Monochloramine Disinfection Research Articles

Formation of filamentous fungal biofilms in water and the transformation of resistance to chlor(am)ine disinfection

Biofilms are composed of complex multi-species in nature, potentially threatening drinking water safety. In this work, the formation of single- and multi-species fungal biofilms formed by Aspergillus niger (A. niger) and Aspergillus flavus (A. flavus), and the inactivation of mature biofilms using chlor(am)ine were firstly investigated. Results revealed that the antagonistic interaction occurred between A. niger and A. flavus. Chloramination at 20 mg/L for 30 min achieved 74.74 % and 76.04 % inactivation of A. flavus and multi-species biofilm, which were 1.69- and 1.84-fold higher than that of chlorine at the same condition. However, no significant difference was observed in the inactivation of A. niger biofilm between chlorine and monochloramine disinfection due to the lower amount of extracellular polymeric substance produced by it (p > 0.05). The inactivation of biofilm by monochloramine fitted the Weibull model well. According to the Weibull model, the monochloramine resistance of biofilm were as follows: A. flavus > multi-species > A. niger biofilm. Besides, an increase in reactive oxygen levels, damage of cell membrane, and leakage of intracellular substances in biofilms were observed after chlor(am)ination. More intracellular polysaccharides and proteins were leaked in chloramination inactivation (p < 0.05). This study provides important implications for controlling fungal biofilm.

Modeling chloramine stability and disinfection byproduct formation in groundwater high in bromide

AbstractBromide can promote monochloramine decomposition and disinfection byproduct (DBP) formation. Monochloramine and total chlorine stability as well as total trihalomethane and haloacetic acid formation were examined in groundwater with high bromide levels (300–1700 μg/L) following chlorine or KMnO₄ preoxidation. An N,N‐Diethyl‐p‐phenylenediamine (DPD)‐based total chlorine method detected chloramines and brominated amines (e.g., NH2Br, NHBrCl). An indophenol‐based monochloramine method showed minimal interference from brominated amines. Differences between these methods' measurements likely indicated brominated amine concentrations. Substantial total chlorine demands (up to ~3.5 mg/L in 4 days) following chlorine preoxidation were observed due to the presence of brominated amines. Total chlorine measurements were more stable and DBP formation was limited following KMnO₄ preoxidation because ammonia was dosed before chlorine, which inhibited brominated amine formation. A kinetic model developed elsewhere for dissolved organic matter (DOM)‐free water generally tracked with experimental results but some deviations occurred possibly because DOM consumed bromochloramine or its reaction intermediates.

Water Safety Plan, Monochloramine Disinfection and Extensive Environmental Sampling Effectively Control Legionella and Other Waterborne Pathogens in Nosocomial Settings: The Ten-Year Experience of an Italian Hospital.

Legionella contamination control is crucial in healthcare settings where patients suffer an increased risk of disease and fatal outcome. To ensure an effective management of this health hazard, the accurate application of a hospital-specific Water Safety Plan (WSP), the choice of a suitable water disinfection system and an extensive monitoring program are required. Here, the ten-year experience of an Italian hospital is reported: since its commissioning, Legionellosis risk management has been entrusted to a multi-disciplinary Working Group, applying the principles of the World Health Organization's WSP. The disinfection strategy to prevent Legionella and other waterborne pathogens relies on the treatment of domestic hot water with a system ensuring the in situ production and dosage of monochloramine. An average of 250 samples/year were collected and analyzed to allow an accurate assessment of the microbiological status of water network. With the aim of increasing the monitoring sensitivity, in addition to the standard culture method, an optimized MALDI-ToF MS-based strategy was applied, allowing the identification of Legionella species and other relevant opportunistic pathogens. Data collected so far confirmed the effectiveness of this multidisciplinary approach: the fraction of positive samples never overcame 1% on a yearly basis and Legionnaires' Disease cases never occurred.

Development of Resistance in Escherichia coli Against Repeated Water Disinfection

Pathogen resistance against common disinfectants in drinking water treatment could have serious public health implications, particularly in potable water reuse. Frequent disinfection in potable water reuse has a potential to facilitate resistance development. This study investigated resistance development in Escherichia coli against repeated monochloramine and ferrate disinfection. E. coli cultures repeatedly treated with monochloramine developed resistance after 12 + treatment rounds, whereas repeated ferrate disinfection did not lead to resistance development. Monochloramine induced cells into the viable but nonculturable (VBNC) state in initial disinfection rounds; however, repeated monochloramine treatment caused increases in culturability, which corresponded to decreases in the fraction of VBNC cells post-disinfection. The cumulative number of disinfection episodes (∼12 times) rather than treatment frequency (e.g., every 48, 96, or 144 h) played a critical role in resistance development against monochloramine. In addition to preventing resistance, ferrate effectively inactivated (&amp;gt;3-log10) the evolved monochloramine-stressed cultures, suggesting that the evolutionary adaptations against monochloramine were ineffective against ferrate. The lack of resistance against ferrate renders it a promising disinfection agent that deserves further assessment. This work’s findings demonstrate that repeated disinfection coupled with the type of applied disinfectant can influence bacterial resistance development. Therefore, current and future water disinfection schemes, especially within potable water reuse, need regular monitoring to evaluate the resistance profile of pathogenic bacteria.

Proteomic analysis reveals the mechanism of different environmental stress-induced tolerance of Pseudomonas aeruginosa to monochloramine disinfection

Although drinking water disinfection proved to be an effective strategy to eliminate many pathogens, bacteria can still show disinfection tolerance in drinking water distribution systems. To date, the molecular mechanisms on how environmental stress affects the tolerance of Pseudomonas aeruginosa to monochloramine are not well understood. Here, we investigated how three stress conditions, namely starvation, low temperature, and starvation combined with low temperature, affected the monochloramine tolerance of Pseudomonas aeruginosa, an opportunistic pathogen commonly found in drinking water distribution systems. All stress conditions significantly promoted monochloramine tolerance, among which starvation had the most drastic effects. Proteomic analyses suggested that the three conditions not only triggered a positive antioxidant defense against oxidative damages but also prepared the bacteria to employ a passive defense mechanism against disinfectants via dormancy. Moreover, the expression of antioxidant enzymes reached the maximum under the starvation condition and further low temperature treatment had little effect on bacterial response to oxidative stress. Instead, we found further treatment of the starved cells with low temperature decreased the osmotic stress response and the stringent response, which generally play pivotal roles in disinfection tolerance. Taken together, these findings shed light on how abiotic factors influence the bacterial disinfection tolerance and will aid design of efficient strategies to eliminate Pseudomonas aeruginosa from drinking water.

Effects of monochloramine on culturability, viability and persistence of Pseudomonas putida and tap water mixed bacterial community

Bacterial biofilms are able to persist in drinking water distribution systems (DWDS) even if disinfectants such as monochloramine are used to inhibit bacterial colonization and biofilm formation. While studies have determined the monochloramine concentrations required to inhibit bacterial biofilms, not much is known about how bacterial biofilms develop resistance towards monochloramine. This study covers the development of resistance to monochloramine in both single species and mixed bacterial biofilms. Through culturability tests and flow cytometry, exposing bacterial biofilms to monochloramine disinfection using a sub-lethal concentration (1.5 mg/L Cl2, experimentally determined) was sufficient to cause an increase of the monochloramine's inhibitory concentrations by as much as two times than what is initially required to inhibit biofilm growth. Through persister cultures and 16S rRNA next generation sequencing (NGS) studies, mixed bacterial biofilms experienced to monochloramine exposure resulted in more bacterial genera becoming persistent and resistant towards monochloramine. Through this study, bacterial genera that were persistent towards monochloramine were suggested to share common traits including the ability (1) to readily enter a persister or viable but non-culturable (VBNC) state and (2) to form biofilms primarily comprising proteinaceous extra-polymeric substances (EPS). Both of these traits also suggested that selected bacterial genera tended to be more persistent to monochloramine and produce EPS. This study advances our understanding of bacterial biofilm resistance towards monochloramine and showed the importance of maintaining monochloramine concentrations in DWDS to prevent the development of bacterial resistance towards monochloramine. KEY POINTS: • Monochloramine-resistant biofilm was developed after sub-lethal disinfection. • Mixed-species culture experienced monochloramine showed more persistence to monochloramine. • Ability to enter a persister/VBNC state is a common trait of persistent bacteria genera.

A comprehensive evaluation of monochloramine disinfection on water quality, Legionella and other important microorganisms in a hospital

Opportunistic pathogens such as Legionella are of significant public health concern in hospitals. Microbiological and water chemistry parameters in hot water throughout an Ohio hospital were monitored monthly before and after the installation of a monochloramine disinfection system over 16 months. Water samples from fifteen hot water sampling sites as well as the municipal water supply entering the hospital were analyzed using both culture and qPCR assays for specific microbial pathogens including Legionella, Pseudomonas spp., nontuberculous Mycobacteria [NTM], as well as for heterotrophic bacteria. Legionella culture assays decreased from 68% of all sites being positive prior to monochloramine addition to 6% positive after monochloramine addition, and these trends were parallel to qPCR results. Considering all samples, NTMs by culture were significantly reduced from 61% to 14% positivity (p<0.001) after monochloramine treatment. Mycobacterium genus-specific qPCR positivity was reduced from 92% to 65%, but the change was not significant. Heterotrophic bacteria (heterotrophic bacteria plate counts [HPCs]) exhibited large variability which skewed statistical results on a per room basis. However, when all samples were considered, a significant decrease in HPCs was observed after monochloramine addition. Lastly, Pseudomonas aeruginosa and Vermamoeba vermiformis demonstrated large and significant decrease of qPCR signals post-chloramination. General water chemistry parameters including monochloramine residual, nitrate, nitrite, pH, temperature, metals and total trihalomethanes (TTHMs) were also measured. Significant monochloramine residuals were consistently observed at all sampling sites with very little free ammonia present and no water quality indications of nitrification (e.g., pH decrease, elevated nitrite or nitrate). The addition of monochloramine had no obvious impact on metals (lead, copper and iron) and disinfection by-products.

Effect of ferrate and monochloramine disinfection on the physiological and transcriptomic response of Escherichia coli at late stationary phase

Biological mechanisms of disinfection not only vary by disinfectant but also remain not well understood. We investigated the physiological and transcriptomic response of Escherichia coli at late stationary phase to ferrate and monochloramine in amended lake water. Although ferrate and monochloramine treatments similarly reduced culturable cell concentrations by 3-log10, 64% and 11% of treated cells were viable following monochloramine and ferrate treatment, respectively. This observed induction of viable but non-culturable (VBNC) state following monochloramine treatment but not ferrate is attributed to slower monochloramine disinfection kinetics (by 2.8 times) compared to ferrate. Transcriptomic analysis of E. coli at 15 min of exposure revealed that 3 times as many genes related to translation and transcription were downregulated by monochloramine compared to ferrate, suggesting that monochloramine treatment may be inducing VBNC through reduced protein synthesis and metabolism. Downregulation of universal stress response genes (rpoS, uspA) was attributed to growth-related physiological stressors during late stationary phase which may have contributed to the elevated expression levels of general stress responses pre-disinfection and, subsequently, their significant downregulation post-disinfection. Both disinfectants upregulated oxidative stress response genes (trxC, grxA, soxS), although levels of upregulation were time sensitive. This work shows that bacterial inactivation responses to disinfectants is mediated by complex molecular and growth-related responses.

Inactivation Dynamics of Gram-negative and Gram-positive Microbes in Drinking Water: a Comparative Study of Chlorine and Monochloramine Disinfection

To assure the prevention of microbial contamination and the provision of safe potable water to consumers, efficient disinfection is the final barrier. Chlorine, once a widely applied disinfectant, has essentially been re-considered by many water treatment practitioners. Since the research unveiled chlorine-associated health repercussions, the investigation shifted to more viable disinfection options such as the use of monochloramines, that remains active in the system for relatively long periods. Keeping in view, the present study compared the biocidal competence of chlorine and monochloramine to inactivate the gram-negative Klebsiella pneumoniae and Pseudomonas aeruginosa along with the gram-positive Staphylococcus aureus. A lab-scale testing batch was set up in carefully monitored conditions to investigate the response of these bacterial species to the applied disinfection dosages of 1 and 2 mg/L. Moreover, a referenced batch of control evidenced the accuracy of results. A significant difference in the response to chlorine and monochloramine was recorded both in mixed and mono-cultures of bacteria. The bench-scale inactivation experiments revealed that chlorine and monochloramine greatly damaged K. pneumoniae and S. aureus in monocultures. Whereas these bacterial species revealed greater tolerance when acted together in a mixed-cultures and, hence, an overall lower degree of disinfection was achieved. P. aeruginosa exhibited reduced vulnerability to disinfectants in mixed-cultures, marking K. pneumoniae tolerant to chlorine. Most significant correlation between disinfectant species was found at 30 min of exposure with notable logremoval of K. pneumoniae (p = 0.01), P. aeruginosa (p = 0.003) and S. aureus (p = 0.0001). In conclusion, for prolonged exposures, monochloramine is advisable owing to its immediate microbial inactivation upon contact as well as enhanced stability in drinking water networks. The results could predict the pattern of bacterial inactivation in drinking water distribution networks and fill a major gap in the water sector.

Retrospective Analysis of Nontuberculous Mycobacterial Infection and Monochloramine Disinfection of Municipal Drinking Water in Michigan.

Infections by nontuberculous mycobacteria (NTM) are primarily acquired from environmental sources, including exposure to municipally treated drinking water. Higher levels of NTM have been reported in drinking water disinfected with monochloramine than in that disinfected with chlorine. However, the relationships between water treatment practices and NTM infection are unclear. The objective of this study was to examine a possible relationship between residual disinfectant used for municipal drinking water treatment (monochloramine or chlorine) and NTM infection. We retrospectively reviewed NTM diagnostic tests performed at a single health care center during a 15-year period. Information on municipal water treatment practices, including disinfectant and primary source water type, was obtained for 140 cities. Based on a logistic regression model, municipal drinking water disinfection with monochloramine compared to chlorine was not associated with NTM infection (P = 0.24). An additional model variable examining water source showed that the likelihood of having an NTM infection was 1.46 times higher for patients residing in cities with drinking water derived from surface water than for those residing in cities with drinking water derived from groundwater (odds ratio [OR], 1.46; 95% confidence interval [CI], 1.03 to 2.08; P = 0.04). In an inverse propensity score weighted regression, monochloramine disinfection was also not associated with NTM infection. A moderate effect on NTM infection rates was observed in the weighted regression for municipal drinking water derived from surface water, though the results were not statistically significant (OR, 1.24; 95% CI, 0.92 to 1.69; P = 0.17).IMPORTANCE Infections by nontuberculous mycobacteria (NTM) result in significant morbidity, mortality, and health care costs. NTM are primarily acquired from environmental sources, including exposure to municipally treated drinking water. Higher levels of NTM have been reported in drinking water disinfected with monochloramine than in drinking water disinfected with chlorine. Our results suggest that municipal drinking water disinfection with monochloramine compared to chlorine is not associated with higher risk of NTM infection. This is important given that regulations that limit drinking water concentrations of disinfection by-products, which are formed primarily when chlorine disinfection is used, incentivize drinking water utilities to change from chlorine disinfection to monochloramine disinfection.

MSphere of Influence: Engineering Microbes.

Patrick J. McNamara works in the field of environmental engineering. In this mSphere of Influence article, he reflects on how the papers "Bacterial community structure in the drinking water microbiome is governed by filtration processes" (A. J. Pinto, C. Xi, and L. Raskin, Environ Sci Technol 46:8851-8859, 2012, https://doi.org/10.1021/es302042t) and "Differential resistance of drinking water bacterial populations to monochloramine disinfection" (T. Chiao, T. M. Clancy, A. Pinto, C. Xi, and L. Raskin, Environ Sci Technol 48:4038-4047, 2014, https://doi.org/10.1021/es4055725) by Lutgarde Raskin and colleagues made an impact on him by providing a foundation for the study of microbial ecology in engineering drinking water treatment plants and drinking water distribution systems.

The Seasonality of Nitrite Concentrations in a Chloraminated Drinking Water Distribution System.

We studied the seasonal variation of nitrite exposure in a drinking water distribution system (DWDS) with monochloramine disinfection in the Helsinki Metropolitan Area. In Finland, tap water is the main source of drinking water, and thus the nitrite in tap water increases nitrite exposure. Our data included both the obligatory monitoring and a sampling campaign data from a sampling campaign. Seasonality was evaluated by comparing a nitrite time series to temperature and by calculating the seasonal indices of the nitrite time series. The main drivers of nitrite seasonality were the temperature and the water age. We observed that with low water ages (median: 6.7 h) the highest nitrite exposure occurred during the summer months, and with higher water ages (median: 31 h) during the winter months. With the highest water age (190 h), nitrite concentrations were the lowest. At a low temperature, the high nitrite concentrations in the winter were caused by the decelerated ammonium oxidation. The dominant reaction at low water ages was ammonium oxidation into nitrite and, at high water ages, it was nitrite oxidation into nitrate. These results help to direct monitoring appropriately to gain exact knowledge of nitrite exposure. Also, possible future process changes and additional disinfection measures can be designed appropriately to minimize extra nitrite exposure.

Detection of viable but non-culturable legionella in hospital water network following monochloramine disinfection

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. To investigate the occurrence of such dormant cells during a long period of continuous MC treatment. 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 <1.5mg/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. 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±0.5mg/L showed VBNC legionella resuscitation. The presence of the amoeba A.polyphaga in the hospital water network was demonstrated. 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.

Effects of Extracellular Polymeric Substance Composition on Bacteria Disinfection by Monochloramine: Application of MALDI-TOF/TOF-MS and Multivariate Analysis.

In our previous study, we reported that the transport of monochloramine is affected by the extracellular polymeric substance (EPS) composition, which in turn affects the cell viability of both biofilm and detached clusters.11 However, although the transport and reaction of monochloramine in biofilm could be observed, the specific biomolecules reacting with the disinfectant and the mechanism of disinfection remains elusive. In this study, the impact of EPS composition on bacteria disinfection by monochloramine was qualitatively determined using both wild-type and isogenic mutant Pseudomonas strains with different EPS-secretion capacity and composition. To evaluate their EPS reactivity and contribution to susceptibility to monochloramine, we investigated the bacteria disinfection process using Fourier transform infrared spectroscopy (FTIR) and matrix-assisted laser desorption-ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). Canonical correlation analysis and partial least-squares regression modeling were employed to explore the changes that EPS underwent during the monochloramine disinfection process. The analyses results suggested significant reactions of the monochloramine with peptide fragments of proteins that are associated with carbohydrate utilization. Selected enzymes also showed different levels of inhibition by monochloramine when tested.

N-nitrosamine formation by monochloramine, free chlorine, and peracetic acid disinfection with presence of amine precursors in drinking water system

In this study, the formation of eight N-nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine, N-nitrosomethylamine, N-nitrosodi-n-propylamine, N-nitrosodi-n-butylamine, N-Nitrosopiperidine, N-Nitrosopyrrolidine, N-Nitrosomorpholine, were systematically evaluated with respect to seven N-nitrosamine precursors (dimethylamine, trimethylamine, 3-(dimethylaminomethyl)indole, 4-dimethylaminoantipyrine, ethylmethylamine, diethylamine, dipropylamine) and three disinfectants (monochloramine, free chlorine, peracetic acid) under variable dosages, exposure times, and pH in a drinking water system. Without the presence of the seven selected N-nitrosamine precursors N-nitrosamine formation was not observed under any tested condition except very low levels of N-Nitrosopyrrolidine under some conditions. With selected N-nitrosamine precursors present N-nitrosamines formed at different levels under different conditions. The highest N-nitrosamine formation was NDMA with a maximum concentration of 1180 ng/L by monochloramine disinfection with precursors present; much lower levels of N-nitrosamines were formed by free chlorine disinfection; and no detectable level of N-nitrosamines were observed by peracetic acid disinfection except low level of N-Nitrosodi-n-propylamine under some conditions. NDMA formation was not affected by pH while four other N-nitrosamine formations were slightly affected by sample pH tested between 7 and 9, with formation decreasing with increasing pH. Monochloramine exposure time study displayed fast formation of N-nitrosamines, largely formed in four hours of exposure and maximized after seven days. This was a systematic study on the N-nitrosamine formation with the seven major N-nitrosamine precursors presence and absence under different conditions, including peracetic acid disinfection which has not been studied elsewhere.

Inactivation Kinetics and Replication Cycle Inhibition of Adenovirus by Monochloramine

Monochloramine is commonly used as a secondary disinfectant to maintain a residual in drinking water distribution systems in the United States. The mechanism by which waterborne viruses become inactivated by monochloramine remains widely unknown. A more fundamental understanding of how viruses become inactivated is necessary for better detection and control of viruses in drinking water. Human adenovirus (HAdV) is known to be the waterborne virus most resistant to monochloramine disinfection, and this study presents inactivation kinetics over a range of environmental conditions. Several steps in the HAdV replication cycle were investigated to determine which steps become inhibited by monochloramine disinfection. Interestingly, monochloramine-inactivated HAdV could bind to host cells, but genome replication and early and late mRNA transcription were inhibited. We conclude that monochloramine exposure inhibited a replication cycle event after binding but prior to early viral protein synthesis.

C-, N-DBP formation and quantification by differential spectra in MBR treated municipal wastewater exposed to chlorine and chloramine

Formation of various carbonaceous and nitrogenous disinfection by-products (DBPs) during chlorine and monochloramine disinfection of recycled municipal wastewater produced by membrane bioreactor (MBR) was studied and quantified using differential ultraviolet (UV) absorbance and fluorescence spectral parameters.Chlorination resulted in extremely high yields of trihalomethanes (THMs) and haloacetonitriles (HANs). Monochloramine disinfection decreased total halogenated DBP yields by one order of magnitude, while doubled the N-nitrosodimethylamine (NDMA) formation. Extending reaction time increased DBP formation.The differential log-transformed UV spectral parameters including DLnA350 (differential logarithm of absorbance at 350nm) and DSloop300–340 (slope differential of the log-transformed spectra at wavelength range 300–340nm), and differential Excitation/Emission Matrix (EEM) fluorescence spectral parameters including DI(λ280λ310) (differential fluorescence intensity for proteins) and DΦi,n (i=T, II and III; differential of integrated EEM intensities for gross DOM, humic acid-like and fulvic acid-like components) had strong exponential correlations to THM4 formation (R2>0.99) and linearly correlated to HAN4 yield during disinfection of MBR effluents. It indicated that THM and HAN formation was related to the halogenation of proteins and humic substances. No quantitative correlation was found between NDMA yields and the studied spectroscopic parameters.

Effect of monochloramine treatment on colonization of a hospital water distribution system by Legionella spp.: a 1 year experience study.

Contamination of hot water distribution systems by Legionella represents a great challenge due to difficulties associated with inactivating microorganisms, preserving the water characteristics. The aim of this study was to examine over the course of 1 year in 11 fixed sites, the impact of monochloramine disinfection on Legionella, heterotrophic bacteria (36 °C), Pseudomonas aeruginosa contamination, and chemical parameters of a plumbing system in an Italian hospital. Three days after installation (T0), in the presence of monochloramine concentration between 1.5 and 2 mg/L, 10/11 sites (91%) were contaminated by L. pneumophila serogroups 3 and 10. After these results, the disinfectant dosage was increased to between 6 and 10 mg/L, reducing the level of Legionella by three logarithmic unit by 2 months postinstallation (T2) until 6 months later (T3). One year later (T4), there was a significant reduction (p = 0.0002) at 8/11 (73%) sites. Our data showed also a significant reduction of heterotrophic bacteria (36 °C) in 6/11 (55%) sites at T4 (p = 0.0004), by contrast the contamination of P. aeruginosa found at T0 in two sites persisted up until T4. The results of the present study show that monochloramine is a promising disinfectant that can prevent Legionella contamination of hospital water supplies.

Shift in the microbial ecology of a hospital hot water system following the introduction of an on-site monochloramine disinfection system.

Drinking water distribution systems, including premise plumbing, contain a diverse microbiological community that may include opportunistic pathogens. On-site supplemental disinfection systems have been proposed as a control method for opportunistic pathogens in premise plumbing. The majority of on-site disinfection systems to date have been installed in hospitals due to the high concentration of opportunistic pathogen susceptible occupants. The installation of on-site supplemental disinfection systems in hospitals allows for evaluation of the impact of on-site disinfection systems on drinking water system microbial ecology prior to widespread application. This study evaluated the impact of supplemental monochloramine on the microbial ecology of a hospital’s hot water system. Samples were taken three months and immediately prior to monochloramine treatment and monthly for the first six months of treatment, and all samples were subjected to high throughput Illumina 16S rRNA region sequencing. The microbial community composition of monochloramine treated samples was dramatically different than the baseline months. There was an immediate shift towards decreased relative abundance of Betaproteobacteria, and increased relative abundance of Firmicutes, Alphaproteobacteria, Gammaproteobacteria, Cyanobacteria and Actinobacteria. Following treatment, microbial populations grouped by sampling location rather than sampling time. Over the course of treatment the relative abundance of certain genera containing opportunistic pathogens and genera containing denitrifying bacteria increased. The results demonstrate the driving influence of supplemental disinfection on premise plumbing microbial ecology and suggest the value of further investigation into the overall effects of premise plumbing disinfection strategies on microbial ecology and not solely specific target microorganisms.

Differential Resistance of Drinking Water Bacterial Populations to Monochloramine Disinfection.

The impact of monochloramine disinfection on the complex bacterial community structure in drinking water systems was investigated using culture-dependent and culture-independent methods. Changes in viable bacterial diversity were monitored using culture-independent methods that distinguish between live and dead cells based on membrane integrity, providing a highly conservative measure of viability. Samples were collected from lab-scale and full-scale drinking water filters exposed to monochloramine for a range of contact times. Culture-independent detection of live cells was based on propidium monoazide (PMA) treatment to selectively remove DNA from membrane-compromised cells. Quantitative PCR (qPCR) and pyrosequencing of 16S rRNA genes was used to quantify the DNA of live bacteria and characterize the bacterial communities, respectively. The inactivation rate determined by the culture-independent PMA-qPCR method (1.5-log removal at 664 mg·min/L) was lower than the inactivation rate measured by the culture-based methods (4-log removal at 66 mg·min/L). Moreover, drastic changes in the live bacterial community structure were detected during monochloramine disinfection using PMA-pyrosequencing, while the community structure appeared to remain stable when pyrosequencing was performed on samples that were not subject to PMA treatment. Genera that increased in relative abundance during monochloramine treatment include Legionella, Escherichia, and Geobacter in the lab-scale system and Mycobacterium, Sphingomonas, and Coxiella in the full-scale system. These results demonstrate that bacterial populations in drinking water exhibit differential resistance to monochloramine, and that the disinfection process selects for resistant bacterial populations.