Particle-associated and free-living Legionella spp. in drinking water

Area of Science:

• Environmental microbiology
• Waterborne pathogens
• Public health

Background:

• Legionella species are opportunistic pathogens causing legionellosis, including Legionnaires' disease.
• Legionella pneumophila (Lp) persists in drinking water distribution systems (DWDSs) due to resistance and protection by biofilms/amoebae.
• Understanding Legionella's association with particles versus free-living states is critical for effective remediation.

Purpose of the Study:

• To quantify free-living versus particle-associated Legionella species and Lp in drinking water.
• To investigate the influence of water source type and sampling site on Legionella presence and diversity.

Main Methods:

• Citizen scientists collected first-draw and flushed drinking water samples across the U.S. over three seasons.
• Microorganisms were size-fractionated using membrane filtration.
• Legionella quantification was performed using digital PCR, and diversity was assessed via amplicon sequencing.

Main Results:

• Free-living Legionella spp. were significantly more concentrated than particle-associated Legionella spp. (p=2.86×10^-9).
• Surface water systems had significantly higher total Legionella spp. concentrations than groundwater systems (p=0.020).
• Legionella pneumophila detection was sporadic; site strongly influenced Legionella species diversity.

Conclusions:

• Source water type and site are significant factors influencing Legionella spp. in DWDSs and plumbing.
• Consumers are more likely exposed to free-living Legionella spp. than particle-associated forms in tap water.
• Findings inform strategies for managing Legionella risks in drinking water systems.