The objective is to determine if the relationship between Legionella and its amoeboid host is one of necessity or more opportunistic in nature.

- Is there a correlation between the presence of amoeba and Legionella spp. in water samples?

- Is the LIVE/DEAD® stain suitable for determining the presence of and quantify live and dead amoeba from water samples?

- Is the presence of amoeba is correlated with the type of disinfectant used in water systems?

Shivi Selvaratnam, Ph.D.

Legionella is an Opportunistic Waterborne Pathogen that exists as a free-living organism and an intracellular parasite in which several amoeba species serve as the host organism.  Often the life cycle of Legionella is portrayed as dependent upon the existence of an amoeboid host which is present in a complex biofilm community. Whether this host-parasite relationship is a necessary or an opportunistic relationship is not well understood. In this paper, we examine potable and non-potable (cooling tower water) water systems for the presence of Legionella spp. and amoeba. We use conventional culture techniques to determine the presence of and quantify Legionella spp. and a LIVE/DEAD® stain to determine the presence of and quantify live and dead amoeba. The LIVE/DEAD stain uses the dyes Syto 9® and propidium iodide to render viable amoeba green and dead amoeba red respectively using epifluorescence microscopy. This technique has been used on other eukaryotic cells but not on amoeba. Data was analyzed to determine if (1) a correlation exists between the presence of amoeba and Legionella spp. and (2) the presence of amoeba is correlated with the type of disinfectant used. Data from an in vitro evaluation of conventional oxidizing biocides will also be presented.

Shivi Selvaratnam joined Weas Engineering in 2016 as the Senior Microbiologist and currently serves as the Director of the Chemistry and Microbiology Labs. Shivi graduated with a Ph.D. in microbiology from Drexel University, PA and subsequently completed her post-doctorate at the University of Notre Dame, IN.  She worked in academia for seven years as an Assistant Professor of Biology where she taught courses in microbiology and conducted research on the effects of pollutants on microbial communities in freshwater ecosystems.  Prior to joining Weas Engineering, Shivi worked as a Technical Environmental Specialist at the Indiana Department of Environmental Management.  Dr. Selvaratnam is the author of numerous publications, invited presentations, and research grants.