Free-living amoebae and their associated bacteria in Austrian cooling towers: a 1-year routine screening

Area of Science:

• Environmental microbiology
• Public health microbiology

Background:

• Free-living amoebae (FLA) are ubiquitous environmental microorganisms.
• FLA can host bacterial pathogens like Legionella pneumophila, enhancing their infectivity.
• Cooling towers are known reservoirs for Legionella and sources of Legionnaires' disease outbreaks.

Purpose of the Study:

• To develop and implement a screening system for host amoebae in routine Legionella monitoring.
• To assess the prevalence of FLA and Legionella in cooling tower systems.
• To evaluate the impact of organic burden on Legionella screening methods.

Main Methods:

• Development of a real-time PCR-based screening system for FLA groups.
• Parallel screening of three cooling towers over one year for FLA and Legionella using culture and molecular methods.
• Assessment of sample suitability for standard Legionella screening based on organic load.

Main Results:

• 83.3% of cooling tower samples tested positive for FLA, with Acanthamoeba being the dominant genus.
• 69.7% of samples were unsuitable for standard Legionella screening due to high organic content.
• Legionella spp. were detected in 25% of samples by culture and 50% by molecular methods; intracellular bacteria were observed in amoebal isolates.

Conclusions:

• Integrating FLA screening into routine Legionella monitoring is crucial for understanding pathogen transmission in cooling towers.
• FLA are prevalent in cooling towers and can impact the effectiveness of standard Legionella detection methods.
• A novel PCR-based FLA screening system offers a valuable tool for environmental surveillance.