Water disinfection with ozone, copper and silver ions, and temperature increase to control Legionella: seven years of experience in a university teaching hospital

Toxicity Mechanisms of Copper Nanoparticles and Copper Surfaces on Bacterial Cells and Viruses

Copper is a metal historically used to prevent infections. One of the most relevant challenges in modern society are infectious disease outbreaks, where copper-based technologies can play a significant role. Currently, copper nanoparticles and surfaces are the most common antimicrobial copper-based technologies. Despite the widespread use of copper on nanoparticles and surfaces, the toxicity mechanism(s) explaining their unique antimicrobial properties are not entirely known. In general, toxicity effects described in bacteria and fungi involve the rupture of membranes, accumulation of ions inside the cell, protein inactivation, and DNA damage. A few studies have associated Cu-toxicity with ROS production and genetic material degradation in viruses. Therefore, understanding the mechanisms of the toxicity of copper nanoparticles and surfaces will contribute to developing and implementing efficient antimicrobial technologies to combat old and new infectious agents that can lead to disease outbreaks such as COVID-19. This review summarizes the current knowledge regarding the microbial toxicity of copper nanoparticles and surfaces and the gaps in this knowledge. In addition, we discuss potential applications derived from discovering new elements of copper toxicity, such as using different molecules or modifications to potentiate toxicity or antimicrobial specificity.

Novel electro-oxidation unit for electro-disinfection of E. coli and some waterborne pathogens during wastewater treatment: batch and continuous experiments

The prime objective of the current investigation is to evaluate a promising alternative method for disinfection wastewater using a novel electro-oxidation unit. The study focused on determining the best-operating conditions from a techno-economic point of view to be applied to continuous flow simulating actual disinfection modules. The treatment unit consisted of a Plexiglas container with a 3 L volume containing nine cylindrical shape electrodes (6 graphite as anode and 3 stainless steel as a cathode) connected to a variable DC power supply. Determination of the best operating parameters was investigated in batch mode on synthetic wastewater by studying the effect of contact time, current density (CD), total dissolved solids concentration (TDS), and bacterial density. Moreover, the continuous mode experiment was considered on real wastewater from an agricultural drain and the secondary wastewater treatment plant effluent before chlorination. The batch mode results revealed that the best applicable operational conditions that achieved the complete removal of E. coli were at a contact time of less than 5 min, TDS of 2000 mg/L, and CD of 4 mA/cm². Application of these conditions on the continuous mode experiment indicated the complete removal of all bacterial indicators after 5 min in the drainage wastewater and after 3 min in the secondary treated wastewater. Physico-chemical characterization also suggested that no chlorine by-products displaying the hydroxide ion formed due to water electrolysis is the main reason for prohibiting the growth of pathogenic microbes. The electrical consumption was calculated in the continuous mode and found to be 0.5 kWh/m³ with an operational cost of about 0.06 $/m³, including the cost of adding chemicals to increase the TDS. The results proved that this novel electro-oxidation unit is a robust and affordable disinfection method for complete bacterial removal from wastewater and is more environmentally benign than other conventional disinfection methods.

Compromised Effectiveness of Thermal Inactivation of Legionella pneumophila in Water Heater Sediments and Water, and Influence of the Presence of Vermamoeba vermiformis

Intermittent reduction of temperature set-points and periodic shutdowns of water heaters have been proposed to reduce energy consumption in buildings. However, the consequences of such measures on the occurrence and proliferation of Legionella pneumophila (Lp) in hot water systems have not been documented. The impact of single and repeated heat shocks was investigated using an environmental strain of L. pneumophila and a reference strain of V. vermiformis. Heat shocks at temperatures ranging from 50 °C to 70 °C were applied for 1 h and 4 h in water and water heaters loose deposits (sludge). The regrowth potential of heat-treated culturable L. pneumophila in presence of V. vermiformis in water heaters sludges was evaluated. A 2.5-log loss of culturability of L. pneumophila was observed in simulated drinking water at 60 °C while a 4-log reduction was reached in water heaters loose deposits. Persistence of Lp after 4 h at 55 °C was shown and the presence of V. vermiformis in water heater’s loose deposits resulted in a drastic amplification (5-log). Results show that thermal inactivation by heat shock is only efficient at elevated temperatures (50 °C) in both water and loose deposits. The few remaining organisms can rapidly proliferate during storage at lower temperature in the presence of hosts.

Dynamics of Legionella Community Interactions in Response to Temperature and Disinfection Treatment: 7 Years of Investigation

In man-made water distribution systems, Legionella community interactions remain unknown, due to their ability to change from sessile to planktonic states or live in viable but non-culturable forms, in response to anthropic and environmental stress. During 7 years of hospital Legionella surveillance, in 191 hot water positive samples, the interactions among the Legionella species, temperature, and disinfection treatment were evaluated. Legionella was isolated following ISO 11731:2017, and identification was performed by mip gene sequencing and sequence-based typing (SBT) for L. anisa or L. rubrilucens and L. pneumophila, respectively. The species with the higher frequency of isolation was L. pneumophila serogroup 1 (78.53%; 4865.36 ± 25,479.11 cfu/L), followed by L. anisa (54.45%; 558.79 ± 2637.41 cfu/L) and L. rubrilucens (21.99%; 307.73 ± 1574.95 cfu/L), which were sometimes present together. Spearman's rho correlation test was conducted among the species with respect to temperature and disinfectant (H₂O₂/Ag⁺). The results showed a generally positive interaction among these species sharing the same environment, except for competition between L. anisa and L. rubrilucens. High temperature (48.83 ± 2.59 °C) and disinfection treatment (11.58 ± 4.99 mg/L) affected the presence of these species. An exception was observed with L. anisa, which showed disinfection treatment resistance. For the purposes of environmental surveillance, it is fundamental to better understand the interactions and dynamic of the Legionella community in man-made water systems in order to choose the proper physical or chemical treatments. The simultaneous presence of different Legionella species could result in an increased resistance to high temperature and disinfectant treatment, leading to changes in contamination level and species diversity.

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

In large-building water systems, Legionella pneumophila is exposed to common environmental stressors such as copper. The aim of this study was to evaluate the susceptibility to copper of L. pneumophila isolates recovered from various sites: two clinical and seven environmental isolates from hot water system biofilm and water and from cooling tower water. After a 1-week acclimation in simulated drinking water, strains were exposed to various copper concentrations (0.8 to 5 mg/liter) for over 672 h. Complete loss of culturability was observed for three isolates following copper exposure to 5 mg/liter for 672 h. Two sequence type 1427 (ST1427)-like isolates were highly sensitive to copper, while the other two, isolated from biofilm samples, maintained higher culturability. The expression of the copper resistance gene copA evaluated by reverse transcription-quantitative PCR (RT-qPCR) was significantly higher for the biofilm isolates. All four ST1427-like isolates were recovered from the same water system during an outbreak. Whole-genome sequencing results confirmed that the four isolates are very close phylogenetically, differing by only 29 single nucleotide polymorphisms, suggesting in situ adaptation to microenvironmental conditions, possibly due to epigenetic regulation. These results indicate that the immediate environment within a building water distribution system influences the tolerance of L. pneumophila to copper. Increased contact of L. pneumophila biofilm strains with copper piping or copper alloys in the heat exchanger might lead to local adaptation. The phenotypic differences observed between water and biofilm isolates from the hot water system of a health care facility warrants further investigation to assess the relevance of evaluating disinfection performances based on water sampling alone.IMPORTANCELegionella pneumophila is a pathogen indigenous to natural and large building water systems in the bulk and the biofilm phases. The immediate environment within a system can impact the tolerance of L. pneumophila to environmental stressors, including copper. In health care facilities, copper levels in water can vary, depending on water quality, plumbing materials, and age. This study evaluated the impact of the isolation site (water versus biofilm, hot water system versus cooling tower) within building water systems. Closely related strains isolated from a health care facility hot water system exhibited variable tolerance to copper stress, shown by differential expression of copA, with biofilm isolates displaying highest expression and tolerance. Relying on the detection of L. pneumophila in water samples following exposure to environmental stressors such as copper may underestimate the prevalence of L. pneumophila, leading to inappropriate risk management strategies and increasing the risk of exposure for vulnerable patients.

Environmental Management of Legionella in Domestic Water Systems: Consolidated and Innovative Approaches for Disinfection Methods and Risk Assessment

Legionella is able to remain in water as free-living planktonic bacteria or to grow within biofilms that adhere to the pipes. It is also able to enter amoebas or to switch into a viable but not culturable (VBNC) state, which contributes to its resistance to harsh conditions and hinders its detection in water. Factors regulating Legionella growth, such as environmental conditions, type and concentration of available organic and inorganic nutrients, presence of protozoa, spatial location of microorganisms, metal plumbing components, and associated corrosion products are important for Legionella survival and growth. Finally, water treatment and distribution conditions may affect each of these factors. A deeper comprehension of Legionella interactions in water distribution systems with the environmental conditions is needed for better control of the colonization. To this purpose, the implementation of water management plans is the main prevention measure against Legionella. A water management program requires coordination among building managers, health care providers, and Public Health professionals. The review reports a comprehensive view of the state of the art and the promising perspectives of both monitoring and disinfection methods against Legionella in water, focusing on the main current challenges concerning the Public Health sector.

Making Swimming Pools Safer: Does Copper-Silver Ionization with Chlorine Lower the Toxicity and Disinfection Byproduct Formation?

Swimming pools are commonly treated with chlorine, which reacts with the natural organic matter and organic matter introduced by swimmers and form disinfection byproducts (DBPs) that are associated with respiratory-related issues, including asthma, in avid swimmers. We investigated a complementary disinfectant to chlorine, copper-silver ionization (CSI), with the aim of lowering the amount of chlorine used in pools and limiting health risks from DBPs. We sampled an indoor and outdoor pool treated with CSI-chlorine during the swimming season in 2017-2018 and measured 71 DBPs, speciated total organic halogen, in vitro mammalian cell cytotoxicity, and N-acetyl-l-cysteine (NAC) thiol reactivity as a cytotoxicity predictor. Controlled, simulated swimming pools were also investigated. Emerging DBP concentrations decreased by as much as 80% and cytotoxicity decreased as much as 70% in the indoor pool when a lower chlorine residual (1.0 mg/L) and CSI was used. Some DBPs were quantified for the first time in pools, including chloroacetaldehyde (up to 10.6 μg/L), the most cytotoxic haloacetaldehyde studied to date and a major driver of the measured cytotoxicity in this study. Three highly toxic iodinated haloacetic acids (iodoacetic acid, bromoiodoacetic acid, and chloroiodoacetic acid) were also quantified in pools for the first time. We also found that the NAC thiol reactivity was significantly correlated to cytotoxicity, which could be useful for predicting the cytotoxicity of swimming pool waters in future studies.

Response of high-, mid- and low-abundant taxa and potential pathogens to eight disinfection methods and their interactions in domestic hot water system

Eight disinfection methods were applied to control biofilm contamination in domestic hot water system. The inactivation efficiency, responses of high- (≥1%), mid- (0.1% ~ 1%) and low-abundant taxa (≤0.1%) to disinfection, and interactions within and across three sub-communities were investigated. Ultraviolet was the most effective disinfection method for total bacteria and Escherichia coli, and chlorine dioxide had the highest inactivation efficiency on heterotrophic bacteria, while silver ions exhibited poor performance on all of them. At the phylum level, the responses of microorganisms to eight disinfection methods were different, but Proteobacteria and Firmicutes dominated in most samples. Eight disinfection methods had a greater impact on the proportion of high- and mid-abundant taxa than that of low-abundant taxa, and led to dissimilar transformations of genera among high-, mid- and low-abundant taxa in each sample. High-, mid- and low-abundant taxa of different samples showed similar structures and were roughly clustered into three Groups. Moreover, high-abundant taxa had more complex internal interactions than mid- and low-abundant taxa, and mainly presented co-occurrence patterns. The associations between high- and low-abundant taxa were close, and some low-abundant genera were identified as hub bacteria, such as Paracoccus, Thioalkalispira and Flavitalea. Furthermore, a total of 23 potential pathogens were detected in this study, and they mainly showed positive interactions, with Mycobacteria and Streptococcus as keystone genera. These results highlight the dissimilar responses of high-, mid- and low-abundant taxa to disinfection, and the critical role of some low-abundant genera in the microbial network, as well as the co-occurrence patterns among potential pathogens.

In-Situ Deposition of Metal Oxides Nanoparticles in Cellulose Derivative and Its Utilization for Wastewater Disinfection

The target of this work is to investigate and assess the utilization of the synthesized in-situ deposition of metal oxide nanoparticles such as nano-nickel oxide (nNiO), nanocopper oxides (nCuO) and nanoiron oxides (nFe₃O₄) in aminated cellulose (Acell), as a protected and compelling antibacterial channel of contamination from domestic wastewater. The prepared Acell and nNiO/Acell, nCuO/Acell and nFe₃O₄/Acell nanocomposites were characterized by field emission-scanning electron microscopy (FE-SEM), Fourier transform-infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), selected area diffraction pattern (SAED) and X-ray diffraction techniques (XRD). TEM declared the synthesis of nNiO, nCuO and nFe₃O₄ with regular size of 10, 23 and 43 nm, correspondingly. The antibacterial impact of both nNiO/Acell, nCuO/Acell and nFe₃O₄/Acell nanocomposites was inspected against Gram-positive microorganisms (Enterococcus faecalis, Staphylococcus aureus) and Gram-negative microbes (Escherichia coli, Salmonella typhi) utilizing agar disk diffusion routes. Furthermore, the ability of the synthesized nanocomposites as sterilizers for optional domestic wastewater was studied. The data for the disk diffusion obtained revealed that nFe₃O₄/Acell had a greater antibacterial impact than nCuO/Acell and nNiO/Acell. In addition, the purification of domestic wastewater utilizing 1.0 mg of nFe₃O₄, nCuO and nNiO in 1 gm of Acell was accomplished by killing 99.6%, 94.5% and 92.0% of total and fecal coliforms inside 10 mins, respectively.

Legionellosis and Recent Advances in Technologies for Legionella Control in Premise Plumbing Systems: A Review

This review discusses Legionella, among the most prolific and publicly well-known waterborne pathogens, and advances in potential treatment technologies. The number of cases associated with Legionella continues to rise, as does its public awareness. Currently, cases associated with premise plumbing account for the largest number of legionellosis cases in the United States. So, while it is important to understand Legionella as such, it is also important to investigate how to treat drinking water in premise plumbing for Legionella and other waterborne pathogens. While there are currently several methods recognized as potential means of inactivating waterborne pathogens, several shortcomings continue to plague its implementation. These methods are generally of two types. Firstly, there are chemical treatments such as chlorine, chlorine dioxide, monochloramine, ozone, and copper-silver ionization. Secondly, there are physical treatments such as thermal inactivation and media filtration. Their shortcomings range from being labor-intensive and costly to having negative health effects if not properly operated. Recently developed technologies including ultraviolet (UV) irradiation using light emitting diodes (LEDs) and innovative carbon nanotube (CNT) filters can better control waterborne pathogens by allowing for the simultaneous use of different treatment measures in plumbing systems.

Advances in Legionella Control by a New Formulation of Hydrogen Peroxide and Silver Salts in a Hospital Hot Water Network

Legionella surveillance is an important issue in public health, linked to the severity of disease and the difficulty associated with eradicating this bacterium from the water environment. Different treatments are suggested to reduce Legionella risk, however long-term studies of their efficiency are lacking. This study focused on the activity of a new formulation of hydrogen peroxide and silver salts, WTP828, in the hospital hot water network (HWN) to contain Legionella contamination during two years of treatment. The effectiveness of WTP828 was tested measuring physical-chemical and microbiological parameters such as Legionella, Pseudomonas aeruginosa (P. aeruginosa), and a heterotopic plate count (HPC) at 36 °C. Legionella isolates were identified by serotyping and genotyping. WTP 828 induced a reduction in Legionella–positive sites (60% to 36%) and contamination levels (2.12 to 1.7 log₁₀ CFU/L), with isolates belonging to L. pneumophila SG1 (ST1 and ST104), L. anisa and L. rubrilucens widely distributed in HWN. No relevant contamination was found for other parameters tested. The long-term effect of WTP828 on Legionella containment suggest the easy and safe application of this disinfectant, that combined with knowledge of building characteristics, an adequate environmental monitoring and risk assessment plan, become the key elements in preventing Legionella contamination and exposure.

Kinetics and thermodynamic studies for removal of methylene blue dye by biosynthesize copper oxide nanoparticles and its antibacterial activity

The present study deals with the green approach for the biosynthesis of copper oxide-Aloe vera (CuO-A) based nanoparticles using leaf extract of Aloe barbadensis miller. Synthesized nanoparticles were characterized through different techniques like TEM and FTIR. As the size decreases and surface area increases, these are prominently used as a very good adsorbent. The effects of different parameters like adsorbent dosage, pH, contact time, initial dye concentration and temperature are optimised to get the maximum removal of methylene blue dye from the solution. The maximum dye removal was found to be 98.89% with initial concentration of 100 mg/L at alkaline pH in 210 min., with shaking speed of 150 rpm. The Langmuir result reveals a better consistency than the Freundlich model with 95.5 mg/g. Lagergren's model was used to study the kinetics of the system. Mechanistic behaviour was study through intra-particle diffusion study and Boyd plot. Thermodynamic study showed spontaneous and endothermic nature of the adsorption. Furthermore, synthesized CuO-A nanoparticles showed good antibacterial activity against different strains of bacteria. The zone of inhibition was found to be 11 mm, 12 mm, 8 mm and 9 mm in Pseudomonas, Klebsiella, Staphylococcus and E.coli, respectively.

Role of hot water temperature and water system use on Legionella control in a tertiary hospital: An 8-year longitudinal study

Although measures to minimize Legionella colonization in sanitary hot water installations are well established, there is little evidence of their long-term effectiveness in hospital buildings. During an 8-year period, hot water in a large hospital building was sampled monthly in areas with suitable dimensioning and recirculation and in areas with dead legs and low-use taps. In the former areas, the percentage of Legionella-negative samples was 83.2% when the temperature was ≥55%, 64.9% when between 50.1 °C and 54.0 °C, and 51.6% when ≤50 °C (p for trend <0.001). In the highest temperature group, no samples with ≥10³ cfu/L were observed. In poorly designed areas, only 44.7% of samples were negative, and 28.9% presented ≥10³ cfu/L although reaching 55 °C. In these areas, multivariate analysis showed that if hot water supplies were not used daily, the risk of Legionella colonization was greater than two-fold (odds ratio: 2.84; 95% confidence interval: 1.26-6.41), and the risk of finding Legionella concentrations ≥10³ cfu/L was more than three-fold (odds ratio: 3.18; 95% confidence interval: 1.36-7.46), regardless the temperature. These findings indicate that the effectiveness of maintaining sanitary hot water at a minimum temperature of 55 °C is significantly better than that at 50 °C for the environmental control of Legionella but only in installations with suitable dimensioning and recirculation. In installations that do not meet these conditions, high temperatures alone result in insufficient control.

Different Uses of Ozone: Environmental and Corporate Sustainability. Literature Review and Case Study

An extensive and interdisciplinary literature review was carried out to evaluate the uses of synthetically produced ozone in many different application areas. The objective of the study was to investigate the disinfectant and purifying effectiveness of this natural compound and evaluate its use as an economically and environmentally sustainable alternative to treatments that often involve the adoption of pharmaceutical agents. Being a natural substance, the potential environmental sustainability of the use of ozone in areas such as water disinfectant; pesticide action in agriculture; and antibiotic, anti-inflammatory and antiviral actions in animal husbandry and fish farming are of interest. In addition to environmental sustainability, economic sustainability is also important for companies employing ozone in their processes. Thus, a case study was proposed that represents the use of ozone in a pilot swine farm located in Northern Italy, both as an alternative to pharmaceutical drugs for the animals and as an air and water purifier. The case study demonstrates the economic sustainability of ozone use, especially in the medium run, along with its ability to reduce animal mortality (by about 2%), as well as decrease use of pharmaceutical antibiotics.

Copper-silver ionization at a US hospital: Interaction of treated drinking water with plumbing materials, aesthetics and other considerations

Tap water sampling and surface analysis of copper pipe/bathroom porcelain were performed to explore the fate of copper and silver during the first nine months of copper-silver ionization (CSI) applied to cold and hot water at a hospital in Cincinnati, Ohio. Ions dosed by CSI into the water at its point of entry to the hospital were inadvertently removed from hot water by a cation-exchange softener in one building (average removal of 72% copper and 51% silver). Copper at the tap was replenished from corrosion of the building's copper pipes but was typically unable to reach 200 μg/L in first-draw and flushed hot and cold water samples. Cold water lines had >20 μg/L silver at most of the taps that were sampled, which further increased after flushing. However, silver plating onto copper pipe surfaces (in the cold water line but particularly in the hot water line) prevented reaching 20 μg/L silver in cold and/or hot water of some taps. Aesthetically displeasing purple/grey stains in bathroom porcelain were attributed to chlorargyrite [AgCl(s)], an insoluble precipitate that formed when CSI-dosed Ag(+) ions combined with Cl(-) ions that were present in the incoming water. Overall, CSI aims to control Legionella bacteria in drinking water, but plumbing material interactions, aesthetics and other implications also deserve consideration to holistically evaluate in-building drinking water disinfection.

Predictive modeling for hot water inactivation of planktonic and biofilm-associated Sphingomonas parapaucimobilis to support hot water sanitization programs

Hot water sanitization is a common means to maintain microbial control in process equipment for industries where microorganisms can degrade product or cause safety issues. This study compared the hot water inactivation kinetics of planktonic and biofilm-associated Sphingomonas parapaucimobilis at temperatures relevant to sanitization processes used in the pharmaceutical industry, viz. 65, 70, 75, and 80°C. Biofilms exhibited greater resistance to hot water than the planktonic cells. Both linear and nonlinear statistical models were developed to predict the log reduction as a function of temperature and time. Nonlinear Michaelis-Menten modeling provided the best fit for the inactivation data. Using the model, predictions were calculated to determine the times at which specific log reductions are achieved. While ≥80°C is the most commonly cited temperature for hot water sanitization, the predictive modeling suggests that temperatures ≥75°C are also effective at inactivating planktonic and biofilm bacteria in timeframes appropriate for the pharmaceutical industry.

Control of Legionella Contamination and Risk of Corrosion in Hospital Water Networks following Various Disinfection Procedures

Physical and chemical disinfection methods have been proposed with the aim of controlling Legionella water contamination. To date, the most effective procedures for reducing bacterial contamination have not yet been defined. The aim of this study was to assess the long-term effectiveness of various disinfection procedures in order to reduce both culturable and nonculturable (NC) legionellae in different hospital water networks treated with heat, chlorine dioxide, monochloramine, and hydrogen peroxide. The temperature levels and biocide concentrations that proved to give reliable results were analyzed. In order to study the possible effects on the water pipes, we verified the extent of corrosion on experimental coupons after applying each method for 6 months. The percentage of positive points was at its lowest after treatment with monochloramine, followed by chlorine dioxide, hydrogen peroxide, and hyperthermia. Different selections of Legionella spp. were observed, as networks treated with chlorine-based disinfectants were contaminated mainly by Legionella pneumophila serogroup 1, hyperthermia was associated with serogroups 2 to 14, and hydrogen peroxide treatment was associated mainly with non-pneumophila species. NC cells were detected only in heat-treated waters, and also when the temperature was approximately 60°C. The corrosion rates of the coupons were within a satisfactory limit for water networks, but the morphologies differed. We confirm here that chemical disinfection controls Legionella colonization more effectively than hyperthermia does. Monochloramine was the most effective treatment, while hydrogen peroxide may be a promising alternative to chlorine-based disinfectants due to its ability to select for other, less virulent or nonpathogenic species.

Combination of Heat Shock and Enhanced Thermal Regime to Control the Growth of a Persistent Legionella pneumophila Strain

Following nosocomial cases of Legionella pneumophila, the investigation of a hot water system revealed that 81.5% of sampled taps were positive for L. pneumophila, despite the presence of protective levels of copper in the water. A significant reduction of L. pneumophila counts was observed by culture after heat shock disinfection. The following corrective measures were implemented to control L. pneumophila: increasing the hot water temperature (55 to 60 °C), flushing taps weekly with hot water, removing excess lengths of piping and maintaining a water temperature of 55 °C throughout the system. A gradual reduction in L. pneumophila counts was observed using the culture method and qPCR in the 18 months after implementation of the corrective measures. However, low level contamination was retained in areas with hydraulic deficiencies, highlighting the importance of maintaining a good thermal regime at all points within the system to control the population of L. pneumophila.

Temperature diagnostic to identify high risk areas and optimize Legionella pneumophila surveillance in hot water distribution systems

Legionella pneumophila is frequently detected in hot water distribution systems and thermal control is a common measure implemented by health care facilities. A risk assessment based on water temperature profiling and temperature distribution within the network is proposed, to guide effective monitoring strategies and allow the identification of high risk areas. Temperature and heat loss at control points (water heater, recirculation, representative points-of-use) were monitored in various sections of five health care facilities hot water distribution systems and results used to develop a temperature-based risk assessment tool. Detailed investigations show that defective return valves in faucets can cause widespread temperature losses because of hot and cold water mixing. Systems in which water temperature coming out of the water heaters was kept consistently above 60 °C and maintained above 55 °C across the network were negative for Legionella by culture or qPCR. For systems not meeting these temperature criteria, risk areas for L. pneumophila were identified using temperature profiling and system's characterization; higher risk was confirmed by more frequent microbiological detection by culture and qPCR. Results confirmed that maintaining sufficiently high temperatures within hot water distribution systems suppressed L. pneumophila culturability. However, the risk remains as shown by the persistence of L. pneumophila by qPCR.

Synthesis and antimicrobial activity of monodisperse copper nanoparticles

Metallic monodisperse copper nanoparticles at a relatively high concentration (300 ppm CuNPs) have been synthesized by the reduction of copper salt with hydrazine in the aqueous SDS solution. The average particles size and the distribution size were characterized by Dynamic Light Scattering (DLS), Nanosight-Nanoparticle Tracking Analysis (NTA). The morphology and structure of nanoparticles were investigated using Scanning Electron Microscopy (SEM). The chemical composition of the copper nanoparticles was determined by X-ray Photoelectron Spectroscopy (XPS). Monodisperse copper nanoparticles with average diameter 50 nm were received. UV/vis absorption spectra confirmed the formation of the nanoparticles with the characteristic peak 550 nm. The antimicrobial studies showed that the copper nanoparticles had high activity against Gram-positive bacteria, standard and clinical strains, including methicillin-resistant Staphylococcus aureus, comparable to silver nanoparticles and some antibiotics. They also exhibited antifungal activity against Candida species.

Application of nanometal oxides in situ in nonwoven polyester fabric for the removal of bacterial indicators of pollution from wastewater

The objective of this study is to investigate and assess the use of in situ deposit nanosilver (nAg₂O) or nanocopper oxides (nCuO) into nonwoven polyester fabric (NWPF) as a safe and effective antibacterial filter of pollution from domestic wastewater. The bactericidal effect of both nAg₂O and nCuO was examined against Gram-negative bacteria (Escherichia coli, Salmonella typhi) and Gram-positive bacteria (Enterococcus faecalis, Staphylococcus aureus) using agar diffusion disk method. In addition, the capability of nAg₂O and nCuO as disinfectants for secondary treated domestic wastewater was investigated as a case study. Transmission electron microscope (TEM) confirmed the formation of nAg₂O and nCuO particles with average particle sizes of 15 and 41 nm, respectively. Disk diffusion results showed that nAg₂O had a higher bactericidal effect than nCuO. Moreover, the disinfection of secondary treated wastewater using 1.27 mg/cm³ of nAg₂O in the nonwoven fabric was capable of hindering 99.6% and 91.7% of total and fecal coliforms within 10 minutes with a residual value of 18 and 15 MPN-index/100 mL, respectively. The residual total and fecal coliform concentrations were far less than that stated in the national and international limits for wastewater reuse in agriculture purpose.

Inhibitory effects of silver ions on Legionella pneumophila grown on agar, intracellular in Acanthamoeba castellanii and in artificial biofilms

AIMS

We undertook a series of experiments to investigate the susceptibility of Legionella pneumophila grown under extracellular and intracellular conditions and other water-related bacteria to silver ions.

METHODS AND RESULTS

In this study, the antimicrobial effect of silver ions to intra- and extra-cellular grown Legionella bacteria was investigated. The minimal inhibitory concentration (MIC) after 24 h exposure, leading to a 5 log reduction, was c. 64 μg l(-1) AgNO(3) for extracellular grown Legionella and other tested Gram-positive and Gram-negative bacteria. In contrast, the MIC for intracellularly grown Legionella was up to 4096 μg l(-1) AgNO(3) after 24 h. Furthermore, the heterotrophic bacteria grown within a biofilm model were killed at a concentration of 4-16 μg l(-1) AgNO(3). In contrast, biofilm-associated Legionella were less sensitive (MIC 128-512 μg l(-1) AgNO(3)).

CONCLUSION

Intracellularly and biofilm-grown legionellae are less sensitive against silver compared with agar-grown bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

The reduced sensitivity of Legionella grown in amoebae might explain why the effect of silver decontamination requires an extended exposure in field trials.

Epidemiological investigation of a legionellosis outbreak in a Slovenian nursing home, August 2010

BACKGROUND

August 2010 marked the beginning of the largest outbreak of legionellosis in a Slovenian nursing home. This article presents our experiences with the outbreak investigation.

METHODS

In order to collect the necessary patient epidemiological data, we used individual epidemiological questionnaires. Samples were available from 15 patients and were subject to laboratory investigation. Urine and sputum samples were difficult to obtain due to the underlying diseases of the patients. Serological diagnostics constituted an important part of the epidemiological investigation. Sixty-four environmental samples were taken to identify the sources of infection. By genotyping, we assessed the affinity of the allelic profile of Legionella pneumophila serogroup 1 in environmental samples and in patient samples.

RESULTS

Legionnaires' disease was diagnosed in 10 patients based on a combination of various tests. Legionella pneumophila serogroup 1, Legionella pneumophila serogroups 2-14, and Legionella sp., in concentrations of < 10 to 61,000 CFU/l, were isolated from 51 out of 64 environmental samples. The source of the outbreak was confirmed by genotyping the isolates from patients and the isolates from the water supply system. The 2 isolates had identical allelic profiles corresponding to that of L. pneumophila serogroup 1 allelic profile 2,3,9,10,2,1,6, designated sequence type 23 (according to the European Working Group for Legionella Infections).

CONCLUSION

We describe a Legionella pneumophila serogroup 1 outbreak in a Slovenian nursing home. The source of infection was demonstrated using sequence-based typing. Water flow disturbances were determined as the most probable cause of Legionella growth. Overall, the risk of a Legionella outbreak is underestimated in Slovenia.

Controlling Legionella in hospital drinking water: an evidence-based review of disinfection methods

Hospital-acquired Legionnaires' disease is directly linked to the presence of Legionella in hospital drinking water. Disinfecting the drinking water system is an effective preventive measure. The efficacy of any disinfection measures should be validated in a stepwise fashion from laboratory assessment to a controlled multiple-hospital evaluation over a prolonged period of time. In this review, we evaluate systemic disinfection methods (copper-silver ionization, chlorine dioxide, monochloramine, ultraviolet light, and hyperchlorination), a focal disinfection method (point-of-use filtration), and short-term disinfection methods in outbreak situations (superheat-and-flush with or without hyperchlorination). The infection control practitioner should take the lead in selection of the disinfection system and the vendor. Formal appraisals by other hospitals with experience of the system under consideration is indicated. Routine performance of surveillance cultures of drinking water to detect Legionella and monitoring of disinfectant concentrations are necessary to ensure long-term efficacy.

Longitudinal evaluation of the efficacy of heat treatment procedures against Legionella spp. in hospital water systems by using a flow cytometric assay

Legionella spp. are frequently isolated in hospital water systems. Heat shock (30 min at 70°C) is recommended by the World Health Organization to control its multiplication. The aim of the study was to evaluate retrospectively the efficacy of heat treatments by using a flow cytometry assay (FCA) able to identify viable but nonculturable (VBNC) cells. The study included Legionella strains (L. pneumophila [3 clusters] and L. anisa [1 cluster]) isolated from four hot water circuits of different hospital buildings in Saint-Etienne, France, during a 20-year prospective surveillance. The strains recovered from the different circuits were not epidemiologically related, but the strains isolated within a same circuit over time exhibited an identical genotypic profile. After an in vitro treatment of 30 min at 70°C, the mean percentage of viable cells and VBNC cells varied from 4.6% to 71.7%. The in vitro differences in heat sensitivity were in agreement with the observed efficacy of preventive and corrective heating measures used to control water contamination. These results suggest that Legionella strains can become heat resistant after heating treatments for a long time and that flow cytometry could be helpful to check the efficacy of heat treatments on Legionella spp. and to optimize the decontamination processes applied to water systems for the control of Legionella proliferation.

Colonization of a therapeutic spa with Legionella spp: a public health issue

Traditional geothermally heated therapeutic spas, widely distributed in Europe, use water that is not disinfected. The colonization of therapeutic spas by Legionella spp. has been reported and several outbreaks and sporadic cases of legionellosis have been associated with the use of these facilities. We tested the effectiveness of hyperchlorination and the combination of hyperchlorination and ultraviolet light (UV) disinfection against legionellae which were persistently detected in the water used to supply the therapeutic spa. The hyperchlorination of the water distribution system was performed with a free residual chlorine concentration of 50 mg/l for 4h. An initial reduction in the numbers of legionellae was determined, but it rapidly increased to the original values. A UV unit was installed at the entrance to the spa's water distribution system and a new hyperchlorination procedure was performed immediately before UV irradiation (40 mJ/cm(2)), which was in use continuously for a nine-month period. While legionellae were not recovered during the irradiation period, these organisms were detected immediately after deactivation of the UV unit. We demonstrated that UV disinfection provides effective control of Legionella spp., with the advantage of being a method that, unlike chemical disinfectants, does not affect the physicochemical composition of the water. These findings suggest that UV irradiation, applied at key points in therapeutic spas, can be used to control colonization of water distribution systems by Legionella spp.

A cluster of cases of nosocomial legionnaires disease linked to a contaminated hospital decorative water fountain

BACKGROUND

Nosocomial outbreaks of Legionnaires disease have been linked to contaminated water in hospitals. Immunocompromised patients are particularly vulnerable and, when infected, have a high mortality rate. We report the investigation of a cluster of cases of nosocomial pneumonia attributable to Legionella pneumophila serogroup 1 that occurred among patients on our stem cell transplantation unit.

METHODS

We conducted a record review to identify common points of potential exposure, followed by environmental and water sampling for Legionella species from those sources. We used an air sampler to in an attempt to detect aerosolized Legionella and pulsed-field gel electrophoresis to compare clinical and environmental isolates.

RESULTS

The most likely sources identified were the water supply in the patients' rooms and a decorative fountain in the radiation oncology suite. Samples from the patients' rooms did not grow Legionella species. Cultures of the fountain, which had been restarted 4 months earlier after being shut off for 5 months, yielded L. pneumophila serogroup 1. The isolates from both patients and the fountain were identical by pulsed-field gel electrophoresis. Both patients developed pneumonia within 10 days of completing radiation therapy, and each reported having observed the fountain at close range. Both patients' infections were identified early and treated promptly, and both recovered.

CONCLUSIONS

This cluster was caused by contamination of a decorative fountain despite its being equipped with a filter and ozone generator. Fountains are a potential source of nosocomial Legionnaires disease despite standard maintenance and sanitizing measures. In our opinion, fountains present unacceptable risk in hospitals serving immunocompromised patients.

Strain specificity in antimicrobial activity of silver and copper nanoparticles

The antimicrobial properties of silver and copper nanoparticles were investigated using Escherichia coli (four strains), Bacillus subtilis and Staphylococcus aureus (three strains). The average sizes of the silver and copper nanoparticles were 3 nm and 9 nm, respectively, as determined through transmission electron microscopy. Energy-dispersive X-ray spectra of silver and copper nanoparticles revealed that while silver was in its pure form, an oxide layer existed on the copper nanoparticles. The bactericidal effect of silver and copper nanoparticles were compared based on diameter of inhibition zone in disk diffusion tests and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of nanoparticles dispersed in batch cultures. Bacterial sensitivity to nanoparticles was found to vary depending on the microbial species. Disk diffusion studies with E. coli and S. aureus revealed greater effectiveness of the silver nanoparticles compared to the copper nanoparticles. B. subtilis depicted the highest sensitivity to nanoparticles compared to the other strains and was more adversely affected by the copper nanoparticles. Good correlation was observed between MIC and MBC (r2=0.98) measured in liquid cultures. For copper nanoparticles a good negative correlation was observed between the inhibition zone observed in disk diffusion test and MIC/MBC determined based on liquid cultures with the various strains (r2=-0.75). Although strain-specific variation in MIC/MBC was negligible for S. aureus, some strain-specific variation was observed for E. coli.

In vitro efficacy of copper and silver ions in eradicating Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Acinetobacter baumannii: implications for on-site disinfection for hospital infection control

Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Acinetobacter baumannii are major opportunistic waterborne pathogens causing hospital-acquired infections. Copper-silver ionization has been shown to be effective in controlling Legionella colonization in hospital water systems. The objective was to determine the efficacy of copper and silver ions alone and in combination in eradicating P. aeruginosa, S. maltophilia and A. baumannii at the concentration applied to Legionella control. Kill curve experiments and mathematical modeling were conducted at copper and silver ion concentrations of 0.1, 0.2, 0.4, 0.8 and 0.01, 0.02, 0.04, 0.08 mg/L, respectively. The combinations of copper and silver ions were tested at concentrations of 0.2/0.02 and 0.4/0.04 mg/L, respectively. Initial organism concentration was ca. of 3 x 10(6)cfu/mL, and viability of the test organisms was assessed at predetermined time intervals. Samples (0.1 mL) withdrawn were mixed with 10 microL neutralizer solution immediately, serially diluted and plated in duplicate onto blood agar plates. The culture plates were incubated for 48 h at 37 degrees C and enumerated for the cfu (detection limit 10 cfu/mL). The results showed all copper ion concentrations tested (0.1-0.8 mg/L) achieved more than 99.999% reduction of P. aeruginosa which appears to be more susceptible to copper ions than S. maltophilia and A. baumannii. Silver ions concentration of 0.08 mg/L achieved more than 99.999% reduction of P. aeruginosa, S. maltophilia and A. baumannii in 6, 12 and 96 h, respectively. Combination of copper and silver ions exhibited a synergistic effect against P. aeruginosa and A. baumannii while the combination exhibited an antagonistic effect against S. maltophilia. Ionization may have a potential to eradicate P. aeruginosa, S. maltophilia and A. baumannii from hospital water systems.

The use of copper and silver in carbon point-of-use filters for the suppression of Legionella throughput in domestic water systems

AIMS

To evaluate throughput of seeded Legionella pneumophila bacteria in domestic point-of-use filters.

METHODS AND RESULTS

The filters were challenged with tap water seeded with Leg. pneumophila. After multiple challenge events (4.25 x 10(11) CFU per filter), the levels of Legionella were lower in the effluent from the filter containing both copper and silver (mean 4.48 x 10(3) CFU ml(-1)) than in the effluent from the filter containing copper only (1.26 x 10(4) CFU ml(-1); P < 0.001). After a single challenge event of approx. 5 x 10(9) CFU L. pneumophila per filter, there was no significant difference between the levels of Legionella in the effluents from a carbon filter containing copper and a carbon filter with no metals (mean 6.87 x 10(2) and 6.89 x 10(2) CFU ml(-1), respectively; P = 0.985).

CONCLUSIONS

Legionella was detected in filter effluent up to 6 weeks after being challenged, indicating that while filters may reduce the levels during an initial contamination event, the exposure is extended as the accumulated bacteria slough off over time.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has provided an understanding of the response of Legionella to the use of silver and copper in domestic point-of-use carbon filters.

Is copper–silver ionisation safe and effective in controlling legionella?

Copper-silver ionisation is gaining popularity worldwide as a water disinfection method. We review the literature that supports the effectiveness and safety of the copper-silver ionisation pertaining to legionella control in water distribution systems. A search between January 1997 and January 2007 was conducted in relevant health databases: Medline, Embase, NHS CRD, Cochrane Library Plus, Web of Knowledge, IME (Spanish Medical Index) and IBECS (Health Sciences Bibliographic Index). Ten published studies were selected according to inclusion and exclusion criteria previously established; most of these were experimental. Legionella levels decrease with the application of any of the procedures used in these studies and the procedures can be combined to obtain better outcomes. No studies containing an economic evaluation were found. We conclude that copper-silver ionisation is an effective method to control legionella, bearing in mind that eradication cannot be achieved by any method in isolation. Maintaining high temperatures in the water system can maximise effectiveness of the method. Copper-silver appears to be safe, as long as ion levels are monitored and kept within international recommended levels. More studies with concurrent control group, long follow-up and economic evaluation are required to properly assess this procedure.

Thermal disinfection of hotels, hospitals, and athletic venues hot water distribution systems contaminated by Legionella species

Legionella spp. (> or = 500 cfu liter(-1)) were detected in 92 of 497 water distribution systems (WDS) examined. Thermal disinfection was applied at 33 WDS. After the first and second application of the disinfection procedure, 15 (45.4%) and 3 (9%) positive for remedial actions WDS were found, respectively. Legionella pneumophila was more resistant to thermal disinfection than Legionella non-pneumophila spp. (relative risk [RR]=5.4, 95% confidence intervals [CI]=1-35). WDS of hotels with oil heater were more easily disinfected than those with electrical or solar heater (RR=0.4 95% CI=0.2-0.8). Thermal disinfection seems not to be efficient enough to eliminate legionellae, unless repeatedly applied and in combination with extended heat flushing, and faucets chlorine disinfection.

Inactivation of Pseudomonas aeruginosa and Aeromonas hydrophila by silver in tap water

This study was conducted to assess the efficacy of silver as a secondary disinfectant to replace or reduce the level of chlorine utilized in water distribution systems. Pseudomonas aeruginosa and Aeromonas hydrophila are opportunistic pathogens present in drinking water and have been associated with waterborne disease. After 8 hours of exposure to 100 microg/L of silver, there was a >6-log10 reduction in P. aeruginosa in tap water at room temperature at pH7 and a 5.55-log10 reduction in the presence of 3 mg/L humic acid. Similar reductions were observed at pH9. At 4 degrees C, reductions greater than 4-log10 were observed after 24 hours. For A. hydrophila, a >6-log10 reduction occurred at both pH7 and pH9 within nine hours. The World Health Organization has determined that this amount of silver could be used for water disinfection without health risks. Furthermore, silver shows promise as a secondary disinfectant, even in the presence of organic matter in concentrations that would reduce the effectiveness of free chlorine.

Silver as a disinfectant

Silver has been used as an antimicrobial for thousands of years. Over the past several decades, it has been introduced into numerous new venues such as in the treatment of water, in dietary supplements, in medical applications, and to produce antimicrobial coatings and products. Silver is often used as an alternative disinfectant in applications in which the use of traditional disinfectants such as chlorine may result in the formation of toxic by-products or cause corrosion of surfaces. Silver has also been demonstrated to produce a synergistic effect in combination with several other disinfectants. Many mechanisms of the antibacterial effect of silver have been described, but its antiviral and antiprotozoal mechanisms are not well understood. Both microbial tolerance and resistance to silver have been reported; however, the effect of silver has been observed against a wide variety of microorganisms over a period of years. Further research is needed to determine the antimicrobial efficacy of silver in these new applications and the effects of its long-term usage.

Biodiversity of amoebae and amoeba-resisting bacteria in a hospital water network

Free-living amoebae (FLA) are ubiquitous organisms that have been isolated from various domestic water systems, such as cooling towers and hospital water networks. In addition to their own pathogenicity, FLA can also act as Trojan horses and be naturally infected with amoeba-resisting bacteria (ARB) that may be involved in human infections, such as pneumonia. We investigated the biodiversity of bacteria and their amoebal hosts in a hospital water network. Using amoebal enrichment on nonnutrient agar, we isolated 15 protist strains from 200 (7.5%) samples. One thermotolerant Hartmannella vermiformis isolate harbored both Legionella pneumophila and Bradyrhizobium japonicum. By using amoebal coculture with axenic Acanthamoeba castellanii as the cellular background, we recovered at least one ARB from 45.5% of the samples. Four new ARB isolates were recovered by culture, and one of these isolates was widely present in the water network. Alphaproteobacteria (such as Rhodoplanes, Methylobacterium, Bradyrhizobium, Afipia, and Bosea) were recovered from 30.5% of the samples, mycobacteria (Mycobacterium gordonae, Mycobacterium kansasii, and Mycobacterium xenopi) were recovered from 20.5% of the samples, and Gammaproteobacteria (Legionella) were recovered from 5.5% of the samples. No Chlamydia or Chlamydia-like organisms were recovered by amoebal coculture or detected by PCR. The observed strong association between the presence of amoebae and the presence of Legionella (P < 0.001) and mycobacteria (P = 0.009) further suggests that FLA are a reservoir for these ARB and underlines the importance of considering amoebae when water control measures are designed.

Clinical and environmental distribution of Legionella pneumophila in a university hospital in Italy: efficacy of ultraviolet disinfection

The molecular epidemiology of Legionella pneumophila in the 'V. Monaldi' University Hospital was studied. Seven cases of nosocomial Legionnaires' disease were diagnosed between 1999 and 2003. Two clinical legionella strains obtained from two patients in the adult cardiac surgery unit (CSU) and 30 environmental legionella strains from the paediatric and adult CSUs, neonatal intensive care unit (NICU) and the cardiorespiratory intensive care unit (CR-ICU) were serotyped and genotyped. L. pneumophila serogroup 1/Philadelphia with an identical pulsed-field gel electrophoresis (PFGE) profile A was isolated from two patients in the adult CSU, and from three and one water samples taken in the adult CSU and the paediatric CSU, respectively, from 2001 to 2002. Furthermore, L. pneumophila serogroup 3 with an identical PFGE profile B was identified in 20 environmental strains from all wards, L. pneumophila serogroup 3 with PFGE profile C was identified in a single environmental strain from the CR-ICU, and non-pneumophila Legionella with identical PFGE profile D was identified in five environmental strains from the adult CSU, paediatric CSU and NICU. Ultraviolet irradiation was effective in disinfection of the hospital water supplies in the adult and paediatric CSUs contaminated by L. pneumophila clone associated with nosocomial Legionnaires' disease. In conclusion, these data demonstrate that two cases of nosocomial legionellosis were caused by the persistence of a single clone of L. pneumophila serogroup 1/Philadelphia in the hospital environment, and that disinfection by ultraviolet irradiation may represent an effective measure to prevent nosocomial Legionnaires' disease.