Protozoan bacterivory and Escherichia coli survival in drinking water distribution systems

Climate Change: Water Temperature and Invertebrate Propagation in Drinking-Water Distribution Systems, Effects, and Risk Assessment

This paper provides a summary of the knowledge of drinking-water temperature increases and present daily, seasonal, and yearly temperature data of drinking-water distribution systems (DWDS). The increasing water temperatures lead to challenges in DWDS management, and we must assume a promotion of invertebrates as pipe inhabitants. Macro-, meio-, and microinvertebrates were found in nearly all DWDS. Data in relation to diversity and abundance clearly point out a high probability of mass development, and invertebrate monitoring must be the focus of any DWDS management. The water temperature of DWDS is increasing due to climate change effects, and as a consequence, the growth and reproduction of invertebrates is increasing. The seasonal development of a chironomid (Paratanytarus grimmii) and longtime development of water lice (Asellus aquaticus) are given. Due to increased water temperatures, a third generation of water lice per year has been observed, which is one reason for the observed mass development. This leads to an impact on drinking-water quality and an increased health risk, as invertebrates can serve as a host or vehicle for potential harmful microbes. More research is needed especially on (i) water temperature monitoring in drinking-water distribution systems, (ii) invertebrate development, and (iii) health risks.

Potential biofilm control strategies for extended spaceflight missions

Biofilms, surface-adherent microbial communities, are associated with microbial fouling and corrosion in terrestrial water-distribution systems. Biofilms are also present in human spaceflight, particularly in the Water Recovery System (WRS) on the International Space Station (ISS). The WRS is comprised of the Urine Processor Assembly (UPA) and the Water Processor Assembly (WPA) which together recycles wastewater from human urine and recovered humidity from the ISS atmosphere. These wastewaters and various process streams are continually inoculated with microorganisms primarily arising from the space crew microbiome. Biofilm-related fouling has been encountered and addressed in spacecraft in low Earth orbit, including ISS and the Russian Mir Space Station. However, planned future missions beyond low Earth orbit to the Moon and Mars present additional challenges, as resupplying spare parts or support materials would be impractical and the mission timeline would be in the order of years in the case of a mission to Mars. In addition, future missions are expected to include a period of dormancy in which the WRS would be unused for an extended duration. The concepts developed in this review arose from a workshop including NASA personnel and representatives with biofilm expertise from a wide range of industrial and academic backgrounds. Here, we address current strategies that are employed on Earth for biofilm control, including antifouling coatings and biocides and mechanisms for mitigating biofilm growth and damage. These ideas are presented in the context of their applicability to spaceflight and identify proposed new topics of biofilm control that need to be addressed in order to facilitate future extended, crewed, spaceflight missions.

Successional trophic complexity and biogeographical structure of eukaryotic communities in waterworks' rapid sand filters

As groundwater-fed waterworks clean their raw inlet water with sand filters, a variety of pro- and eukaryotic microbial communities develop on these filters. While several studies have targeted the prokaryotic sand filter communities, little is known about the eukaryotic communities, despite the obvious need for knowledge of microorganisms that get in contact with human drinking water. With a new general eukaryotic primer set (18S, V1-V3 region), we performed FLX-454 sequencing of material from 21 waterworks' sand filters varying in age (3-40 years) and geographical location on a 250 km east-west axis in Denmark, and put the data in context of their previously published prokaryotic communities. We find that filters vary highly in trophic complexity depending on age, from simple systems with bacteria and protozoa (3-6 years) to complex, mature systems with nematodes, rotifers and turbellarians as apex predators (40 years). Unlike the bacterial communities, the eukaryotic communities display a clear distance-decay relationship that predominates over environmental variations, indicating that the underlying aquifers feeding the filters harbor distinct eukaryotic communities with limited dispersal in between. Our findings have implications for waterworks' filter management, and offer a window down to the largely unexplored eukaryotic microbiology of groundwater aquifers.

The Impact of Protozoan Predation on the Pathogenicity of Vibrio cholerae

In the aquatic environment, Vibrio spp. interact with many living organisms that can serve as a replication niche, including heterotrophic protists, or protozoa. Protozoa engulf bacteria and package them into phagosomes where the cells are exposed to low pH, antimicrobial peptides, reactive oxygen/nitrogen species, proteolytic enzymes, and low concentrations of essential metal ions such as iron. However, some bacteria can resist these digestive processes. For example, Vibrio cholerae and Vibrio harveyi can resist intracellular digestion. In order to survive intracellularly, bacteria have acquired and/or developed specific factors that help them to resist the unfavorable conditions encountered inside of the phagosomes. Many of these intra-phagosomal factors used to kill and digest bacteria are highly conserved between eukaryotic cells and thus are also expressed by the innate immune system in the gastrointestinal tract as the first line of defense against bacterial pathogens. Since pathogenic bacteria have been shown to be hypervirulent after they have passed through protozoa, the resistance to digestion by protist hosts in their natural environment plays a key role in enhancing the infectious potential of pathogenic Vibrio spp. This review will investigate the current knowledge in interactions of bacteria with protozoa and human host to better understand the mechanisms used by both protozoa and human hosts to kill bacteria and the bacterial response to them.

Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates

The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (γ), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under γ as high as 85,000 s^-1. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under γ similar to those encountered in the industrial environment. This technological advance may enable research into these topics.

Biocarriers Improve Bioaugmentation Efficiency of a Rapid Sand Filter for the Treatment of 2,6-Dichlorobenzamide-Contaminated Drinking Water

Aminobacter sp. MSH1 immobilized in an alginate matrix in porous stones was tested in a pilot system as an alternative inoculation strategy to the use of free suspended cells for biological removal of micropollutant concentrations of 2,6-dichlorobenzamide (BAM) in drinking water treatment plants (DWTPs). BAM removal rates and MSH1 cell numbers were recorded during operation and assessed with specific BAM degradation rates obtained in lab conditions using either freshly grown cells or starved cells to explain reactor performance. Both reactors inoculated with either suspended or immobilized cells showed immediate BAM removal under the threshold of 0.1 μg/L, but the duration of sufficient BAM removal was 2-fold (44 days) longer for immobilized cells. The longer sufficient BAM removal in case of immobilized cells compared to suspended cells was mainly explained by a lower initial loss of MSH1 cells at operational start due to volume replacement and shear. Overall loss of activity in the reactors though was due to starvation, and final removal rates did not differ between reactors inoculated with immobilized and suspended cells. Management of assimilable organic carbon, in addition to cell immobilization, appears crucial for guaranteeing long-term BAM degradation activity of MSH1 in DWTP units.

Anti-biofilm Activity as a Health Issue

The formation and persistence of surface-attached microbial communities, known as biofilms, are responsible for 75% of human microbial infections (National Institutes of Health). Biofilm lifestyle confers several advantages to the pathogens, notably during the colonization process of medical devices and/or patients’ organs. In addition, sessile bacteria have a high tolerance to exogenous stress including anti-infectious agents. Biofilms are highly competitive communities and some microorganisms exhibit anti-biofilm capacities such as bacterial growth inhibition, exclusion or competition, which enable them to acquire advantages and become dominant. The deciphering and control of anti-biofilm properties represent future challenges in human infection control. The aim of this review is to compare and discuss the mechanisms of natural bacterial anti-biofilm strategies/mechanisms recently identified in pathogenic, commensal and probiotic bacteria and the main synthetic strategies used in clinical practice, particularly for catheter-related infections.

Biological Stability of Drinking Water: Controlling Factors, Methods, and Challenges

Biological stability of drinking water refers to the concept of providing consumers with drinking water of same microbial quality at the tap as produced at the water treatment facility. However, uncontrolled growth of bacteria can occur during distribution in water mains and premise plumbing, and can lead to hygienic (e.g., development of opportunistic pathogens), aesthetic (e.g., deterioration of taste, odor, color) or operational (e.g., fouling or biocorrosion of pipes) problems. Drinking water contains diverse microorganisms competing for limited available nutrients for growth. Bacterial growth and interactions are regulated by factors, such as (i) type and concentration of available organic and inorganic nutrients, (ii) type and concentration of residual disinfectant, (iii) presence of predators, such as protozoa and invertebrates, (iv) environmental conditions, such as water temperature, and (v) spatial location of microorganisms (bulk water, sediment, or biofilm). Water treatment and distribution conditions in water mains and premise plumbing affect each of these factors and shape bacterial community characteristics (abundance, composition, viability) in distribution systems. Improved understanding of bacterial interactions in distribution systems and of environmental conditions impact is needed for better control of bacterial communities during drinking water production and distribution. This article reviews (i) existing knowledge on biological stability controlling factors and (ii) how these factors are affected by drinking water production and distribution conditions. In addition, (iii) the concept of biological stability is discussed in light of experience with well-established and new analytical methods, enabling high throughput analysis and in-depth characterization of bacterial communities in drinking water. We discussed, how knowledge gained from novel techniques will improve design and monitoring of water treatment and distribution systems in order to maintain good drinking water microbial quality up to consumer's tap. A new definition and methodological approach for biological stability is proposed.

The Interaction between Heterotrophic Bacteria and Coliform, Fecal Coliform, Fecal Streptococci Bacteria in the Water Supply Networks

BACKGROUND

This study investigated the interaction between heterotrophic bacteria and coliform, fecal coliforms, fecal streptococci bacteria in water supply networks.

METHODS

This study was conducted during 2013 on water supply distribution network in Aq Qala City, Golestan Province, Northern Iran and standard methods were applied for microbiological analysis. The surface method was applied to test the heterotrophic bacteria and MPN method was used for coliform, fecal coliform and fecal streptococci bacteria measurements.

RESULTS

In 114 samples, heterotrophic bacteria count were over 500 CFU/ml, which the amount of fecal coliform, coliform, and fecal streptococci were 8, 32, and 20 CFU/100 ml, respectively. However, in the other 242 samples, with heterotrophic bacteria count being less than 500 CFU/ml, the amount of fecal coliform, coliform, and fecal streptococci was 7, 23, and 11 CFU/100ml, respectively. The relationship between heterotrophic bacteria, coliforms and fecal streptococci was highly significant (P<0.05). We observed the concentration of coliforms, fecal streptococci bacteria being high, whenever the concentration of heterotrophic bacteria in the water network systems was high.

CONCLUSION

Interaction between heterotrophic bacteria and coliform, fecal coliforms, fecal streptococci bacteria in the Aq Qala City water supply networks was not notable. It can be due to high concentrations of organic carbon, bio-films and nutrients, which are necessary for growth, and survival of all microorganisms.

Biodegradation of microcystins during gravity-driven membrane (GDM) ultrafiltration

Gravity-driven membrane (GDM) ultrafiltration systems require little maintenance: they operate without electricity at ultra-low pressure in dead-end mode and without control of the biofilm formation. These systems are already in use for water purification in some regions of the world where adequate treatment and distribution of drinking water is not readily available. However, many water bodies worldwide exhibit harmful blooms of cyanobacteria that severely lower the water quality due to the production of toxic microcystins (MCs). We studied the performance of a GDM system during an artificial Microcystis aeruginosa bloom in lake water and its simulated collapse (i.e., the massive release of microcystins) over a period of 21 days. Presence of live or destroyed cyanobacterial cells in the feed water decreased the permeate flux in the Microcystis treatments considerably. At the same time, the microbial biofilms on the filter membranes could successfully reduce the amount of microcystins in the filtrate below the critical threshold concentration of 1 µg L(-1) MC for human consumption in three out of four replicates after 15 days. We found pronounced differences in the composition of bacterial communities of the biofilms on the filter membranes. Bacterial genera that could be related to microcystin degradation substantially enriched in the biofilms amended with microcystin-containing cyanobacteria. In addition to bacteria previously characterized as microcystin degraders, members of other bacterial clades potentially involved in MC degradation could be identified.

Predation and transport of persistent pathogens in GAC and slow sand filters: a threat to drinking water safety?

Zooplankton has been shown to transport internalized pathogens throughout engineered drinking water systems. In this study, experimental measurements from GAC and SSF filtration tests using high influent concentrations of Cryptosporidium (1.3 × 10(6) and 3.3 × 10(4) oocysts L(-1)) and Giardia (4.8 × 10(4) cysts L(-1)) are presented and compared. A predation and transport conceptual model was developed to extrapolate these results to environmental conditions of typical (oo)cyst concentrations in surface water in order to predict concentrations of internalized (oo)cysts in filtered water. Pilot test results were used to estimate transport and survival ratios of internalized (oo)cysts following predation by rotifers in the filter beds. Preliminary indications of lower transport and survival ratios in SSF were found as compared with GAC filters. A probability of infection due to internalized (oo)cysts in filtered water was calculated under likeliest environmental conditions and under a worst-case scenario. Estimated risks under the likeliest environmental scenario were found to fall below the tolerable risk target of 10(-4) infections per person per year. A discussion is presented on the health significance of persistent pathogens that are internalized by zooplankton during granular filtration processes and released into treated water.

Biostability in distribution systems in one city in southern China: characteristics, modeling and control strategy

This study investigated the bacterial regrowth in drinking water distribution systems receiving finished water from an advanced drinking water treatment plant in one city in southern China. Thirteen nodes in two water supply zones with different aged pipelines were selected to monitor water temperature, dissolved oxygen (DO), chloramine residual, assimilable organic carbon (AOC), and heterotrophic plate counts (HPC). Regression and principal component analyses indicated that HPC had a strong correlation with chloramine residual. Based on Chick-Watson's Law and the Monod equation, biostability curves under different conditions were developed to achieve the goal of HPC < or = 100 CFU/mL. The biostability curves could interpret the scenario under various AOC concentrations and predict the required chloramine residual concentration under the condition of high AOC level. The simulation was also carried out to predict the scenario with a stricter HPC goal (< or = 50 CFU/mL) and determine the required chloramine residual. The biological regrowth control strategy was assessed using biostability curve analysis. The results indicated that maintaining high chloramine residual concentration was the most practical way to achieve the goal of HPC < or = 100 CFU/mL. Biostability curves could be a very useful tool for biostability control in distribution systems. This work could provide some new insights towards biostability control in real distribution systems.

Growth dynamic of Naegleria fowleri in a microbial freshwater biofilm

The presence of pathogenic free-living amoebae (FLA) such as Naegleria fowleri in freshwater environments is a potential public health risk. Although its occurrence in various water sources has been well reported, its presence and associated factors in biofilm remain unknown. In this study, the density of N. fowleri in biofilms spontaneously growing on glass slides fed by raw freshwater were followed at 32 °C and 42 °C for 45 days. The biofilms were collected with their substrata and characterized for their structure, numbered for their bacterial density, thermophilic free-living amoebae, and pathogenic N. fowleri. The cell density of N. fowleri within the biofilms was significantly affected both by the temperature and the nutrient level (bacteria/amoeba ratio). At 32 °C, the density remained constantly low (1-10 N. fowleri/cm(2)) indicating that the amoebae were in a survival state, whereas at 42 °C the density reached 30-900 N. fowleri/cm(2) indicating an active growth phase. The nutrient level, as well, strongly affected the apparent specific growth rate (μ) of N. fowleri in the range of 0.03-0.23 h(-1). At 42 °C a hyperbolic relationship was found between μ and the bacteria/amoeba ratio. A ratio of 10(6) to 10(7) bacteria/amoeba was needed to approach the apparent μ(max) value (0.23 h(-1)). Data analysis also showed that a threshold for the nutrient level of close to 10(4) bacteria/amoeba is needed to detect the growth of N. fowleri in freshwater biofilm. This study emphasizes the important role of the temperature and bacteria as prey to promote not only the growth of N. fowleri, but also its survival.

Relationships between free-living protozoa, cultivable Legionella spp., and water quality characteristics in three drinking water supplies in the Caribbean

The study whose results are presented here aimed at identifying free-living protozoa (FLP) and conditions favoring the growth of these organisms and cultivable Legionella spp. in drinking water supplies in a tropical region. Treated and distributed water (±30°C) of the water supplies of three Caribbean islands were sampled and investigated with molecular techniques, based on the 18S rRNA gene. The protozoan host Hartmannella vermiformis and cultivable Legionella pneumophila were observed in all three supplies. Operational taxonomic units (OTUs) with the highest similarity to the potential or candidate hosts Acanthamoeba spp., Echinamoeba exundans, E. thermarum, and an Neoparamoeba sp. were detected as well. In total, 59 OTUs of FLP were identified. The estimated protozoan richness did not differ significantly between the three supplies. In supply CA-1, the concentration of H. vermiformis correlated with the concentration of Legionella spp. and clones related to Amoebozoa predominated (82%) in the protozoan community. These observations, the low turbidity (<0.2 nephelometric turbidity units [NTU]), and the varying ATP concentrations (1 to 12 ng liter(-1)) suggest that biofilms promoted protozoan growth in this supply. Ciliophora represented 25% of the protozoan OTUs in supply CA-2 with elevated ATP concentrations (maximum, 55 ng liter(-1)) correlating with turbidity (maximum, 62 NTU) caused by corroding iron pipes. Cercozoan types represented 70% of the protozoan clones in supply CA-3 with ATP concentrations of <1 ng liter(-1) and turbidity of <0.5 NTU in most samples of distributed water. The absence of H. vermiformis in most samples from supply CA-3 suggests that growth of this protozoan is limited at ATP concentrations of <1 ng liter(-1).

Campylobacter epidemiology: an aquatic perspective

Members of the genus Campylobacter have established themselves as the most common human gastro-enteric pathogens throughout much of the developed world. The ubiquitous distribution of Campylobacter spp. in animal reservoirs and food products derived thereof make such vehicles primary risk factors in contracting campylobacteriosis. The contamination rates, identification of common pathogenic serotypes and extended survival of Campylobacter in surface waters illustrates the potential, but yet to be quantified, campylobacteriosis risk associated with untreated water. The existence and potential pathogenicity of viable but nonculturable forms of Campylobacter remains a contentious subject. Furthermore, the role of such forms in the epidemiology of Campylobacter related disease and their involvement in the large number of waterborne gastroenteritis outbreaks from which a disease agent cannot be isolated remains to be fully clarified. This article presents a survey of current perspectives with regard to the survival and epidemiology of Campylobacter spp. in natural water systems.

Survival of Mycobacterium avium attached to polyethylene terephtalate (PET) water bottles

AIMS

The main objective of our study was to assess the persistence of Mycobacterium avium in an oligotrophic environment such as bottled groundwater.

METHODS AND RESULTS

Filtered groundwater samples were spiked with washed Myco. avium suspension and stored in dark and under static conditions, at 20 degrees C, for 3 months in 500 ml PET bottles. The loss of Myco. avium cultivability was slow in water. On the contrary, after a 3-month storage at 20 degrees C, growth of attached cells was observed and cell adhesiveness to the PET wall increased with time. It could probably be because of the presence of an extracellular matrix.

CONCLUSIONS

This study has shown the great stability of Myco. avium in bulk water as well as their adhesiveness and their growth on a PET bottle wall in an oligotrophic environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Slowly growing mycobacteria are well adapted to oligotrophic environments such as groundwater. As they stick very well to surfaces, they could be used for determining the efficiency of the cleaning of contaminated surfaces.

Identification and phylogeny of eukaryotic 18S rDNA phylotypes detected in chlorinated finished drinking water samples from three Parisian surface water treatment plants

AIMS

We performed a preliminary assessment of the eukaryotic 18S rDNA diversity present in finished drinking water samples from three different surface water treatment plants supplying water to the city of Paris (France).

METHODS AND RESULTS

A molecular analysis was performed on a sample from each site based on sequencing of PCR amplified and cloned 18S ribosomal RNA genes. Overall, the 18S rDNA sequences combined from all samples could be affiliated to the Amoebozoa (20.8% of the phylotypes), Ciliophora (25%), Metazoa (33.3%), Fungi (8.3%), Cercozoa (4.2%) and unclassified eukaryotes (8.3%) groups.

CONCLUSIONS

The 18S rDNA sequences affiliated to the Amoebozoa, Ciliophora and Metazoa lineages were found to be the most abundant phylotypes observed in the drinking water samples. Phylotypes found to be present in two, or all three, samples (41.7% of the total) may represent groups with members adapted to drinking water treatment plant (DWTP) ecosystem conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that finished drinking water can contain 18S rDNA sequences representing a variety of eukaryotic taxa. Further research is needed to better characterize the eukaryotic biodiversity of DWTPs and the effects of the finished drinking water diversity on the downstream water distribution network.

Free-living protozoa in two unchlorinated drinking water supplies, identified by phylogenic analysis of 18S rRNA gene sequences

Free-living protozoan communities in water supplies may include hosts for Legionella pneumophila and other undesired bacteria, as well as pathogens. This study aimed at identifying free-living protozoa in two unchlorinated groundwater supplies, using cultivation-independent molecular approaches. For this purpose, samples (<20 degrees C) of treated water, distributed water, and distribution system biofilms were collected from supply A, with a low concentration of natural organic matter (NOM) (<0.5 ppm of C), and from supply B, with a high NOM concentration (7.9 ppm of C). Eukaryotic communities were studied using terminal restriction fragment length polymorphism and clone library analyses of partial 18S rRNA gene fragments and a Hartmannella vermiformis-specific quantitative PCR (qPCR). In both supplies, highly diverse eukaryotic communities were observed, including free-living protozoa, fungi, and metazoa. Sequences of protozoa clustered with Amoebozoa (10 operational taxonomic units [OTUs]), Cercozoa (39 OTUs), Choanozoa (26 OTUs), Ciliophora (29 OTUs), Euglenozoa (13 OTUs), Myzozoa (5 OTUs), and Stramenopiles (5 OTUs). A large variety of protozoa were present in both supplies, but the estimated values for protozoan richness did not differ significantly. H. vermiformis was observed in both supplies but was not a predominant protozoan. One OTU with the highest similarity to Acanthamoeba polyphaga, an opportunistic human pathogen and a host for undesired bacteria, was observed in supply A. The high level of NOM in supply B corresponded with an elevated level of active biomass and with elevated concentrations of H. vermiformis in distributed water. Hence, the application of qPCR may be promising in elucidating the relationship between drinking water quality and the presence of specific protozoa.

Protection of waterborne pathogens by higher organisms in drinking water: a review

Higher organisms are ubiquitous in surface waters, and some species can proliferate in granular filters of water treatment plants and colonize distribution systems. Meanwhile, some waterborne pathogens are known to maintain viability inside amoebae or nematodes. The well-documented case of Legionella replication within amoebae is only one example of a bacterial pathogen that can be amplified inside the vacuoles of protozoa and then benefit from the protection of a resistant structure that favours its transport and persistence through water systems. Yet the role of most zooplankton organisms (rotifers, copepods, cladocerans) in pathogen transmission through drinking water remains poorly understood, since their capacity to digest waterborne pathogens has not been well characterized to date. This review aims at (i) evaluating the scientific observations of diverse associations between superior organisms and pathogenic microorganisms in a drinking water perspective and (ii) identifying the missing data that impede the establishment of cause-and-effect relationships that would permit a better appreciation of the sanitary risk arising from such associations. Additional studies are needed to (i) document the occurrence of invertebrate-associated pathogens in relevant field conditions, such as distribution systems; (ii) assess the fate of microorganisms ingested by higher organisms in terms of viability and (or) infectivity; and (iii) study the impact of internalization by zooplankton on pathogen resistance to water disinfection processes, including advanced treatments such as UV disinfection.

Biofilm processes in biologically active carbon water purification

This review paper serves to describe the composition and activity of a biologically active carbon (BAC) biofilm used in water purification. An analysis of several physical-chemical, biochemical and microbiological methods (indicators) used to characterize the BAC biofilm's composition and activity is provided. As well, the ability of the biofilm to remove and biodegrade waterborne organic substances and pollutants will be reviewed, with context to other industrial processes such as pre-ozonation and post-membrane filtration. Strategies to control the growth of the BAC biofilm, such as varying the nutrient loading rate, manipulating influent DO and pH levels, altering the frequency of BAC filter backwashing and applying oxidative disinfection, will be described in detail along with their respective process control challenges.

Phagotrophic protozoa: A new weapon against pathogens?

Immune suppression is one of the most important factors contributing mortality in systemic diseases like HIV, cancer or diabetes. Moreover, in autoimmune diseases immune suppression itself becomes the only choice of therapy. Finally, fatal bacterial infections occur. As antibiotics get stronger, severity of their side effects increase and more resistant organisms develop. The war between antibiotics and pathogens becomes a never ending story while human body gets weaker day by day. Therefore we should develop new methods against bacterial infections. We have suggested that the protists controlling the bacterial growth effectively in aquatic environments could be used in the human body to cope with human pathogens. Million years of a balanced aquatic ecosystem could be a clue for us to search for better and more natural fighting methods against human infectious agents.

Effect of wall shear rate on biofilm deposition and grazing in drinking water flow chambers

The effect of four-wall shear rates (34.9, 74.8, 142.5, and 194.5 s(-1)) on bacterial deposition on glass slides in drinking water flow chambers was studied. Biofilm image acquisition was performed over a 50-day period. Bacterial accumulation and surface coverage curves were obtained. Microscopic observations allowed us to obtain information about the dynamics and spatial distribution of the biofilm. During the first stage of biofilm formation (210-518 h), bacterial accumulation was a function of the wall shear rate: the higher the wall shear rate, the faster the bacterial deposition (1.1 and 1.9 x 10(4) bacterial cells . cm(-2) for wall shear rates of 34.9 and 142.5 s(-1), respectively). A new similarity relationship characteristic of a non-dimensional time and function of the wall shear rate was proposed to describe initial bacterial deposition. After 50 days of exposure to drinking water, surface coverage was more or less identical under the entire wall shear rates (7.44 +/- 0.9%), suggesting that biofilm bacterial density cannot be controlled using hydrodynamics. However, the spatial distribution of the biofilm was clearly different. Under low wall shear rate, aggregates were composed of bacterial cells able to "vibrate" independently on the surface, whereas, under a high wall shear rate, aggregates were more cohesive. Therefore, susceptibility to the hydraulic discontinuities occurring in drinking water system may not be similar. In all the flow chambers, significant decreases in bacterial biomass (up to 77%) were associated with the presence of amoebae. This grazing preferentially targeted small, isolated cells.

Nematodes as a source of total coliforms in a distribution system

In a distribution system of a large North American city, recurring total coliforms and atypical coliforms were detected at the exit (distribution pumps) of a storage reservoir. The presence of total coliforms and atypical coliforms was noted when the pumps were in operation and the water temperature was higher than 18 °C. The total coliform and atypical coliform concentrations at the volute pump casings ranged from 0 to 93.5 colony forming units (cfu)/100 mL. Significant concentrations of nematodes were also detected at this sampling location, averaging 12.0 nematodes/L in 2001 and 17.4 nematodes/L in 2002. The hypothesis that coliforms were released from the nematodes during their transit through the high-pressure pump was tested by recovering nematodes by filtering large volumes of water and grinding the nematodes in the laboratory, using various techniques. Total coliform and heterotrophic bacteria concentrations ranged from 0 to 27 cfu/nematode and 0 to 643 cfu/nematode, respectively. The origin of the nematodes was traced back to the sand filters located at the two water treatment plants. The importance of invertebrates in the distribution system should not be dismissed and the associated health risks, if any, should be assessed.

Effect of Phosphorus on survival of Escherichia coli in drinking water biofilms

The effect of phosphorus addition on survival of Escherichia coli in an experimental drinking water distribution system was investigated. Higher phosphorus concentrations prolonged the survival of culturable E. coli in water and biofilms. Although phosphorus addition did not affect viable but not culturable (VBNC) E. coli in biofilms, these structures could act as a reservoir of VBNC forms of E. coli in drinking water distribution systems.

Vulnerability of pathogenic biofilms to Micavibrio aeruginosavorus

The host specificity of the gram-negative exoparasitic predatory bacterium Micavibrio aeruginosavorus was examined. M. aeruginosavorus preyed on Pseudomonas aeruginosa, as previously reported, as well as Burkholderia cepacia, Klebsiella pneumoniae, and numerous clinical isolates of these species. In a static assay, a reduction in biofilm biomass was observed as early as 3 hours after exposure to M. aeruginosavorus, and an approximately 100-fold reduction in biofilm cell viability was detected following a 24-h exposure to the predator. We observed that an initial titer of Micavibrio as low as 10 PFU/well or a time of exposure to the predator as short as 30 min was sufficient to reduce a P. aeruginosa biofilm. The ability of Micavibrio to reduce an existing biofilm was confirmed by scanning electron microscopy. In static and flow cell experiments, M. aeruginosavorus was able to modify the overall P. aeruginosa biofilm structure and markedly decreased the viability of P. aeruginosa. The altered biofilm structure was likely caused by an increase in cell-cell interactions brought about by the presence of the predator or active predation. We also conducted a screen to identify genes important for P. aeruginosa-Micavibrio interaction, but no candidates were isolated among the approximately 10,000 mutants tested.

Bacteria removal in septic effluent: influence of biofilm and protozoa

Numerous biological, physical and chemical parameters are involved in the retention and removal of bacteria in wastewater treatment systems. Biological parameters, such as biofilms and protozoa grazing activity, are often mentioned but few studies provide a better understanding of their influence. In this study, the effect of bacterivorous protozoa on pathogenic indicator bacteria removal was investigated in septic effluent and in the presence of a biofilm coating glass slides. Endogenous bacteria from septic effluent were quantified. First, bacteria removal was compared between septic effluents treated or not with an inhibitor of protozoa (cycloheximide). The mortality rates were 10 times lower in treated effluent (96 CFU mL(-1) d(-1)) than in untreated effluent (1100 CFU mL(-1) d(-1)). Secondly, the efficiency of bacteria removal was studied (i) with a biofilm surface and active protozoa, (ii) with a biofilm surface and inactivated protozoa, (iii) with a clean surface. Protozoa in the presence of a biofilm were responsible for 60% of bacteria removal. Biofilm without protozoa and a clean surface each removed similar quantities of bacteria. Grazing by protozoa could be an important biological mechanism for bacterial elimination in wastewater treatment systems.

Iron uptake is essential for Escherichia coli survival in drinking water

AIMS

The aim of this study was to elucidate if the need for iron for Escherichia coli to remain cultivable in a poorly nutritive medium such as the drinking water uses the iron transport system via the siderophores.

METHODS AND RESULTS

Environmental strains of E. coli (isolated from a drinking water network), referenced strains of E. coli and mutants deficient in TonB, an essential protein for iron(III) acquisition, were incubated for 3 weeks at 25 degrees C, in sterile drinking water with and without lepidocrocite (gamma-FeOOH), an insoluble iron corrosion product. Only cells with a functional iron transport system were able to survive throughout the weeks.

CONCLUSIONS

The iron transport system via protein TonB plays an essential role on the survival of E. coli in a weakly nutritive medium like drinking water.

SIGNIFICANCE AND IMPACTS OF THE STUDY

Iron is a key parameter involved in coliform persistence in drinking water distribution systems.

Biofilm formation and phenotypic variation enhance predation-driven persistence of Vibrio cholerae

Persistence of the opportunistic bacterial pathogen Vibrio cholerae in aquatic environments is the principal cause for seasonal occurrence of cholera epidemics. This causality has been explained by postulating that V. cholerae forms biofilms in association with animate and inanimate surfaces. Alternatively, it has been proposed that bacterial pathogens are an integral part of the natural microbial food web and thus their survival is constrained by protozoan predation. Here, we report that both explanations are interrelated. Our data show that biofilms are the protective agent enabling V. cholerae to survive protozoan grazing while their planktonic counterparts are eliminated. Grazing on planktonic V. cholerae was found to select for the biofilm-enhancing rugose phase variant, which is adapted to the surface-associated niche by the production of exopolymers. Interestingly, grazing resistance in V. cholerae biofilms was not attained by exopolymer production alone but was accomplished by the secretion of an antiprotozoal factor that inhibits protozoan feeding activity. We identified that the cell density-dependent regulator hapR controls the production of this factor in biofilms. The inhibitory effect of V. cholerae biofilms was found to be widespread among toxigenic and nontoxigenic isolates. Our results provide a mechanistic explanation for the adaptive advantage of surface-associated growth in the environmental persistence of V. cholerae and suggest an important contribution of protozoan predation in the selective enrichment of biofilm-forming strains in the out-of-host environment.

Bacterial-protozoa interactions; an update on the role these phenomena play towards human illness

The usage of water with poor microbiological quality increases the risk of human illness. This review discusses and updates current thinking on the nature of the interaction between a range of human bacterial pathogens and waterborne protozoa. The importance of protozoa acting as protective environments for pathogenic bacteria from disinfection and of promoting extended survival in otherwise hostile environments is highlighted. The significance of biofilms in water systems, and new relationships between Salmonella and Campylobacter and water-borne protozoa are also discussed. The protection of pathogenic bacteria from disinfection within protozoa and/or biofilms has important implications for water safety.

Susceptibility of biofilms to Bdellovibrio bacteriovorus attack

Biofilms are communities of microorganisms attached to a surface, and the growth of these surface attached communities is thought to provide microorganisms with protection against a range of biotic and abiotic agents. The capability of the gram-negative predatory bacterium Bdellovibrio bacteriovorus to control and reduce an existing Escherichia coli biofilm was evaluated in a static assay. A reduction in biofilm biomass was observed as early as 3 h after exposure to the predator, and an 87% reduction in crystal violet staining corresponding to a 4-log reduction in biofilm cell viability was seen after a 24-h exposure period. We observed that an initial titer of Bdellovibrio as low as 10(2) PFU/well or an exposure to the predator as short as 30 min is sufficient to reduce a preformed biofilm. The ability of B. bacteriovorus to reduce an existing biofilm was confirmed by scanning electron microscopy. The reduction in biofilm biomass obtained after the first 24 h of exposure to the predator remained unchanged even after longer exposure periods and reinoculation of the samples with fresh Bdellovibrio; however, no genetically stable resistant population of the host bacteria could be detected. Our data suggest that growth in a biofilm does not prevent predation by Bdellovibrio but allows a level of survival from attack greater than that observed for planktonic cells. In flow cell experiments B. bacteriovorus was able to decrease the biomass of both E. coli and Pseudomonas fluorescens biofilms as determined by phase-contrast and epifluorescence microscopy.

Mycobacteria in drinking water distribution systems: ecology and significance for human health

In contrast to the notorious pathogens Mycobacterium tuberculosis and M. leprae, the majority of the mycobacterial species described to date are generally not considered as obligate human pathogens. The natural reservoirs of these non-primary pathogenic mycobacteria include aquatic and terrestrial environments. Under certain circumstances, e.g., skin lesions, pulmonary or immune dysfunctions and chronic diseases, these environmental mycobacteria (EM) may cause disease. EM such as M. avium, M. kansasii, and M. xenopi have frequently been isolated from drinking water and hospital water distribution systems. Biofilm formation, amoeba-associated lifestyle, and resistance to chlorine have been recognized as important factors that contribute to the survival, colonization and persistence of EM in water distribution systems. Although the presence of EM in tap water has been linked to nosocomial infections and pseudo-infections, it remains unclear if these EM provide a health risk for immunocompromised people, in particular AIDS patients. In this regard, control strategies based on maintenance of an effective disinfectant residual and low concentration of nutrients have been proposed to keep EM numbers to a minimum in water distribution systems.

Legionella pneumophila associated with the protozoan Hartmannella vermiformis in a model multi-species biofilm has reduced susceptibility to disinfectants

Legionella pneumophila will infect biofilm-associated protozoa, and in this way might be protected from disinfectants in potable water systems. A base biofilm containing Pseudomonas aeruginosa, Klebsiella pneumoniae, and Flavobacterium spp. was grown on steel coupons in potable water prior to the addition of L. pneumophila and the protozoan H. vermiformis. After 7 d, coupons were removed and treated with 0.5 mgl(-1) free residual chlorine (FRC) or 0.5 mgl(-1) monochloramine (MCA) for 15, 60, or 180 min or 24 h. In a second experiment, only L. pneumophila and the base biofilm organisms were present but with an identical treatment protocol. Treatment of L. pneumophila for 180 min in a system without H. vermiformis resulted in log reductions of 2.07 and 2.11 for FRC and MCA, respectively. When H. vermiformis was present, however, the treatment resulted in log reductions of 0.67 and 0.81 for FRC and MCA, respectively. A similar pattern was observed for 15 and 60 min contact times. These results indicate that L. pneumophila was less susceptible to MCA or FRC when associated with biofilm-associated H. vermiformis in a model potable water biofilm.

Effect of oxygen on survival of faecal pollution indicators in drinking water

AIMS

The aim of this study was to determine the effect of oxygen on the survival of faecal pollution indicators including Escherichia coli in nondisinfected drinking water.

METHODS AND RESULTS

Aerobic and anaerobic drinking water microcosms were inoculated with E. coli ATCC 25922 or raw sewage. Survival of E. coli was monitored by membrane filtration combined with cultivation on standard media, and by in situ hybridization with 16S rRNA-targeted fluorescent oligonucleotide probes. Anaerobic conditions significantly increased the survival of E. coli in drinking water compared with aerobic conditions. Escherichia coli ATCC 25922 showed a biphasic decrease in survival under aerobic conditions with an initial first-order decay rate of -0.11 day(-1) followed by a more rapid rate of -0.35 day(-1). In contrast, the first-order decay rate under anaerobic conditions was only -0.02 day(-1). After 35 days, <0.01% of the initial E. coli ATCC 25922 population remained detectable in aerobic microcosms compared with 48% in anaerobic microcosms. A poor survival was observed under aerobic conditions regardless of whether E. coli ATCC 25922 or sewage-derived E. coli was examined, and regardless of the detection method used (CFU or fluorescent in situ hybridization). Aerobic conditions in drinking water also appeared to decrease the survival of faecal enterococci, somatic coliphages and coliforms other than E. coli.

CONCLUSIONS

The results indicate that oxygen is a major regulator of the survival of E. coli in nondisinfected drinking water. The results also suggest that faecal pollution indicators other than E. coli may persist longer in drinking water under anaerobic conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effect of oxygen should be considered when evaluating the survival potential of enteric pathogens in oligotrophic environments.

Behavior of an Aeromonas hydrophila aroA live vaccine in water microcosms

Genetically modified auxotrophic mutants of different fish pathogens have been used as live vaccines in laboratory experiments, but the behavior of the strains after release into aquatic ecosystems has not been characterized. We previously constructed and characterized an aroA mutant of Aeromonas hydrophila and studied the protection afforded by this mutant as a live vaccine in rainbow trout. In this work, we describe the survival of this strain in aquatic microcosms prepared from fish water tanks. The aroA mutant disappeared rapidly in nonfiltered, nonautoclaved fish tank water, declining below detection levels after 15 days, suggesting an inhibitory effect of the autochthonous microflora of the water. When the aroA strain was used to inoculate sterilized water, its culturability was lower than that of wild-type strain A. hydrophila AG2; after long periods of incubation, aroA cells were able to enter a viable but nonculturable state. Entry into this nonculturable state was accompanied by changes in the cell morphology from rods to spheres, but the cells appeared to remain potentially viable, as assessed by the preservation of cell membrane integrity. Supplementation of the culture medium with sodium pyruvate favored the culturability and resuscitation of the two A. hydrophila strains at low temperatures (6 and 16 degrees C). These results contribute to a better understanding of the behavior of the aroA strain in natural environments and suggest that the inactivation of the aroA gene may be beneficial for the safety of this live vaccine for aquacultures.

In vitro laser ablation of laboratory developed biofilms using an Nd:YAG laser of 532 nm wavelength

We studied the laser ablation of laboratory-developed biofilm on titanium and glass surfaces. Specifically, Pseudoalteromonas carrageenovora, a marine biofilm forming bacterium was used to generate laboratory biofilm. Two fluences, 0.05 and 0.1 J/cm(2) and three durations of irradiation, 30 s, 5 min, and 10 min were tested using an Nd;YAG laser of 532 nm wavelength (in the green light area). Nonirradiated coupons with biofilm served as control. The biofilm removal efficiency increased with the increase in laser fluence and duration of irradiation. The maximum biofilm area cover on control coupons of glass and titanium was 62.5 and 76.0%, respectively. Upon irradiation with fluence 0.1 J/cm(2) for the very short duration of 30 s, this reduced to 5.6 and 12.4% and at 10 min to 2.17 and 0.7% on glass and titanium coupons, respectively, while the controls did not show any reductions (62.5 and 76.0% respectively, for glass and titanium coupons). The biofilm TRC (Total Resuscitated Cells) reduction during this period was even more prominent than the area cover, indicating that the remaining biofilm portions on coupons after irradiation were largely composed of dead bacterial cells. The TRC in the irradiation chamber medium for short durations of irradiation showed a significant increase, indicating that the laser irradiation removed live bacteria from the biofilm. The re-growth of the resuscitated cells showed they could grow like the control cells but with a significant lag. The laser's efficiency in the removal of biofilm was better seen on titanium coupons than on glass. Our results showed that a low-power pulsed laser irradiation could be used to remove biofilm formed on hard surfaces.

Protistan grazing analysis by flow cytometry using prey labeled by in vivo expression of fluorescent proteins

Selective grazing by protists can profoundly influence bacterial community structure, and yet direct, quantitative observation of grazing selectivity has been difficult to achieve. In this investigation, flow cytometry was used to study grazing by the marine heterotrophic flagellate Paraphysomonas imperforata on live bacterial cells genetically modified to express the fluorescent protein markers green fluorescent protein (GFP) and red fluorescent protein (RFP). Broad-host-range plasmids were constructed that express fluorescent proteins in three bacterial prey species, Escherichia coli, Enterobacter aerogenes, and Pseudomonas putida. Micromonas pusilla, an alga with red autofluorescence, was also used as prey. Predator-prey interactions were quantified by using a FACScan flow cytometer and analyzed by using a Perl program described here. Grazing preference of P. imperforata was influenced by prey type, size, and condition. In competitive feeding trials, P. imperforata consumed algal prey at significantly lower rates than FP (fluorescent protein)-labeled bacteria of similar or different size. Within-species size selection was also observed, but only for P. putida, the largest prey species examined; smaller cells of P. putida were grazed preferentially. No significant difference in clearance rate was observed between GFP- and RFP-labeled strains of the same prey species or between wild-type and GFP-labeled strains. In contrast, the common chemical staining method, 5-(4,6-dichloro-triazin-2-yl)-amino fluorescein hydrochloride, depressed clearance rates for bacterial prey compared to unlabeled or RFP-labeled cells.

Biofilm responses to ageing and to a high phosphate load in a bench-scale drinking water system

The effects of ageing and of phosphate load on drinking water biofilms developed on a polycarbonate substratum in the pseudo-equilibrium state have been evaluated. Phosphate was added in an amount higher than the stochiometric nutrient requirements of bacteria, at concentrations commonly applied in a drinking water distribution system for corrosion control. Multiple parameters were monitored: heterotrophic plate counts (HPCs), total direct counts (TDCs) and potential exoproteolytic activity (PEPA) in order to characterise changes in bacterial biofilms. The total carbohydrate, amino acid and phosphate contents of biofilms were analysed to characterise and monitor the biochemical composition of the biofilm.The three enumeration methods showed that a pseudo-equilibrium state was reached after 7 weeks of colonisation after which, the bacterial growth rate in the biofilm was 0.1 log per week on average. Bulk phosphate addition doubled the phosphate in the biofilm, but did not affect the other biological, physiological or chemical parameters measured. Polysaccharides increased in the biofilm with ageing and the dynamics of individual carbohydrate synthesis also varied with the age of the biofilm. Once pseudo-equilibrium, it was found that the total proteins were globally constant, whereas the spectra of some individual amino acids of the proteins had significantly changed.

The genetics of nontuberculous mycobacterial infection

The molecular aetiology of familial susceptibility to disseminated mycobacterial disease, usually involving weakly pathogenic strains of mycobacteria, has now been elucidated in more than 30 families. Mutations have been identified in five genes in the interleukin-12-dependent interferon-gamma pathway, highlighting the importance of this pathway in human mycobacterial immunity. Knowledge derived from the study of these rare patients contributes to our understanding of the immune response to common mycobacterial pathogens such as Mycobacterium tuberculosis and Mycobacterium leprae, which remain major public health problems globally. This knowledge can be applied to the rational development of novel therapies and vaccines for these important mycobacterial diseases.

Survival of Escherichia coli O157:H7 in private drinking water wells: influences of protozoan grazing and elevated copper concentrations

The survival characteristics of Escherichia coli O157:H7 in private drinking water wells were investigated to assess the potential for human exposure. A non-toxigenic, chromosomally lux-marked strain of E. coli O157:H7 was inoculated into well water from four different sites in the North East of Scotland. These waters differed significantly in their heavy metal contents as well as nutrient and bacterial grazer concentrations. Grazing and other biological factors were studied using filtered (3 and 0.2 microm) and autoclaved water. The survival of E. coli O157:H7 was primarily decreased by elevated copper concentrations. This hypothesis was supported by acute toxicity assay data. In addition, significant protozoan predation effects were observed in untreated water when compared with survival rates in filtered water. The combination of these two factors in particular determines the survival time of the pathogen in a private water well. It therefore appears that wells with higher water quality as assessed using the European Union Drinking Water Directive standards will also allow survival of E. coli O157:H7 for much longer periods.

Geomicrobiology: how molecular-scale interactions underpin biogeochemical systems

Microorganisms populate every habitable environment on Earth and, through their metabolic activity, affect the chemistry and physical properties of their surroundings. They have done this for billions of years. Over the past decade, genetic, biochemical, and genomic approaches have allowed us to document the diversity of microbial life in geologic systems without cultivation, as well as to begin to elucidate their function. With expansion of culture-independent analyses of microbial communities, it will be possible to quantify gene activity at the species level. Genome-enabled biogeochemical modeling may provide an opportunity to determine how communities function, and how they shape and are shaped by their environments.

The fate of Escherichia coli through water treatment and in distribution

The removal of E. coli bacteria at each stage of water treatment is presented, showing how the filtration stages contribute most to reduction of bacterial numbers in the water. At treatment works without filtration stages, the emphasis is put on catchment management to limit contamination of the raw water and ensure that the numbers of viable E. coli in the source water remain low. Routine monitoring of the raw water provides data on seasonal trends in numbers of E. coli bacteria and allows effective management of supply. In the UK there is no evidence that E. coli grows in the water distribution system, whether in the planktonic stage or within biofilms (O'Neill et al. 1997). The detection of E. coli in the distribution system is rare and prompts a thorough investigation. Repeat samples are taken from the point which originally failed, along with a number of hydraulically linked samples including samples from hydrants. The response to the detection of E. coli is discussed. A series of experiments carried out on a pilot pipe system is briefly described and the results discussed in relation to the routine samples taken in the Thames Water Supply area.

Phenotype characterization of genetically defined microorganisms and growth of bacteriophage in biofilms

Phenotypic characterization will be a pivotal aspect of future research in understanding the biofilm mode of growth. We hope that the concepts and techniques presented in this chapter will benefit other investigators in this field. Although initial studies will necessarily involve monocultures, eventually mixed culture work will have to be performed to understand biofilm growth in the natural environment. As the study of biofilm-phage interactions is new, there is considerable fundamental work that needs to be addressed. Here, we anticipate that some phage are better adapted to growth in biofilms, some are adept in growing in mixed culture biofilms, and others are better adapted to infecting planktonic organisms. Whereas biofilms are now widely accepted as a fundamental aspect of microbial growth in nature, the field of phage ecology is quite new and an exciting challenge for the future.