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Relationship between Organic Carbon and Opportunistic Pathogens in Simulated Glass Water Heaters.

Williams K, Pruden A, Falkinham JO, Edwards M, Williams K, Pruden A, Iii JO, Edwards M - Pathogens (2015)

Bottom Line: R2 > 0.89).R2 = 0.82 to 0.97, for 2 out of 4 time points) and over a limited TOC range (0-1000 µg/L), no other correlations were identified between other OPPPs and added TOC.These results suggest that reducing organic carbon in distributed water is not adequate as a sole strategy for controlling OPPPs, although it may have promise in conjunction with other approaches.

View Article: PubMed Central - PubMed

Affiliation: Via Department of Civil and Environmental Engineering, Virginia Tech, 401 Durham Hall, Blacksburg, VA 24060, USA. kwilli@vt.edu.

ABSTRACT
Controlling organic carbon levels in municipal water has been hypothesized to limit downstream growth of bacteria and opportunistic pathogens in premise plumbing (OPPPs). Here, the relationships between influent organic carbon (0-15,000 µg ozonated fulvic acid /L) and the number of total bacteria [16S rRNA genes and heterotrophic plate counts (HPCs)] and a wide range of OPPPs (gene copy numbers of Acanthamoeba polyphaga, Vermamoeba vermiformis, Legionella pneumophila, and Mycobacterium avium) were examined in the bulk water of 120-mL simulated glass water heaters (SGWHs). The SGWHs were operated at 32-37 °C, which is representative of conditions encountered at the bottom of electric water heaters, with water changes of 80% three times per week to simulate low use. This design presented advantages of controlled and replicated (triplicate) conditions and avoided other potential limitations to OPPP growth in order to isolate the variable of organic carbon. Over seventeen months, strong correlations were observed between total organic carbon (TOC) and both 16S rRNA gene copy numbers and HPC counts (avg. R2 > 0.89). Although M. avium gene copies were occasionally correlated with TOC (avg. R2 = 0.82 to 0.97, for 2 out of 4 time points) and over a limited TOC range (0-1000 µg/L), no other correlations were identified between other OPPPs and added TOC. These results suggest that reducing organic carbon in distributed water is not adequate as a sole strategy for controlling OPPPs, although it may have promise in conjunction with other approaches.

No MeSH data available.


Related in: MedlinePlus

Comparison of (Top) L. pneumophila, (middle) A. polyphaga, and (Bottom) M. avium concentrations over time under a regular flow regime (3X per week 80% water change—Experiment A2) determined using qPCR.
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pathogens-04-00355-f002: Comparison of (Top) L. pneumophila, (middle) A. polyphaga, and (Bottom) M. avium concentrations over time under a regular flow regime (3X per week 80% water change—Experiment A2) determined using qPCR.

Mentions: L. pneumophila numbers did not correlate (either positively or negatively) with increasing TOC concentrations under any of the conditions investigated in this study. L. pneumophila from all SGWHs was measured in triplicate using qPCR for a total of 10 time points and the R2 with respect to added TOC ranged from −0.567 to 0.231 with a median R2 value of 0.174. Attempts were made to cultivate L. pneumophila for nine total time points in each of the three experiments and in no instances were colonies recovered. Despite the three variations in the experimental conditions that were expressly intended to induce the growth of L. pneumophila, added TOC was never found to be a driving factor for either Legionella amplification or persistence. In a typical experiment, concentrations of L. pneumophila initially present (>1.0 × 105 gene copies/mL) decreased by several orders of magnitude as L. pneumophila cells and their DNA washed out from the SGWHs via the 80% water changes (Figure 2). A washout model, assuming that 20% of the original DNA remained in the SGWH after each water change, was plotted for comparison, which was in reasonable agreement with the overall trends considering that this model did not account for the retention of DNA in biofilms or the sustained release to effluent water. Overall, though L. pneumophila qPCR gene counts were frequently maintained above the washout model prediction, there was little evidence of increases above that expected from the initial inoculum.


Relationship between Organic Carbon and Opportunistic Pathogens in Simulated Glass Water Heaters.

Williams K, Pruden A, Falkinham JO, Edwards M, Williams K, Pruden A, Iii JO, Edwards M - Pathogens (2015)

Comparison of (Top) L. pneumophila, (middle) A. polyphaga, and (Bottom) M. avium concentrations over time under a regular flow regime (3X per week 80% water change—Experiment A2) determined using qPCR.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493478&req=5

pathogens-04-00355-f002: Comparison of (Top) L. pneumophila, (middle) A. polyphaga, and (Bottom) M. avium concentrations over time under a regular flow regime (3X per week 80% water change—Experiment A2) determined using qPCR.
Mentions: L. pneumophila numbers did not correlate (either positively or negatively) with increasing TOC concentrations under any of the conditions investigated in this study. L. pneumophila from all SGWHs was measured in triplicate using qPCR for a total of 10 time points and the R2 with respect to added TOC ranged from −0.567 to 0.231 with a median R2 value of 0.174. Attempts were made to cultivate L. pneumophila for nine total time points in each of the three experiments and in no instances were colonies recovered. Despite the three variations in the experimental conditions that were expressly intended to induce the growth of L. pneumophila, added TOC was never found to be a driving factor for either Legionella amplification or persistence. In a typical experiment, concentrations of L. pneumophila initially present (>1.0 × 105 gene copies/mL) decreased by several orders of magnitude as L. pneumophila cells and their DNA washed out from the SGWHs via the 80% water changes (Figure 2). A washout model, assuming that 20% of the original DNA remained in the SGWH after each water change, was plotted for comparison, which was in reasonable agreement with the overall trends considering that this model did not account for the retention of DNA in biofilms or the sustained release to effluent water. Overall, though L. pneumophila qPCR gene counts were frequently maintained above the washout model prediction, there was little evidence of increases above that expected from the initial inoculum.

Bottom Line: R2 > 0.89).R2 = 0.82 to 0.97, for 2 out of 4 time points) and over a limited TOC range (0-1000 µg/L), no other correlations were identified between other OPPPs and added TOC.These results suggest that reducing organic carbon in distributed water is not adequate as a sole strategy for controlling OPPPs, although it may have promise in conjunction with other approaches.

View Article: PubMed Central - PubMed

Affiliation: Via Department of Civil and Environmental Engineering, Virginia Tech, 401 Durham Hall, Blacksburg, VA 24060, USA. kwilli@vt.edu.

ABSTRACT
Controlling organic carbon levels in municipal water has been hypothesized to limit downstream growth of bacteria and opportunistic pathogens in premise plumbing (OPPPs). Here, the relationships between influent organic carbon (0-15,000 µg ozonated fulvic acid /L) and the number of total bacteria [16S rRNA genes and heterotrophic plate counts (HPCs)] and a wide range of OPPPs (gene copy numbers of Acanthamoeba polyphaga, Vermamoeba vermiformis, Legionella pneumophila, and Mycobacterium avium) were examined in the bulk water of 120-mL simulated glass water heaters (SGWHs). The SGWHs were operated at 32-37 °C, which is representative of conditions encountered at the bottom of electric water heaters, with water changes of 80% three times per week to simulate low use. This design presented advantages of controlled and replicated (triplicate) conditions and avoided other potential limitations to OPPP growth in order to isolate the variable of organic carbon. Over seventeen months, strong correlations were observed between total organic carbon (TOC) and both 16S rRNA gene copy numbers and HPC counts (avg. R2 > 0.89). Although M. avium gene copies were occasionally correlated with TOC (avg. R2 = 0.82 to 0.97, for 2 out of 4 time points) and over a limited TOC range (0-1000 µg/L), no other correlations were identified between other OPPPs and added TOC. These results suggest that reducing organic carbon in distributed water is not adequate as a sole strategy for controlling OPPPs, although it may have promise in conjunction with other approaches.

No MeSH data available.


Related in: MedlinePlus