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

Abstract

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.     

Mycobacterium avium complex--the role of potable water in disease transmission

Mycobacterium avium complex (MAC) is a group of opportunistic pathogens of major public health concern. It is responsible for a wide spectrum of disease dependent on subspecies, route of infection and patients pre-existing conditions. Presently, there is limited research on the incidence of MAC infection that considers both pulmonary and other clinical manifestations. MAC has been isolated from various terrestrial and aquatic environments including natural waters, engineered water systems and soils. Identifying the specific environmental sources responsible for human infection is essential in minimizing disease prevalence. This paper reviews current literature and case studies regarding the wide spectrum of disease caused by MAC and the role of potable water in disease transmission. Potable water was recognized as a putative pathway for MAC infection. Contaminated potable water sources associated with human infection included warm water distribution systems, showers, faucets, household drinking water, swimming pools and hot tub spas. MAC can maintain long-term contamination of potable water sources through its high resistance to disinfectants, association with biofilms and intracellular parasitism of free-living protozoa. Further research is required to investigate the efficiency of water treatment processes against MAC and into construction and maintenance of warm water distribution systems and the role they play in MAC proliferation.     

The effect of material choice on biofilm formation in a model warm water distribution system

Water distribution systems (WDS) are composed of a variety of materials and may harbour potential pathogens within surface-attached microbial biofilms. Biofilm formation on four plumbing materials, viz. copper, stainless steel 316 (SS316), ethylene propylene diene monomer (EPDM) and cross-linked polyethylene (PEX), was investigated using scanning electron microscope (SEM)/confocal microscopy, ATP-/culture-based analysis, and molecular analysis. Material ‘inserts’ were incorporated into a mains water fed, model WDS. All materials supported biofilm growth to various degrees. After 84 days, copper and SS316 showed no significant overall differences in terms of the level of biofilm formation observed, whilst PEX supported a significantly higher level ofbiofilm. EPDM exhibited gross contamination by a complex, multispecies biofilm, at a level significantly higherthan was observed on the other materials, regardless of the analytical method used. PCR-DGGE analysis showed clear differences in the composition of the biofilm community on all materials after 84 days. The primary conclusion of this study has been to identify EPDM as a potentially unsuitable material for use as a major component in WDS.     

Isolation and automated ribotyping of Mycobacterium lentiflavum from drinking water distribution system and clinical specimens

Automated ribotyping as a tool for identifying of nontuberculous mycobacteria was evaluated. We created a database comprising of riboprints of 60 strains, representing 32 species of nontuberculous mycobacteria. It was shown that combined ribopatterns generated after digestion with EcoRI and PvuII were distinguishable between species of both slow-growing and rapid-growing mycobacteria. The findings were in good agreement with the 16S rRNA gene sequencing results, allowing correct identification of Mycobacterium lentiflavum isolated from clinical specimens and from biofilms growing in public water distribution system. The automated ribotyping was powerful in discriminating between M. lentiflavum and closely related species M. simiae and M. palustre. Mycobacterium lentiflavum strains from drinking water biofilms were resistant to two to four antimycobacterial drugs. The drinking water distribution system may, thus, be a source of nontuberculous mycobacteria resistant to multiple drugs.     

结核分枝杆菌毒素-抗毒素系统与生物膜

结核分枝杆菌(Mycobacterium tuberculosis)是引起结核病的病原菌。其处于持续生存的休眠状态时,可导致长期无症状感染,称为结核潜伏感染。研究显示,结核分枝杆菌染色体中存在大量 “毒素-抗毒素系统”(toxin-antitoxin system,TAS),某些TAS在潜伏感染中发挥作用,可调节细菌生长和诱导细菌进入休眠状态;某些TAS参与生物膜形成和应激反应,但其影响生物膜形成的机制尚未阐明。生物膜中的结核分枝杆菌对多种抗结核药物耐药,且能抵抗宿主免疫系统防御;休眠状态的结核分枝杆菌对抗结核药物通常也是耐受的,给结核病治疗带来了巨大挑战。本文就近年来结核分枝杆菌TAS与生物膜的研究及抗结核药物对生物膜形成的影响进行综述。     

A biofilm model to understand the onset of sulfate reduction in denitrifying membrane biofilm reactors

This work presents a multispecies biofilm model that describes the co‐existence of nitrate‐ and sulfate‐reducing bacteria in the H₂‐based membrane biofilm reactor (MBfR). The new model adapts the framework of a biofilm model for simultaneous nitrate and perchlorate removal by considering the unique metabolic and physiological characteristics of autotrophic sulfate‐reducing bacteria that use H₂ as their electron donor. To evaluate the model, the simulated effluent H₂, UAP (substrate‐utilization‐associated products), and BAP (biomass‐associated products) concentrations are compared to experimental results, and the simulated biomass distributions are compared to real‐time quantitative polymerase chain reaction (qPCR) data in the experiments for parameter optimization. Model outputs and experimental results match for all major trends and explain when sulfate reduction does or does not occur in parallel with denitrification. The onset of sulfate reduction occurs only when the nitrate concentration at the fiber's outer surface is low enough so that the growth rate of the denitrifying bacteria is equal to that of the sulfate‐reducing bacteria. An example shows how to use the model to design an MBfR that achieves satisfactory nitrate reduction, but suppresses sulfate reduction. Biotechnol. Bioeng. 2013; 110: 763–772. © 2012 Wiley Periodicals, Inc.     

Bacterial species in biofilm cultivated from the end of the Seoul water distribution system

AIMS: To investigate changes in the bacterial population and the safety of the biofilm at the end of the drinking water distribution system in Seoul (Korea), selective media and bacterial community analyses were applied to a semi-pilot galvanized iron pipe (GIP) model. METHODS AND RESULTS: No total coliforms or faecal streptococci were detected on m-Endo or m-Enterococcus agar. No Salmonella spp. and Shigella spp. were detected on bismuth sulphite agar or Hektoen enteric agar, respectively. The latter two media detected coliforms, where m-Endo was negative. Biofilm formation started within 1 week (ca 104 CFU cm(-2)) and exceeded 105 CFU cm(-2) within 6 weeks. Although the fatty acid methyl ester analysis revealed dynamic changes in bacterial composition, Micrococcus, Bacillus, and Pseudomonas spp. were persistent members of the biofilm community. Micrococcus spp. was detected most frequently and in high numbers. CONCLUSIONS: Coliforms and Enterococcus species can be recovered from biofilms in water distribution systems. SIGNIFICANCE AND IMPACT OF THE STUDY: This study illustrates the role of biofilms in the chronic deterioration of the water-distribution system in Seoul (Korea).     

供水系统非结核分枝杆菌生长因素及控制措施研究进展

近年来,非结核分枝杆菌感染在世界范围内日益普遍,严重威胁公众健康。供水系统是非结核分枝杆菌重要环境来源和主要传播途径,但目前对供水系统非结核分枝杆菌生长因素及控制措施的认识仍有较多不足。本文介绍了供水系统非结核分枝杆菌的生长传播特征,探讨了多个工程环境因素(如消毒剂、有机碳、管材和温度)和生物因子(如生物膜、阿米巴原虫和细菌)对非结核分枝杆菌丰度和物种多样性特征的影响,分析了供水全流程不同阶段控制措施对非结核分枝杆菌的控制效用,提出了深化认识供水系统非结核分枝杆菌的研究需求。     

Identification of active bacterial communities in a model drinking water biofilm system using 16S rRNA-based clone libraries

Recent phylogenetic studies have used DNA as the target molecule for the development of environmental 16S rRNA gene clone libraries. As DNA may persist in the environment, DNA-based libraries cannot be used to identify metabolically active bacteria in water systems. In this study, an annular reactor was used to generate model drinking water biofilms grown on polycarbonate slides. High-quality RNA was extracted from 2-month-old biofilms and used to generate 16S rRNA-based clones. Sequencing analyses of 16S rRNA-based clones suggested that the active bacterial fraction consisted of a few dominant bacterial groups related to Nevskia ramosa and to uncultured bacteria. Several of these bacterial groups were closely related to clones characterized in a DNA-based clone library also generated in this study. Altogether, these results suggest that some of the predominant drinking water bacteria identified using DNA-based techniques are indeed active.     

Role of hydrophobicity in bacterial adherence to carbon nanostructures and biofilm formation

The role of cell and surface hydrophobicity in the adherence of the waterborne bacterium Mycobacterium smegmatis to nanostructures and biofilm formation was investigated. Carbon nanostructures (CNs) were synthesized using a flame reactor and deposited on stainless steel grids and foils, and on silicon wafers that had different initial surface hydrophobicities. Surface hydrophobicity was measured as the contact angle of water droplets. The surfaces were incubated in suspensions of isogenic hydrophobic and hydrophilic strains of M. smegmatis and temporal measurements of the numbers of adherent cells were made. The hydrophobic, rough mutant of M. smegmatis adhered more readily and formed denser biofilms on all surfaces compared to its hydrophilic, smooth parent. Biofilm formation led to alterations in the hydrophobicity of the substratum surfaces, demonstrating that bacterial cells attached to CNs are capable of modifying the surface characteristics.     

Amoebae in domestic water systems: resistance to disinfection treatments and implication in Legionella persistence

AIMS: Monitoring of microbial changes during and after application of various disinfection treatments in a model domestic water system. METHODS AND RESULTS: A pilot-scale domestic water system consisting of seven galvanized steel re-circulation loops and copper dead legs was constructed. Culture techniques, confocal laser scanning microscopy after fluorescent in situ hybridization and viability staining with the BacLight LIVE/DEAD kit were used for planktonic and biofilm flora monitoring. Before starting the treatments, the system was highly contaminated with Legionella pneumophila and biofilm populations mainly consisted of beta-proteobacteria. In the water and the biofilm of the loops, continuous application of chlorine dioxide (0.5 mg l(-1)), or chlorine (2.5 mg l(-1)) were very effective in reducing the microbial flora, including L. pneumophila. Heterotrophic bacteria, although strongly reduced, were still detectable after ozone application (0.5 mg l(-1)), whereas with monochloramine (0.5 mg l(-1)) and copper-silver ionization (0.8/0.02 mg l(-1)), the contamination remained significantly higher. Monochloramine and copper-silver did not remove the biofilm. During copper-silver application, Legionella re-growth was observed. Only chlorine dioxide led to detectable effects in the dead leg. Amoebae could not be eliminated, and after interrupting the treatments, L. pneumophila quickly recovered their initial levels, in all cases. CONCLUSIONS: Chlorine dioxide, applied as a continuous treatment, was identified in this study as the most efficient for controlling L. pneumophila in a domestic water system. Chlorine dioxide showed a longer residual activity, leading to improved performance in the dead leg. Amoebae resisted to all the treatments applied and probably acted as reservoirs for L. pneumophila, allowing a quick re-colonization of the system once the treatments were interrupted. SIGNIFICANCE AND IMPACT OF THE STUDY: Control of microbial contamination requires maintenance of a constant disinfectant residual throughout the water system. Treatment strategies targeting free-living amoebae should lead to improved control of L. pneumophila. Such treatment strategies still have to be investigated.     

Development and experimental evaluation of a steady-state, multispecies biofilm model

A steady-state model for quantifying the space competition in multispecies biofilms is developed. The model includes multiple active species, inert biomass, substrate utilization and diffusion within the biofilm, external mass transport, and detachment phenomena. It predicts the steady-state values of biofilm thickness, species distribution, and substrate fluxes. An experimental evaluation is carried out in completely mixed biofilm reactors in which slow-growing nitrifying bacteria compete with acetate-utilizing heterotrophs. The experimental results show that the model successfully describes the space competition. In particular, increasing acetate concentrations causes NH(4) (+)-N fluxes to decrease, because nitrifiers are forced deeper into the biofilm, where they experience greater mass-transport resistance.     

城市生活饮用水中非结核分枝杆菌调查

目的 调查上海市生活饮用水中非结核分枝杆菌的状况及主要菌种分布。方法 应用过滤法收集细菌, 并在改良罗氏培养基上培养; 通过16S rRNA 测序鉴定菌种。结果 上海市生活饮用水中非结核分枝杆菌的检出率为16. 7% , 其中自来水厂原水、出厂水和居民生活饮用终端水的检出率分别为60% 、25% 和10. 3% 。分离鉴定的非结核分枝杆菌菌种为戈登分枝杆菌及偶发分枝杆菌, 分别占90% 及10% 。结论 在上海市居民生活饮用水系统中存在非结核分枝杆菌, 因此, 应当采取有效的控制方法以保护公众的健康。