199556 Role of Amoeba in Legionella pathogenicity and Potential Impacts on Public Water Systems

Wednesday, November 11, 2009

Helen Lau, PhD , Office of Research and Development/National Exposure Research Laboratory, US Environmental Protection Agency, Cincinnati, OH
Nicholas J. Ashbolt, PhD , Office of Research and Development/National Exposure Research Laboratory, US Environmental Protection Agency, Cincinnati, OH
Since legionellosis became a reported disease in 2001, Legionella is now the most commonly identified agent causing waterborne disease outbreaks in the US. Although Legionella spp. are natural freshwater inhabitants, it is the propagation of certain strains within biofilms, more specifically within protozoan species inhabiting biofilms of buildings and municipal water distribution systems that could account for its ability to cause disease. The purpose of this study was to investigate Legionella growth within amoebae and potential virulence of various environmental and clinical isolates. Virulence was assessed by determining Legionella lung clearance in A/J mice and by growth in Acanthamoeba polyphaga and in a murine and human macrophage-like cell lines, J774 and THP-1, respectively. The L. pneumophila clinical isolate displayed delayed clearance from lungs compared to the L. longbeacheae clinical isolate, and proliferated in J774 and THP-1 cells whereas L. longbeacheae did not. Additionally, both clinical strains multiplied in the presence of A. polyphaga. However, an environmental isolate of L. dumoffii was unable to proliferate in the presence of A. polyphaga, J774 and THP-1 cells and was rapidly cleared from the lungs of infected mice. These preliminary results suggest the ability to grow within amoebae can be used as a screening tool for potentially pathogenic Legionella strains, since both clinical isolates and not L. dumoffii in this study, grew in the presence of A. polyphaga. This study underscores the need to understand the role protozoa and biofilms play in selecting, propagating and releasing opportunistic pathogens into drinking and non-potable irrigation waters.

Learning Objectives:
1. Evaluate various virulence assays for Legionella isolates to determine potential pathogenicity to humans 2. Identify any correlation between amoeba growth and Legionella virulence in water systems 3. Explain the need to understand biofilm ecology as well as Legionella diversity and numbers in order to protect public health from pathogens that can grow post water treatment and in the presence of chlorine disinfectants

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: I am a research microbiologist with the US EPA investigation the relationship between amoeba and Legionella pathogenicity. I obtained my PhD degree from the University of Michigan in 2007 and since then have conducted post-doctoral research in the area mentioned in my abstract. I have also written a review manuscript in this subject area that has been accepted for publication in the Journal of Applied Microbiology.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.