Detection of highly macrolide-resistant Legionella pneumophila strains from a hotel water network using systematic whole-genome sequencing

Objectives Implementation of an antibiotic resistance detection tool in Legionella daily surveillance at the French National Reference Centre for Legionella. Methods Systematic WGS of Legionella pneumophila isolates and bioinformatics detection of specific mutations linked to antibiotic resistance. Phenotypic validation of antibiotic resistance detected by WGS was performed by the broth microdilution method. Results More than 3000 L. pneumophila strains were screened for antibiotic resistance. A macrolide resistance-associated A2052G mutation in the 23S rRNA gene was identified in the genome of eight isolates from a hotel water network. High-level macrolide resistance (i.e. MICs of 1024-2048 mg/L for azithromycin and erythromycin) with no cross-resistance to other antimicrobials was phenotypically confirmed by antimicrobial susceptibility testing for the eight isolates. Conclusions Systematic WGS of L. pneumophila is a powerful tool for first-line high-throughput screening of antibiotic resistance before phenotypic validation.