Effect of disinfectant, water age, and pipe materials on bacterial and eukaryotic community structure in drinking water biofilm

Overlooked Role of Fungi in Drinking Water Taste and Odor Issues

Taste and odor (T&O) are among the most frequently encountered aesthetic issues in drinking water. While fungi have been reported to produce offensive odors, their contribution to T&O in drinking water remains understudied and often overlooked. In this study, the profiles of fungal community and odorants produced by 10 native fungal isolates were investigated in 36 samples collected from two drinking water treatment plants and a premise plumbing system. A total of 17 odorants were identified with Penicillium, Aspergillus, Paecilomyces, and Alternaria genera exhibiting the highest odorant yields. Significant concentrations of musty/earthy compounds were produced by these fungal isolates, such as 2-methylisoborneol (2-MIB) (26-256 ng/L), geosmin (10-13 ng/L), and 2-isobutyl-3-methoxy-pyrazine (IBMP) (3-13 ng/L). The high odor activity value of the odorants primarily occurred within 4 d, while toxicity continued to increase during the 8 d incubation. UV treatment in premise plumbing significantly (p < 0.05) reduced the gene read counts of Ascomycota phylum, Aspergillus spp., Fusarium spp., Rhizopus spp., and Trichoderma spp., by 2.3-4.0 times. These findings underscore the previously underestimated role of fungi in contributing to T&O issues in drinking water and corresponding risks to consumers and indicate UV as a promising strategy for fungal control in drinking water.

Impacts of water treatments on bacterial communities of biofilm and loose deposits in drinking water distribution systems

Treated drinking water is delivered to customers through drinking water distribution systems (DWDSs). Although studies have focused on exploring the microbial ecology of DWDSs, knowledge about the effects of different water treatments on the bacterial community of biofilm and loose deposits in DWDS is limited. This study assessed the effects of additional treatments on the bacterial communities developed in 10 months' old pilot DWDSs. The results showed a similar bacterial community in the pipe-wall biofilm, which was dominated by Novosphingobium spp. (20-82 %) and Sphingomonas spp. (11-53 %), regardless of the treatment applied. The bacterial communities that were retained in the distribution systems (including pipe-wall biofilm and loose deposits) were similar to the particle-associated bacteria (PAB) in the corresponding supply water. The additional treatments showed clear effects of the removal and/or introduction of particles. The genera Aeromonas spp., Clostridium spp., Legionella spp., and Pseudomonas spp., which contain opportunistic pathogenic species, were only detected among the PAB in ion exchange system. Our study demonstrated that the biofilm community is consistent across treatments, and the contribution from bacteria in loose deposits is important but can be controlled by removing particles. These findings offer more insight into the origin and development of microbial ecology in DWDSs and suggest paths for further research on the possibility of managing the microbial ecology in distribution systems.

Quantitative Microbial Risk Assessment Framework Incorporating Water Ages with Legionella pneumophila Growth Rates

Water age in drinking water systems is often used as a proxy for water quality but is rarely used as a direct input in assessing microbial risk. This study directly linked water ages in a premise plumbing system to concentrations of Legionella pneumophila via a growth model. In turn, the L. pneumophila concentrations were used for a quantitative microbial risk assessment to calculate the associated probabilities of infection (Pinf) and clinically severe illness (Pcsi) due to showering. Risk reductions achieved by purging devices, which reduce water age, were also quantified. The median annual Pinf exceeded the commonly used 1 in 10,000 (10-4) risk benchmark in all scenarios, but the median annual Pcsi was always 1-3 orders of magnitude below 10-4. The median annual Pcsi was lower in homes with two occupants (4.7 × 10-7) than with one occupant (7.5 × 10-7) due to more frequent use of water fixtures, which reduced water ages. The median annual Pcsi for homes with one occupant was reduced by 39-43% with scheduled purging 1-2 times per day. Smart purging devices, which purge only after a certain period of nonuse, maintained these lower annual Pcsi values while reducing additional water consumption by 45-62%.

Introducing bacterial community turnover times to elucidate temporal and spatial hotspots of biological instability in a large Austrian drinking water distribution network

Ensuring biological stability in drinking water distribution systems (DWDSs) is important to reduce the risk of aesthetic, operational and hygienic impairments of the distributed water. Drinking water after treatment often changes in quality during transport due to interactions with pipe-associated biofilms, temperature increases and disinfectant residual decay leading to potential biological instability. To comprehensively assess the potential for biological instability in a large chlorinated DWDS, a tool-box of bacterial biomass and activity parameters was applied, introducing bacterial community turnover times (BaCTT) as a direct, sensitive and easy-to-interpret quantitative parameter based on the combination of 3H-leucine incorporation with bacterial biomass. Using BaCTT, hotspots and periods of bacterial growth and potential biological instability could be identified in the DWDS that is fed by water with high bacterial growth potential. A de-coupling of biomass from activity parameters was observed, suggesting that bacterial biomass parameters depict seasonally fluctuating raw water quality rather than processes related to biological stability of the finished water in the DWDS. BaCTT, on the other hand, were significantly correlated to water age, disinfectant residual, temperature and a seasonal factor, indicating a higher potential of biological instability at more distant sampling sites and later in the year. As demonstrated, BaCTT is suggested as a novel, sensitive and very useful parameter for assessing the biological instability potential. However, additional studies in other DWDSs are needed to investigate the general applicability of BaCTT depending on water source, applied treatment processes, biofilm growth potential on different pipe materials, or size, age and complexity of the DWDS.

Metabolic response of bacterial community to sodium hypochlorite and ammonia nitrogen affected the antibiotic resistance genes in pipelines biofilm

The biofilm is important for the antibiotic resistance genes (ARGs) propagation in drinking water pipelines. This study investigated the influence of chlorine disinfection and ammonia nitrogen on the ARGs in pipelines biofilm using metagenomic and metabolomics analysis. Chlorine disinfection reduced the relative abundance of unclassified_c_Actinobacteria, Acidimicrobium, and Candidatus_Pelagibacter to 394-430 TPM, 114-123 TPM, and 49-54 TPM, respectively. Correspondingly, the ARGs Saur_rpoC_DAP, macB, and mfd was reduced to 8-12 TPM, 81-92 TPM and 30-35 TPM, respectively. The results of metabolomics suggested that chlorine disinfection suppressed the pathways of ABC transporters, fatty acid biosynthesis, biosynthesis of unsaturated fatty acids, and biosynthesis of amino acids. These pathways were related to the cell membrane integrality and extracellular polymeric substances (EPS) secretion. Chlorine disinfection induced the decrease of EPS-related genes, resulting in the lower relative abundance of bacterial community and their antibiotic resistance. However, added approximately 0.5 mg/L NH3-N induced up-regulation of these metabolic pathways. In addition, NH3-N addition increased the relative abundance of enzymes related to inorganic and organic nitrogen metabolic pathway significantly, such as ammonia monooxygenase, glutamine synthetase, and glutamate synthase. Due to the EPS protection and nitrogen metabolism, the relative abundance of the main bacterial genera and the related ARGs increased to the level equal to that in pipelines biofilm with no disinfection. Therefore, NH3-N reduced the ARGs removal efficiency of chlorine disinfection. It is necessary to take measures to improve the removal rate of NH3-N and ARGs for preventing their risks in drinking water.

Characterizing the development of biofilm in polyethylene pipes in the non-chlorinated Danish drinking-water distribution system

In newly commissioned drinking-water polyethylene (PE) pipes, biofilm develops on the inner pipe surface. The microbial community composition from colonization to the establishment of mature biofilms is less known, including the effect on the distributed water quality. Biofilm development was followed through 1.5 years in PE-pipe side streams at two locations of a full-scale, non-chlorinated drinking-water distribution system (leaving a waterworks versus 5-6 km from a waterworks) along with inlet and outlet water quality. Mature biofilms were established after ∼8-9 months, dominated by Proteobacteria, Actinobacteria and Saccharibacteria (61-93% relative abundance), with a higher diversity (OTUs/Shannon Index/16S rRNA gene amplicon sequencing) in pipes in the far end of the distribution system. Comamonadaceae, and specifically Aquabacterium (>30% of reads), dominated young (∼1.5-month-old) biofilms. Young biofilms were linked to increased microbiological counts in drinking water (HPC/ATP/qPCR), while the establishment of mature biofilms led to a drop in HPC and benefited the water quality, highlighting the importance of optimizing commissioning procedures for rapidly achieving mature and stable biofilms.

Bacterial communities of planktonic bacteria and mature biofilm in service lines and premise plumbing of a Megacity: Composition, Diversity, and influencing factors

Although simulated studies have provided valuable knowledge regarding the communities of planktonic bacteria and biofilms, the lack of systematic field studies have hampered the understanding of microbiology in real-world service lines and premise plumbing. In this study, the bacterial communities of water and biofilm were explored, with a special focus on the lifetime development of biofilm communities and their key influencing factors. The 16S rRNA gene sequencing results showed that both the planktonic bacteria and biofilm were dominated by Proteobacteria. Among the 15,084 observed amplicon sequence variants (ASVs), the 33 core ASVs covered 72.8 %, while the 12 shared core ASVs accounted for 62.2 % of the total sequences. Remarkably, it was found that the species richness and diversity of biofilm communities correlated with pipe age. The relative abundance of ASV2 (f_Sphingomonadaceae) was lower for pipe ages 40-50 years (7.9 %) than for pipe ages 10-20 years (59.3 %), while the relative abundance of ASV10 (f_Hyphomonadaceae) was higher for pipe ages 40-50 years (19.5 %) than its presence at pipe ages 20-30 years (1.9 %). The community of the premise plumbing biofilm had significantly higher species richness and diversity than that of the service line, while the steel-plastics composite pipe interior lined with polyethylene (S-PE) harbored significantly more diverse biofilm than the galvanized steel pipes (S-Zn). Interestingly, S-PE was enriched with ASV27 (g_Mycobacterium), while S-Zn pipes were enriched with ASV13 (g_Pseudomonas). Moreover, the network analysis showed that five rare ASVs, not core ASVs, were keystone members in biofilm communities, indicating the importance of rare members in the function and stability of biofilm communities. This manuscript provides novel insights into real-world service lines and premise plumbing microbiology, regarding lifetime dynamics (pipe age 10-50 years), and the influences of pipe types (premise plumbing vs. service line) and pipe materials (S-Zn vs. S-PE).

Occurrences and implications of pathogenic and antibiotic-resistant bacteria in different stages of drinking water treatment plants and distribution systems

Different stages of drinking water treatment plants (DWTPs) play specific roles in diverse contaminants' removal present in natural water sources. Although the stages are recorded to promote adequate treatment of water, the occurrence of pathogenic bacteria (PB) and antibiotic-resistant bacteria (ARB) in the treated water and the changes in their diversity and abundance as it passed down to the end users through the drinking water distribution systems (DWDSs), is a great concern, especially to human health. This could imply that the different stages and the distribution system provide a good microenvironment for their growth. Hence, it becomes pertinent to constantly monitor and document the diversity of PB and ARB present at each stage of the treatment and distribution system. This review aimed at documenting the occurrence of PB and ARB at different stages of treatment and distribution systems as well as the implication of their occurrence globally. An exhaustive literature search from Web of Science, Science-Direct database, Google Scholar, Academic Research Databases like the National Center for Biotechnology Information, Scopus, and SpringerLink was done. The obtained information showed that the different treatment stages and distribution systems influence the PB and ARB that proliferate. To minimize the human health risks associated with the occurrence of these PB, the present review, suggests the development of advanced technologies that can promote quick monitoring of PB/ARB at each treatment stage and distribution system as well as reduction of the cost of environomics analysis to promote better microbial analysis.

Responses of drinking water bulk and biofilm microbiota to elevated water age in bench-scale simulated distribution systems

Reductions in nonresidential water demand during the COVID-19 pandemic highlighted the importance of understanding how water age impacts drinking water quality and microbiota in piped distribution systems. Using benchtop model distribution systems, we aimed to characterize the impacts of elevated water age on microbiota in bulk water and pipe wall biofilms. Five replicate constant-flow reactors were fed with municipal chloraminated tap water for 6 months prior to building closures and 7 months after. After building closures, chloramine levels entering the reactors dropped; in the reactor bulk water and biofilms the mean cell counts and ATP concentrations increased over an order of magnitude while the detection of opportunistic pathogens remained low. Water age, and the corresponding physicochemical changes, strongly influenced microbial abundance and community composition. Differential initial microbial colonization also had a lasting influence on microbial communities in each reactor (i.e., historical contingency).

Microbial ecology of drinking water from source to tap

As drinking water travels from its source, through various treatment processes, hundreds to thousands of kilometres of distribution network pipes, to the taps in private homes and public buildings, it is exposed to numerous environmental changes, as well as other microbes living in both water and on surfaces. This review aims to identify the key locations and factors that are associated with changes in the drinking water microbiome throughout conventional urban drinking water systems from the source to the tap water. Over the past 15 years, improvements in cultivation-independent methods have enabled studies that allow us to answer such questions. As a result, we are beginning to move towards predicting the impacts of disturbances and interventions resulting ultimately in management of drinking water systems and microbial communities rather than mere observation. Many challenges still exist to achieve effective management, particularly within the premise plumbing environment, which exhibits diverse and inconsistent conditions that may lead to alterations in the microbiota, potentially presenting public health risks. Finally, we recommend the establishment of global collaborative projects on the drinking water microbiome that will enhance our current knowledge and lead to tools for operators and researchers alike to improve global access to high-quality drinking water.

Deciphering the diversity and assemblage mechanisms of nontuberculous mycobacteria community in four drinking water distribution systems with different disinfectants

Nontuberculous mycobacteria (NTM) represent an emerging health concern due to their escalating infections worldwide. Although drinking water distribution systems (DWDSs) have been considered as NTM reservoirs and a potential infection route, NTM community at the species level remain largely elusive in DWDSs. This study employed high-throughput sequencing coupled with qPCR to profile NTM community and estimate their abundances at the species level in water and biofilm samples in four DWDSs using three different disinfectants (i.e. free chlorine, chloramine and chlorine dioxide). Results demonstrated the dominance of Mycobacterium paragordonae and Mycobacterium mucogenicum in both biofilm and water across four DWDSs, whereas Mycobacterium abscessus and Mycobacterium chelonae, the two clinically significant species, exhibited low abundance but high prevalence. Comparable NTM community was observed in biofilm across these four DWDSs. Distinct separation of NTM community between SH-chloramine DWDSs water and other DWDSs highlighted the selective pressure of chloramine on NTM community. Furthermore, the research revealed that biofilm and water exhibited distinct NTM community structures, with biofilm harboring more diverse NTM community. Certain NTM species displayed a preference for biofilm, such as Mycobacterium gordonae, while others, like Mycobacterium mucogenicum, were more abundant in water samples (P < 0.05). In terms of NTM community assembly, stochastic processes dominated biofilm, while comparable role of stochastic and deterministic processes was observed in water. In conclusion, this study offers a pioneering and comprehensive insight into the dynamics and assembly mechanisms of NTM community within four DWDSs treated with three distinct disinfectants. These findings serve as a critical foundation for assessing NTM exposure risks and devising effective management strategies within DWDSs.

Effect and influence mechanism of biofilm formation on the biological stability of reclaimed water

Microorganisms and sediments in reclaimed water adhere to the inner walls of pipes or water tanks, forming biofilms that support the continuous growth of microorganisms. These biofilms provide a protective barrier, shielding bacteria from disinfectants. This study investigated the impact of biofilms on bacterial growth and reproduction in reclaimed water and the factors limiting bacterial growth in reclaimed graywater (GMR) and reclaimed mixed wastewater (MWR). The results revealed that biofilm biomass gradually increased and reached a maximum value on Days 20-25, and the biomass of organisms continued to decrease after 40 days. Biofilms serve as a source of bacteria, continuously releasing them into reclaimed water systems. The presence of biofilms reduced the biological stability of the reclaimed water, leading to water quality deterioration. The concentration of assimilable organic carbon in the reclaimed water showed a positive correlation with the heterotrophic bacterial count and Escherichia coli levels in both the reclaimed water and biofilms. The threshold value of chlorine for inhibiting biofilms in reclaimed water was no <2 mg/L. High concentrations of free chlorine delayed the growth of biofilms but did not reduce the final biomass generated by the biofilms. Carbon was the limiting factor for the biological stability of reclaimed water, while nitrogen, phosphorus, and inorganic salts were not limiting factors. Thus, minimizing the concentration of organic matter in reclaimed water can reduce the nutrient sources available for biofilm formation. This study provides support for advancements in the wastewater reuse industry.

Assessing the Impacts of Lead Corrosion Control on the Microbial Ecology and Abundance of Drinking-Water-Associated Pathogens in a Full-Scale Drinking Water Distribution System

Increases in phosphate availability in drinking water distribution systems (DWDSs) from the use of phosphate-based corrosion control strategies may result in nutrient and microbial community composition shifts in the DWDS. This study assessed the year-long impacts of full-scale DWDS orthophosphate addition on both the microbial ecology and density of drinking-water-associated pathogens that infect the immunocompromised (DWPIs). Using 16S rRNA gene amplicon sequencing and droplet digital PCR, drinking water microbial community composition and DWPI density were examined. Microbial community composition analysis suggested significant compositional changes after the orthophosphate addition. Significant increases in total bacterial density were observed after orthophosphate addition, likely driven by a 2 log 10 increase in nontuberculous mycobacteria (NTM). Linear effect models confirmed the importance of phosphate addition with phosphorus concentration explaining 17% and 12% of the variance in NTM and L. pneumophila density, respectively. To elucidate the impact of phosphate on NTM aggregation, a comparison of planktonic and aggregate fractions of NTM cultures grown at varying phosphate concentrations was conducted. Aggregation assay results suggested that higher phosphate concentrations cause more disaggregation, and the interaction between phosphate and NTM is species specific. This work reveals new insight into the consequences of orthophosphate application on the DWDS microbiome and highlights the importance of proactively monitoring the DWDS for DWPIs.

Response mechanisms of pipe wall biofilms in water supply networks under different disinfection strategy pressures and the effect of mediating halogenated acetonitrile formation

Residual chlorine and biofilm coexistence is inevitable in drinking water transmission and distribution networks. Understanding the microbial response and its mediated effects on disinfection byproducts under different categories of residual chlorine stress is essential to ensure water safety. The aim of our study was to determine the response of pipe wall biofilms to residual chlorine pressure in chlorine and chloramine systems and to understand the microbially mediated effects on the formation and migration of haloacetonitriles (HANs), typical nitrogenous disinfection byproducts. According to the experimental results, the biofilm response changes under pressure, with significant differences noted in morphological characteristics, the extracellular polymeric substances (EPS) spatial structure, bacterial diversity, and functional abundance potential. Upon incubation with residual chlorine (1.0 ± 0.2 mg/L), the biofilm biomass per unit area, EPS, community abundance, and diversity increased in the chloramine group, and the percentage of viable bacteria increased, potentially indicating that the chloramine group provides a richer variety of organic matter precursors. Compared with the chloramine group, the chlorination group exhibited increased haloacetonitrile formation potential (HANFP), with Rhodococcus (43.2%) dominating the system, whereas the prediction abundance of metabolic functions was advantageous, especially with regard to amino acid metabolism, carbohydrate metabolism, and the biodegradation and metabolism of foreign chemicals. Under chlorine stress, pipe wall biofilms play a stronger role in mediating HAN production. It is inferred that chlorine may stimulates microbial interactions, and more metabolites (e.g., EPS) consume chlorine to protect microbial survival. EPS dominates in biofilms, in which proteins exhibit greater HANFP than polysaccharides.

Impact of fixture purging on water age and excess water usage, considering stochastic water demands

Higher water ages are linked with water quality decline as chlorine dissipates, temperatures become more favorable for microbial growth, and metals and organic matter leach from the pipes. Water fixtures with automated purging devices can limit water age in premise plumbing systems, but also increase water use. To develop purging strategies that lower age while also minimizing water use, the stochastic nature of water demands must be considered. In this research, a hydraulic plumbing network model, with stochastic demands at fixtures, was used to compare water age and water use for five purging conditions: purging at regular intervals, "smart" purging (considering the time of last use), purging with different volumes of water, purging at different fixtures, and the purging with different levels of home occupancy. Higher purging frequency and volume resulted in lower water ages, but higher water use. Purging greatly reduced the variability in water ages, avoiding extreme ages entirely. Water age was minimized by scheduling the purging around occupancy behavior, such as before the occupants wake up or return from work. Scheduled purging used more water than smart purging. Purging after 12 h of nonuse used only 55% of the additional water required for purging every 12 h. Purging after 24 h of nonuse at the kitchen tap and shower used only 38% of the additional water required for purging every 24 h, while maintaining lower water ages and removing the variability in water ages. While larger purging volumes had a greater impact on water age, there were diminishing returns. Purging has a larger impact on low-occupancy homes because fixtures have less frequent use. Overall, this research provides a methodology to compare purging strategies that minimize both water age and water use. While the numerical results presented here are only valid for the specific layout and usage habits, they provide insights and trends applicable to other cases.

The Behavior of Polymeric Pipes in Drinking Water Distribution System-Comparison with Other Pipe Materials

The inner walls of the drinking water distribution system (DWDS) are expected to be clean to ensure a safe quality of drinking water. Complex physical, chemical, and biological processes take place when water comes into contact with the pipe surface. This paper describes the impact of leaching different compounds from the water supply pipes into drinking water and subsequent risks. Among these compounds, there are heavy metals. It is necessary to prevent these metals from getting into the DWDS. Those compounds are susceptible to impacting the quality of the water delivered to the population either by leaching dangerous chemicals into water or by enhancing the development of microorganism growth on the pipe surface. The corrosion process of different pipe materials, scale formation mechanisms, and the impact of bacteria formed in corrosion layers are discussed. Water treatment processes and the pipe materials also affect the water composition. Pipe materials act differently in the flowing and stagnation conditions. Moreover, they age differently (e.g., metal-based pipes are subjected to corrosion while polymer-based pipes have a decreased mechanical resistance) and are susceptible to enhanced bacterial film formation. Water distribution pipes are a dynamic environment, therefore, the models that are used must consider the changes that occur over time. Mathematical modeling of the leaching process is complex and includes the description of corrosion development over time, correlated with a model for the biofilm formation and the disinfectants-corrosion products and disinfectants-biofilm interactions. The models used for these processes range from simple longitudinal dispersion models to Monte Carlo simulations and 3D modeling. This review helps to clarify what are the possible sources of compounds responsible for drinking water quality degradation. Additionally, it gives guidance on the measures that are needed to maintain stable and safe drinking water quality.

Efficient inactivation of amoeba spores and their intraspore bacteria by solar/chlorine: Kinetics and mechanisms

Amoebae are widespread in water and serve as environment vectors for pathogens, which may threaten public health. This study evaluated the inactivation of amoeba spores and their intraspore bacteria by solar/chlorine. Dictyostelium discoideum and Burkholderia agricolaris B1qs70 were selected as model amoebae and intraspore bacteria, respectively. Compared to solar irradiation and chlorine, solar/chlorine enhanced the inactivation of amoeba spores and intraspore bacteria, with 5.1 and 5.2-log reduction at 20 min, respectively. The enhancement was similar in real drinking water by solar/chlorine under natural sunlight. However, the spore inactivation decreased to 2.97-log by 20 min solar/chlorine under oxygen-free condition, indicating that ozone played a crucial role in the spore inactivation, as also confirmed by the scavenging test using tert‑butanol to scavenge the ground-state atomic oxygen (O(3P)) as a ozone precursor. Moreover, solar/chlorine induced the shape destruction and structural collapse of amoeba spores by scanning electron microscopy. As for intraspore bacteria, their inactivation was likely ascribed to endogenous reactive oxygen species. As pH increased from 5.0 to 9.0, the inactivation of amoeba spores decreased, whereas that of intraspore bacteria was similar at pH 5.0 and 6.5 during solar/chlorine treatment. This study first reports the efficient inactivation of amoeba spores and their intraspore pathogenic bacteria by solar/chlorine in drinking water.

The bacterial biofilm resistome in drinking water distribution systems: A systematic review

Antibiotic resistance in drinking water systems poses human health risks. Earlier studies, including reviews on antibiotic resistance in drinking water systems are limited to the occurrence, behaviour and fate in bulk raw water and drinking water treatment systems. By comparison, reviews on the bacterial biofilm resistome in drinking water distribution systems are still limited. Therefore, the present systematic review investigates the occurrence, behaviour and fate and, detection methods of bacterial biofilm resistome in the drinking water distribution systems. A total of 12 original articles drawn from 10 countries were retrieved and analyzed. Antibiotic resistant bacteria and antibiotic resistance genes detected in biofilms include those for sulfonamides, tetracycline, and beta-lactamase. The genera detected in biofilms include Staphylococcus, Enterococcus, Pseudomonas, Ralstonia, Mycobacteria, as well as Enterobacteriaceae family and other gram-negative bacteria. The presence of Enterococcus faecium, Staphylococcusaureus, Klebsiella pneumoniae, Acinetobacterbaumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE bacteria) among the detected bacteria points to potential human exposure and health risks especially for susceptible individuals via the consumption of drinking water. Besides, the effects of water quality parameter and residual chlorine, the physico-chemical factors controlling the emergence, persistence and fate of the biofilm resistome are still poorly understood. Culture-based methods, and molecular methods, and their advantages and limitations are discussed. The limited data on the bacterial biofilm resistome in drinking water distribution system points to the need for further research. To this end, future research directions are discussed including understanding the formation, behaviour, and fate of the resistome and the controlling factors.

Seasonal variations of microbial community and antibiotic resistome in a suburb drinking water distribution system in a northern Chinese city

Antibiotic resistance genes (ARGs) are an emerging issue for drinking water safety. However, the seasonal variation of ARGs in drinking water distribution systems (DWDS) is still unclear. This work revealed the tempo-spatial changes of microbial community, ARGs, mobile genetic elements (MGEs) co-occurring with ARGs, ARG hosts in DWDS bulk water by means of metagenome assembly. The microbial community and antibiotic resistome varied with sampling season and site. Temperature, ammonia, chlorite and total plate count (TPC) drove the variations of microbial community structure. Moreover, environmental parameters (total organic carbon (TOC), chlorite, TPC and hardness) shifted antibiotic resistome. ARGs and MGEs co-occurring with ARGs showed higher relative abundance in summer and autumn, which might be attributed to detached pipe biofilm. In particular, ARG-bacitracin and plasmid were the predominant ARG and MGE, respectively. ARG hosts changed with season and site and were more diverse in summer and autumn. In winter and spring, Limnohabitans and Mycobacterium were the major ARG hosts as well as the dominant genera in microbial community. In addition, in summer and autumn, high relative abundance of Achromobacter and Stenotrophomonas were the hosts harboring many kinds of ARGs and MGEs at site in a residential zone (0.4 km from the water treatment plant). Compared with MGEs, microbial community had a greater contribution to the variation of antibiotic resistome. This work gives new insights into the dynamics of ARGs in full-scale DWDS and the underlying factors.

Early succession of biofilm bacterial communities in newly built drinking water pipelines via multi-area analysis

Biofilms inhabiting pipeline walls are critical to drinking water quality and safety. With massive pipeline replacement underway, however, biofilm formation process in newly built pipes and its effects on water quality are unclear. Moreover, differences and connections between biofilms in newly built and old pipes are unknown. In this study, early succession (≤ 120 days) of biofilm bacterial communities (abundance and diversity) in upper, middle and bottom areas of a newly built cement-lined ductile iron pipeline were evaluated using improved Propella™ biofilm reactor and multi-area analysis. A comparison with old pipelines (grey cast iron, 10 years) was performed. In the newly built pipeline, the abundance of biofilm bacteria did not change significantly between 40 and 80 days, but increased significantly between 80 and 120 days. The biofilm bacterial abundance (per unit area) in the bottom area was always higher than that in the upper and middle areas. Based on alpha diversity index and PCoA results, biofilm bacterial community richness, diversity and composition did not change significantly during the 120-day operation. Besides, biofilm shedding from the walls of newly built pipeline significantly increased bacterial abundance in the outlet water. Opportunistic pathogen-containing genera, such as Burkholderia, Acinetobacter and Legionella, were identified in both water and biofilm samples from newly built pipelines. The comparison between new and old pipelines suggested a higher bacterial abundance per unit area at the middle and bottom areas in old pipelines. Moreover, the bacterial community composition of biofilms in old pipelines was similar to that of newly built pipelines. These results contribute to accurate prediction and management of biofilm microbial communities in drinking water pipelines, ensuring the biosafety of drinking water. KEY POINTS: • Biofilm bacterial communities in different areas of pipe wall were revealed. • The abundance of biofilm bacteria increased significantly between 80 and 120 days. • Biofilm bacterial community compositions of newly built and old pipes were similar.

Mechanisms of survival mediated by the stringent response in Pseudomonas aeruginosa under environmental stress in drinking water systems: Nitrogen deficiency and bacterial competition

Pseudomonas aeruginosa causes public health problems in drinking water systems. This study investigated the potential role of the stringent response in regulating the adaptive physiological metabolic behaviors of P. aeruginosa to low nitrogen stress and bacterial competition in drinking water systems. The results indicated that guanosine tetraphosphate (ppGpp) concentrations in P. aeruginosa increased to 135.5 pmol/g SS under short-term nitrogen deficiency. Meanwhile, the expression levels of the ppGpp synthesis genes (ppx, relA) and degradation gene (spoT) were upregulated by 37.0% and downregulated by 26.8%, respectively, indicating that the stringent response was triggered. The triggered stringent response inhibited the growth of P. aeruginosa and enhanced the metabolic activity of P. aeruginosa to adapt to nutrient deprivation. The interspecific competition significantly affected the regulation of the stringent response in P. aeruginosa. During short-term nitrogen deficiency, the extracellular polymeric substances concentration of P. aeruginosa decreased significantly, leading to desorption and diffusion of attached bacteria and increased ecological risks. The regulatory effect of stringent response on P. aeruginosa gradually weakened under long-term nitrogen deficiency. However, the expression of pathogenic genes (nalD/PA3310) and flagellar assembly genes (fliC) in P. aeruginosa was upregulated by the stringent response, which increased the risk of disease.

Insight into the dynamics of drinking water resistome in China

Antibiotic resistance (AR) is a serious environmental hazard of the current age. Antibiotic resistance genes (ARGs) are the fundamental entities that spread AR in the environment. ARGs are likely to be transferred from the non-pathogenic to pathogenic microbes that might ultimately be responsible for the AR in humans and other organisms. Drinking water (DW) is the primary interaction route between ARGs and humans. Being the highest producer and consumer of antibiotics China poses a potential threat to developing superbugs and ARGs dissemination. Herein, we comprehensively seek to review the ARGs from dominant DW sources in China. Furthermore, the origin and influencing factors of the ARGs to the DW in China have been evaluated. Commonly used methods, both classical and modern, are being compiled. In addition, the risk posed and mitigation strategies of DW ARGs in China have been outlined. Overall, we believe this review would contribute to the assessment of ARGs in DW of China and their dissemination to humans and other animals and ultimately help the policymakers and scientists in the field to counteract this problem on an emergency basis.

Co-occurrence of phthalate esters and perfluoroalkyl substances affected bacterial community and pathogenic bacteria growth in rural drinking water distribution systems

The adverse health effects of phthalate esters (PAEs) and perfluoroalkyl substances (PFAS) in drinking water have attracted considerable attention. Our study investigated the effects of PAEs and PFAS on the bacterial community and the growth of potential human pathogenic bacteria in rural drinking water distribution systems. Our results showed that the total concentration of PAEs and PFAS ranged from 1.02 × 10² to 1.65 × 10⁴ ng/L, from 4.40 to 1.84 × 10² ng/L in rural drinking water of China, respectively. PAEs concentration gradually increased and PFAS slowly decreased along the pipeline distribution, compared to concentrations in the effluents of rural drinking water treatment plants. The co-occurrence of higher concentrations of PAEs and PFAS changed the structure and function of the bacterial communities found within these environments. The bacterial community enhanced their ability to respond to fluctuating environmental conditions through up-regulation of functional genes related to extracellular signaling and interaction, as well as genes related to replication and repair. Under these conditions, co-occurrence of PAEs and PFAS promoted the growth of potential human pathogenic bacteria (HPB), therefore increasing the risk of the development of associated diseases among exposed persons. The main HPB observed in this study included Burkholderia mallei, Mycobacterium tuberculosis, Klebsiella pneumoniae, Acinetobacter calcoaceticus, Escherichia coli, and Pseudomonas aeruginosa. Contaminants including particles, microorganisms, PAEs and PFAS were found to be released from corrosion scales and deposits of pipes and taps, resulting in the increase of the cytotoxicity and microbial risk of rural tap water. These results are important to efforts to improve the safety of rural drinking water.

Charting the landscape of the environmental exposome

The exposome depicts the total exposures in the lifetime of an organism. Human exposome comprises exposures from environmental and humanistic sources. Biological, chemical, and physical environmental exposures pose potential health threats, especially to susceptible populations. Although still in its nascent stage, we are beginning to recognize the vast and dynamic nature of the exposome. In this review, we systematically summarize the biological and chemical environmental exposomes in three broad environmental matrices-air, soil, and water; each contains several distinct subcategories, along with a brief introduction to the physical exposome. Disease-related environmental exposures are highlighted, and humans are also a major source of disease-related biological exposures. We further discuss the interactions between biological, chemical, and physical exposomes. Finally, we propose a list of outstanding challenges under the exposome research framework that need to be addressed to move the field forward. Taken together, we present a detailed landscape of environmental exposome to prime researchers to join this exciting new field.

Diversity and dynamics of bacterial communities in the drinking water distribution network of a mid-sized city in Brazil

This study assessed the bacterial community composition of a drinking water system (DWS) serving a mid-sized city (120,000 inhabitants) in Brazil. Water samples, including raw and treated water, were collected at seven points throughout the DWS. DNA was extracted and analysed using high-throughput sequencing (Ion Torrent). Free chlorine and turbidity were measured in situ. Results showed that the highest relative abundance of 16S rRNA genes was from phyla Proteobacteria, followed by Bacteroidetes and Actinobacteria. The next most abundant phylum was Cyanobacteria, represented by Arthronema, Calothrix, and Synechococcus. An interesting observation was that the DNA-based analysis suggested a bacterial community change in the distribution network, with treated reservoir water being very different from the network samples. This suggests active microbiology within the distribution network and a tendency for bacterial diversity to decrease after chlorine disinfection but increase after pipeline distribution. In raw water, a predominance of Proteobacteria was observed with reduced Cyanobacteria, showing a negative correlation. In treated water, Proteobacteria were negatively correlated with Bacteroidetes. Finally, 16S rRNA genes from Firmicutes (especially Staphylococcus) had a high abundance in the chlorinated water, which may indicate the phylum's resistance to chlorine residuals. Opportunistic pathogens, e.g., Mycobacteria, Legionella, and Staphylococcus, were also observed.

Microstructural, mechanical, and electrochemical analysis of carbon doped AISI carbon steels

The effect of carbon doping contents on the microstructure, hardness, and corrosion properties of heat-treated AISI steel grades of plain carbon steel was investigated in this study. Various microstructures including coarse ferrite-pearlite, fine ferrite-pearlite, martensite, and bainite were developed by different heat treatments i.e. annealing, normalizing, quenching, and austempering, respectively. The developed microstructures, micro-hardness, and corrosion properties were investigated by a light optical microscope, scanning electron microscope, electromechanical (Vickers Hardness tester), and electrochemical (Gamry Potentiostat) equipment, respectively. The highest corrosion rates were observed in bainitic microstructures (2.68-12.12 mpy), whereas the lowest were found in the fine ferritic-pearlitic microstructures (1.57-6.36 mpy). A direct correlation has been observed between carbon concentration and corrosion rate, i.e. carbon content resulted in an increase in corrosion rate (2.37 mpy for AISI 1020 to 9.67 mpy for AISI 1050 in annealed condition).

Understanding point-of-use tap water quality: From instrument measurement to intelligent analysis using sample filtration

In most cases, point-of-use tap water quality is not routinely monitored due to widely-dispersed sampling sites and the costly tests. Although previous studies have revealed the variation of drinking water quality during distribution in municipal networks, the influence of aging pipes in buildings on quality is still unknown and this makes it difficult for water utilities to conduct regular maintenance. Herein, we have undertaken a survey of tap water samples across 8 districts in Beijing (China) to evaluate the potential effects of pipe age on point-of-use water quality, including turbidity, organic matter characteristics, and bacterial community. By grouping the collected samples according to the pipe age and source water respectively, the results suggested that bacterial diversity is significantly influenced by the pipe age. However, bacterial community structure is clearly influenced by the source water. Similarly, aging pipes in buildings are also responsible for the deterioration of the final water quality, and their effects have been closely linked to selected water quality parameters by evaluating the relevant factors. Moreover, the interrelationships between physico-chemical parameters and bacteria abundance were identified. For example, pH, Ca²⁺, Mg²⁺, Na⁺ and K⁺ showed a positive relationship with Bacillus abundance. In addition, an intelligent analysis method for understanding pipe age, organic matter concentration, and hardness (i.e., Ca²⁺ and Mg²⁺ concentration), based on image analysis of filtered membranes has been developed. The accuracy of prediction was encouraging, but can be improved with the collection of more data from tap water samples. We expect that this method can be exploited by the public to monitor their tap water and provide a feasible and cost-effective approach for water suppliers to locate aging/deteriorating pipes which need to be replaced or maintained.

Pilot investigation on biostability of drinking water distribution systems under water source switching

Water quality deterioration of drinking water distribution systems (DWDSs) caused by water source switching has been reported previously. However, systematic investigation of the biostability of DWDS under water source switching is limited. Aged pipes, including three commonly used pipe materials dug out from a practical DWDS, were used to systematically investigate the biofilm stability mechanism of DWDS under water source switching to quality-improved water. An increase in adenosine triphosphate (ATP) concentration in the bulk water during the initial stage of the switching period was observed, indicating the risk of biofilm release through aged pipe surfaces after water source switching. Sloughing of biofilms might contribute to temporary instability. From day 35, the ATP concentration in the polyethylene (PE) and plastic stainless steel composite (PS) pipes were maintained at approximately 2.40 and 2.56 ng/L, respectively. In contrast, the ATP concentration in the ductile iron (DI) pipes was higher, at approximately 3.43 ng/L from day 42. The water quality variation could cause areas of the biofilm to slough and reduce the biomass of biofilm, causing partial alteration of the microbial community. 16S rRNA gene amplicon sequencing-based functional prediction revealed that the biofilm could increase the abundance of chlorine-resistant bacteria attributed to the increase in Pseudomonas and Methylobacterium after switching to quality-improved water. Moreover, the profiles of specific pathways linked to human diseases, antibiotic resistance, and antibiotic biosynthesis revealed that the safety of the biofilm could improve after switching to quality-improved water. KEY POINTS: • The PE and PS biofilm showed improved resistance to water quality perturbation. • Greater number of Methylobacterium was found in the biofilm after water source switching. • 3.16S gene-based metagenomics prediction revealed that the safety of the biofilm under water source switching.

It’s a Long Way to the Tap: Microbiome and DNA-Based Omics at the Core of Drinking Water Quality

Microbial communities interact with us and affect our health in ways that are only beginning to be understood. Microorganisms have been detected in every ecosystem on Earth, as well as in any built environment that has been investigated. Drinking water sources, drinking water treatment plants and distribution systems provide peculiar microbial ecological niches, dismantling the belief of the “biological simplicity” of drinking water. Nevertheless, drinking water microbiomes are understudied compared to other microbiomes. Recent DNA sequencing and meta-omics advancements allow a deeper understanding of drinking water microbiota. Thus, moving beyond the limits of day-to-day testing for specific pathogenic microbes, new approaches aim at predicting microbiome changes driven by disturbances at the macro-scale and overtime. This will foster an effective and proactive management of water sources, improving the drinking water supply system and the monitoring activities to lower public health risk. Here, we want to give a new angle on drinking water microbiome research. Starting from a selection of 231 scientific publications on this topic, we emphasize the value of biodiversity in drinking water ecosystems and how it can be related with industrialization. We then discuss how microbiome research can support sustainable drinking water management, encouraging collaborations across sectors and involving the society through responsible research and innovation.

Microbiomes in drinking water treatment and distribution: A meta-analysis from source to tap

A meta-analysis of existing and available Illumina 16S rRNA datasets from drinking water source, treatment and drinking water distribution systems (DWDS) were collated to compare changes in abundance and diversity throughout. Samples from bulk water and biofilm were used to assess principles governing microbial community assembly and the value of amplicon sequencing to water utilities. Individual phyla relationships were explored to identify competitive or synergistic factors governing DWDS microbiomes. The relative importance of stochasticity in the assembly of the DWDS microbiome was considered to identify the significance of source and treatment in determining communities in DWDS. Treatment of water significantly reduces overall species abundance and richness, with chlorination of water providing the most impact to individual taxa relationships. The assembly of microbial communities in the bulk water of the source, primary treatment process and DWDS is governed by more stochastic processes, as is the DWDS biofilm. DWDS biofilm is significantly different from bulk water in terms of local contribution to beta diversity, type and abundance of taxa present. Water immediately post chlorination has a more deterministic microbial assembly, highlighting the significance of this process in changing the microbiome, although elevated levels of stochasticity in DWDS samples suggest that this may not be the case at customer taps. 16S rRNA sequencing is becoming more routine, and may have several uses for water utilities, including: detection and risk assessment of potential pathogens such as those within the genera of Legionella and Mycobacterium; assessing the risk of nitrification in DWDS; providing improved indicators of process performance and monitoring for significant changes in the microbial community to detect contamination. Combining this with quantitative methods like flow cytometry will allow a greater depth of understanding of the DWDS microbiome.

Household slow sand filters in continuous and intermittent flows and their efficiency in microorganism's removal from river water

This study aimed to evaluate the efficiency of four household slow sand filter (HSSF) models for the removal of microorganisms from river water throughout the development of their biological layers (schmutzdecke). Two models were designed to be operated continuously (HSSF-CC and HSSF-CT) and two intermittently (HSSF-ID and HSSF-IF). Filters were fed daily with 48 L pre-treated river water (24 h sedimentation followed by filtration through a non-woven synthetic blanket). Water samples were quantified by coliform group bacteria and analysed by bright field microscopy to visualize the microorganisms. Total coliform reduction was between 1.42 ± 0.59 log and 2.96 ± 0.58 log, with continuous models showing a better performance (p-values < 0.004). Escherichia coli reduction varied from 1.49 ± 0.58 log to 2.09 ± 0.66 log and HSSF-IF, HSSF-CC and HSSF-CT presented a similar performance (p-values > 0.06), slightly better than the one presented by HSSF-ID (p-value=0.04). Microorganisms, such as algae, protozoa and helminths were detected by microscopy in raw water and pre-treated water. Algae were the most significant group in these samples, although they were not visualized by bright field microscopy in the filtered water. Results showed the potential of HSSF in microbiological risk reduction from river water, which increases the range of point-of-use water treatments in rural communities. However, additional studies of the HSSF biological layer must be performed.

Impact of pipe material and chlorination on the biofilm structure and microbial communities

Pipe material and residual chlorine are key factors for the drinking water distribution system, and understanding the biofilm ecosystem is vital for water quality safeguard. The aim of our study was to determine the influence of pipe materials (ductile iron, steel, polyethylene) and chlorination on the biofilm structure and microbial community, as shown by the physicochemical properties, extracellular polymeric substances (EPS) structural characteristics, bacterial community composition, and functional traits. EPS spatial properties were studied based on a semi-quantitative confocal laser scanning microscope (CLSM) description. Regarding the impact of chlorination, residule chlorine (1.0 ± 0.3 mg L^-1 free chlorine) could inhibit the bacteria colonization, and initiate a potential response to external disinfectants revealed by the EPS spatial distribution changes and communities variation compared to unchlorinated system. Regarding the impact of pipe material, polyethylene (PE) biofilms displayed lower biomass, loose zoogloea structure, lower proteins and polysaccharides content, and poor microbial diversity in contrast to ductile iron and steel biofilms. Pipe material was the more possible driving factor of the biofilm community composition compared to the chlorination based on principal coordinates analysis (PCoA) and permutational multivariate analysis of variance (PERMANOVA). Actinobacteria was dominant in the PE biofilms (45.57%-83.32%), while Alphaproteobacteria (34.30%-73.22%) and Gammaproteobacteria (6.46%-36.82%) were the major classes in the steel and ductile iron biofilms. The genus Rhodococcus was predominant in the PE biofilms. Rhodococcus, Pseudomonas, and Sphingomonas seemed to have a better growth advantage in the chlorinated system and display a stronger disinfectant resistance. Functional sketch prediction indicated the potential impact of pipe material and chlorination on functional pathway abundnce, possible functional pathways associated with infectious disease included. This study provides insights into the impact of pipe material and chlorination on biofilm structure and microbial community and might help to develop monitoring or maintenance strategies to protect the biosafety of the drinking water.

The effect of disinfectants on the microbial community on environmental healthcare surfaces using next generation sequencing

BACKGROUND

Healthcare-associated infections are a significant economic burden and cause of avoidable morbidity and mortality within healthcare systems. The contribution of environmental contamination to healthcare-associated infection transmission has been recognized, but the mechanisms by which transmission occurs are still being investigated. The objective of this study was to characterize the microbial communities of disinfected, non-critical healthcare surfaces using next generation sequencing technology.

METHODS

Composite environmental surface samples were from high-touch surfaces in rooms of patients isolated for infections with multidrug-resistant organisms during their hospitalization. Information on the disinfectant product used and cleaning type (routine or terminal) was collected. 16S rRNA gene amplicon sequencing and analysis were performed. Community analysis was conducted to determine the bacterial composition and compare the detection of target pathogens by culture from 94 Contact Precaution rooms.

RESULTS

Overall percent agreement between culture and sequence methods ranged from 52%-88%. A significant difference was observed in bacterial composition between rooms cleaned with bleach and those cleaned with a quaternary ammonium compound for composite 2 (overbed table, intravenous pole, and inner room door handle) (ANOSIM R = 0.66, P = .005) but not composite 1 (bed rails, television remote control unit, call buttons, and telephone).

CONCLUSIONS

Surfaces in bleach-cleaned rooms contained a higher proportion of gram-positive microbiota, whereas rooms cleaned with quaternary ammonium compound contained a higher proportion of gram-negative microbiota, suggesting disinfectant products may impact the healthcare environment microbiome.

The Impact of Pipe Material on the Diversity of Microbial Communities in Drinking Water Distribution Systems

As many cities around the world face the prospect of replacing aging drinking water distribution systems (DWDS), water utilities must make careful decisions on new pipe material (e.g., cement-lined or PVC) for these systems. These decisions are informed by cost, physical integrity, and impact on microbiological and physicochemical water quality. Indeed, pipe material can impact the development of biofilm in DWDS that can harbor pathogens and impact drinking water quality. Annular reactors (ARs) with cast iron and cement coupons fed with chloraminated water from a municipal DWDS were used to investigate the impact of pipe material on biofilm development and composition over 16 months. The ARs were plumbed as closely as possible to the water main in the basement of an academic building to simulate distribution system conditions. Biofilm communities on coupons were characterized using 16S rRNA sequencing. In the cast iron reactors, β-proteobacteria, Actinobacteria, and α-proteobacteria were similarly relatively abundant (24.1, 22.5, and 22.4%, respectively) while in the cement reactors, α-proteobacteria and Actinobacteria were more relatively abundant (36.3 and 35.2%, respectively) compared to β-proteobacteria (12.8%). Mean alpha diversity (estimated with Shannon H and Faith's Phylogenetic Difference indices) was greater in cast iron reactors (Shannon: 5.00 ± 0.41; Faith's PD: 15.40 ± 2.88) than in cement reactors (Shannon: 4.16 ± 0.78; Faith's PD: 13.00 ± 2.01). PCoA of Bray-Curtis dissimilarities indicated that communities in cast iron ARs, cement ARs, bulk distribution system water, and distribution system pipe biofilm were distinct. The mean relative abundance of Mycobacterium spp. was greater in the cement reactors (34.8 ± 18.6%) than in the cast iron reactors (21.7 ± 11.9%). In contrast, the mean relative abundance of Legionella spp. trended higher in biofilm from cast iron reactors (0.5 ± 0.7%) than biofilm in cement reactors (0.01 ± 0.01%). These results suggest that pipe material is associated with differences in the diversity, bacterial composition, and opportunistic pathogen prevalence in biofilm of DWDS.

Characterizing the premise plumbing microbiome in both water and biofilms of a 50-year-old building

The premise plumbing portion of drinking water distribution systems (DWDS) has several characteristics that may favor microbial growth in the form of biofilms. These microbial communities are implicated as infectious sources for the spread of opportunistic waterborne pathogens by supporting their complex ecology and transmission through DWDS outlets to susceptible individuals. However, there is limited understanding of the drinking water biofilms in real premise plumbing networks due to challenges with accessibility. Using a combination of culture-dependent and culture-independent approaches, this study comprehensively characterized the premise plumbing microbiome of a 50-year-old university building, inclusive of water and biofilm samples. Microbial diversity in the water samples were more taxonomically diverse in comparison to the mature drinking water biofilms, which were dominated with biofilm-formers and opportunistic pathogens, such as Mycobacterium spp. A model opportunistic pathogen, Legionella spp., was only detectable in water samples using quantitative PCR but could not be detected in any of the drinking water biofilms using either qPCR or culture-dependent approaches, highlighting the limitations of detection methods in these environments. This study presents preliminary findings on the microbial dynamics and complexity in premise plumbing networks, which may support public health management and the development of strategies to eliminate microbial risks to human health.

Legionella: A Promising Supplementary Indicator of Microbial Drinking Water Quality in Municipal Engineered Water Systems

Opportunistic pathogens (OPs) are natural inhabitants and the predominant disease causative biotic agents in municipal engineered water systems (EWSs). In EWSs, OPs occur at high frequencies and concentrations, cause drinking-water-related disease outbreaks, and are a major factor threatening public health. Therefore, the prevalence of OPs in EWSs represents microbial drinking water quality. Closely or routinely monitoring the dynamics of OPs in municipal EWSs is thus critical to ensuring drinking water quality and protecting public health. Monitoring the dynamics of conventional (fecal) indicators (e.g., total coliforms, fecal coliforms, and Escherichia coli) is the customary or even exclusive means of assessing microbial drinking water quality. However, those indicators infer only fecal contamination due to treatment (e.g., disinfection within water utilities) failure and EWS infrastructure issues (e.g., water main breaks and infiltration), whereas OPs are not contaminants in drinking water. In addition, those indicators appear in EWSs at low concentrations (often absent in well-maintained EWSs) and are uncorrelated with OPs. For instance, conventional indicators decay, while OPs regrow with increasing hydraulic residence time. As a result, conventional indicators are poor indicators of OPs (the major aspect of microbial drinking water quality) in EWSs. An additional or supplementary indicator that can well infer the prevalence of OPs in EWSs is highly needed. This systematic review argues that Legionella as a dominant OP-containing genus and natural inhabitant in EWSs is a promising candidate for such a supplementary indicator. Through comprehensively comparing the behavior (i.e., occurrence, growth and regrowth, spatiotemporal variations in concentrations, resistance to disinfectant residuals, and responses to physicochemical water quality parameters) of major OPs (e.g., Legionella especially L. pneumophila, Mycobacterium, and Pseudomonas especially P. aeruginosa), this review proves that Legionella is a promising supplementary indicator for the prevalence of OPs in EWSs while other OPs lack this indication feature. Legionella as a dominant natural inhabitant in EWSs occurs frequently, has a high concentration, and correlates with more microbial and physicochemical water quality parameters than other common OPs. Legionella and OPs in EWSs share multiple key features such as high disinfectant resistance, biofilm formation, proliferation within amoebae, and significant spatiotemporal variations in concentrations. Therefore, the presence and concentration of Legionella well indicate the presence and concentrations of OPs (especially L. pneumophila) and microbial drinking water quality in EWSs. In addition, Legionella concentration indicates the efficacies of disinfectant residuals in EWSs. Furthermore, with the development of modern Legionella quantification methods (especially quantitative polymerase chain reactions), monitoring Legionella in ESWs is becoming easier, more affordable, and less labor-intensive. Those features make Legionella a proper supplementary indicator for microbial drinking water quality (especially the prevalence of OPs) in EWSs. Water authorities may use Legionella and conventional indicators in combination to more comprehensively assess microbial drinking water quality in municipal EWSs. Future work should further explore the indication role of Legionella in EWSs and propose drinking water Legionella concentration limits that indicate serious public health effects and require enhanced treatment (e.g., booster disinfection).

Bacterial community change and antibiotic resistance promotion after exposure to sulfadiazine and the role of UV/H2O2-GAC treatment

Effects of sulfadiazine on bacterial community and antibiotic resistance genes (ARGs) in drinking water distribution systems (DWDSs) were investigated in this study. Three DWDSs, including sand filtered (SF) DWDSs, granular active carbon (GAC) filtration DWDSs, and UV/H₂O₂-GAC DWDSs, were used to deliver sand filtered water, GAC filtered water, and UV/H₂O₂-GAC treated water, respectively. UV/H₂O₂-GAC filtration can remove the dissolved organic matter effectively, which resulted in the lowest bacterial diversity, biomass and ARGs in effluents and biofilm of DWDSs. When sulfadiazine was added to the sand filtered water, the dehydrogenase concentration and bacterial activity of bacterial community increased in effluents and biofilm of different DWDSs, inducing more extracellular polymeric substances (EPS) production. The proteins increasement percentage was 26.9%, 11.7% and 19.1% in biofilm of three DWDSs, respectively. And the proteins increased to 830.30 ± 20.56 μg cm^-2, 687.04 ± 18.65 μg cm^-2 and 586.07 ± 16.24 μg cm^-2, respectively. The increase of EPS promoted biofilm formation and increased the chlorine-resistance capability of bacteria. Therefore, the relative abundance of Clostridium_sensu_stricto_1 increased to 12.22%, 10.41% and 0.33% in biofilm of the three DWDSs, respectively. Candidatus_Odyssella also increased in the effluents and biofilm of the three DWDSs. These antibiotic resistance bacteria increase in DWDSs also induced the ARGs promotion, including sul1, sul2, sul3, mexA and class 1 integrons (int1). However, UV/H₂O₂-GAC filtration induced the lowest increase of dehydrogenase and EPS production through sulfadiazine removal efficiently, resulting in the least bacterial community change and ARGs promotion in UV/H₂O₂-GAC DWDSs.

"Touch microbiome" as a potential tool for forensic investigation: A pilot study

Human skin hosts a variety of microbes that can be transferred to surfaces ("touch microbiome"). These microorganisms can be considered as forensic markers similarly to "touch DNA". With this pilot study, we wanted to evaluate the transferability and persistence of the "touch microbiome" on a surface after the deposition of a fingerprint and its exposure for 30 days at room temperature. Eleven volunteers were enrolled in the study. Skin microbiome samples were collected by swabbing the palm of their hands; additionally, donors were asked to touch a glass microscope slide to deposit their fingerprints, that were then swabbed. Both human and microbial DNA was isolated and quantified. Amelogenin locus and 16 human STRs were amplified, whereas the V4 region of 16 S rRNA gene was sequenced using Illumina MiSeq platform. STR profiles were successfully typed for 5 out of 22 "touch DNA" samples, while a microbiome profile was obtained for 20 out of 22 "touch microbiome" samples. Six skin core microbiome taxa were identified, as well as unique donor characterizing taxa. These unique taxa may have relevance for personal identification studies and may be useful to provide forensic intelligence information also when "touch DNA" fails. Additional future studies including greater datasets, additional time points and a greater number of surfaces may clarify the applicability of "touch microbiome" studies to real forensic contexts.

Effects of microbial inactivation approaches on quantity and properties of extracellular polymeric substances in the process of wastewater treatment and reclamation: A review

Microbial extracellular polymeric substances (EPS) have a profound role in various wastewater treatment and reclamation processes, in which a variety of technologies are used for disinfection and microbial growth inhibition. These treatment processes can induce significant changes in the quantity and properties of EPS, and altered EPS could further adversely affect the wastewater treatment and reclamation system, including membrane filtration, disinfection, and water distribution. To clarify the effects of microbial inactivation approaches on EPS, these effects were classified into four categories: (1) chemical reactions, (2) cell lysis, (3) changing EPS-producing metabolic processes, and (4) altering microbial community. Across these different effects, treatments with free chlorine, methylisothiazolone, TiO₂, and UV irradiation typically enhance EPS production. Among the residual microorganisms in EPS matrices after various microbial inactivation treatments, one of the most prominent is Mycobacterium. With respect to EPS properties, proteins and humic acids in EPS are usually more susceptible to treatment processes than polysaccharides. The affected EPS properties include changes in molecular weight, hydrophobicity, and adhesion ability. All of these changes can undermine wastewater treatment and reclamation processes. Therefore, effects on EPS quantity and properties should be considered during the application of microbial inactivation and growth inhibition techniques.

Microbial communities of biofilms developed in a chlorinated drinking water distribution system: A field study of antibiotic resistance and biodiversity

Antibiotic resistance and biodiversity were investigated in microbial communities attached to inner surfaces of water supply fittings in a chlorinated drinking water distribution system (DWDS) supplied by two independent water treatment plants (WTPs) drawing the same source water. The investigation of the effect of the season, the applied water treatment technology, and type, material, and age of water supply fittings on both antibiotic resistance and biodiversity in biofilms involved collection of tubercles during summer and winter seasons throughout the DWDS. A total of 16 samples were collected (8 per season) from areas supplied by two independent WTPs. Culturable aerobic antibiotic resistant bacteria (ARB) proved more prevalent in summer. Various antibiotic resistance genes (ARGs) were detected, confirming the role of biofilms as ARGs reservoirs, but the abundances of quantified genes (sulI, ermB, qacEΔ1, intI1) were low (a range of <LOQ to 2313 gene copies/mg dry mass of tubercles) throughout the DWDS. In terms of microbial community composition, Proteobacteria were dominant in each sample (51.51-97.13%), and the most abundant genus was Desulfovibrio (0.01-66.69%) belonging to sulphate-reducing bacteria. Biodiversity of microbial communities was shaped by many coexisting factors, including season, water supply fitting material, and sampling site location. Spatial distribution analysis revealed that although only samples collected at the same sampling sites were similar to each other in terms of antibiotic resistance, some samples collected in the close proximity were similar in terms of biodiversity. This suggests that antibiotic resistance spreads only locally over small distances in drinking water biofilms. Although actual drinking water biofilms have been previously investigated in terms of microbial biodiversity, this is the first study that characterised both antibiotic resistance and biodiversity of microbial communities attached to inner surfaces of a real DWDS functioning for decades.

Causes, Factors, and Control Measures of Opportunistic Premise Plumbing Pathogens—A Critical Review

This review critically analyses the chemical and physical parameters that influence the occurrence of opportunistic pathogens in the drinking water distribution system, specifically in premise plumbing. A comprehensive literature review reveals significant impacts of water age, disinfectant residual (type and concentration), temperature, pH, and pipe materials. Evidence suggests that there is substantial interplay between these parameters; however, the dynamics of such relationships is yet to be elucidated. There is a correlation between premise plumbing system characteristics, including those featuring water and energy conservation measures, and increased water quality issues and public health concerns. Other interconnected issues exacerbated by high water age, such as disinfectant decay and reduced corrosion control efficiency, deserve closer attention. Some common features and trends in the occurrence of opportunistic pathogens have been identified through a thorough analysis of the available literature. It is proposed that the efforts to reduce or eliminate their incidence might best focus on these common features.

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

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

Occurrence and quantification of culturable and viable but non-culturable (VBNC) pathogens in biofilm on different pipes from a metropolitan drinking water distribution system

Waterborne pathogens have been found in biofilms grown in drinking water distribution system (DWDS). However, there is a lack of quantitative study on the culturability of pathogens in biofilms from metropolitan DWDS. In this study, we quantified culturable and viable but non-culturable (VBNC) Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and Vibrio cholerae in biofilms collected from five kinds of pipes (galvanized steel pipe, steel pipe, stainless steel clad pipe, ductile cast iron pipe and polyethylene pipe) and associated drinking water at an actual chlorinated DWDS in use from China. The results of these comprehensive analyses revealed that pipe material is a significant factor influencing the culturability of pathogen and microbial communities. Network analysis of the culturable pathogens and 16S rRNA gene inferred potential interactions between microbiome and culturability of pathogens. Although the water quality met the Chinese national standard of drinking water, however, VBNC pathogens were detected in both biofilms and water from the DWDS. This investigation suggests that stainless steel clad pipe (SSCP) was a better choice for pathogen control compared with other metal pipes. To our knowledge, this is the first study on culturable and VBNC pathogens in biofilms of different pipe materials in metropolitan DWDS.

Electrochemical biofilm control by reconstructing microbial community in agricultural water distribution systems

Biofilm causes considerable technical challenges in agricultural water distribution systems. Electrochemical treatment (ECT) is a potential technique for controlling biofilm in the systems. Given the limited information on how ECT performance changes of irrigation systems and microbial biofilm community shifts. In this study, the effect of anti-biofilm was assessed. Illumina Miseq high-throughput sequencing, combined with molecular ecological network analysis, were applied to detect the effects of ECT on attached biofilm microbial communities. We found that ECT effectively mitigated biofilm formation with the fixed-biofilm biomass reduced by 37.5 %-79.9 %. ECT significantly shifted the bacterial community structures in the biofilm, reduced the communities' diversity, and changed the dominant species. Molecular ecological network analysis showed that the complexity and size of bacterial networks were destabilized under ECT and decreased the interactions among bacterial species. The reconstruction in bacterial community and networks were responsible for the decline in extracellular polymer substances and biofilm biomass. However, chlorine-resistant bacteria were found increased after ECT, and higher relative abundance and low biofilm removal was identified in continuous ECT as compared with intermittent ECT. These results aimed to highlight the opportunity for biofouling mitigation by ECT for irrigation systems, and reveal the potential anti-biofilm microbial mechanisms of ECT.

Hydrodynamics and surface properties influence biofilm proliferation

A biofilm is an interface-associated colloidal dispersion of bacterial cells and excreted polymers in which microorganisms find protection from their environment. Successful colonization of a surface by a bacterial community is typically a detriment to human health and property. Insight into the biofilm life-cycle provides clues on how their proliferation can be suppressed. In this review, we follow a cell through the cycle of attachment, growth, and departure from a colony. Among the abundance of factors that guide the three phases, we focus on hydrodynamics and stratum properties due to the synergistic effect such properties have on bacteria rejection and removal. Cell motion, whether facilitated by the environment via medium flow or self-actuated by use of an appendage, drastically improves the survivability of a bacterium. Once in the vicinity of a stratum, a single cell is exposed to near-surface interactions, such as van der Waals, electrostatic and specific interactions, similarly to any other colloidal particle. The success of the attachment and the potential for detachment is heavily influenced by surface properties such as material type and topography. The growth of the colony is similarly guided by mainstream flow and the convective transport throughout the biofilm. Beyond the growth phase, hydrodynamic traction forces on a biofilm can elicit strongly non-linear viscoelastic responses from the biofilm soft matter. As the colony exhausts the means of survival at a particular location, a set of trigger signals activates mechanisms of bacterial release, a life-cycle phase also facilitated by fluid flow. A review of biofilm-relevant hydrodynamics and startum properties provides insight into future research avenues.

The role of biofilm in the development and dissemination of ubiquitous pathogens in drinking water distribution systems: an overview of surveillance, outbreaks, and prevention

A variety of pathogenic microorganisms can survive in the drinking water distribution systems (DWDS) by forming stable biofilms and, thus, continually disseminating their population through the system's dynamic water bodies. The ingestion of the pathogen-contaminated water could trigger a broad spectrum of illnesses and well-being-related obstacles. These waterborne diseases are a significant concern for babies, pregnant women, and significantly low-immune individuals. This review highlights the recent advances in understanding the microbiological aspects of drinking water quality, biofilm formation and its dynamics, health issues caused by the emerging microbes in biofilm, and approaches for biofilm investigation its prevention and suppression in DWDS.

Metagenomic and network analyses decipher profiles and co-occurrence patterns of antibiotic resistome and bacterial taxa in the reclaimed wastewater distribution system

Metagenomic and network analyses were applied to decipher the profiles and co-occurrence of resistome and microbial taxa in the reclaimed wastewater distribution system, including reclaimed wastewater and two types of biofilms, i.e., surface layer biofilms and inner layer biofilms. The effects of chlorination, UV irradiation and no disinfection treatment on ARG relative abundance and composition were systemically investigated. The reclaimed wastewater possesses more diverse and abundant ARGs than biofilms and total ARG relative abundance followed the order of reclaimed wastewater samples > surface layer biofilms > inner layer biofilms. Multidrug, bacitracin, sulfonamide, aminoglycoside, beta-lactam, and macrolide-lincosamide-streptogramin resistance genes were the six most dominant ARG types and their sum accounted for 90.1 %-96.0 % of the total ARG relative abundance in different samples. Beta-lactam resistance gene was the discriminative ARG type for reclaimed wastewater. Bacitracin resistance gene and bacA were the discriminative ARG type and subtype for biofilms. Chlorination significantly reduced ARG relative abundance in the reclaimed wastewater. Nevertheless, it could not reduce ARG relative abundance in biofilms. Regarding to the total ARG profiles, there were no obvious increasing or decreasing trends over time during one year period. Co-occurrence results revealed twenty-six genera were deduced as the potential hosts of twenty-two ARG subtypes.

Spatial and Temporal Dynamics in Attached and Suspended Bacterial Communities in Three Drinking Water Distribution Systems with Variable Biological Stability

Microbial presence and regrowth in drinking water distribution systems (DWDSs) is routinely monitored to assess the biological stability of drinking water without a residual disinfectant, but the conventional microbiological culture methods currently used target only a very small fraction of the complete DWDS microbiome. Here, we sequenced 16S rRNA gene amplicons to elucidate the attached and suspended prokaryotic community dynamics within three nonchlorinated DWDSs with variable regrowth conditions distributing similarly treated surface water from the same source. One rural location, with less regrowth related issues, differed most strikingly from the other two urban locations by the exclusive presence of Pseudonocardia (Actinobacteria) in the biofilm and the absence of Limnobacter (Betaproteobacteriales) in the water and loose deposits during summer. There was a dominant seasonal effect on the drinking water microbiomes at all three locations. For one urban location, it was established that the most significant changes in the microbial community composition on a spatial scale occurred shortly after freshly treated water entered the DWDS. However, summerly regrowth of Limnobacter, one of the dominant genera in the distributed drinking water, already occurred in the clean water reservoir at the treatment plant before further distribution. The highlighted bacterial lineages within these highly diverse DWDS communities might be important new indicators for undesirable regrowth conditions affecting the final drinking water quality.

Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) in drinking water fountains in urban parks

The presence of Staphylococcus aureus in drinking water is a concern because of its potential to cause human infection and also because of its multiple antimicrobial resistance. This study evaluated the water quality of drinking water fountains and mist makers in four municipal parks of São Paulo for 13 months. Although all samples met bacteriological water quality criteria according to Brazilian regulations, the absence of residual chlorine (<0.1 mg/L) was observed. These data were significantly correlated with the frequency of S. aureus that was found in 25.2% of the samples. The mecA gene was detected in 36.7% of the isolates demonstrating its potential for resistance to several antimicrobials. Furthermore, 27.3% isolates carrying the mecA gene had methicillin-resistant Staphylococcus aureus (MRSA) phenotypic potential. The presence of S. aureus with characteristics of microbial resistance in water for human consumption is an unprecedented finding. Hence, conducting surveillance for opportunistic bacteria, such as staphylococci in drinking water, is reasonable to take control measures and to protect human health, especially in public places with high attendance.

Unchartered waters: the unintended impacts of residual chlorine on water quality and biofilms

Disinfection residuals in drinking water protect water quality and public heath by limiting planktonic microbial regrowth during distribution. However, we do not consider the consequences and selective pressures of such residuals on the ubiquitous biofilms that persist on the vast internal surface area of drinking water distribution systems. Using a full scale experimental facility, integrated analyses were applied to determine the physical, chemical and biological impacts of different free chlorine regimes on biofilm characteristics (composition, structure and microbiome) and water quality. Unexpectedly, higher free chlorine concentrations resulted in greater water quality degredation, observable as elevated inorganic loading and greater discolouration (a major cause of water quality complaints and a mask for other failures). High-chlorine concentrations also reduced biofilm cell concentrations but selected for a distinct biofilm bacterial community and inorganic composition, presenting unique risks. The results challenge the assumption that a measurable free chlorine residual necessarily assures drinking water safety.