Variation of Legionella spp. with Lake Depth and Season in Two Norwegian Drinking Water Sources

Abstract

In Norway, placement of the water treatment plant intake within the lake hypolimnion is considered a hygienic barrier against pathogens of fecal origin. It is unclear, however, whether this practice provides a barrier against opportunistic pathogens such as Legionella. In this study, water samples were collected at 10 m depth intervals near the drinking water intakes of two lakes. Legionella and one of their common hosts, Acanthamoeba spp., were quantified using culture-based assays (Legionella pneumophila only) and real-time quantitative PCR (qPCR). L. pneumophila and Acanthamoeba spp. were never detected by qPCR; Legionella spp., however, were present in all samples at concentrations ranging from 2.33 to 4.14 log10[copies/L] in lake A and from 2.69 to 4.27 log10[copies/L] in lake B. For most sampling months in both lakes, there was no significant difference between total bacteria and Legionella spp. concentrations at the intake depth versus those on the lake surface. The results of this limited investigation of two Norwegian water supplies suggest that placement of water treatment plant intakes within the hypolimnion may not afford a sufficient hygienic barrier against Legionella.

The benefits of flushing for mitigating Legionella spp. in non-chlorinated building plumbing systems

“…However, no seasonal variation in the Legionella concentration in the cold water supply was observed in this study. These results align with our previous study of Legionella in the water intakes to the treatment plants feeding our pilot system (Meegoda et al, 2022). Furthermore, the Legionella concentration range in this study matches well with a previous study by Wullings and van der Kooij (2006), which is also from a distribution system without residual disinfection.…”

“…The increase in the concentration of Legionella in the water distribution system could be due to detachment from biofilms (Waak et al, 2018) or to Legionella growth. In contrast, the total bacterial concentration at the pilot inlet was, on average, 0.53 log 10 [copies/L] less than that at the water intake (Meegoda et al, 2022). Thus, the relative abundance of Legionella increased from 0.001% (at the intake) to 0.05% (at the pilot inlet) of the total biomass in the distribution system.…”

“…Negative control filters were prepared by filtering 1 L of autoclaved MilliQ water or 100 mL of eluting solution (for biofilm samples). DNA was extracted and preserved using ZymoBIOMICS DNA Miniprep kit (Zymo Research) as described in Meegoda et al (2022).…”

“…Marker genes were targeted by qPCR to quantify total bacteria (16S rRNA gene), genus Legionella (ssrA), L. pneumophila (mip), and V. vermiformis (18S rRNA gene) using reaction conditions and amplification protocols described previously (Meegoda et al, 2022) and summarized in Supplementary Table 2. Reference targets (Supplementary Table 3) used for standard curves were synthesized as gBlocks TM gene fragments (Integrated DNA Technologies, Inc.;…”

Protozoan-Priming and Magnesium Conditioning Enhance Legionella pneumophila Dissemination and Monochloramine Resistance

“…Public health concerns associated with opportunistic pathogens (OPs) in engineered water systems are increasing in the developed world. − Ubiquitous in soils, groundwater, and surface waters, many OPs also colonize biofilms in drinking water distribution and building water systems, ultimately leading to human exposure and possible infection. − Several species of Legionella are OPs of interest. Most notable is Legionella pneumophila ( Lp ), which is responsible for over 90% of reported Legionnaires’ disease cases, , although there is increasing interest in other species such as Legionella bozemanii, Legionella longbeachae, and Legionella anisa. , Lp has been found commonly in drinking water from cold-water and hot-water taps across the U.S .…”