Natural Organic Matter, Orthophosphate, pH, and Growth Phase Can Limit Copper Antimicrobial Efficacy for Legionella in Drinking Water

Abstract

Copper (Cu) is a promising antimicrobial for premise plumbing, where ions can be dosed directly via copper silver ionization or released naturally via corrosion of Cu pipes, but Cu sometimes inhibits and other times stimulates Legionella growth. Our overarching hypothesis was that water chemistry and growth phase control the net effect of Cu on Legionella. The combined effects of pH, phosphate concentration, and natural organic matter (NOM) were comprehensively examined over a range of conditions relevant to drinking water in bench-scale pure culture experiments, illuminating the effects of Cu speciation and precipitation. It was found that cupric ions (Cu2+) were drastically reduced at pH > 7.0 or in the presence of ligand-forming phosphates or NOM. Further, exponential phase L. pneumophila were 2.5× more susceptible to Cu toxicity relative to early stationary phase cultures. While Cu2+ ion was the most effective biocidal form of Cu, other inorganic ligands also had some biocidal impacts. A comparison of 33 large drinking water utilities’ field-data from 1990 and 2018 showed that Cu2+ levels likely decreased more dramatically (>10×) than did the total or soluble Cu (2×) over recent decades. The overall findings aid in improving the efficacy of Cu as an actively dosed or passively released antimicrobial against L. pneumophila.

Copper Pipe, Lack of Corrosion Control, and Very Low pH May Have Influenced the Trajectory of the Flint Legionnaires’ Disease Outbreak

“…pneumophila in Detroit water with copper pipes and the extra iron nutrients rose to the range of those observed for PEX using TFR water (Figure ), confirming reports from other studies that the presence of the copper pipe can sometimes increase aspects of L. pneumophila growth when orthophosphate is present. ,, …”

Facile and Green Synthesis of Bifunctional Carbon Dots for Detection of Cu2+ and ClO– in Aqueous Solution

“…Fluorescence-sensing materials have been playing an indispensable role in the field of environmental and biological systems. − Traditional small-molecule probes, though showing high quantum yields, multiple fluorescence colors, and clear luminescence mechanisms, − are usually inhibited in aqueous applications for their inevitable deficiencies, such as complex synthesis, , utilization of organic solvents, and poor water solubility. , For an effective detection of the targets in aqueous solutions, developing novel fluorescence materials through a facile and green synthesis is still full of challenges for material scientists.…”

Local Adaptation of Legionella pneumophila within a Hospital Hot Water System Increases Tolerance to Copper

“…In an engineered water system context, L. pneumophila would likely enter water after being expelled from a host cell, in the transmissive state. Post-exponential-phase cells are also markedly more resistant to stress than exponential-phase bacteria (36,(52)(53)(54)(55). Second, cells were acclimatized in simulated drinking water at room temperature for 1 week prior to copper exposure.…”

“…L. pneumophila has been recovered from water within copper pipe premise plumbing carrying up to 0.8 mg Cu/liter (8,9), and culturable L. pneumophila has been observed at levels up to 8 mg/liter in a laboratory study (34). Recovery of culturable L. pneumophila in simulated drinking water distribution systems was observed at copper concentrations between 0.8 mg/liter and 3.12 mg/liter (35,36). Copper has also been reported to inhibit the growth of L. pneumophila (37).…”

“…Copper has also been reported to inhibit the growth of L. pneumophila (37). These reported differences in copper effect on L. pneumophila could be related to environmental factors such as water chemistry or L. pneumophila growth phase (36), or to intrinsic factors such as the variable ability of each strain to tolerate copper, underlined by the genetic makeup of each strain or adaptive evolution of tolerance due to previous exposure. Indeed, L. pneumophila strains may behave differently depending on the environment from which they are isolated and/or environmental conditions to which they have adapted.…”