Event Contact

Speaker Information

Dr. Mary Jo Kirisits
Professor, University of Texas at Austin
Department of Civil, Architectural, and Environmental Engineering

Title: Particle-associated and planktonic Legionella spp. at the tap  

Abstract: The Legionella genus houses several opportunistic pathogens that cause legionellosis.  Legionella pneumophila (Lp), the leading observed cause of legionellosis, persists in drinking water distribution systems (DWDSs) and building plumbing systems due to factors such as intrinsic disinfectant resistance and shielding by biofilms and free-living amoebae. However, the extent to which Lp and other Legionella spp. in drinking water occur in the planktonic phase versus associating with free-living amoebae or particles is unclear. In this study, we quantified planktonic and particle-associated Lp and Legionella spp. in first-draw and flushed drinking water samples from taps at 19 sites across the U.S. and across three seasons. Planktonic and particle-associated microorganisms were size fractionated via membrane filtration, and Legionella spp. and Lp were quantified by digital polymerase chain reaction. Additionally, amplicon sequencing targeting the Legionella genus was used to explore the diversity of Legionella spp. at each site. The concentration of planktonic Legionella spp. was significantly higher than that of particle-associated Legionella spp. (p<0.001) in paired samples at each site, and significantly higher concentrations of total Legionella spp. were found in surface water than in groundwater systems (p=0.020). Lp detection was geographically and temporally sporadic, with detections occurring at seven sites. Sequencing results showed that the site strongly influenced the specific Legionella spp. present. These results emphasize the influence of source water type and site on Legionella spp. in DWDSs and building plumbing. Further, this study suggests that consumers are more frequently exposed to planktonic than to particle-associated Legionella spp. at the tap. 

Bio: Mary Jo Kirisits is the Stanley P. Finch Centennial Professor in Engineering in the Environmental and Water Resources Engineering program at The University of Texas (UT) at Austin.  She completed her BS degree in Civil Engineering at the State University of New York at Buffalo and her MS and PhD degrees in Environmental Engineering at the University of Illinois at Urbana-Champaign.  After concluding a postdoctoral appointment at Northwestern University in the Department of Civil and Environmental Engineering, she joined the faculty at UT.  Her research interests include drinking-water biofiltration, opportunistic human pathogens, SARS-CoV-2 in wastewater, and the impact of nanomaterials on antimicrobial resistance in bacteria.  She currently is leading a multi-institution project funded by the U.S. EPA on opportunistic pathogens and disinfection by-products in drinking water distribution systems.