Title : Antibiotic resistance and transcriptomic profiling of legionella pneumophila in drinking water
Abstract:
Legionella pneumophila persists in engineered water systems and is the causative agent of Legionnaires’ disease. Despite its clinical importance, little is known about whether environmental populations are undergoing gradual changes in their antimicrobial susceptibility. We compared isolates collected in 2013-2014 with those obtained in 2024-2025 from the same sites in a drinking water distribution system in northern Israel. The analysis showed both temporal and spatial variation: Ciprofloxacin activity remained relatively stable, whereas levofloxacin exhibited a broader MIC range among recent isolates, suggesting increased variability and the presence of less susceptible subpopulations. Tigecycline showed consistently higher MIC values in the 2025 collection, indicating at a significance rise in resistance. Among macrolides, azithromycin maintained moderate activity, while erythromycin stood out as the most active agent, with uniformly low MIC values across all isolates. Moreover, isolates recovered from nearby sites within the same distribution system exhibited significantly different susceptibility profiles, reflecting the influence of local environmental conditions.
Transcriptomic RNASeq analysis detected 311 differentially expressed genes between the historic and contemporary strains, indicating a significant change in gene expression patterns related to stress response, membrane transport, and efflux mechanisms that may drive the observed shifts in antibiotic susceptibility.
These findings emphasize that L. pneumophila susceptibility is not static as was previously assumed but is likely shaped by ecological and temporal factors. The study underscores the importance of long-term environmental surveillance to track the evolution of this pathogen and provides new insights into how micro-scale dynamics within water systems can influence antimicrobial susceptibility patterns.
