methods were then implemented to perform strain-level characterization of environmental Legionella isolates from central Arizona. Results demonstrate that a MALDI-TOF-MS method involving BCYE agar-based culturing and protein extraction-based sample preparation yield high-quality mass spectra. Twenty-eight environmental Legionella isolates originating from two separate drinking water distribution systems were analyzed. Multiple species were detected, and strain-level characterization was achieved, with 12 unique strains distinguished. In addition, isolates of L. pneumophila, the most common species observed in the study, were correctly assigned to specific sampling sites. These results demonstrate the potential for this technique to be applied for sub-species characterization of Legionella with significant benefits over established methodologies.