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

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.publishedVersio

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

Flushing is a common corrective action recommended by Legionella management guidelines to remove stagnant water and replenish disinfectant. Due to water age and different local regulations, buildings may receive water with low or no residual disinfectant. In such situations, the evidence for flushing efficacy is often anecdotal, and the benefits are poorly quantified. Using a pilot-scale premise plumbing system, flushed shower outlets were evaluated against non-flushed outlets during simulated periods of both active and low water demand. Water and biofilm concentrations of total bacteria, Legionella spp., and Vermamoeba vermiformis were quantified using real-time quantitative PCR. Even after all outlets returned to active water demand, flushed shower outlets continued to have lower quantities of Legionella compared to non-flushed outlets for several days, but the decrease was of little practical benefit (<0.5 log10[copies/L]). During prolonged periods of low water demand, however, there was no apparent benefit to flushing. Total bacteria grew to stationary phase within 3 ± 1 days, while Legionella spp. took 12 ± 6 days, regardless of whether the pipes had recently been flushed or not. Flushing with hot or cold water had little to no effect on the concentrations of total bacteria and Legionella in pipe wall biofilms. Flushing with cold water (9.6 and 13.2°C) decreased total bacteria concentrations in the water by 0.96 and 1.00 log10[copies/L], respectively and by 1.27 and 1.74 log10[copies/L] with hot water (49 and 60°C, respectively) but the difference in Legionella spp. concentrations between flushing with cold (1.55 log10[copies/L] for both) and hot water (1.32 to 1.88 log10[copies/L], respectively) was negligible. This suggests that hot water flushing, even at 60°C, provides little or no added benefit for managing Legionella in non-chlorinated building plumbing systems versus cold water flushing. Finally, the immediate benefits of flushing in terms of reductions in total bacteria and Legionella in the water were comparable as well as the rates at which those populations recovered during post-flush or post-shower stagnation

Biofilm Cohesive Strength as a Basis for Biofilm Recalcitrance: Are Bacterial Biofilms Overdesigned?

Bacterial biofilms are highly resistant to common antibacterial treatments, and several physiological explanations have been offered to explain the recalcitrant nature of bacterial biofilms. Herein, a biophysical aspect of biofilm recalcitrance is being reported on. While engineering structures are often overdesigned with a factor of safety (FOS) usually under 10, experimental measurements of biofilm cohesive strength suggest that the FOS is on the order of thousands. In other words, bacterial biofilms appear to be designed to withstand extreme forces rather than typical or average loads. In scenarios requiring the removal or control of unwanted biofilms, this emphasizes the importance of considering strategies for structurally weakening the biofilms in conjunction with bacterial inactivation

Combined UMN-MPCA 2014-2017 lake data on Secchi depth, CDOM, Chlorophyll and total suspended solids

The data are in an Excel spreadsheet with rows representing data for a given lake collected on a specific date. Columns provide lake name or unique lake identifier, sampling date, aquatic ecoregion for the lake, results for CDOM (a440), chlorophyll, Secchi depth, and total suspended solids concentrations, and logarithms of the values for the four water quality variables.This file contains approximately 1460 records on four water quality variables measured on near-surface water samples of lakes in Minnesota (primarily) and also in Wisconsin and Michigan collected by our research group from 2014 to 2017 and similar data collected by the Minnesota Pollution Control Agency in its annual lake water quality assessment program from 2015 to 2017. The variables are Secchi depth (SD), colored dissolved organic matter (CDOM) measured as the Napierian light absorption coefficient at 440 nm, chlorophyll-a, and total suspended solids concentrations. The database was used for a published paper to analyze the effects of CDOM on SD and show that high CDOM levels limit light penetration and thus SD in colored lakes.National Science Foundation, Legislative-Citizen Commission on Minnesota Resources, University of Minnesot

Effect of dissolved iron on CDOM and other optical properties for dissolved organic matter in lakes and rivers of the Upper Great Lakes states

Three data files are included. The first contains the 2014-2016 field and lab data for 450 sets of measurements on 280 lakes across the NLF, NCHF and NMW ecoregions in Minnesota, Wisconsin, and Michigan. In addition to site names, location information (latitude/longitude), ecoregion, and sampling date, the file contains data on Secchi depth, CDOM measured as a(440), DOC, dissolved iron, chlorophyll-a, specific UV absorbance at 254 nm, SUVA(254), and spectral slopes. The second contains data on concentrations of total, dissolved and particulate iron fractions in 2018 samples from 19 high-CDOM sites (lakes and rivers) in the NLF ecoregion of northern Minnesota plus vertical profile information on a(440), dissolved iron, light penetration, and basic limnological parameters in three NLF lakes with widely varying a(440) levels. The third file contains a(440) and dissolved iron concentrations for six lakes from a laboratory experiment in which known amounts of dissolved iron were added to water samples from six water bodies with a wide range of a(440) levels plus additional spectral absorbance information from the samples.These files contain the raw field and lab data collected during sampling of lakes and a few rivers in 2014-2016 to evaluate the importance of dissolved iron concentrations in affecting apparent levels of colored dissolved organic matter (CDOM), as measured spectrophotometrically by light absorption coefficient at 440 nm, a(440), with additional sampling in 2018 for more specific purposes. Approximately 450 sets of measurements were made on 280 lakes/rivers during the field seasons of 2014-2016, with most of the sampling in two ecoregions of Minnesota -- the Northern Lakes and Forests (NLF) and the North Central Hardwood Forests (NCHF). Additional samples collected in these two ecoregions in neighboring Wisconsin and Michigan in 2016 and in the Northern Minnesota Wetlands (NMW) ecoregion of Minnesota also are in the database. Data collected in 2018 included depth profiles of a(440), iron, dissolved organic carbon (DOC), and basic water quality parameters on three NLF lakes and samples on about 20 colored lakes and rivers to evaluate the importance of particulate iron as a component of total iron. Experimental data for addition of dissolved iron (Fe(III)) to six lakes also is included.National Science Foundation, Legislative-Citizen Commission on Minnesota Resources, University of Minnesot

Comparison of the microbiomes of two drinking water distribution systems—with and without residual chloramine disinfection

Background Residual disinfection is often used to suppress biological growth in drinking water distribution systems (DWDSs), but not without undesirable side effects. In this study, water-main biofilms, drinking water, and bacteria under corrosion tubercles were analyzed from a chloraminated DWDS (USA) and a no-residual DWDS (Norway). Using quantitative real-time PCR, we quantified bacterial 16S rRNA genes and ammonia monooxygenase genes (amoA) of Nitrosomonas oligotropha and ammonia-oxidizing archaea—organisms that may contribute to chloramine loss. PCR-amplified 16S rRNA genes were sequenced to assess community taxa and diversity. Results The chloraminated DWDS had lower biofilm biomass (P=1×10−6) but higher N. oligotropha-like amoA genes (P=2×10−7) than the no-residual DWDS (medians =4.7×104 and 1.1×103amoA copies cm−2, chloraminated and no residual, respectively); archaeal amoA genes were only detected in the no-residual DWDS (median =2.8×104 copies cm−2). Unlike the no-residual DWDS, biofilms in the chloraminated DWDS had lower within-sample diversity than the corresponding drinking water (P<1×10−4). Chloramine was also associated with biofilms dominated by the genera, Mycobacterium and Nitrosomonas (≤91.7% and ≤39.6% of sequences, respectively). Under-tubercle communities from both systems contained corrosion-associated taxa, especially Desulfovibrio spp. (≤98.4% of sequences). Conclusions Although residual chloramine appeared to decrease biofilm biomass and alpha diversity as intended, it selected for environmental mycobacteria and Nitrosomonas oligotropha—taxa that may pose water quality challenges. Drinking water contained common freshwater plankton and did not resemble corresponding biofilm communities in either DWDS; monitoring of tap water alone may therefore miss significant constituents of the DWDS microbiome. Corrosion-associated Desulfovibrio spp. were observed under tubercles in both systems but were particularly dominant in the chloraminated DWDS, possibly due to the addition of sulfate from the coagulant alum