Interactive effects of temperature, organic carbon, and pipe material on microbiota composition and Legionella pneumophila in hot water plumbing systems

Abstract

BackgroundSeveral biotic and abiotic factors have been reported to influence the proliferation of microbes, including Legionella pneumophila, in hot water premise plumbing systems, but their combined effects have not been systematically evaluated. Here, we utilize simulated household water heaters to examine the effects of stepwise increases in temperature (32–53 °C), pipe material (copper vs. cross-linked polyethylene (PEX)), and influent assimilable organic carbon (0–700 μg/L) on opportunistic pathogen gene copy numbers and the microbiota composition, as determined by quantitative polymerase chain reaction and 16S rRNA gene amplicon sequencing.ResultsTemperature had an overarching influence on both the microbiota composition and L. pneumophila numbers. L. pneumophila peaked at 41 °C in the presence of PEX (1.58 × 105 gene copies/mL). At 53 °C, L. pneumophila was not detected. Several operational taxonomic units (OTUs) persisted across all conditions, accounting for 50% of the microbiota composition from 32 to 49 °C and 20% at 53 °C. Pipe material most strongly influenced microbiota composition at lower temperatures, driven by five to six OTUs enriched with each material. Copper pipes supported less L. pneumophila than PEX pipes (mean 2.5 log10 lower) at temperatures ≤ 41 °C, but showed no difference in total bacterial numbers. Differences between pipe materials diminished with elevated temperature, probably resulting from decreased release of copper ions. At temperatures ≤ 45 °C, influent assimilable organic carbon correlated well with total bacterial numbers, but not with L. pneumophila numbers. At 53 °C, PEX pipes leached organic carbon, reducing the importance of dosed organic carbon. L. pneumophila numbers correlated with a Legionella OTU and a Methylophilus OTU identified by amplicon sequencing.ConclusionsTemperature was the most effective factor for the control of L. pneumophila, while microbiota composition shifted with each stepwise temperature increase. While copper pipe may also help shape the microbiota composition and limit L. pneumophila proliferation, its benefits might be constrained at higher temperatures. Influent assimilable organic carbon affected total bacterial numbers, but had minimal influence on opportunistic pathogen gene numbers or microbiota composition. These findings provide guidance among multiple control measures for the growth of opportunistic pathogens in hot water plumbing and insight into the mediating role of microbial ecological factors.Electronic supplementary materialThe online version of this article (10.1186/s40168-017-0348-5) contains supplementary material, which is available to authorized users.

Interactive Effects of Copper Pipe, Stagnation, Corrosion Control, and Disinfectant Residual Influenced Reduction of Legionella pneumophila during Simulations of the Flint Water Crisis

“…Each SPPR was equipped with either eight pieces of 20 mm × 10 mm cross-sectional PEX (n = 18) or solid copper (n = 18) pipe material. Pipe coupons had been aged in the bottles for six years in prior experiments, described elsewhere [ 8 , 9 , 10 , 27 ], which provided a benefit of well-aged premise plumbing pipe materials and mature biofilms at the start of the experiment.…”

“…However, lower LD incidence associated with residential exposure was noted from August 2015 onwards and our sampling during this period revealed undetectable or very low levels of L. pneumophila in residential plumbing [ 1 , 3 ]. While temporal associations between the switch in water supply with reduced levels of chlorine, high levels of iron, elevated temperature for Flint River water, and the resulting outbreak of LD were predictable based on prior work [ 7 , 8 , 9 , 10 ], and duly noted for the Flint outbreak [ 1 , 3 , 5 ], precise patterns of the outbreak in relation to large health care facilities versus residential single family homes are still the subject of scientific and public interest [ 5 , 11 ].…”

Nitrification in Premise Plumbing: A Review

“…Gomez-Alvarez et al (2016) found that the onset of severe nitrification resulted in increases in total biomass in the system [110]. The increase in biomass and concentrations of bacteria during nitrification are likely partially explained by the assimible organic carbon (AOC) introduced to the system as a result of nitrification [111][112][113]. Increases in AOC along, however, have not been shown to cause increased concentrations of OPPP, indicating the importance of other nitrification side-effects on the increased growth of OPPP seen during nitrification events [109,112,113].…”

“…The increase in biomass and concentrations of bacteria during nitrification are likely partially explained by the assimible organic carbon (AOC) introduced to the system as a result of nitrification [111][112][113]. Increases in AOC along, however, have not been shown to cause increased concentrations of OPPP, indicating the importance of other nitrification side-effects on the increased growth of OPPP seen during nitrification events [109,112,113]. Given the lack of inactivation of NTM after the introduction of chloramines, reintroduction of chloramines into premise plumbing systems after periods of stagnation and minimal chloramine residual, that promoted growth of NTM, may not be able to control the growth and release of these pathogens [108].…”

Microbial contamination screening and interpretation for biological laboratory environments

“…For example, a chronic exposure to some fungi can cause asthma, but early life exposure to various mold and its derivatives can protect children from allergic and autoimmune diseases[3]. A growing number of studies have helped us estimate the microbial diversity in various indoor environments, and revealed that microbial diversity is closely related to the geographic locations[4], weather conditions[5, 6], populations[7], functions[8], and internal ventilation conditions[9].…”