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Chlorine Disinfection of Legionella spp., L. pneumophila, and Acanthamoeba under Warm Water Premise Plumbing Conditions

Martin RL, Harrison K, Proctor CR, Martin A, Williams K, Pruden A, Edwards MA.

Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, USA.

Microorganisms 2020 Sep 22;8(9):1452.

Abstract: Premise plumbing conditions can contribute to low chlorine or chloramine disinfectant residuals and reactions that encourage opportunistic pathogen growth and create risk of Legionnaires' Disease outbreaks. This bench-scale study investigated the growth of Legionella spp. and Acanthamoeba in direct contact with premise plumbing materials-glass-only control, cross-linked polyethylene (PEX) pipe, magnesium anode rods, iron pipe, iron oxide, pH 10, or a combination of factors. Simulated glass water heaters (SGWHs) were colonized by Legionella pneumophila and exposed to a sequence of 0, 0.1, 0.25, and 0.5 mg/L chlorine or chloramine, at two levels of total organic carbon (TOC), over 8 weeks. Legionella pneumophila thrived in the presence of the magnesium anode by itself and or combination with other factors. In most cases, 0.5 mg/L Cl2 caused a significant rapid reduction of L. pneumophilaLegionella spp., or total bacteria (16S rRNA) gene copy numbers, but at higher TOC (>1.0 mg C/L), a chlorine residual of 0.5 mg/L Cl2 was not effective. Notably, Acanthamoeba was not significantly reduced by the 0.5 mg/L chlorine dose.


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

Martin RL, Strom OR, Pruden A, Edwards MA.

Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, USA.

Pathogens 2020 Sep 4;9(9):730.

Abstract: Flint, MI experienced two outbreaks of Legionnaires' Disease (LD) during the summers of 2014 and 2015, coinciding with use of Flint River as a drinking water source without corrosion control. Using simulated distribution systems (SDSs) followed by stagnant simulated premise (i.e., building) plumbing reactors (SPPRs) containing cross-linked polyethylene (PEX) or copper pipe, we reproduced trends in water chemistry and Legionella proliferation observed in the field when Flint River versus Detroit water were used before, during, and after the outbreak. Specifically, due to high chlorine demand in the SDSs, SPPRs with treated Flint River water were chlorine deficient and had elevated L. pneumophila numbers in the PEX condition. SPPRs with Detroit water, which had lower chlorine demand and higher residual chlorine, lost all culturable L. pneumophila within two months. L. pneumophila also diminished more rapidly with time in Flint River SPPRs with copper pipe, presumably due to the bacteriostatic properties of elevated copper concentrations caused by lack of corrosion control and stagnation. This study confirms hypothesized mechanisms by which the switch in water chemistry, pipe materials, and different flow patterns in Flint premise plumbing may have contributed to observed LD outbreak patterns.


Safety and Effectiveness of Monochloramine Treatment for Disinfecting Hospital Water Networks

Marchesi I, Paduano S, Frezza G, Sircana L, Vecchi E, Zuccarello P, Oliveri Conti G, Ferrante M, Borella P, Bargellini A.

Department of Biomedical, Metabolic and Neural Sciences, Section of Public Health, University of Modena and Reggio Emilia, Modena, Italy.

Int J Environ Res Public Health 2020 Aug 22;17(17):6116.

Abstract: The formation of potentially carcinogenic N-nitrosamines, associated with monochloramine, requires further research due to the growing interest in using this biocide for the secondary disinfection of water in public and private buildings. The aim of our study was to evaluate the possible formation of N-nitrosamines and other toxic disinfection by-products (DBPs) in hospital hot water networks treated with monochloramine. The effectiveness of this biocide in controlling Legionella spp. contamination was also verified. For this purpose, four different monochloramine-treated networks, in terms of the duration of treatment and method of biocide injection, were investigated. Untreated hot water, municipal cold water and, limited to N-nitrosamines analysis, hot water treated with chlorine dioxide were analyzed for comparison. Legionella spp. contamination was successfully controlled without any formation of N-nitrosamines. No nitrification or formation of the regulated DBPs, such as chlorites and trihalomethanes, occurred in monochloramine-treated water networks. However, a stable formulation of hypochlorite, its frequent replacement with a fresh product, and the routine monitoring of free ammonia are recommended to ensure a proper disinfection. Our study confirms that monochloramine may be proposed as an effective and safe strategy for the continuous disinfection of building plumbing systems, preventing vulnerable individuals from being exposed to legionellae and dangerous DBPs.


Legionella pneumophila and Protozoan Hosts: Implications for the Control of Hospital and Potable Water Systems

Nisar MA, Ross KE, Brown MH, Bentham R, Whiley H.

College of Science and Engineering, Flinders University, Adelaide, Australia.

Pathogens 2020 Apr 15;9(4):286.

Abstract: Legionella pneumophila is an opportunistic waterborne pathogen of public health concern. It is the causative agent of Legionnaires' disease (LD) and Pontiac fever and is ubiquitous in manufactured water systems, where protozoan hosts and complex microbial communities provide protection from disinfection procedures. This review collates the literature describing interactions between L. pneumophila and protozoan hosts in hospital and municipal potable water distribution systems. The effectiveness of currently available water disinfection protocols to control L. pneumophila and its protozoan hosts is explored. The studies identified in this systematic literature review demonstrated the failure of common disinfection procedures to achieve long term elimination of L. pneumophila and protozoan hosts from potable water. It has been demonstrated that protozoan hosts facilitate the intracellular replication and packaging of viable L. pneumophila in infectious vesicles; whereas, cyst-forming protozoans provide protection from prolonged environmental stress. Disinfection procedures and protozoan hosts also facilitate biogenesis of viable but non-culturable (VBNC) L. pneumophila which have been shown to be highly resistant to many water disinfection protocols. In conclusion, a better understanding of L. pneumophila-protozoan interactions and the structure of complex microbial biofilms is required for the improved management of L. pneumophila and the prevention of LD.


Persistent Legionella contamination of water faucets in a tertiary hospital in Japan

Nakamura I, Amemura-Maekawa J, Kura F, Kobayashi T, Sato A, Watanabe H, Matsumoto T.

Department of Infection Prevention and Control, Tokyo Medical University Hospital, Tokyo, Japan.

Int J Infect Dis 2020 Apr;93:300-304.

Abstract: Objective: The feasibility of the decontamination procedure for Legionella pneumophila of water systems in healthcare facilities varies by water purification and disinfection methods in each country. We evaluated the efficacy of feasible decontamination strategies in Japan. Methods: This study was conducted at Tokyo Medical University Hospital (1015 beds) between 2015 and 2018. Samples from the water system and cooling tower were cultured periodically. Hyper-chlorination of cool tap water (>0.2 ppm), increases in the temperature of hot water (>55 C), and flushing were used as decontamination strategies. The case of healthcare-associated legionellosis was surveyed. Environmental and clinical isolates were genotyped. Results: 1439 environmental samples were collected; 19 (1.3%) samples tested positive for L. pneumophila from water faucets of patient rooms, toilets, waste rooms, and water sourced from wells. Genotyping of 12 isolates confirmed that the same strains were present in eight environmental isolates and two isolates from patients over three years. Although the environmental contamination of the water system was persistent, the number of positive locations of hospital environments gradually decreased; eight in 2015, four in 2016, three in 2017, and four in 2018, respectively. Conclusions: Monitoring contamination, hyper-chlorination, controlling temperature, and flushing were effective as a Legionella decontamination strategy.


Effect of disinfectant residuals on infection risks from Legionella pneumophila released by biofilms grown under simulated premise plumbing conditions

Huang C, Shen Y, Smith RL, Dong S, Nguyen TH.

Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.

Environ Int 2020 Apr;137:105561.

Abstract: The ubiquitous presence of biofilms in premise plumbing and stagnation, which commonly occurs in premise plumbing, can exacerbate the decay of chlorine residual in drinking water. Using biofilms grown in a simulated premise plumbing setup fed directly with freshly treated water at two full-scale water treatment plants, we previously determined the mass transfer coefficients for chlorine decay in premise plumbing. These coefficients coupled with inactivation kinetics of L. pneumophila released from biofilms reported previously were integrated into a Monte Carlo framework to estimate the infection risk of biofilm-derived L. pneumophila from 1 to 48 h of stagnation. The annual infection risk was significantly higher when water stayed stagnant for up to 48 h in pipes covered internally with biofilms, compared to clean pipes without biofilms. The decay of residual chlorine due to biofilms during 48-hour stagnation led to up to 6 times increase in the annual infection risk compared to the case where biofilms was absent. Global sensitivity analysis revealed that the rate of L. pneumophila detachment from biofilms and the decay of chlorine residual during stagnation are the two most important factors influencing the infection risks. Stagnation caused by water use patterns and water-saving devices in the premise plumbing can lead to increased infection risk by biofilm-derived L. pneumophila. Overall, this study's findings suggested that biofilms could induce chlorine decay and consequently increase L. pneumophila infection risk. Thus, reducing stagnation, maintaining residual chlorine, and suppressing biofilm growth could contribute to better management of L. pneumophila infection risk.


Photocatalytic biocidal effect of copper doped TiO2 nanotube coated surfaces under laminar flow, illuminated with UVA light on Legionella pneumophila

Oder M, Koklič T, Umek P, Podlipec R, trancar J, Dobeic M.

Institute of Food Safety Feed and Environment, University of Ljubljana, Veterinary Faculty, Ljubljana, Slovenia.

PLoS One 2020 Jan 15;15(1):e0227574.

Abstract: Legionella pneumophila can cause a potentially fatal form of humane pneumonia (Legionnaires' disease), which is most problematic in immunocompromised and in elderly people. Legionella species is present at low concentrations in soil, natural and artificial aquatic systems and is therefore constantly entering man-made water systems. The environment temperature for it's ideal growth range is between 32 and 42C, thus hot water pipes represent ideal environment for spread of Legionella. The bacteria are dormant below 20C and do not survive above 60C. The primary method used to control the risk from Legionella is therefore water temperature control. There are several other effective treatments to prevent growth of Legionella in water systems, however current disinfection methods can be applied only intermittently thus allowing Legionella to grow in between treatments. Here we present an alternative disinfection method based on antibacterial coatings with Cu-TiO2 nanotubes deposited on preformed surfaces. In the experiment the microbiocidal efficiency of submicron coatings on polystyrene to the bacterium of the genus Legionella pneumophila with a potential use in a water supply system was tested. The treatment thus constantly prevents growth of Legionella pneumophila in presence of water at room temperature. Here we show that 24-hour illumination with low power UVA light source (15 W/m2 UVA illumination) of copper doped TiO2 nanotube coated surfaces is effective in preventing growth of Legionella pneumophila. Microbiocidal effects of Cu-TiO2 nanotube coatings were dependent on the flow of the medium and the intensity of UV-A light. It was determined that tested submicron coatings have microbiocidal effects specially in a non-flow or low-flow conditions, as in higher flow rates, probably to a greater possibility of Legionella pneumophila sedimentation on the coated polystyrene surfaces, meanwhile no significant differences among bacteria reduction was noted regarding to non or low flow of medium.


Photocatalytic biocidal effect of copper doped TiO2 nanotube coated surfaces under laminar flow, illuminated with UVA light on Legionella pneumophila

Oder M, Koklič T, Umek P, Podlipec R, trancar J, Dobeic M.

Institute of Food Safety Feed and Environment, University of Ljubljana, Veterinary Faculty, Ljubljana, Slovenia.

PLoS One 2020 Jan;15(1):e0227574. 

Abstract: Legionella pneumophila can cause a potentially fatal form of humane pneumonia (Legionnaires' disease), which is most problematic in immunocompromised and in elderly people. Legionella species is present at low concentrations in soil, natural and artificial aquatic systems and is therefore constantly entering man-made water systems. The environment temperature for its ideal growth range is between 32 and 42C, thus hot water pipes represent ideal environment for spread of Legionella. The bacteria are dormant below 20C and do not survive above 60C. The primary method used to control the risk from Legionella is therefore water temperature control. There are several other effective treatments to prevent growth of Legionella in water systems, however current disinfection methods can be applied only intermittently thus allowing Legionella to grow in between treatments. Here we present an alternative disinfection method based on antibacterial coatings with Cu-TiO2 nanotubes deposited on preformed surfaces. In the experiment the microbiocidal efficiency of submicron coatings on polystyrene to the bacterium of the genus Legionella pneumophila with a potential use in a water supply system was tested. The treatment thus constantly prevents growth of Legionella pneumophila in presence of water at room temperature. Here we show that 24-hour illumination with low power UVA light source (15 W/m2 UVA illumination) of copper doped TiO2 nanotube coated surfaces is effective in preventing growth of Legionella pneumophila. Microbiocidal effects of Cu-TiO2 nanotube coatings were dependent on the flow of the medium and the intensity of UV-A light. It was determined that tested submicron coatings have microbiocidal effects specially in a non-flow or low-flow conditions, as in higher flow rates, probably to a greater possibility of Legionella pneumophila sedimentation on the coated polystyrene surfaces, meanwhile no significant differences among bacteria reduction was noted regarding to non or low flow of medium.


Impact of Chlorine and Chloramine on the Detection and Quantification of Legionella pneumophila and Mycobacterium Species

Donohue MJ, Vesper S, Mistry J, Donohue JM.

U.S. Environmental Protection Agency, Cincinnati, Ohio, USA.

Appl Environ Microbiol 2019 Nov;85(24):e01942-19.

Abstract: Potable water can be a source of transmission for legionellosis and nontuberculous mycobacterium (NTM) infections and diseases. Legionellosis is caused largely by Legionella pneumophila, specifically serogroup 1 (Sg1). Mycobacterium aviumMycobacterium intracellulare, and Mycobacterium abscessus are three leading species associated with pulmonary NTM disease. The estimated rates of these diseases are increasing in the United States, and the cost of treatment is high. Therefore, a national assessment of water disinfection efficacy for these pathogens was needed. The disinfectant type and total chlorine residual (TClR) were investigated to understand their influence on the detection and concentrations of the five pathogens in potable water. Samples (n=358) were collected from point-of-use taps (cold or hot) from locations across the United States served by public water utilities that disinfected with chlorine or chloramine. The bacteria were detected and quantified using specific primer and probe quantitative-PCR (qPCR) methods. The total chlorine residual was measured spectrophotometrically. Chlorine was the more potent disinfectant for controlling the three mycobacterial species. Chloramine was effective at controlling L. pneumophila and Sg1. Plotting the TClR associated with positive microbial detection showed that an upward TClR adjustment could reduce the bacterial count in chlorinated water but was not as effective for chloramine. Each species of bacteria responded differently to the disinfection type, concentration, and temperature. There was no unifying condition among the water characteristics studied that achieved microbial control for all. This information will help guide disinfectant decisions aimed at reducing occurrences of these pathogens at consumer taps and as related to the disinfectant type and TClR. IMPORTANCE: The primary purpose of tap water disinfection is to control the presence of microbes. This study evaluated the role of disinfectant choice on the presence at the tap of L. pneumophila, its Sg1 serogroup, and three species of mycobacteria in tap water samples collected at points of human exposure at locations across the United States. The study demonstrates that microbial survival varies based on the microbial species, disinfectant, and TClR.


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

Girolamini L, Dormi A, Pellati T, Somaroli P, Montanari D, Costa A, Savelli F, Martelli A, Grottola A, Fregni Serpini G, Cristino S.

Department of Biological, Geological, and Environmental Sciences, BiGeA, University of Bologna, Bologna, Italy.

Pathogens 2019 Oct;8(4):209. 

Abstract: 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 LegionellaPseudomonas 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.


Antimicrobial Effect of Visible Light-Photoinactivation of Legionella rubrilucens by Irradiation at 450, 470, and 620 nm

Schmid J, Hoenes K, Vatter P, Hessling M.

Ulm University of Applied Sciences, Department of Medical Engineering and Mechatronics, Ulm, Germany.

Antibiotics (Basel) 2019 Oct;8(4):187. 

Abstract: Despite the high number of Legionella infections, there are currently no convincing preventive measures. Photoinactivation with visible light is a promising new approach and the photoinactivation sensitivity properties of planktonic Legionella rubrilucens to 450, 470, and 620 nm irradiation were thus investigated and compared to existing 405 nm inactivation data for obtaining information on responsible endogenous photosensitizers. Legionella were streaked on agar plates and irradiated with different doses by light emitting diodes (LEDs) of different visible wavelengths. When irradiating bacterial samples with blue light of 450 nm, a 5-log reduction could be achieved by applying a dose of 300 J cm-2, whereas at 470 nm, a comparable reduction required about 500 J cm-2. For red irradiation at 620 nm, no inactivation could be observed, even at 500 J cm-2. The declining photoinactivation sensitivity with an increasing wavelength is consistent with the assumption of porphyrins and flavins being among the relevant photosensitizers. These results were obtained for L. rubrilucens, but there is reason to believe that its inactivation behavior is similar to that of pathogenic legionella species. Therefore, this photoinactivation might lead to new future concepts for legionella reduction and prevention in technical applications or even on or inside the human body.


Chlorine and Monochloramine Disinfection of Legionella pneumophila Colonizing Copper and Polyvinyl Chloride Drinking Water Biofilms

Buse HY, J Morris B, Struewing IT, Szabo JG.

U.S. Environmental Protection Agency, Office of Research and Development, National Homeland Security Research Center, Cincinnati, Ohio, USA.

Appl Environ Microbiol 2019;85(7):e02956-18.

Abstract: Building water systems promote the regrowth and survival of opportunistic pathogens, such as Legionella pneumophila, especially within biofilms, where most drinking water microbes reside. However, compared to their planktonic form, disinfection efficacy for the biofilm-associated forms of water-based pathogens is unclear. The aim of this study was to determine the effectiveness of free chlorine and monochloramine in the inactivation of biofilm-associated L. pneumophila strain Philadelphia-1 serogroup 1 (LpP1s1). Mature (1.5- to 2-year-old) drinking water biofilms were developed on copper (Cu) and polyvinyl chloride (PVC) slides within biofilm annular reactors, then colonized with LpP1s1 at approximately 4 log10 CFU cm-2 and exposed to 2 mg liter-1 of free chlorine or monochloramine. Ct (disinfectant concentration time, expressed as mg min liter-1) inactivation values for 2-, 3-, and 4-log10 reductions of planktonic and biofilm LpP1s1 were determined. For planktonic LpP1s1, free chlorine was more effective at inactivation than was monochloramine treatment, and for biofilm associated LpP1s1, monochloramine was more effective on Cu biofilms while free chlorine was more effective on PVC biofilms. In contrast to monochloramine, free chlorine treatment of Cu and PVC biofilms, negatively impacted LpP1s1 16S rRNA gene transcript levels and may act synergistically with Cu surfaces to further reduce transcript levels. Moreover, LpP1s1 cells shed from biofilms into the bulk water were more resistant to disinfection than were prepared planktonic LpP1s1 cells. Results from this study indicate that biofilm association, disinfectant type, and substratum play an important role in the survival of Legionella pneumophila in building water systems. IMPORTANCE: Microbial regrowth within building water systems are promoted by water stagnation, low disinfectant residual, high surface-to-volume ratio, amenable growth temperatures, and colonization of drinking water biofilms. Moreover, biofilms provide protection from environmental stresses, access to higher levels of nutrients, and opportunities for symbiotic interactions with other microbes. Disinfectant efficacy information is historically based on inactivation of pathogens in their planktonic, free-floating forms. However, due to the ecological importance of drinking water biofilms for pathogen survival, this study evaluated the efficacy of two common disinfectants, free chlorine and monochloramine, on Legionella pneumophila colonizing mature, drinking water biofilms established on copper and PVC surfaces. Results showed that inactivation was dependent on the disinfectant type and biofilm substratum. Overall, this, and other related research, will provide a better understanding of Legionella ecological stability and survival and aid policy makers in the management of exposure risks to water-based pathogens within building water systems.


Controlling Legionella pneumophila in Water Systems at Reduced Hot Water Temperatures with Copper and Silver Ionization

Cloutman-Green E, Barbosa VL, Jimenez D, Wong D, Dunn H, Needham B, Ciric L, Hartley JC.

Department of Microbiology, Virology, and Infection Prevention Control, Great Ormond Street Hospital NHS Foundation Trust, London, United Kingdom.

Am J Infect Control 2019 Jul;47(7):761-766.

Abstract: Background: Hospital-acquired Legionnaires' disease is associated with the presence of Legionella pneumophila in hospital water systems. In the United Kingdom, the Department of Health recommends maintaining hot water temperatures >55C and cold water temperatures <20C at the point of delivery to prevent proliferation of L. pneumophila in water systems. In this study, we evaluated the efficacy of copper and silver ionization to control L. pneumophila at deliberately reduced hot water temperatures (43C) within a newly installed water system in a new building linked to a large health care facility in the United Kingdom. Methods: One thousand, five hundred ninety-eight water samples were collected between September 2011 and June 2017. Samples were tested using accredited methods for L. pneumophila, copper and silver ion levels, and total viable counts. Energy consumption and water usage data were also collected to permit carbon emission calculations. Results: The results of 1,598 routine samples from September 2011 to June 2017, and the recordings of temperatures at outlets in this facility, demonstrated effective (100%) L. pneumophila control throughout the study period with an average hot water temperature of 42C. The energy savings and reduction of carbon emissions were calculated to amount to 33% and 24%, respectively, compared to an equivalent temperature-controlled system. Water system management interventions were required to achieve consistently adequate levels of copper and silver across outlets. Conclusions: This study demonstrated that it is possible to control L pneumophila independent of temperature when copper and silver ionization is introduced into a new building in conjunction with an appropriately managed water system.


Environmental Surveillance of Legionella Spp. Colonization in the Water System of a Large Academic Hospital: Analysis of the Four-Year Results on the Effectiveness of the Chlorine Dioxide Disinfection Method

Vincenti S, de Waure C, Raponi M, Teleman AA, Boninti F, Bruno S, Boccia S, Damiani G, Laurenti P.

Fondazione Policlinico Universitario A. Gemelli IRCCS, Roma, Italy.

Sci Total Environ 2019 Mar;657:248-253.

Abstract: The prevention of Legionella colonization of water systems is one of the goals of hospital management. Among chemical disinfection methods, chlorine dioxide (ClO2) has been largely used to control Legionella spp. in water systems. We performed a retrospective study to analyse data deriving from the surveillance plan of the water system in a large academic hospital in Rome (Italy) during the period August 2011 and August 2018. We collected the data deriving from the routine water samples used to monitor Legionella spp. colonization. Data from the water samples collected from 163 selected sampling points (hot water tanks, the return loop and distal outlets) was analysed using a life table analysis in order to investigate the duration of the effectiveness of the ClO2 method in eradicating Legionella spp. The colonization of the water sample by Legionella spp. was considered as the outcome. Our results show that in 81,59% of the sampling points Legionella spp. were never detected at four years of follow up. Chemical and physical characteristics of the water were also compared between the samples which were positive for Legionella spp. and those which were not. No association was found between these factors. The knowledge of the duration over time of the effectiveness of the ClO2 disinfection method could support decision-making processes in the framework of Risk Management activities in hospitals. Future studies could also be conducted in hospitals to compare the long-term cost-effectiveness of different Legionella spp. colonization prevention methods.


Role of Hot Water Temperature and Water System Use on Legionella Control in a Tertiary Hospital: An 8-year Longitudinal Study

Gavald L, Garcia-Nuez M, Quero S, Gutierrez-Milla C, Sabri M.

Department of Preventive Medicine-Hospital Hygiene, Hospital Universitari de Bellvitge-IDIBELL, Barcelona, Spain.

Water Res 2019 Feb;149:460-466.

Abstract: 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 ≥55C, 64.9% when between 50.1C and 54.0C, and 51.6% when ≤50C (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 55C. 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 55C is significantly better than that at 50C 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.


Electrically Heatable Carbon Nanotube Point-Of-Use Filters for Effective Separation and In-Situ Inactivation of Legionella pneumophila

Oh Y, Noga R, Shanov V, Ryu H, Chandra H, Yadav B, Yadav J, Chae S.

Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221, U.S.A.

Chem Eng J 2019;366:21-26.

Abstract: Despite municipal chlorination and secondary disinfection, opportunistic waterborne pathogens (e.g., Legionella spp.) persist in public and private water distribution systems. As a potential source of healthcare-acquired infections, this warrants development of novel pathogen removal and inactivation systems. In this study, electrically heatable carbon nanotube (CNT) point-of-use (POU) filters have been designed to remove and inactivate Legionella pneumophila in water.

The CNT/polymer composite membranes effectively removed Legionella (>99.99%) (i.e., below detection limit) and were able to inactive them on the membrane surface at 100% efficiency within 60 s using ohmic heating at 20 V. The novel POU filters could be used as a final barrier to provide efficient rejection of pathogens and thereby simultaneously eliminate microorganisms in public and private water supplies.



Effectiveness of a Neutral Electrolysed Oxidising Water (NEOW) Device in Reducing Legionella pneumophila in a Water Distribution System: A Comparison Between Culture, qPCR and PMA-qPCR Detection Methods

Bonetta S, Pignata C, Bonetta S, Meucci L, Giacosa D, Marino E, Gorrasi I, Gilli G, Carraro E.

Department of Public Health and Pediatrics, University of Torino, Torino, Italy.

Chemosphere 2018 Nov;210:550-556.

Abstract: Disinfection of hot water systems is critical for reducing Legionnaires' disease in high-risk buildings. The use of neutral electrolysed oxidising water (NEOW) is a promising method for the control of microorganisms in hot water systems. However, full-scale evaluations of the efficacy of NEOW devices to control Legionella pneumophila are currently lacking. The aim of this study was to assess the effectiveness of a NEOW device in reducing L. pneumophila in a hotel water network. Water samples (n=67) were collected from different sites of a hotel distribution system before and after the installation of the NEOW device at the 1st, 4th, 8th and 12th week. Detection of L. pneumophila was performed comparing culture, qPCR and PMA-qPCR methods. Total bacterial counts (22C and 37C), Pseudomonas spp. and physico-chemical parameters were also monitored. The NEOW treatment resulted in a reduction of the amount of L. pneumophila positive samples (-32%) and of the number of heavily contaminated points (>104 CFU/L and >103 CFU/L) (-100% and -96%, respectively). Treatment maintained L. pneumophila at low levels (<102 CFU/L), which do not require specific intervention measures. The effectiveness of the disinfection system was also confirmed by PMA-qPCR (p<0.001). The use of PMA resulted in a signal decrease in almost all samples upon the disinfection treatment. The NEOW disinfection device appears to be a promising approach to reduce the colonisation of hot water systems by L. pneumophila; however, further investigations are needed to ascertain its efficiency over longer time periods.


Electrochemical Disinfection of Groundwater for Civil Use - An Example of an Effective Endogenous Advanced Oxidation Process

De Battisti A, Formaglio P, Ferro S, Al Aukidy M, Verlicchi P.

Department of Engineering, University of Ferrara, Ferrara, Italy.

Chemosphere 2018 Sep;207:101-109.

Abstract: Lab-scale experiments using real groundwater were carried out using the CabECO reactor system in order to evaluate its suitability for producing safe water, acceptable for civil purposes. Trials were carried out in discontinuous and in continuous mode, analyzing the influence of electrical and hydraulic process parameters on the quality of treated water. The use of highly boron-doped diamond electrodes in the reactor allowed the electrosynthesis of considerable amounts of ozone. Because of the relatively high amount of chloride in the groundwater samples, a mixture of HOCl/ClO- was also synthesized. Somewhat unexpectedly, the increase in the current density in the explored range 100-1000 A m-2 was accompanied by an increase in the faradaic yield of the electrosynthesis of oxidants, which was more pronounced for ozone than for free chlorine. As reported in literature, the main radical intermediate in the relevant reactions is OH, which can lead to different oxidation products, namely ozone and HOCl/ClO-. The electrolytic treatment also caused a decrease in the concentration of minor components, including NH4+ and Br-. Other byproducts were ClO3- and ClO4-, although their concentration levels were low. Moreover, due to alkali formation at the cathode surface, the precipitation of calcium and magnesium carbonates was also observed. In addition, the experimental investigation showed that even Pseudomonas aeruginosa and Legionella could be completely removed in the treated stream, due to the unique capacity of the reactor to synthesize biocidal agents like ozone, HOCl/ClO-, and chloramines. These effects were particularly evident during batch experiments.


Preventing Healthcare-Associated Legionellosis: Results After 3 Years of Continuous Disinfection of Hot Water with Monochloramine and an Effective Water Safety Plan

Coniglio MA, Ferrante M, Yassin MH.

Legionella Reference Laboratory, Department of Medical, Surgical Sciences and Advanced Technologies "G.F. Ingrassia", University of Catania, Catania, Italy.

Int J Environ Res Public Health 2018 Jul;15(8):1594.

Abstract: The purpose of this study is to report the experience of the implementation and application of a 3-year Water Safety Plan (WSP) together with the secondary disinfection of water by monochloramine to control and prevent healthcare-associated legionellosis in an Italian hospital strongly colonized by Legionella. Risk assessment was carried out by the WSP team. The main critical control points focused on in developing the WSP for the control of Legionella was the water distribution system. A sampling plan for the detection of Legionella was implemented. A widespread contamination of the hot water distribution system by L. pneumophila sg5 was found. Results after 3 years of the continuous disinfection of hot water with monochloramine indicate the eradication of Legionella. The implementation and application of a WSP in a hospital, together with the disinfection of the water distribution system with monochloramine, can be effective in controlling the growth of Legionella and in preventing nosocomial legionellosis.


Occurrence of Legionella Spp. In Water-Main Biofilms from Two Drinking Water Distribution Systems

Waak MB, LaPara TM, Hall C, Hozalski RM.

Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, Minnesota, USA.

Environ Sci Technol 2018 Jul;52(14):7630-7639.

Abstract: The maintenance of a chlorine or chloramine residual to suppress waterborne pathogens in drinking water distribution systems is common practice in the United States but less common in Europe. In this study, we investigated the occurrence of Bacteria and Legionella spp. in water-main biofilms and tap water from a chloraminated distribution system in the United States and a system in Norway with no residual using real-time quantitative polymerase chain reaction (qPCR). Despite generally higher temperatures and assimilable organic carbon levels in the chloraminated system, total Bacteria and Legionella spp. were significantly lower in water-main biofilms and tap water of that system (p<0.05). Legionella spp. were not detected in the biofilms of the chloraminated system (0 of 35 samples) but were frequently detected in biofilms from the no-residual system (10 of 23 samples; maximum concentration = 7.8104 gene copies cm-2). This investigation suggests water-main biofilms may serve as a source of Legionella for tap water and premise plumbing systems, and residual chloramine may aid in reducing their abundance.


Plasmas Ozone Inactivation of Legionella in Deionized Water and Wastewater

Li J, Li X, Li K, Tao T.

School of Environmental Science and Engineering, Zhejiang Gongshang University, Zhejiang, Hangzhou, China.

Environ Sci Pollut Res Int 2018 Apr;25(10):9697-9707.

Abstract: The results show that ozone concentration Apr determination using ultraviolet spectrophotometry (UV-2450) at 258 nm is easier than using indigo method at 600 nm. A strong linear relationship was found between purge time and O3 concentration in deionized water. Ozone concentration can be predicted in deionized water. A higher O3 flow rate or lower temperature led to a higher O3 concentration. Ozone concentration was stable in 60 min, so that ozone self-decomposition could be ignored at ozone concentrations below 0.4 mg L-1. A higher temperature led to a higher inactivation efficiency and rate, and that a lower temperature led to a lower ozone decay rate and inactivation efficiency even if ozone solubility increased when temperature decreased. The fastest inactivation rate occurred before c0t = 165 μg L-1 s, but the inactivation rate decreased after c0t = 165 μg L-1 s with tail phenomena. The tail phenomena were clearly observed and may be caused by oxidization of lipopolysaccharides (LPS), cell membrane, etc. The activation energy Ea =55,4040.3 J mol-1 were obtained for Legionella inactivation with ozone in deionized water. Ozone maximum decay rate was positively proportional to COD concentration. COD impacted on ozone concentration seriously. Higher COD concentration resulted in higher ozone decay rate. COD could result in ozone concentration decrement rapidly to a steady value in 5 s. Higher initial ozone concentration resulted in higher germ inactivation rate. Higher initial COD concentration resulted in lower Legionella inactivation efficiency. COD was easier to react with ozone than Legionella. The relationship among the initial COD concentrations COD0, the initial O3 concentration c0, and the O3 contact time t necessary for a 99.999% reduction of Legionella in wastewater can be expressed in some equations. O3 disinfection time t necessary for a 99.999% reduction of Legionella can be predicted by Eqs. (10) and (11).


Microbial Community Composition of Tap Water and Biofilms Treated with or without Copper-Silver Ionization

Stken A, Haverkamp THA, Dirven HAAM, Gilfillan GD, Leithaug M, Lund V.

Dept. Zoonotic, Food and Waterborne Infections, Norwegian Institute of Public Health, Oslo, Norway.

Environ Sci Technol 2018 Mar;52(6):3354-3364.

Abstract: Copper-silver ionization (CSI) is an in-house water disinfection method primarily installed to eradicate Legionella bacteria from drinking water distribution systems (DWDS). Its effect on the abundance of culturable Legionella and Legionella infections has been documented in several studies. However, the effect of CSI on other bacteria in DWDS is largely unknown. To investigate these effects, we characterized drinking water and biofilm communities in a hospital using CSI, in a neighboring building without CSI, and in treated drinking water at the local water treatment plant. We used 16S rDNA amplicon sequencing and Legionella culturing. The sequencing results revealed three distinct water groups: (1) cold-water samples (no CSI), (2) warm-water samples at the research institute (no CSI), and (3) warm-water samples at the hospital (after CSI; ANOSIM, p<0.001). Differences between the biofilm communities exposed and not exposed to CSI were less clear (ANOSIM, p=0.022). No Legionella were cultured, but limited numbers of Legionella sequences were recovered from all 25 water samples (0.2-1.4% relative abundance). The clustering pattern indicated local selection of Legionella types (Kruskal-Wallis, p<0.001). Furthermore, one unclassified Betaproteobacteria OTU was highly enriched in CSI-treated warm water samples at the hospital (Kruskal-Wallis, p<0.001).


Inactivation Kinetics and Efficiencies of UV-LEDs against Pseudomonas aeruginosa, Legionella pneumophila, and Surrogate Microorganisms

Rattanakul SOguma K.

Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan.

Water Res 2018 Mar;130:31-37.

Abstract: To demonstrate the effectiveness of UV light-emitting diodes (UV-LEDs) to disinfect water, UV-LEDs at peak emission wavelengths of 265, 280, and 300 nm were adopted to inactivate pathogenic species, including Pseudomonas aeruginosa and Legionella pneumophila, and surrogate species, including Escherichia coli, Bacillus subtilis spores, and bacteriophage Qβ in water, compared to conventional low-pressure UV lamp emitting at 254 nm. The inactivation profiles of each species showed either a linear or sigmoidal survival curve, which both fit well with the Geeraerd's model. Based on the inactivation rate constant, the 265-nm UV-LED showed most effective fluence, except for with E. coli which showed similar inactivation rates at 265 and 254 nm. Electrical energy consumption required for 3-log10 inactivation (EE,3) was lowest for the 280-nm UV-LED for all microbial species tested. Taken together, the findings of this study determined the inactivation profiles and kinetics of both pathogenic bacteria and surrogate species under UV-LED exposure at different wavelengths. We also demonstrated that not only inactivation rate constants, but also energy efficiency should be considered when selecting an emission wavelength for UV-LEDs.


Effect of Heat Shock on Hot Water Plumbing Microbiota and Legionella pneumophila Control

Ji P, Rhoads WJ, Edwards MA, Pruden A.

Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, USA.

Microbiome 2018 Feb;6(1):30.

Abstract: Background: Heat shock is a potential control strategy for Legionella pneumophila in hot water plumbing systems. However, it is not consistently effective, with little understanding of its influence on the broader plumbing microbiome. Here, we employed a lab-scale recirculating hot water plumbing rig to compare the pre- and post-"heat shock" (i.e., 40 60 40C) microbiota at distal taps. In addition, we used a second plumbing rig to represent a well-managed system at 60C and conducted a "control" sampling at 60C, subsequently reducing the temperature to 40C to observe the effects on Legionella and the microbiota under a simulated "thermal disruption" scenario. Results: According to 16S rRNA gene amplicon sequencing, in the heat shock scenario, there was no significant difference or statistically significant, but small, difference in the microbial community composition at the distal taps pre- versus post-heat shock (both biofilm and water; weighted and unweighted UniFrac distance matrices). While heat shock did lead to decreased total bacteria numbers at distal taps, it did not measurably alter the richness or evenness of the microbiota. Quantitative PCR measurements demonstrated that L. pneumophila relative abundance at distal taps also was not significantly different at 2-month post-heat shock relative to the pre-heat shock condition, while relative abundance of Vermamoeba vermiformis, a known Legionella host, did increase. In the thermal disruption scenario, relative abundance of planktonic L. pneumophila (quantitative PCR data) increased to levels comparable to those observed in the heat shock scenario within 2 months of switching long-term operation at 60 to 40C. Overall, water use frequency and water heater temperature set point exhibited a stronger effect than one-time heat shock on the microbial composition and Legionella levels at distal taps. Conclusions: While heat shock may be effective for instantaneous Legionella control and reduction in total bacteria numbers, water heater temperature set point and water use frequency are more promising factors for long-term Legionella and microbial community control, illustrating the importance of maintaining consistent elevated temperatures in the system relative to short-term heat shock.


Detection of Viable but Non-Culturable Legionella in Hospital Water Network Following Monochloramine Disinfection

Casini B, Baggiani A, Totaro M, Mansi A, Costa AL, Aquino F, Miccoli M, Valentini P, Bruschi F, Lopalco PL, Privitera G.

Department of Translational Research, N.T.M.S., University of Pisa, Pisa, Italy.

J Hosp Infect 2018 Jan;98(1):46-52.

Abstract: Background: Prevention of legionellosis remains a critical issue in healthcare settings where monochloramine (MC) disinfection was recently introduced as an alternative to chlorine dioxide in controlling Legionella spp. contamination of the hospital water network. Continuous treatments with low MC doses in some instances have induced a viable but non-culturable state (VBNC) of Legionella spp. Aim: To investigate the occurrence of such dormant cells during a long period of continuous MC treatment. Methods: Between November 2010 and April 2015, 162 water and biofilm samples were collected, and Legionella spp. isolated in accordance with standard procedures. In sampling sites where MC was <1.5 mg/L, VBNC cells were investigated by ethidium monoazide bromide (EMA)-real-time polymerase chain reaction (qPCR) and 'resuscitation' test into Acanthamoeba polyphaga CCAP 1501/18. According to the Health Protection Agency protocol, free-living protozoa were researched in 60 five-litre water samples. Findings: In all, 136 out of 156 (87.2%) of the samples taken from sites previously positive for L. pneumophila ST269 were negative by culture, but only 47 (34.5%) negative by qPCR. Although no positive results were obtained by EMA-qPCR, four out of 22 samples associated with MC concentration of 1.3 0.5 mg/L showed VBNC legionella resuscitation. The presence of the amoeba A. polyphaga in the hospital water network was demonstrated. Conclusion: Our study is the first report evidencing the emergence of VNBC legionella during a long period of continuous MC treatment of a hospital water network, highlighting the importance of keeping an appropriate and uninterrupted MC dosage to ensure the control of legionella colonization in hospital water supplies.


Rate of Legionella pneumophila Colonization in Hospital Hot Water Network After Time Flow Taps Installation

Totaro M, Valentini P, Costa AL, Giorgi S, Casini B, Baggiani A.

Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy.

J Hosp Infect 2018 Jan;98(1):60-63.

Abstract: In hospital water systems legionellae may be resistant to disinfectants in pipework, which is a problem particularly in areas where there is low flow or stagnation of water. We evaluated legionella colonization of a water network of an Italian hospital after time flow taps (TFTs) installation in proximity to dead legs. The water volume flushed was 64 L/day from May 2016, and 192 L/day from December 2016. Before TFTs installation, Legionella pneumophila sg2-14 was detected in all points (41043.1104 cfu/L). All sites remained positive (2.91041.9104 cfu/L) through November 2016. From December 2016 legionella persisted in one point only (2102 to 6.8103 cfu/L). TFTs with chemical disinfection may reduce legionella colonization associated with dead legs.


Microbial Communities Shaped by Treatment Processes in a Drinking Water Treatment Plant and Their Contribution and Threat to Drinking Water Safety

Li Q, Yu SLi L, Liu G, Gu Z, Liu M, Liu ZYe YXia QRen L.

State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, China.

Front Microbiol 2017 Dec;8:2465.

Abstract: Bacteria play an important role in water purification in drinking water treatment systems. On one hand, bacteria present in the untreated water may help in its purification through biodegradation of the contaminants. On the other hand, some bacteria may be human pathogens and pose a threat to consumers. The present study investigated bacterial communities using Illumina MiSeq sequencing of 16S rRNA genes and their functions were predicted using PICRUSt in a treatment system, including the biofilms on sand filters and biological activated carbon (BAC) filters, in 4 months. In addition, quantitative analyses of specific bacterial populations were performed by real-time quantitative polymerase chain reaction (qPCR). The bacterial community composition of post-ozonation effluent, BAC effluent and disinfected water varied with sampling time. However, the bacterial community structures at other treatment steps were relatively stable, despite great variations of source water quality, resulting in stable treatment performance. Illumina MiSeq sequencing illustrated that Proteobacteria was dominant bacterial phylum. Chlorine disinfection significantly influenced the microbial community structure, while other treatment processes were synergetic. Bacterial communities in water and biofilms were distinct, and distinctions of bacterial communities also existed between different biofilms. By contrast, the functional composition of biofilms on different filters were similar. Some functional genes related to pollutant degradation were found widely distributed throughout the treatment processes. The distributions of Mycobacterium spp. and Legionella spp. in water and biofilms were revealed by real-time quantitative polymerase chain reaction (qPCR). Most bacteria, including potential pathogens, could be effectively removed by chlorine disinfection. However, some bacteria presented great resistance to chlorine. qPCRs showed that Mycobacterium spp. could not be effectively removed by chlorine. These resistant bacteria and, especially potential pathogens should receive more attention. Redundancy analysis (RDA) showed that turbidity, ammonia nitrogen and total organic carbon (TOC) exerted significant effects on community profiles. Overall, this study provides insight into variations of microbial communities in the treatment processes and aids the optimization of drinking water treatment plant design and operation for public health.


Legionella Persistence in Manufactured Water Systems: Pasteurization Potentially Selecting for Thermal Tolerance

Whiley H, Bentham R, Brown MH.

College of Science and Engineering, Flinders University, Bedford, Australia.

Front Microbiol 2017 Jul;8:1330.

Abstract: Legionella is an opportunistic waterborne pathogen of increasing public health significance. Pasteurization, otherwise known as super-heat and flush (increasing water temperature to above 70C and flushing all outlets), has been identified as an important mechanism for the disinfection of Legionella in manufactured water systems. However, several studies have reported that this procedure was ineffective at remediating water distribution systems as Legionella was able to maintain long term persistent contamination. Up to 25% of L. pneumophila cells survived heat treatment of 70C, but all of these were in a viable but non-culturable state. This demonstrates the limitations of the culture method of Legionella detection currently used to evaluate disinfection protocols. In addition, it has been demonstrated that pasteurization and nutrient starvation can select for thermal tolerant strains, where L. pneumophila was consistently identified as having greater thermal tolerance compared to other Legionella species. This review demonstrates that further research is needed to investigate the effectiveness of pasteurization as a disinfection method. In particular, it focuses on the potential for pasteurization to select for thermal tolerant L. pneumophila strains which, as the primary causative agent of Legionnaires disease, have greater public health significance compared to other Legionella species.


Interactive Effects of Corrosion, Copper, and Chloramines on Legionella and Mycobacteria in Hot Water Plumbing

Rhoads WJ, Pruden A, Edwards MA.

Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA.

Environ Sci Technol 2017 Jun;51(12):7065-7075.

Abstract: Complexities associated with drinking water plumbing systems can result in undesirable interactions among plumbing components that undermine engineering controls for opportunistic pathogens (OPs). In this study, we examine the effects of plumbing system materials and two commonly applied disinfectants, copper and chloramines, on water chemistry and the growth of Legionella and mycobacteria across a transect of bench- and pilot-scale hot water experiments carried out with the same municipal water supply. We discovered that copper released from corrosion of plumbing materials can initiate evolution of >1100 times more hydrogen (H2) from water heater sacrificial anode rods than does presence of copper dosed as soluble cupric ions. H2 is a favorable electron donor for autotrophs and causes fixation of organic carbon that could serve as a nutrient for OPs. Dosed cupric ions acted as a disinfectant in stratified stagnant pipes, inhibiting culturable Legionella and biofilm formation, but promoted Legionella growth in pipes subject to convective mixing. This difference was presumably due to continuous delivery of nutrients to biofilm on the pipes under convective mixing conditions. Chloramines eliminated culturable Legionella and prevented L. pneumophila from recolonizing biofilms, but M. avium gene numbers increased by 0.14-0.76 logs in the bulk water and were unaffected in the biofilm. This study provides practical confirmation of past discrepancies in the literature regarding the variable effects of copper on Legionella growth and confirms prior reports of trade-offs between Legionella and mycobacteria if chloramines are applied as secondary disinfectant residual.


From Source to Filter: Changes in Bacterial Community Composition During Potable Water Treatment

Zanacic E, McMartin DW, Stavrinides J.

Faculty of Engineering and Applied Science, University of Regina, Regina, Canada.

Can J Microbiol 2017 Jun;63(6):546-558.

Abstract: Rural communities rely on surface water reservoirs for potable water. Effective removal of chemical contaminants and bacterial pathogens from these reservoirs requires an understanding of the bacterial community diversity that is present. In this study, we carried out a 16S rRNA-based profiling approach to describe the bacterial consortia in the raw surface water entering the water treatment plants of 2 rural communities. Our results show that source water is dominated by the Proteobacteria, Bacteroidetes, and Cyanobacteria, with some evidence of seasonal effects altering the predominant groups at each location. A subsequent community analysis of transects of a biological carbon filter in the water treatment plant revealed a significant increase in the proportion of Proteobacteria, Acidobacteria, Planctomycetes, and Nitrospirae relative to raw water. Also, very few enteric coliforms were identified in either the source water or within the filter, although Mycobacterium was of high abundance and was found throughout the filter along with Aeromonas, Legionella, and Pseudomonas. This study provides valuable insight into bacterial community composition within drinking water treatment facilities, and the importance of implementing appropriate disinfection practices to ensure safe potable water for rural communities.


UV-C Inactivation of Legionella rubrilucens

Schmid J, Hoenes K, Rath M, Vatter P, Hessling M.

Ulm University of Applied Sciences, Ulm, Germany.

GMS Hyg Infect Control 2017 Apr;12:Doc06.

Abstract: Background: Despite the great health significance of Legionella, there is only little information on their UV sensitivity. Besides Legionella pneumophila only L. longbeachae has been investigated so far. Methods: In this study L. rubrilucens has been spread on buffered charcoal yeast extract agar and irradiated with the 254 nm UV-C emission of a mercury vapor lamp. The disinfection success is measured by colony counting after incubation and comparison of the number of colonies on irradiated and unirradiated reference agar plates. Results: The average log-reduction dose is 1.08 mJ/cm2 for free L. rubrilucens, which is at the lower end of the so far published Legionella log-reduction values, but all three Legionella species show similar UV-C sensitivities. Conclusion: The log-reduction dose of legionellae in amoebae has not been investigated, but with the observed high UV-C sensitivity for free Legionella, the idea of a future point-of-use disinfection by small UV-C LEDs in water-taps or shower heads appears to be realistic, even if legionellae are more resistant in amoebae.


Application of Hydrogen Peroxide as an Innovative Method of Treatment for Legionella Control in a Hospital Water Network

Casini B, Aquino F, Totaro M, Miccoli M, Galli I, Manfredini L, Giustarini C, Costa AL, Tuvo B, Valentini P, Privitera G, Baggiani A.

Department Translational Research, N.T.M.S., University of Pisa, Pisa, Italy.

Pathogens 2017 Apr;6(2):15.

Abstract: Objectives: To evaluate the effectiveness of hydrogen peroxide (HP) use as a disinfectant in the hospital water network for the control of Legionella spp. colonization. Methods: Following the detection of high levels of Legionella contamination in a 136-bed general hospital water network, an HP treatment of the hot water supply (25 mg/L) was adopted. During a period of 34 months, the effectiveness of HP on Legionella colonization was assessed. Legionella was isolated in accordance with ISO-11731 and identification was carried out by sequencing of the mip gene. Results: Before HP treatment, L. pneumophila sg 2-15 was isolated in all sites with a mean count of 99508279 cfu/L. After one-month of HP treatment, we observed the disappearance of L. pneumophila 2-15, however other Legionella species previously not seen were found; Legionella pneumophila 1 was isolated in one out of four sampling sites (2000 cfu/L) and other non-pneumophila species were present in all sites (mean load 30002887 cfu/L). Starting from September 2013, HP treatment was modified by adding food-grade polyphosphates, and in the following months, we observed a progressive reduction of the mean load of all species (p<0.05), resulting in substantial disappearance of Legionella colonization. Conclusion: Hydrogen peroxide demonstrated good efficacy in controlling Legionella. Although in the initial phases of treatment it appeared unable to eliminate all Legionella species, by maintaining HP levels at 25 mg/L and adding food-grade polyphosphates, a progressive and complete control of colonization was obtained.


Photoinactivation of Legionella rubrilucens by Visible Light

Schmid J, Hoenes K, Rath M, Vatter P, Spellerberg B, Hessling M.

Ulm University of Applied Sciences, Ulm, Germany.

Eur J Microbiol Immunol (Bp) 2017 Apr;7(2):146-149.

Abstract: In this study, the photoinactivation of Legionella by visible light is investigated. The success of this approach would offer new prospects for technical water disinfection and maybe even for therapeutic measures in cases of Legionella infections. Therefore, Legionella rubrilucens was dispensed on buffered charcoal yeast extract medium agar plates and illuminated with different doses of violet light generated by 405 nm light-emitting diodes (LEDs). A strong photoinactivation effect was observed. A dose of 125 J/cm2 reduced the bacterial concentration by more than 5 orders of magnitude compared to Legionella on unirradiated agar plates. The necessary dose for a one log-level reduction was about 24 J/cm2. These results were obtained for extracellular L. rubrilucens, but other Legionella species may exhibit a similar behavior.


Kinetic Analysis of Legionella Inactivation Using Ozone in Wastewater

Li J, Li K, Zhou Y, Li X, Tao T.

School of Environmental Science and Engineering, Zhejiang Gongshang University, Zhejiang, China.

Chemosphere 2017 Feb;168:630-637.

Abstract: Legionella inactivation using ozone was studied in wastewater using kinetic analysis and modeling. The experimental results indicate that the relationship between the ozone concentration, germ concentration, and chemical oxygen demand (COD) can be used to predict variations in germ and COD concentrations. The ozone reaction with COD and inactivation of Legionella occurred simultaneously, but the reaction with COD likely occurred at a higher rate than the inactivation, as COD is more easily oxidized by ozone than Legionella. Higher initial COD concentrations resulted in a lower inactivation rate and higher lnN/N0. Higher temperature led to a higher inactivation efficiency. The relationship of the initial O3 concentration and Legionella inactivation rate was not linear, and thus, the Ct value required for a 99.99% reduction was not constant. The initial O3 concentration was more important than the contact time, and a reduction of the initial O3 concentration could not be compensated by increasing the contact time. The Ct values were compared over a narrow range of initial concentrations; the Ct values could only be contrasted when the initial O3 concentrations were very similar. A higher initial O3 concentration led to a higher inflection point value for the lnN/N0 vs C0t curve. Energy consumption using a plasma corona was lower than when using boron-doped diamond electrodes.