Biofilms In Water Distribution Systems Research Articles

Modelling drinking water biofilms: Bacterial adhesion and Legionella pneumophila necrotrophic growth

We propose a mathematical model to simulate the establishment and growth of a drinking water distribution system biofilm, focusing on the influence of ionic strength on bacterial adhesion and persistence of Legionella pneumophila. Specifically, we consider how ionic strength affects interaction energies during the initial phase of biofilm formation and we include the dependence of the attachment flux, modelled as a linear rate with respect to free floating cells, on it. The model also incorporates a novel necrotrophic kinetics to simulate the Legionella pneumophila metabolism. The biofilm is modelled as a 1D free boundary domain, and its evolution is governed by hyperbolic–parabolic PDEs. The initial attachment phase is modelled by considering a vanishing initial value for the free boundary. The model is investigated numerically highlighting the impact of the necrotrophic kinetic parameters, the influence of ionic strength on the initial stage of biofilm formation through bacterial attachment, and how variations in nutrient levels affect system dynamics. The numerical results demonstrate that: the ionic strength mainly governs bacterial adhesion for young biofilms and affects the biofilm ecology also in presence of a biocide; the necrotrophic metabolism of Legionella pneumophila favours its persistence in oligotrophic biofilms.

P363 Mycoflora diversity in stored water from selected households in nairobi

Poster session 3, September 23, 2022, 12:30 PM - 1:30 PMIntroduction: Water is a very vital natural resource for all life on earth as it is used widely. Water plays an important role in the world economy, the uses can be categorized into; commercial use where it is used in hostels, restaurants, offices, and other commercial activities. Fungi are ubiquitous in nature; they produce spores that are small-sized, able to stay airborne for a long duration, and transported over long distances during air dispersal. These are major sources of allergens and airway irritants that are detrimental to health. Biofilms in water distribution systems and storage containers provide favorable habitat for microorganisms as they accumulate better in solid-liquid interfaces that enable them to be embedded in the gelatinous matrix of extracellular polymers excreted by the microorganisms leading to resistance of microbes from environmental stresses. Fungi hydrophobicity and adaptability have enabled them to assemble and colonize different surfaces in domestic settings. The potential health effects caused by fungi in treated water are still not well highlighted and thus the need to carry out this study to investigate the mycoflora isolated from stored water.MethodsThis was a cross-sectional study conducted from 2019-2021, whereby 120 water samples were collected from stored containers in households in Nairobi county Kenya. The fungal strains were plated onto Sabouraud's dextrose agar (SDA), Potato Dextrose Agar, and Czapecks Agar media with chloramphenicol (0.05 mg/mL) (Oxoid, U.K.). The plates were incubated for 7 days at 25°C. Fungal identification was done by direct microscopy and morphological features.ResultsA total of 101 fungal species were isolated from water samples. Yeasts 48 (47.5%), Rhodotorula 34 (33.6%) accounted for the unicellular fungi. Among Filamentous mycoflora, the most common isolated fungi were Aspergillus species 13(12.8%), followed by Fusarium spp 4 (3.9%) with Mucor and |Rhizopus species accounting for 1 (0.9%) respectively. Yeasts species were the most common species isolated from water species and Aspergillus species were more frequently isolated from filamentous fungi.ConclusionYeasts species were the most common species isolated from water species and the roles they play in biofilm needs to be further investigated.

From farm-scale to lab-scale: The characterization of engineered irrigation water distribution system biofilm models using an artificial freshwater source

Contaminants in freshwater environments, as well as the associated negative impacts on agricultural produce, have emerged as a critical theme of the water–energy–food nexus affecting food safety and irrigation management. Agricultural produce exposed to irrigation with questionable freshwater can internalize and concentrate pollutants. However, the potential risks posed by the ubiquitous presence of biofilms within irrigation water distribution systems (IWDS) remains overlooked, even though such biofilms may harbor and spread pathogenic, chemical, and other environmental pollutants. Our limited knowledge about the role and functional attributes of IWDS biofilms can be blamed mostly to experimental challenges encountered during attempted studies of these biofilms in their natural environments. Hence, a laboratory-based experimental system designed to simulate a freshwater environment was combined with a biofilm reactor capable of recreating the piping environments in water distribution systems. This experimental system was then tested to assess the robustness and repeatability of experimental early-stage biofilms with respect to physical structure and microbial community, using state-of-the-art confocal microscopy and next-generation sequencing, respectively. The results demonstrated the suitability of this laboratory-based experimental system for studying the impacts of selected pollutants on irrigation water distribution systems.

Epidemiology and Ecology of Opportunistic Premise Plumbing Pathogens: Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa.

BackgroundLegionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa are opportunistic premise plumbing pathogens (OPPPs) that persist and grow in household plumbing, habitats they share with humans. Infections caused by these OPPPs involve individuals with preexisting risk factors and frequently require hospitalization.ObjectivesThe objectives of this report are to alert professionals of the impact of OPPPs, the fact that 30% of the population may be exposed to OPPPs, and the need to develop means to reduce OPPP exposure. We herein present a review of the epidemiology and ecology of these three bacterial OPPPs, specifically to identify common and unique features.MethodsA Water Research Foundation–sponsored workshop gathered experts from across the United States to review the characteristics of OPPPs, identify problems, and develop a list of research priorities to address critical knowledge gaps with respect to increasing OPPP-associated disease.DiscussionOPPPs share the common characteristics of disinfectant resistance and growth in biofilms in water distribution systems or premise plumbing. Thus, they share a number of habitats with humans (e.g., showers) that can lead to exposure and infection. The frequency of OPPP-infected individuals is rising and will likely continue to rise as the number of at-risk individuals is increasing. Improved reporting of OPPP disease and increased understanding of the genetic, physiologic, and structural characteristics governing the persistence and growth of OPPPs in drinking water distribution systems and premise plumbing is needed.ConclusionsBecause broadly effective community-level engineering interventions for the control of OPPPs have yet to be identified, and because the number of at-risk individuals will continue to rise, it is likely that OPPP-related infections will continue to increase. However, it is possible that individuals can take measures (e.g., raise hot water heater temperatures and filter water) to reduce home exposures.CitationFalkinham JO III, Hilborn ED, Arduino MJ, Pruden A, Edwards MA. 2015. Epidemiology and ecology of opportunistic premise plumbing pathogens: Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. Environ Health Perspect 123:749–758; http://dx.doi.org/10.1289/ehp.1408692

Microbial community structures in a closed raw water distribution system biofilm as revealed by 454-pyrosequencing analysis and the effect of microbial biofilm communities on raw water quality

This is the first report on the characterization of the microbial biofilm community structure and water quality change along a closed and stable raw water distribution system. 454-pyrosequencing was employed to investigate the microbial communities in four biofilm samples. 25,426 optimized sequences were obtained. Results showed Proteobacteria was the dominant phylum in each biofilm sample. The abundance of Nitrospiraes in M6 biofilm, Firmicutes in M8 biofilm, Actinobacteria in M9 biofilm were higher by comparing with other three biofilm samples. The M6 microbial biofilm community structure was similar to that of M7, dissimilar to that of M9. Dissolved oxygen and nitrogen was probably major factors to influence the microbial biofilm communities. Nitrospiraes in M6 biofilm and Firmicutes in M8 biofilm were crucial to remove ammonia nitrogen and nitrate in raw water. How to enrich functional microbes in biofilm to pretreat raw water is an important area of future research.

Application of metabolomics to understanding biofilms in water distribution systems: a pilot study

Biofilms formed in pipes are known to contribute to waterborne diseases, accelerate corrosion and cause aesthetic taste and odour issues within the potable water supply network. This paper describes a pilot study, undertaken to assess the potential of using metabolomics to monitor bacterial activity in biofilms of an urban water network. Using samples from a water mains flushing programme, it was found that a profile of intracellular and extracellular metabolites associated with microbial activity could be obtained by analysing samples using gas chromatography mass spectrometry. Chemometric analysis of the chromatograms in conjunction with data from the mass spectrometer showed that it is possible to differentiate between biofilms from different pipe materials and planktonic bacteria. This research demonstrates that metabolomics has the potential for investigating biofilms and other microbial activity within water networks, and could provide a means for enhancing monitoring programmes, understanding the source of water quality complaints, and optimising water network management strategies.

Chemical modification of polyvinyl chloride and silicone elastomer in inhibiting adhesion of Aeromonas hydrophila.

Disease-causing bacteria of the genus Aeromonas are able to adhere to pipe materials, colonizing the surfaces and forming biofilms in water distribution systems. The aim of our research was to study how the modification of materials used commonly in the water industry can reduce bacterial cell attachment. Polyvinyl chloride and silicone elastomer surfaces were activated and modified with reactive organo-silanes by coupling or co-crosslinking silanes with the native material. Both the native and modified surfaces were tested using the bacterial strain Aeromonas hydrophila, which was isolated from the Polish water distribution system. The surface tension of both the native and modified surfaces was measured. To determine cell viability and bacterial adhesion two methods were used, namely plate count and luminometry. Results were expressed in colony-forming units (c.f.u.) and in relative light units (RLU) per cm2. Almost all the chemically modified surfaces exhibited higher anti-adhesive and anti-microbial properties in comparison to the native surfaces. Among the modifying agents examined, poly[dimethylsiloxane-co-(N,N-dimethyl-N-n-octylammoniopropyl chloride) methylsiloxane)] terminated with hydroxydimethylsilyl groups (20 %) in silicone elastomer gave the most desirable results. The surface tension of this modifier, was comparable to the non-polar native surface. However, almost half of this value was due to the result of polar forces. In this case, in an adhesion analysis, only 1 RLU cm−2 and less than 1 c.f.u. cm−2 were noted. For the native gumosil, the results were 9,375 RLU cm−2 and 2.5 × 108 c.f.u. cm−2, respectively. The antibacterial activity of active organo-silanes was associated only with the carrier surface because no antibacterial compounds were detected in liquid culture media, in concentrations that were able to inhibit cell growth.

Plumbing of hospital premises is a reservoir for opportunistically pathogenic microorganisms: a review

Several bacterial species that are natural inhabitants of potable water distribution system biofilms are opportunistic pathogens important to sensitive patients in healthcare facilities. Waterborne healthcare-associated infections (HAI) may occur during the many uses of potable water in the healthcare environment. Prevention of infection is made more challenging by lack of data on infection rate and gaps in understanding of the ecology, virulence, and infectious dose of these opportunistic pathogens. Some healthcare facilities have been successful in reducing infections by following current water safety guidelines. This review describes several infections, and remediation steps that have been implemented to reduce waterborne HAIs.

Heterotrophic bacteria in drinking water distribution system: a review

The microbiological quality of drinking water in municipal water distribution systems (WDS) depends on several factors. Free residual chlorine and/or chloramines are typically used to minimize bacterial recontamination and/or regrowth in WDS. Despite such preventive measures, regrowth of heterotrophic (HPC) and opportunistic bacteria in bulk water and biofilms has yet to be controlled completely. No approach has shown complete success in eliminating biofilms or HPC bacteria from bulk water and pipe surfaces. Biofilms can provide shelter for pathogenic bacteria and protect these bacteria from disinfectants. Some HPC bacteria may be associated with aesthetic and non-life threatening diseases. Research to date has achieved important success in understanding occurrence and regrowth of bacteria in bulk water and biofilms in WDS. To achieve comprehensive understanding and to provide efficient control against bacteria regrowth, future research on bacteria regrowth dynamics and their implications is warranted. In this study, a review was performed on the literature published in this area. The findings and limitations of these papers are summarized. Occurrences of bacteria in WDS, factors affecting bacteria regrowth in bulk water and biofilms, bacteria control strategies, sources of nutrients, human health risks from bacterial exposure, modelling of bacteria regrowth and methods of bacteria sampling and detection and quantification are investigated. Advances to date are noted, and future research needs are identified. Finally, research directions are proposed to effectively control HPC and opportunistic bacteria in bulk water and biofilms in WDS.

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.

Biofilm formation by Mycobacterium avium isolates originating from humans, swine and birds

BackgroundMycobacterium avium includes the subspecies avium, silvaticum, paratuberculosis and hominissuis, and M. avium subspecies has been isolated from various environments all over the world including from biofilms in water distribution systems. The aim of this study was to examine isolates of M. avium subsp. avium and M. avium subsp. hominissuis of different origin for biofilm formation and to look for correlations between biofilm formation and RFLP-types, and to standardise the method to test for biofilm formation. In order to determine the best screening method, a panel of 14 isolates of M. avium subsp. avium and M. avium subsp. hominissuis, were tested for their ability to form biofilm in microtiter plates under different conditions. Subsequently, 83 additional isolates from humans, swine and birds were tested for biofilm formation. The isolates were tested for the presence of selected genes involved in the synthesis of glycopeptidolipids (GPLs) in the cell wall of M. avium, which is believed to be important for biofilm formation. Colony morphology and hsp65 sequvar were also determined.ResultsNine isolates from swine produced biofilm. There was a significant higher frequency of porcine isolates forming biofilm compared to human isolates. All isolates were previously characterised by IS1311- and IS1245-RFLP typing. The ability to form biofilm did not correlate with the RFLP-type, hsp65 sequevar, colony morphology or the presence of gene sequences related to GPL synthesis.ConclusionThe observed differences in biofilm forming abilities between porcine and human isolates raises questions regarding the importance of biofilm formation for infectious potential. The optimised method worked well for screening of multiple isolates.

Impact on water distribution system biofilm densities from reverse osmosis membrane treatment of supply water

The quality of potable water is such that the concentration of nutrients available for growth of microorganisms within distribution systems is limited. In such systems carbon is often the growth limiting nutrient. Research conducted in the Netherlands has indicated that low levels (<10 μg/L) of available organic carbon in water is sufficient to maintain an actively growing population of heterotrophic, or organic carbon utilizing, bacteria in aquatic systems. However, the ability of commercially available and cost effective technologies to achieve such low concentrations of assimilable organic carbon in full-scale water systems is doubtful. Reverse osmosis (RO) systems have been used for many years to effectively remove contaminants from source waters. We challenged a water distribution system simulator (DSS) with water from a municipal system and water that was treated using an RO system under two concentrations of residual free chlorine to evaluate the effect of this disinfectant on biofilms in contact with low nutrient water. Our results showed that biofilm densities in the DSS carrying low nutrient RO treated water were lower than biofilm densities taken from the DSS when it carried water directly obtained from a municipal system.Key words: water distribution systems, reverse osmosis, biofilms, heterotrophic plate count, HPC, chlorine, assimilable organic carbon.

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.

Poultry’s Persistence Problem: Drug-Resistant Campylobacter in Chicken

Vol. 113, No. 5 EnvironewsOpen AccessPoultry’s Persistence Problem: Drug-Resistant Campylobacter in Chickenis accompanied byFluoroquinolone-Resistant Campylobacter Isolates from Conventional and Antibiotic-Free Chicken Products Charles W. Schmidt Charles W. Schmidt Search for more papers by this author Published:1 May 2005https://doi.org/10.1289/ehp.113-a325AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Mounting evidence suggests that the poultry industry’s use of antibiotics promotes antibiotic resistance among the foodborne bacteria that infect humans. One such bacterium is Campylobacter, a pathogen common to chicken products. Every year more than 1 million Americans develop Campylobacter-induced food poisoning from eating undercooked contaminated chicken. Resistant strains of Campylobacter are a growing public health threat, particularly among elderly and immunocompromised patients. This month, researchers from the Johns Hopkins Bloomberg School of Public Health provide evidence suggesting that chickens raised without antibiotics are less likely to carry antibiotic-resistant strains of Campylobacter[EHP113:557–560].The study focused on fluoroquinolones (FQs), a class of antimicrobials used to control the bacterium Escherichia coli in broiler chickens. Of the two FQs initially approved for use in poultry, Sara Flox WSP and Baytril, only the latter remains on the market. The Food and Drug Administration is seeking to repeal approval for Baytril due to concerns that it contributes to microbial resistance.The authors collected chicken products from two “antibiotic-free” producers (Bell & Evans and Eberly Poultry) and two of the nation’s largest conventional producers (Tyson Foods and Perdue Farms). The conventional producers claimed to have stopped using FQs in February 2002. The authors began sampling chicken products one year later, in 2003. All samples were obtained from grocery stores in or near Baltimore, Maryland.Chicken samples were processed using standard isolation techniques; however, at the final step, Campylobacter enrichments were streaked onto agar plates both with and without ciprofloxacin (a second-generation FQ used to treat human disease). The ciprofloxacin supplement enabled the authors to identify FQ-resistant Campylobacter isolates from among a mix of susceptible and resistant strains.Campylobacter was detected on 84% of all the samples tested. FQ-resistant strains were detected on 17% using unsupplemented agar and on 40% using supplemented agar. Abstention from FQ use by poultry producers did not increase the likelihood of Campylobacter contamination. Moreover, conventional products were up to 460 times more likely to carry resistant strains than their antibiotic-free counterparts. Of particular interest is that FQ resistance in conventional products persisted for one year after cessation of industrial use.Based on these findings, the authors suggest that even without antibiotics, resistant populations may remain prevalent over time. Persistence of these resistant populations may result from residual contamination in poultry houses, the authors suggest. For example, biofilms in water distribution systems can harbor Campylobacter and thus could serve as reservoirs for resistant populations. These findings suggest the need to further improve poultry house cleaning and disinfection, they write.The authors say it is important to measure the prevalence of, and causes for, FQ-resistant strains in the food supply. To this end, they point out that supplemented agar may provide a much more sensitive tool than conventional methods for detecting resistant strains of the bacterium.Chicken surprise. New data show that antibiotic-resistant Campylobacter (left) can persist in poultry populations—and products—long after producers stop using the drugs.FiguresReferencesRelatedDetailsRelated articlesFluoroquinolone-Resistant Campylobacter Isolates from Conventional and Antibiotic-Free Chicken Products2 February 2005Environmental Health Perspectives Vol. 113, No. 5 May 2005Metrics About Article Metrics Publication History Originally published1 May 2005Published in print1 May 2005 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Population diversity in model potable water biofilms receiving chlorine or chloramine residual

Most water utilities use chlorine or chloramine to produce potable water. These disinfecting agents react with water to produce residual oxidants within a water distribution system (WDS) to control bacterial growth. While monochloramine is considered more stable than chlorine, little is known about the effect it has on WDS biofilms. Community structure of 10-week old WDS biofilms exposed to disinfectants was assessed after developing model biofilms from unamended distribution water. Four biofilm types were developed on polycarbonate slides within annular reactors while receiving chlorine, chloramine, or inactivated disinfectant residual. Eubacteria were identified through 16S rDNA sequence analysis. The model WDS biofilm exposed to chloramine mainly contained Mycobacterium and Dechloromonas sequences, while a variety of alpha- and additional beta-proteobacteria dominated the 16S rDNA clone libraries in the other three biofilms. Additionally, bacterial clones distantly related to Legionella were found in one of the biofilms receiving water with inactivated chlorine residual. The biofilm reactor receiving chloraminated water required increasing amounts of disinfectant after 2 weeks to maintain chlorine residual. In contrast, free chlorine residual remained steady in the reactor that received chlorinated water. The differences in bacterial populations of potable water biofilms suggest that disinfecting agents can influence biofilm development. These results also suggest that biofilm communities in distribution systems are capable of changing in response to disinfection practices.

Contamination potential of drinking water distribution network biofilms

Drinking water distribution system biofilms were investigated for the presence of hygienically relevant microorganisms. Early biofilm formation was evaluated in biofilm reactors on stainless steel, copper, polyvinyl chloride (PVC) and polyethylene coupons exposed to unchlorinated drinking water. After 12 to 18 months, a plateau phase of biofilm development was reached. Surface colonization on the materials ranged between 4 x 10(6) and 3 x 10(7) cells/cm2, with heterotrophic plate count (HPC) bacteria between 9 x 10(3) and 7 x 10(5) colony-forming units (cfu)/cm2. Established biofilms were investigated in 18 pipe sections (2 to 99 years old) cut out from distribution pipelines. Materials included cast iron, galvanized steel, cement and PVC. Colonization ranged from 4 x 10(5) to 2 x 10(8) cells/cm2, HPC levels varied between 1 and 2 x 10(5) cfu/cm2. No correlation was found between extent of colonization and age of the pipes. Using cultural detection methods, coliform bacteria were rarely found, while Escherichia coli, Pseudomonas aeruginosa and Legionella spp. were not detected in the biofilms. In regular operation, distribution system biofilms do not seem to be common habitats for pathogens. However, nutrient-leaching materials like rubber-coated valves were observed with massive biofilms which harboured coliform bacteria contaminating drinking water.

Survival of Mycobacterium avium in a model distribution system

A pilot study was designed to examine the impact of nutrient levels, pipe materials, and disinfection on the survival of M. avium in model drinking water distribution system biofilms. Studies showed that the survival of the organism was dependant upon a complex interaction between pipe surface, nutrient levels, and disinfectants. The findings showed that when no disinfection was applied, M. avium could be recovered from biofilms at nutrient levels of 50 μg/L assimilable organic carbon. M. avium concentrations were lower on copper pipe surfaces following disinfection with free chlorine as compared to monochloramine. However, due to the interference of corrosion products, chloramination of iron pipe surfaces controlled M. avium levels better than free chlorine. These data demonstrate the significance of pipe materials on the survival of M. avium complex in biofilms. Elimination of competitive heterotrophic bacteria on copper pipe surfaces by the application of disinfection resulted in a population of nearly 100% M. avium. Heat treatment of M. avium biofilms was affected by the pipe composition and organic content of the water. Effluent temperatures >53°C were required to control the occurrence of M. avium in the pipeline system. Although additional studies are required using improved detection methods, the results of this investigation suggest that reducing the biodegradable organic material in drinking water, control of corrosion, maintenance of an effective disinfectant residual, and management of hot water temperatures can help limit the occurrence of M. avium complex in drinking water biofilms.

Assessment of bismuth thiols and conventional disinfectants on drinking water biofilms.

Biofilms in water distribution systems represent a far more significant reservoir of micro-organisms than the water phase. Biofilms are (i) resistant to disinfectants, (ii) nuclei for microbial regrowth, (iii) a refuge for pathogens, (iv) accompanied by taste and odour problems, and (v) corrode surfaces. The effects of the current strategies for disinfection of drinking water systems in large buildings (chlorination, copper and silver ionization, and hyper-heating) were compared with a new generation of bismuth thiol (BT) biocides. Multispecies biofilms were treated with 0.8 mg l(-1) of free chlorine, 400 and 40 microg l(-1) of copper and silver ions, respectively, at 55 and 70 degrees C, and bismuth-2,3-dimercaptopropanol (BisBAL). Furthermore, the effect of combined heat and BisBAL on planktonic cell viability was examined in monoculture using Escherichia coli suspensions. Inactivation rates for BisBAL were similar to copper-silver ions, where the effects were slower than for free chlorine or temperature. The BisBAL effect on E. coli monocultures was augmented greatly by increasing temperatures. Like copper-silver ions, BTs show more persistent residual effects than chlorine and hyper-heating in water systems. BT efficiency increased with temperature. Like copper-silver ions, BT action is relatively slow. BT presents a new approach to containing water biofilms. BT action is not as rapid, but is more thorough than chlorine, and less caustic. BTs may also be more efficacious in hot water systems. At sub-minimum inhibition concentration levels, BTs uniquely inhibit bacterial exopolysaccharide, thereby retarding biofilm formation. Thus, the combination of bactericidal and residual effects may prevent slime build-up in hot water systems.

Contamination potential of biofilms in water distribution systems

Biofilms are ubiquitous in drinking water systems, either in the form of thin and patchy colonies or as surface-covering multiple layers. In biofilters they are used for the elimination of biologically degradable substances. However, they occur in other sites, e.g., on the walls of containers and pipes, on sediment and on suspended particles. They can rise problems by contamination of the water phase by detaching biofilm organisms. Biofilms provide a possible habitat for hygienically relevant microbes in which they can persist and even multiply. Here they are protected against disinfectants, in particular if located in corrosion products, sediments or ingested by protozoa which feed on biofilm cells. Biofilms are related to the occurrence of “black water” and malodours. They are involved in the corrosion of metals, mineral materials and synthetic polymers. The limiting factor for biofilm growth is usually the availability of nutrients, mainly provided either by biodegradable substances leaching from materials or from by the water phase. The extent of biofilm growth and of the occurrence of hygienically relevant organisms is still unknown and to be investigated. However, latest research indicates that such organisms do not multiply in large numbers in drinking water biofilms; it is possible that drinking water biofilms can inhibit the propagation of invading pathogens.

Helicobacter sp. recovered from drinking water biofilm sampled from a water distribution system

Workers examining the transmission route(s) and reservoir(s) of infection for Helicobacter pylori have postulated several environmental reservoirs for the organism, including water. Such work has, to date, concentrated on the bulk liquid in drinking water systems rather than on biofilms. Previous investigations by the authors have suggested biofilms in water distribution systems are a possible reservoir of infection. This current study comprised of an analysis of a section of cast iron mains distribution pipe removed from an urban environment in the north-east of Scotland during routine maintenance work. Immediately upon removal of the pipe section, the interior lumen was swabbed to remove the biofilm layer. Subsequent analysis for the presence of Helicobacter DNA using a nested PCR approach produced a positive result. This data provides the first evidence for the existence of Helicobacter in biofilms found in water distribution systems anywhere in the world.