S13: The potential impact of protozoa in Legionella control and monitoring in cooling towers

Cooling towers are structures that recirculate and cool water in air conditioning systems of buildings that include businesses, hospitals, schools and other public venues. The design, operation and environmental conditions of cooling towers appear to affect the growth of biofilm microorganisms, including Legionella.  Amoebae and other protozoa are also present in such structures and have been shown to enhance the growth and virulence of Legionella species. Our previous work has shown that novel Legionella-like pathogens of amoebae are more abundant in cooling towers than in nature. In addition, ciliated protozoa can produce fecal pellets that contain large numbers of concentrated viable Legionella cells, and the pellet form may provide enhanced survival of the pathogens under various environmental stresses.  Therefore, such interactions between protozoa and Legionella species may affect the efficacy of biocides and may alter interpretations of results of routine sampling and monitoring for Legionella. This presentation will highlight protozoan-Legionella interactions and will also discuss potential problems with guidelines for cooling tower treatment and the monitoring of Legionella concentrations in cooling tower water.