Biofilms In Drinking Water Distribution Systems Research Articles

The stress response mechanisms and resistance change of chlorine-resistant microbial community at multi-phase interface under residual antibiotics in drinking water distribution system

The presence of multiple trace amounts of antibiotics in drinking water has recently drawn much attention. However, synergistic effects between disinfectants and antibiotics often occur in pipeline due to the presence of residual disinfectants. How this interaction affects the drinking water microbial community remains unknown. Herein, reactors with 2 h of hydraulic retention time (HRT) were constructed to simulate the drinking water distribution system (DWDS), and the antibiotics were continuously discharged to the reactor. Sulfamethoxazole (SMX) was used as a representative antibiotic, and treatment protocols with and without disinfectants were compared. High-throughput sequencing and metagenome were used to study the microbial community and function in polyethylene (PE) and ductile cast iron (DI) (protected by cement mortar lining) pipes. By measuring the enzyme activity and ATP content, we found that disinfectant exposure could not only increase the secretion of biofilm EPS, but also improve the bacterial activity to a certain extent. The synergistic effect of antibiotics and disinfectants could increase the activity of oxidative stress-related enzymes in microbial communities, and the main effect was antibiotic stress. This study not only provides insights into how to inhibit the transmission process of antibiotic resistance genes (ARGs) in biofilm in DWDS, but also provides enlightenment for the harm of ARGs in all carriers where biofilms may exist in water plants.

Niche Differentiation of Biofilm Microorganisms in a Full-scale Municipal Drinking Water Distribution System in China and Their Implication for Biofilm Control.

Biofilms on the inner surface of a drinking water distribution system (DWDS) affect water quality and stability. Understanding the niche differentiation of biofilm microbial communities is necessary for the efficient control of DWDS biofilms. However, biofilm studies are difficult to conduct in the actual DWDS because of inaccessibility to the pipes buried underground. Taking the opportunity of infrastructure construction and relevant pipeline replacement in China, biofilms in a DWDS (a water main and its branch pipes) were collected in situ, followed by analysis on the abundances and community structures of bacterial and archaeal using quantitative PCR and high-throughput sequencing, respectively. Results showed that archaea were detected only in the biofilms of the water main, with a range of 9.4×103~1.1×105 copies/cm2. By contrast, bacteria were detected in the biofilms of branch pipes and the distal part of the water main, with a range of 8.8×103~9.6×106 copies/cm2. Among the biofilm samples, the archaeal community in the central part of the water main showed the highest richness and diversity. Nitrosopumilus was found to be predominant (86.22%) in the biofilms of the proximal part of the water main. However, Methanobrevibacter (87.15%) predominated in the distal part of the water main. The bacterial community of the water main and branch pipes was primarily composed of Firmicutes and Proteobacteria at the phylum level, respectively. Regardless of archaea or bacteria, only few operational taxonomic units (OTUs) (<0.5% of total OTUs) were shared by all the biofilms, indicating the niche differentiation of biofilm microorganisms. Moreover, the high Mn content in the biofilms of the distal sampling location (D3) in the water main was linked to the predominance of Bacillus. Functional gene prediction revealed that the proportion of infectious disease-related genes was 0.44-0.67% in the tested biofilms. Furthermore, functional genes related to the resistance of the bacterial community to disinfections and antibiotics were detected in all the samples, that is, glutathione metabolism-relating genes (0.14-0.65%) and beta-lactam resistance gene (0.01-0.05%). The results of this study indicate the ubiquity of archaea and bacteria in the biofilms of water main and branch pipes, respectively, and pipe diameters could be a major influencing factor on bacterial community structure. In the water main, the key finding was the predominant existence of archaea, particularly Nitrosopumilus and methanogen. Hence, their routine monitoring and probable influences on water quality in pipelines with large diameter should be given more attention. Besides, since Mn-related Bacillus and suspected pathogenic Enterococcus were detected in the biofilm, supplementation of disinfectant may be a feasible strategy for inhibiting their growth and ensuring water quality. In addition, the monitoring on their abundance variation could help to determine the frequency and methods of pipeline maintenance.

Zwitterionic poly(sulfobetaine methacrylate)-based hydrogel coating for drinking water distribution systems to inhibit adhesion of waterborne bacteria.

Presence of biofilms in drinking water distribution systems (DWDS) can be a nuisance, leading to several operational and maintenance issues (i.e., increased secondary disinfectants demand, pipe damage or increased flow resistance), and so far, no single control practice was found to be sufficiently effective. Here, we propose poly (sulfobetaine methacrylate) (P(SBMA))-based hydrogel coating application as a biofilm control strategy in DWDS. The P(SBMA) coating was synthetized through photoinitiated free radical polymerization on polydimethylsiloxane with different combinations of SBMA as a monomer, and N, N'-methylenebis (acrylamide) (BIS) as a cross-linker. The most stable coating in terms of its mechanical properties was obtained using 20% SBMA with a 20:1 SBMA:BIS ratio. The coating was characterized using Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, and water contact angle measurements. The anti-adhesive performance of the coating was evaluated in a parallel-plate flow chamber system against adhesion of four bacterial strains representing genera commonly identified in DWDS biofilm communities, Sphingomonas and Pseudomonas. The selected strains exhibited varying adhesion behaviors in terms of attachment density and bacteria distribution on the surface. Despite these differences, after 4h, presence of the P(SBMA)-based hydrogel coating significantly reduced the number of adhering bacteria by 97%, 94%, 98% and 99%, for Sphingomonas Sph5, Sphingomonas Sph10, Pseudomonas extremorientalis and Pseudomonas aeruginosa, respectively, compared to non-coated surfaces. These findings motivate further research into a potential application of a hydrogel anti-adhesive coating as a localized biofilm control strategy in DWDS, especially on materials known to promote excessive biofilm growth.

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.

Characterization of Legionella pneumophila Populations by Multilocus Variable Number of Tandem Repeats (MLVA) Genotyping from Drinking Water and Biofilm in Hospitals from Different Regions of the West Bank

The West Bank can be considered a high-risk area for Legionnaires’ disease (LD) due to its hot climate, intermittent water supply and roof storage of drinking water. Legionella, mostly L. pneumophila, are responsible for LD, a severe, community-acquired and nosocomial pneumonia. To date, no extensive assessment of Legionella spp and L. pneumophila using cultivation in combination with molecular approaches in the West Bank has been published. Two years of environmental surveillance of Legionella in water and biofilms in the drinking water distribution systems (DWDS) of eight hospitals was carried out; 180 L. pneumophila strains were isolated, mostly from biofilms in DWDS. Most of the isolates were identified as serogroup (Sg) 1 (60%) and 6 (30%), while a minor fraction comprised Sg 8 and 10. Multilocus Variable number of tandem repeats Analysis using 13 loci (MLVA-8(12)) was applied as a high-resolution genotyping method and compared to the standard Sequence Based Typing (SBT). The isolates were genotyped in 27 MLVA-8(12) genotypes (Gt), comprising four MLVA clonal complexes (VACC 1; 2; 5; 11). The major fraction of isolates constituted Sequence Type (ST)1 and ST461. Most of the MLVA-genotypes were highly diverse and often unique. The MLVA-genotype composition showed substantial regional variability. In general, the applied MLVA-method made it possible to reproducibly genotype the isolates, and was consistent with SBT but showed a higher resolution. The advantage of the higher resolution was most evident for the subdivision of the large strain sets of ST1 and ST461; these STs were shown to be highly pneumonia-relevant in a former study. This shows that the resolution by MLVA is advantageous for back-tracking risk sites and for the avoidance of outbreaks of L. pneumophila. Overall, our results provide important insights into the detailed population structure of L. pneumophila, allowing for better risk assessment for DWDS.

Influence of phosphate dosing on biofilm development on Drinking Water Distribution Systems infrastructure surfaces

Phosphate is added to drinking water by UK water companies as a treatment to prevent the corrosion and metal leaching, like lead, in pipes. However, phosphate is a nutrient for microorganisms, and it can favour biofilm formation in Drinking Water Distribution Systems (DWDS), which can alter the water quality and safety. This study analyses the effect of phosphate addition on biofilm formation over different materials and its consequences for drinking water quality by i) using controlled experimental pipeline facility representative of a real-scale DWDS with high-density polyethylene coupons and ii) using a small-scale DWDS biofilm reactors with lead coupons. Biofilms developed over one month were exposed to the effect of different phosphate dosing and compare with UK normal water phosphate concentrations. During the experiment, physico-chemical analysis of water and microbial analysis of biofilms was carried out. Sequencing analysis of the 16s rRNA gene, from extracted DNA obtained from biofilms, provided information on any bacterial changes, and Scanning Electron Microscopy gave information about the biofilm organization. The results indicate that microorganisms find more difficult to establish and develop biofilms under high phosphate dosing, resulting in biofilms with less cells. Also, some physico-chemical parameter seems to be affected by phosphate dosing, like chlorine and lead. It is expected that differences in the biofilm community will be found depending on phosphate dosing. This study will provide information on the effect of phosphate on biofilm development in different pipes materials, which will facilitate to adjust an optimal phosphate dose to prevent plumbosolvency in DWDS.

Optimization of ultrasonic parameters for effective detachment of biofilm cells in an actual drinking water distribution system

It is important to obtain a considerable quantity of DNA from oligotrophic environments such as a drinking water distribution system (DWDS) to study microbial communities by molecular biotechnology, and DNA yield is always one of the biggest problems when performing metagenomic sequencing on drinking water samples. To obtain as many microbes as possible, ultrasound has been widely used in cell detachment, but studies on the optimal ultrasonic parameters for biofilm in DWDS have rarely been seen. The effects of three ultrasonic parameters, including power, duration, and the number of ultrasound treatments (USTs) on the selected monoculture bacteria (Pelomonas sp.) biofilm were studied first. Then the optimal values of each ultrasonic parameter were initially determined. Based on these values, three levels of each ultrasonic parameter were selected, and then an orthogonal experiment was conducted to further study drinking water biofilm, and finally the optimal ultrasonic parameters for the effective separation of biofilm cells in DWDS were determined. The results showed that the optimal ultrasonic power, duration, and the number of USTs are 13 W, 1 min, and 15, respectively. A 20-min interval is needed between two USTs. The present optimal UST, which does not lose DNA quality, can increase the amount of extractable DNA by at least 4.78 times compared to samples without UST. This study provides a pretreatment methodology for extracting more and reliable DNA from biofilm in DWDS, and can better solve the problem of DNA collection in oligotrophic environments.

Effect of temperature increase in bacterial and fungal communities of chlorinated drinking water distribution systems

Drinking Water Distribution Systems (DWDS) are diverse ecosystems where the majority of microorganisms live forming biofilms, which can alter the water quality if they are mobilised to the bulk water. Biofilm communities can be affected by the increase of temperature due to climate change, thus compromise the distribution of safe water. To understand the effect of temperature on biofilms in DWDS, biofilm was developed for 30 days at 16 °C and 24 °C using a full-scale experimental DWDS facility. Samples were collected at the end of the experiment from removable coupons inserted into the pipes. DNA was extracted and the 16S rRNA and ITS rRNA genes were sequenced and analysed, for the bacterial and fungal diversity respectively. Differences in bacterial and fungal diversity at both temperatures were observed at family level. At 16 °C bacterial community was dominated by Comamonadaceae (21.48 %), Pseudomonadaceae (16.41 %) and Sphingobacteriaceae (12.99 %). However, at 24 °C the most abundant family was Pseudomonadaceae (50.60 %) followed by Sphingomonadaceae (9.59 %) and Sinobacteraceae (7.82 %). Fungal diversity showed that at 16 °C the most abundant family was Nectriaceae (68.9 %), followed by Helotiales (24.5 %) and Filobasidiales (1.5 %). However, at 24 °C the community was dominated by Nectriaceae (98.15 %) and the following families showed a low relative abundance, Rhizopodaceae (0.95 %) and Cryptomycota (0.24 %). Temperature is a key factor for microbial growth in DWDS and affect the composition of the microbial communities. Temperature increase leads changes and a loss in complexity in bacterial and fungal communities of biofilms, which can affect the water quality.

Mycobacterial metabolic characteristics in a water meter biofilm revealed by metagenomics and metatranscriptomics

Mycobacteria represent one of the most persistent bacterial populations in drinking water distribution system (DWDS) biofilm communities; however, mycobacterial in situ metabolic profiles are largely unknown. In this study, the metabolic characteristics of mycobacteria in a household water meter biofilm were unveiled using a coupled metagenomic/metatranscriptomic approach. The water meter biofilm appeared to express nitrogenase genes (nifDKH) and a full complement of genes coding for several carbon-fixation pathways, especially the Calvin cycle, suggesting the CO2 sequestration and dinitrogen fixation potential of the biofilm. These findings indicate that it may be difficult to prevent the formation of DWDS biofilms simply by controlling the availability of organic carbon or nitrogen. The composite genome of mycobacteria (CG-M) was reconstructed based on the obtained omics data. CG-M shared similar genome phylogeny and virulence-factor profiles with Mycobacterium avium complex, suggesting that population CG-M might represent a member of mycobacteria with pathogenicity. According to the gene expression patterns, population CG-M showed the metabolic potential to assimilate CO2 via the Calvin cycle and/or anaplerotic reactions, and even to grow autotrophically with CO as the sole carbon and energy source. This suggests that organic carbon may not be a limiting factor for mycobacterial growth in DWDSs. Moreover, our results suggest that mycobacterial aromatic degradation is primarily achieved through the catechol meta-cleavage pathway, and biofilm mycobacteria could prefer phosphate as the phosphorus source.

Competition between Naegleria fowleri and Free Living Amoeba Colonizing Laboratory Scale and Operational Drinking Water Distribution Systems.

Free living amoebae (FLA), including pathogenic Naegleria fowleri, can colonize and grow within pipe wall biofilms of drinking water distribution systems (DWDSs). Studies on the interactions between various FLA species in biofilms are limited. Understanding the interaction between FLA and the broader biofilm ecology could help better predict DWDS susceptibility to N. fowleri colonization. The aim of this study was to determine if N. fowleri and other FLAs ( Naegleria, Vermamoeba, Willaertia, and Vahlkampfia spp.) cocolonize DWDS biofilm. FLAs commonly isolated from DWDSs ( N. fowleri, V. vermiformis, and N. lovaniensis) were introduced into laboratory-scale biomonitors to determine the impact of these amoebae on N. fowleri's presence and viability. Over 18 months, a single viable amoebae ( N. fowleri, N. lovaniensis, or V. vermiformis) was detected in each biofilm sample, with the exception of N. lovaniensis and N. fowleri, which briefly cocolonized biofilm following their coinoculation. The analysis of biofilm and bulk water samples from operational DWDSs revealed a similar lack of cocolonization with a single FLA detected in 99% ( n = 242) of samples. Interestingly, various Naegleria spp. did colonize the same DWDS locations but at different times. This knowledge furthers the understanding of ecological factors which enable N. fowleri to colonize and survive within operational DWDSs and could aid water utilities to control its occurrence.

Pyrosequencing analysis of source water switch and sulfate-induced bacterial community transformation in simulated drinking water distribution pipes.

Inter-basin water transfer and source water switching will be increasingly launched due to significant population increase and the shortage of the local water resources in cities around the world. Source water switch may cause physiochemical and microbiological de-stabilization of pipe material, biofilms, and loose deposits in drinking water distribution system (DWDS). Great sulfate alteration during source water switch had been deemed as the main cause of a red water case that occurred in a northern China city. To ascertain the relationship between water quality changing and bacterial communities of biofilms in DWDS and possible bacteria risk in a red water case, water quality changing experiments in simulated DWDSs were conducted for approximately 2years. Twenty-five corrosion scale samples and eight water samples collected from pipe harvest sites or during experimental periods were analyzed for their bacterial community composition by 454-pyrosequencing technology. Taxonomy results together with redundancy analysis (RDA) or canonical correspondence analysis (CCA) and hierarchical cluster analysis all indicated that bacterial community of samples with groundwater (GW) or surface water (SW) supply history and their variations under high sulfate water were rather different owing to different water source histories and the original pipe scale characteristics. Potential opportunistic pathogens: Burkholderia, Escherichia-Shigella, Mycobacterium, Serratia, Ralstonia, Novosphingobium, Flavobacterium, Sphingomonas, and Sphingopyxis were observed in scale or water samples.

Interaction of ciprofloxacin chlorination products with bacteria in drinking water distribution systems

The interaction of ciprofloxacin chlorination products (CIP-CPs) with bacteria in drinking water distribution systems (DWDSs) was investigated. The piperazine ring of CIP was destroyed by chlorination. Among of CIP-CPs, by the bacterial role, 7.63% of the derivative with two carboxylic groups went through decarboxylation to form desethylene ciprofloxacin, and then loss of C2H5N group generated aniline compound. Furthermore, 12.3% of the aniline compound, 7.60% of chlorinated aniline compound and 1.35% of defluorinated product were bio-mineralized. Therefore, the chlorine and bacteria played synergistic effects on transformation of CIP-CPs in DWDSs, contributing to the obvious decrease of genotoxicity in effluents. Correspondingly, the TEQ4-NQO decreased from 667μg/L to 9.41μg/L. However, compared with DWDSs without CIP-CPs, the relative abundance of mexA and qnrS increased 1-fold in effluents and the relative abundance of qnrA and qnrB increased 3-fold in biofilms in DWDSs with CIP-CPs. mexA and qnrS positively correlated with Hyphomicrobium, Sphingomonas and Novosphingobium (p<0.05), while qnrA and qnrB positively correlated with Shewanella and Helicobacter (p<0.05), indicating the increase of antibiotic resistance genes (ARGs) came from the growth of these bacterial genera by transformation of CIP-CPs in DWDSs. These results suggested that biotransformation of antibiotics might increase ARGs risk in DWDSs.

Biofilm structures (EPS and bacterial communities) in drinking water distribution systems are conditioned by hydraulics and influence discolouration

High-quality drinking water from treatment works is degraded during transport to customer taps through the Drinking Water Distribution System (DWDS). Interactions occurring at the pipe wall-water interface are central to this degradation and are often dominated by complex microbial biofilms that are not well understood. This study uses novel application of confocal microscopy techniques to quantify the composition of extracellular polymeric substances (EPS) and cells of DWDS biofilms together with concurrent evaluation of the bacterial community. An internationally unique, full-scale, experimental DWDS facility was used to investigate the impact of three different hydraulic patterns upon biofilms and subsequently assess their response to increases in shear stress, linking biofilms to water quality impacts such as discolouration. Greater flow variation during growth was associated with increased cell quantity but was inversely related to EPS-to-cell volume ratios and bacterial diversity. Discolouration was caused and EPS was mobilised during flushing of all conditions. Ultimately, biofilms developed under low-varied flow conditions had lowest amounts of biomass, the greatest EPS volumes per cell and the lowest discolouration response. This research shows that the interactions between hydraulics and biofilm physical and community structures are complex but critical to managing biofilms within ageing DWDS infrastructure to limit water quality degradation and protect public health.

Linking discolouration modelling and biofilm behaviour within drinking water distribution systems

High quality drinking water exits modern treatment works, yet water quality degradation such as discolouration continues to occur within drinking water distribution systems (DWDS). Discolouration is observed globally, suggesting a common process despite variations in source, treatment, disinfection and network configurations. The primary cause of discolouration has been identified as mobilisation of particulate material from pipe walls and the verified Prediction of Discolouration in Distribution Systems (PODDS) model uses measurable network hydraulics to simulate this response. In this paper the cohesive properties of discolouration material are explored and it is hypothesised that in simulating the turbidity response, the PODDS model is actually describing the development and cohesive strength behaviour of biofilms. Applying this concept can therefore facilitate a rapid and simple assessment of DWDS biofilm activity. A review of the findings from PODDS studies conducted internationally is presented, focussing on the macro or observable aspects of discolouration. These are compared and contrasted with associated biofilm studies which consider discolouration material at the micro-scale. Combining the results from these (past) studies to improve the understanding of interactions between microbial ecology and discolouration are discussed with a view to DWDS operational strategies that safeguard and optimise drinking water supply.

Biofilm bacterial communities in urban drinking water distribution systems transporting waters with different purification strategies.

Biofilm formation in drinking water distribution systems (DWDS) has many adverse consequences. Knowledge of microbial community structure of DWDS biofilm can aid in the design of an effective control strategy. However, biofilm bacterial community in real DWDS and the impact of drinking water purification strategy remain unclear. The present study investigated the composition and diversity of biofilm bacterial community in real DWDSs transporting waters with different purification strategies (conventional treatment and integrated treatment). High-throughput Illumina MiSeq sequencing analysis illustrated a large shift in the diversity and structure of biofilm bacterial community in real DWDS. Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Nitrospirae, and Cyanobacteria were the major components of biofilm bacterial community. Proteobacteria (mainly Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria) predominated in each DWDS biofilm, but the compositions of the dominant proteobacterial classes and genera and their proportions varied among biofilm samples. Drinking water purification strategy could shape DWDS biofilm bacterial community. Moreover, Pearson's correlation analysis indicated that Actinobacteria was positively correlated with the levels of total alkalinity and dissolved organic carbon in tap water, while Firmicutes had a significant positive correlation with nitrite nitrogen.

Pipe Scales and Biofilms in Drinking-Water Distribution Systems: Undermining Finished Water Quality

Safety and security are two important features of urban drinking-water distribution systems (UDWDS), worldwide, that are often compromised by a suite of physical, hydraulic, and chemical factors adversely impacting quality of potable water reaching consumer taps. Growth of scales and biofilm conglomerates (SBC) coupled with sorption of water chemicals and planktonic microorganisms by SBC has been increasingly recognized as underestimated contaminant sources in aging pipe networks of UDWDS. The main objective of this study was to provide an updated review of factors and processes associated with the increasing frequency of deteriorated finished water quality incidences as a result of SBC effects in UDWDS. This critical review integrated scattered knowledge on the effects of either pipe scales or pipe-anchored biofilm systems on contaminant destabilization and subsequent release into water. It was emphasized that little information exists on combined or concomitantly studied effects of SBC on finished water quality. Important synergistic SBC effects on finished water quality were identified as: (i) those promoting chemical release from pipe scales due to biofilm-induced alterations at the pipe surface/water interface, (ii) the synergistic SBC action on promoting increased release rates of pathogens or toxic chemicals into water, and (iii) the microbially enhanced corrosive phenomena on pipe scales and their constituents. Substantial room for improvement is anticipated for the water and global health research agenda by formulating innovative hypotheses and research designs that water authorities could benefit from as they strive towards further securing access to safe water in urban settings.

Biofilms in drinking water: problems and solutions

The main goal of water companies is to deliver to each consumer microbiologically safe drinking water (DW), adequate in quantity and delivery pressure and acceptable in terms of taste, odour and appearance. Drinking water distribution systems (DWDS) are known to harbour biofilms, even in the continuous presence of a disinfectant. These biofilms are a source of planktonic bacteria, which will remain present when the water is delivered through a consumer’s tap. The presence of biofilms in DWDS constitutes one of the currently recognized hazards affecting the microbiological quality of the product and may lead to a number of unwanted effects on the organoleptic quality of the distributed water. Importantly, biofilms constitute a persistent reservoir of pathogenic microorganisms, which are responsible for several waterborne diseases. Antimicrobial products, particularly chlorine, have been the main weapons used to disinfect DW. Although this strategy is widespread, there are not yet standardized disinfection strategies with reliable efficacy in the control of biofilms. This review covers the advances in the knowledge of public health problems caused by the presence of biofilms in DWDS and the current strategies for DW disinfection and associated biofilms.

Evaluation of Methods for the Extraction of DNA from Drinking Water Distribution System Biofilms

While drinking water biofilms have been characterized in various drinking water distribution systems (DWDS), little is known about the impact of different DNA extraction methods on the subsequent analysis of microbial communities in drinking water biofilms. Since different DNA extraction methods have been shown to affect the outcome of microbial community analysis in other environments, it is necessary to select a DNA extraction method prior to the application of molecular tools to characterize the complex microbial ecology of the DWDS. This study compared the quantity and quality of DNA yields from selected DWDS bacteria with different cell wall properties using five widely used DNA extraction methods. These were further selected and evaluated for their efficiency and reproducibility of DNA extraction from DWDS samples. Terminal restriction fragment length analysis and the 454 pyrosequencing technique were used to interpret the differences in microbial community structure and composition, respectively, from extracted DNA. Such assessments serve as a concrete step towards the determination of an optimal DNA extraction method for drinking water biofilms, which can then provide a reliable comparison of the meta-analysis results obtained in different laboratories.

Use of fluorescent in situ hybridisation for the visualisation of Helicobacter pylori in real drinking water biofilms

A fluorescently labelled peptide nucleic acid (PNA) probe has been applied for the in situ detection of Helicobacter pylori in drinking water biofilms. The method was originally applied to real pipe samples removed from a drinking water distribution system (DWDS) but the curvature and the heavy fouling of the pipes prevented an accurate detection of the bacterium by epifluorescence microscopy. Therefore, two semi-circular flow cells were placed in a bypass of the DWDS, and coupons with up to 72 days of exposure were regularly sampled and analysed for the presence of H. pylori. In the flat surfaces of the coupons, it was possible to sparsely detect cells exhibiting similar morphology to H. pylori that were emitting the PNA probe fluorescent signal. Coupons were also visualised under the microscope before the hybridisation procedure to serve as negative controls and ensure the validity of the method. This work corroborates the findings already published elsewhere that this bacterium might be present in DWDS biofilms. The method requires, however, highly trained personnel for an accurate detection of the pathogen and will need simplification before being routinely used in standard water analysis laboratories.

AFM study of the colonisation of stainless steel by Aquabacterium commune

Abstract Aquabacterium commune, a member of the beta proteobacteria family that is a recently isolated, predominant member of various European drinking water distribution system biofilms, was selected as a test organism in this study. Attachment of A. commune cells onto two increasingly popular pipe materials, stainless steel EN1.4307 and medium density polyethylene (MDPE) was studied at 15 °C, 150 rpm, and a hydraulic retention time of 10.5 h in a rotating annular biofilm (RAB) reactor. Planktonic and sessile growth was monitored by spread plate technique. Atomic force microscopy (AFM) was used to obtain information about surface topography and biofilm formation pattern. Our study has shown that: (i) Steady-state conditions were reached after ca. 100 h for both materials; (ii) biofilm cell density on MDPE slides is four times greater than on stainless; (iii) the primary colonization of MDPE and stainless steel occurred at the edge of the slides; and (iv) no preferential attachment to stainless steel grain boundaries was observed. Stainless-steel manufacturers and suppliers, researchers, and companies working in the drinking-water sector will benefit from this paper. It is suggested that electropolishing of stainless-steel pipes for drinking water installations is not necessary to remove specific biofilm formation sites (i.e. grain boundaries). Furthermore, this paper provides, for the first time, some fundamental information for the continuous cultivation of the recently isolated drinking water microorganism, A. commune.