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Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap.

Rhoads WJ, Ji P, Pruden A, Edwards MA - Microbiome (2015)

Bottom Line: For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm.We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers.We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

View Article: PubMed Central - PubMed

Affiliation: Charles E. Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, 24061, USA. wrhoads@vt.edu.

ABSTRACT

Background: Lowering water heater temperature set points and using less drinking water are common approaches to conserving water and energy; yet, there are discrepancies in past literature regarding the effects of water heater temperature and water use patterns on the occurrence of opportunistic pathogens, in particular Legionella pneumophila. Our objective was to conduct a controlled, replicated pilot-scale investigation to address this knowledge gap using continuously recirculating water heaters to examine five water heater set points (39-58 °C) under three water use conditions. We hypothesized that L. pneumophila levels at the tap depend on the collective influence of water heater temperature, flow frequency, and the resident plumbing ecology.

Results: We confirmed temperature setting to be a critical factor in suppressing L. pneumophila growth both in continuously recirculating hot water lines and at distal taps. For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm. However, L. pneumophila still persisted up to 58 °C, with evidence that it was growing under the conditions of this study. Further, exposure to 51 °C water in a low-use tap appeared to optimally select for L. pneumophila (e.g., 125 times greater numbers than in high-use taps). We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers. We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

Conclusions: Our study provides a new window of understanding into the microbial ecology of potable hot water systems and helps to resolve past discrepancies in the literature regarding the influence of water temperature and stagnation on L. pneumophila, which is the cause of a growing number of outbreaks. This work is especially timely, given society's movement towards "green" buildings and the need to reconcile innovations in building design with public health.

No MeSH data available.


Related in: MedlinePlus

Relative levels of L. pneumophila and ecologically relevant microbes in the influent and recirculating line. Log L. pneumophila, Legionella spp., and V. vermiformis nested within total bacteria concentrations (gene copies/mL) in the influent and recirculating lines for a the baseline sampling (both systems set to 39 °C at 5 months), b exp. 2 (control system set to 39 °C, experimental system set to 51 °C at 13 months), and c exp. 3 (control system set to 39 °C, experimental system set to 58 °C at 15 months)
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Fig6: Relative levels of L. pneumophila and ecologically relevant microbes in the influent and recirculating line. Log L. pneumophila, Legionella spp., and V. vermiformis nested within total bacteria concentrations (gene copies/mL) in the influent and recirculating lines for a the baseline sampling (both systems set to 39 °C at 5 months), b exp. 2 (control system set to 39 °C, experimental system set to 51 °C at 13 months), and c exp. 3 (control system set to 39 °C, experimental system set to 58 °C at 15 months)

Mentions: Relationships were explored among total bacteria, Legionella spp., and V. vermiformis to gain insight into how L. pneumophila behaved in the context of the broader plumbing microbiome (Figs. 6 and 7). Remarkably, elevated temperatures did not have a significant effect on the levels of total bacteria in the recirculating lines or at the tap (Kruskal-Wallis test, p value = 0.27, n = 58). While it was expected that the disinfecting properties of the hotter water would reduce total microbial populations, our results suggest that instead the elevated temperature merely shifted the microbiome composition, which can be seen by reductions in the other specific targets in the experimental relative to the control system (Figs. 6 and 7).Fig. 6


Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap.

Rhoads WJ, Ji P, Pruden A, Edwards MA - Microbiome (2015)

Relative levels of L. pneumophila and ecologically relevant microbes in the influent and recirculating line. Log L. pneumophila, Legionella spp., and V. vermiformis nested within total bacteria concentrations (gene copies/mL) in the influent and recirculating lines for a the baseline sampling (both systems set to 39 °C at 5 months), b exp. 2 (control system set to 39 °C, experimental system set to 51 °C at 13 months), and c exp. 3 (control system set to 39 °C, experimental system set to 58 °C at 15 months)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4666224&req=5

Fig6: Relative levels of L. pneumophila and ecologically relevant microbes in the influent and recirculating line. Log L. pneumophila, Legionella spp., and V. vermiformis nested within total bacteria concentrations (gene copies/mL) in the influent and recirculating lines for a the baseline sampling (both systems set to 39 °C at 5 months), b exp. 2 (control system set to 39 °C, experimental system set to 51 °C at 13 months), and c exp. 3 (control system set to 39 °C, experimental system set to 58 °C at 15 months)
Mentions: Relationships were explored among total bacteria, Legionella spp., and V. vermiformis to gain insight into how L. pneumophila behaved in the context of the broader plumbing microbiome (Figs. 6 and 7). Remarkably, elevated temperatures did not have a significant effect on the levels of total bacteria in the recirculating lines or at the tap (Kruskal-Wallis test, p value = 0.27, n = 58). While it was expected that the disinfecting properties of the hotter water would reduce total microbial populations, our results suggest that instead the elevated temperature merely shifted the microbiome composition, which can be seen by reductions in the other specific targets in the experimental relative to the control system (Figs. 6 and 7).Fig. 6

Bottom Line: For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm.We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers.We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

View Article: PubMed Central - PubMed

Affiliation: Charles E. Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, 24061, USA. wrhoads@vt.edu.

ABSTRACT

Background: Lowering water heater temperature set points and using less drinking water are common approaches to conserving water and energy; yet, there are discrepancies in past literature regarding the effects of water heater temperature and water use patterns on the occurrence of opportunistic pathogens, in particular Legionella pneumophila. Our objective was to conduct a controlled, replicated pilot-scale investigation to address this knowledge gap using continuously recirculating water heaters to examine five water heater set points (39-58 °C) under three water use conditions. We hypothesized that L. pneumophila levels at the tap depend on the collective influence of water heater temperature, flow frequency, and the resident plumbing ecology.

Results: We confirmed temperature setting to be a critical factor in suppressing L. pneumophila growth both in continuously recirculating hot water lines and at distal taps. For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm. However, L. pneumophila still persisted up to 58 °C, with evidence that it was growing under the conditions of this study. Further, exposure to 51 °C water in a low-use tap appeared to optimally select for L. pneumophila (e.g., 125 times greater numbers than in high-use taps). We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers. We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

Conclusions: Our study provides a new window of understanding into the microbial ecology of potable hot water systems and helps to resolve past discrepancies in the literature regarding the influence of water temperature and stagnation on L. pneumophila, which is the cause of a growing number of outbreaks. This work is especially timely, given society's movement towards "green" buildings and the need to reconcile innovations in building design with public health.

No MeSH data available.


Related in: MedlinePlus