Occurrence of Legionella spp. in Water-Main Biofilms from Two Drinking Water Distribution Systems

Michael B. Waak, Timothy M. LaPara, Cynthia Hallé, Raymond M. Hozalski

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


The maintenance of a chlorine or chloramine residual to suppress waterborne pathogens in drinking water distribution systems is common practice in the United States but less common in Europe. In this study, we investigated the occurrence of Bacteria and Legionella spp. in water-main biofilms and tap water from a chloraminated distribution system in the United States and a system in Norway with no residual using real-time quantitative polymerase chain reaction (qPCR). Despite generally higher temperatures and assimilable organic carbon levels in the chloraminated system, total Bacteria and Legionella spp. were significantly lower in water-main biofilms and tap water of that system (p < 0.05). Legionella spp. were not detected in the biofilms of the chloraminated system (0 of 35 samples) but were frequently detected in biofilms from the no-residual system (10 of 23 samples; maximum concentration = 7.8 × 104 gene copies cm-2). This investigation suggests water-main biofilms may serve as a source of Legionella for tap water and premise plumbing systems, and residual chloramine may aid in reducing their abundance.

Original languageEnglish (US)
Pages (from-to)7630-7639
Number of pages10
JournalEnvironmental Science and Technology
Issue number14
StatePublished - Jul 17 2018

Bibliographical note

Funding Information:
We wish to thank the two water utilities involved in this study for providing access to their respective drinking water distribution systems. This work was supported primarily with a grant from the water utility in the United States, which wishes to remain anonymous. Additional financial support for partially covering the cost of laboratory supplies was provided by the water utility in Norway. Collaboration between the University of Minnesota and the Norwegian University of Science and Technology, including travel and lodging between the United States and Norway, was made possible with funding from the Norwegian Center for International Cooperation in Education (grant NNA-2012/10128). Kyle Sandberg and Hanna Temme from the University of Minnesota assisted in collecting tap water samples from Norway in 2014. The University of Minnesota Genomics Center analyzed the 16S rRNA gene amplicons via sequencing. Sequence analysis was possible with resources from the Minnesota Supercomputing Institute.

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