Bacterial composition in Swedish raw drinking water reveals three major interacting ubiquitous metacommunities.

BACKGROUND: Surface raw water used as a source for drinking water production is a critical resource, sensitive to contamination. We conducted a study on Swedish raw water sources, aiming to identify mutually co-occurring metacommunities of bacteria, and environmental factors driving such patterns. METHODS: The water sources were different regarding nutrient composition, water quality, and climate characteristics, and displayed various degrees of anthropogenic impact. Water inlet samples were collected at six drinking water treatment plants over 3 years, totaling 230 samples. The bacterial communities of DNA sequenced samples (n = 175), obtained by 16S metabarcoding, were analyzed using a joint model for taxa abundance. RESULTS: Two major groups of well-defined metacommunities of microorganisms were identified, in addition to a third, less distinct, and taxonomically more diverse group. These three metacommunities showed various associations to the measured environmental data. Predictions for the well-defined metacommunities revealed differing sets of favored metabolic pathways and life strategies. In one community, taxa with methanogenic metabolism were common, while a second community was dominated by taxa with carbohydrate and lipid-focused metabolism. CONCLUSION: The identification of ubiquitous persistent co-occurring bacterial metacommunities in freshwater habitats could potentially facilitate microbial source tracking analysis of contamination issues in freshwater sources.

Drinking Water Disinfection by-Products and Congenital Malformations: A Nationwide Register-Based Prospective Study.

BACKGROUND: Drinking water chlorination by-products have been associated with adverse reproductive outcomes, although the findings for congenital malformations are still inconclusive. OBJECTIVE: We conducted a nationwide register-based prospective study to assess whether first trimester maternal exposure to the four most common trihalomethanes [total trihalomethanes (TTHM)] via municipal drinking water was associated with risk of congenital malformation among newborns. METHODS: We included all births during 2005-2015 (live and stillbirths) of mothers residing in Swedish localities having >10,000 inhabitants, two or fewer operating water works, and sufficient municipal TTHM monitoring data. Individual maternal first trimester exposure was obtained by linking TTHM measurements to residential information, categorized into no chlorination and <5, 5-15, and >15µg TTHM/L. We also made chlorination treatment-specific analyses (exclusive use of chloramine or hypochlorite). Outcomes and covariates were obtained via linkage to health care and administrative registers. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression. RESULTS: Based on 623,468 births and a prevalence of congenital malformation of ∼2 cases/100 births, we observed associations between TTHM exposure in areas using chloramine and malformations of the nervous system (OR=1.82; 95% CI: 1.07, 3.12), urinary system (OR=2.06; 95% CI: 1.53, 2.78), genitals (OR=1.77; 95% CI: 1.38, 2.26), and limbs (OR=1.34; 95% CI: 1.10, 1.64), comparing the highest exposed category with the unexposed. No associations were observed in areas using exclusively hypochlorite as the primary water treatment method. By contrast, for malformations of the heart, a significant inverse association was observed only in areas using hypochlorite. DISCUSSION: TTHM exposure was associated with the increased risk of malformations of the nervous system, urinary system, genitals, and limbs in areas exclusively using chloramine. An association between chloramine-related chlorination by-products and congenital malformations has not previously been highlighted and needs further attention. https://doi.org/10.1289/EHP9122.

Exposure to Drinking Water Chlorination by-Products and Fetal Growth and Prematurity: A Nationwide Register-Based Prospective Study.

BACKGROUND: Chlorination is globally used to produce of safe drinking water. Chlorination by-products are easily formed, and there are indications that these are associated with adverse reproductive outcomes. OBJECTIVES: We conducted a nationwide register-based prospective study to assess whether gestational exposure to the four most common chlorination by-products [total trihalomethanes (TTHMs)] via tap water was associated with risk of small for gestational age (SGA), preterm delivery, and very preterm delivery. To date, this is one of the largest studies assessing drinking water TTHM-associated adverse reproductive outcomes. METHODS: We included all singleton births 2005-2015 (live and stillbirths) of mothers residing in Swedish localities having >10,000 inhabitants, ≤2 operating waterworks, adequate information on chlorination treatment, and a sufficient number of routine TTHM measurements in tap water. Individual maternal second and third trimester exposure was obtained by linking TTHM measurements to residential history, categorized into no chlorination, <5, 5-15, and >15µg TTHM/L. Outcomes and covariates were obtained via the linkage to Swedish health and administrative registers. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression using inverse probability weighting. We stratified the analyses by chlorination treatment (chloramine, hypochlorite). RESULTS: Based on approximately 500,000 births, we observed a TTHM dose-dependent association with increased risk of SGA, confined to treatment with hypochlorite, corresponding to a multivariable-adjusted OR=1.20 (95% CI: 1.08, 1.33) comparing drinking water TTHM >15µg to the unexposed. Similar results were obtained when, instead of unexposed, the lowest exposure category (<5µg/L TTHM) was used as reference. No clear associations were observed for preterm delivery and very preterm delivery. DISCUSSION: Chlorination by-products exposure via drinking water was associated with increased risk of SGA in areas with hypochlorite treatment. https://doi.org/10.1289/EHP6012.

Endemic gastrointestinal illness and change in raw water source and drinking water production - A population-based prospective study.

There are indications that drinking water may contribute to endemic gastrointestinal illness (GII) even when the drinking water quality meets current standards, but the knowledge is limited. In this population-based prospective study, we assessed if changes in municipal drinking water production affected the GII incidence, by collecting self-reported GII episodes among the population in two municipalities during calendar time-specific inter-annual periods. About 2600 adults in central Sweden and 2600 adults (including 700 households with children aged 0-9 years) in Southwest Sweden, were followed during a baseline and a follow-up period in 2012-2016. Monthly reports of episodes and symptoms of GII were collected by SMS. The following drinking water related changes were assessed: Change 1 (adults); a municipality with a groundwater treatment, changed to a different groundwater source with UV treatment; Change 2 (adults); a municipality with a surface water treatment changed to a groundwater source with UV treatment; and Change 3a (adults) and 3b (children): a municipality with a surface water treatment changed to a new surface water source, having a treatment with a higher pathogen reduction. We observed no evidence that changes in raw water source and/or improved pathogen removal in the drinking water treatment affected the risk of GII among adults. Among children aged 0-9 years participating in Change 3b, we observed a 24% relative risk reduction in GII incidence. These results suggest that improved water treatment may reduce the disease burden of GII in children even in settings in which water treatment efficacy meets current quality standards.

Drinking water consumption patterns among adults-SMS as a novel tool for collection of repeated self-reported water consumption.

Studies have shown that the average drinking water consumption ranges between 0.075 and 3 L/day for adults with both national and regional differences. For exposure assessment of drinking water hazards, country-specific drinking water consumption data including sources of the consumed water may therefore be warranted. To estimate the amount and source of drinking water consumed among adults in Sweden, we collected self-reported estimates using both traditional methods (telephone interviews, web questionnaire) and a novel method (Short Message Service, SMS questionnaires) in a population from an average sized Swedish municipality. Monthly SMS questionnaires were sent out during one year to obtain longitudinal information as well. SMS showed to be a promising tool for collecting self-reported consumption, as most citizens could participate and the method showed high response rate. Data collected via the SMS questionnaire shows an average consumption of cold tap water of 4.9 glasses/24 h (one glass=200 ml), while the average estimates of cold tap water collected by the traditional methods range from 4.5 to 7.0 glasses/24 h. For statistical distributions, the mean daily consumption of cold tap water for the population was best fitted to a gamma distribution. About 70% of the cold tap water is consumed at home. Based on the results from the SMS study, we suggest using 1 l/day for the average adult population and 2.5 l/day for high consumers for risk assessment of cold tap water consumption. As 46% of the tap water consumed is heated, we suggest using 1.85 l/day for total tap water consumption.

Assessment of drinking water quality at the tap using fluorescence spectroscopy.

Treated drinking water may become contaminated while travelling in the distribution system on the way to consumers. Elevated dissolved organic matter (DOM) at the tap relative to the water leaving the treatment plant is a potential indicator of contamination, and can be measured sensitively, inexpensively and potentially on-line via fluorescence and absorbance spectroscopy. Detecting elevated DOM requires potential contamination events to be distinguished from natural fluctuations in the system, but how much natural variation to expect in a stable distribution system is unknown. In this study, relationships between DOM optical properties, microbial indicator organisms and trace elements were investigated for households connected to a biologically-stable drinking water distribution system. Across the network, humic-like fluorescence intensities showed limited variation (RSD = 3.5-4.4%), with half of measured variation explained by interactions with copper. After accounting for quenching by copper, fluorescence provided a very stable background signal (RSD < 2.2%) against which a ∼2% infiltration of soil water would be detectable. Smaller infiltrations would be detectable in the case of contamination by sewage with a strong tryptophan-like fluorescence signal. These findings indicate that DOM fluorescence is a sensitive indicator of water quality changes in drinking water networks, as long as potential interferents are taken into account.

Gastrointestinal illness linked to incidents in drinking water distribution networks in Sweden.

During recent years, knowledge gaps on drinking water-related gastrointestinal illness have been identified, especially for non-epidemic cases. Pathogen contamination of drinking water during distribution has been suggested to contribute to these cases, but the risk factors are not yet fully understood. During 2014-2015, we conducted an epidemiological study in five municipalities in Sweden, to assess whether incidents in the drinking water distribution system influence the risk of gastrointestinal illness. Telephone interviews were conducted in the affected areas and in reference areas 7-14 days after a reported incident. Symptoms of gastrointestinal illness occurring during the period were documented for each household member. The results showed a significantly elevated risk of vomiting and acute gastrointestinal illness (AGI) in the affected areas, compared to the reference areas (ORvom. = 2.0, 95% CI: 1.2-3.3; ORAGI = 1.9, 95% CI: 1.2-3.0). Certain conditions, or risk factors, during the incidents, such as sewage and drinking water pipelines at the same level in the trench, were associated with an elevated risk of AGI and vomiting. Safety measures taken during repair work, like flushing, were also associated with an elevated risk of AGI and vomiting. These results show that incidents in the drinking water distribution network contribute to endemic gastrointestinal illness, especially AGI and vomiting, and that external pathogen contamination of the drinking water is a likely cause of these cases of gastrointestinal illness. The results also indicate that safety measures used today may not be sufficient for eliminating the risk of gastrointestinal illness.

Measuring sporadic gastrointestinal illness associated with drinking water - an overview of methodologies.

There is an increasing awareness that drinking water contributes to sporadic gastrointestinal illness (GI) in high income countries of the northern hemisphere. A literature search was conducted in order to review: (1) methods used for investigating the effects of public drinking water on GI; (2) evidence of possible dose-response relationship between sporadic GI and drinking water consumption; and (3) association between sporadic GI and factors affecting drinking water quality. Seventy-four articles were selected, key findings and information gaps were identified. In-home intervention studies have only been conducted in areas using surface water sources and intervention studies in communities supplied by ground water are therefore needed. Community-wide intervention studies may constitute a cost-effective alternative to in-home intervention studies. Proxy data that correlate with GI in the community can be used for detecting changes in the incidence of GI. Proxy data can, however, not be used for measuring the prevalence of illness. Local conditions affecting water safety may vary greatly, making direct comparisons between studies difficult unless sufficient knowledge about these conditions is acquired. Drinking water in high-income countries contributes to endemic levels of GI and there are public health benefits for further improvements of drinking water safety.

Efficacy of water treatment processes and endemic gastrointestinal illness - A multi-city study in Sweden.

Outbreaks of acute gastrointestinal illnesses (AGI) have been linked to insufficient drinking water treatment on numerous occasions in the industrialized world, but it is largely unknown to what extent public drinking water influences the endemic level of AGI. This paper aimed to examine endemic AGI and the relationship with pathogen elimination efficacy in public drinking water treatment processes. For this reason, time series data of all telephone calls to the Swedish National Healthcare Guide between November 2007 and February 2014 from twenty Swedish cities were obtained. Calls concerning vomiting, diarrhea or abdominal pain (AGI calls) were separated from other concerns (non-AGI calls). Information on which type of microbial barriers each drinking water treatment plant in these cities have been used were obtained, together with the barriers' theoretical pathogen log reduction efficacy. The total log reduction in the drinking water plants varied between 0.0 and 6.1 units for viruses, 0.0-14.6 units for bacteria and 0.0-7.3 units regarding protozoans. To achieve one general efficacy parameter for each plant, a weighted mean value of the log reductions (WLR) was calculated, with the weights based on how commonly these pathogen groups cause AGI. The WLR in the plants varied between 0.0 and 6.4 units. The effect of different pathogen elimination efficacy on levels of AGI calls relative non-AGI calls was evaluated in regression models, controlling for long term trends, population size, age distribution, and climatological area. Populations receiving drinking water produced with higher total log reduction was associated with a lower relative number of AGI calls. In overall, AGI calls decreased by 4% (OR = 0.96, CI: 0.96-0.97) for each unit increase in the WLR. The findings apply to both groundwater and surface water study sites, but are particularly evident among surface water sites during seasons when viruses are the main cause of AGI. This study proposes that the endemic level of gastroenteritis can indeed be reduced with more advanced treatment processes at many municipal drinking water treatment plants.

Public health burden due to infections by verocytotoxin-producing Escherichia coli (VTEC) and Campylobacter spp. as estimated by cost of illness and different approaches to model disability-adjusted life years.

AIMS: To estimate disability-adjusted life years (DALY) and cost of illness (COI) associated with the gastrointestinal bacterial pathogens Campylobacter and verocytotoxin-producing Escherichia coli (VTEC) in Sweden and to investigate the impact of variability in health outcomes, data availability, and different assumptions about underreporting on DALY. METHODS: Data from the Swedish notification system, public databases, and the literature were used to estimate COI and DALY. DALY was modelled using a deterministic and a stochastic approach, the latter describing variation in health outcomes between individuals. Effects of different assumptions about underreporting of gastroenteritis were evaluated in separate scenarios. RESULTS: COI and DALY were greater for Campylobacter than for VTEC. Years of life lost due to haemolytic uraemic syndrome and years lived with gastroenteritis constituted most of DALY for VTEC and Campylobacter, respectively. Productivity losses due to gastroenteritis constituted the main cost associated with both pathogens. Degree of underreporting had a greater impact on DALY for Campylobacter, due to higher estimated incidence of gastroenteritis associated with campylobacteriosis. CONCLUSIONS: Pathogen-specific health outcomes and data quality may influence the preferred modelling approach. There was a fair agreement between modelling approaches, but the stochastic model reflected the contribution of some rare health outcomes not captured in the deterministic model. Health outcomes excluded due to lack of data lead to an underestimation of the total burden associated with the pathogens. Increased knowledge, especially on the degree of underreporting and the contribution of the pathogens to sequelae, is needed to further improve public health burden estimates for these pathogens in Sweden.

Modeling gene associations for virulence classification of verocytotoxin-producing E. coli (VTEC) from patients and beef.

An evaluation of 22 EHEC genes was carried out for virulence classification of VTEC. The data consisted of 116 patient isolates and 42 beef isolates. The symptoms among patients ranged from mild (diarrhea) to severe (bloody diarrhea and HUS). A cluster of genes-efa1, eae, ecf4, paa, and ureC-were more frequent in patient isolates than beef isolates. They also contributed to the classification of high virulence isolates compared with low virulence isolates. These genes may together constitute a general virulence factor, being also associated with well-known virulence serogroups: O157, O26, O103, O111, O145, O121, and O118. In a regression model of patient versus beef isolates, the combined presence of efa1 and paa proved a particularly efficient indicator of patient isolates (OR: 32.9). In contrast, a single gene, vtx22 (subtype vtx2 of vtx2) was a relatively efficient predictor of high virulence among patient isolates (OR: 41.6), but not of virulence in general. Significant interaction effects observed between genes need to be addressed and clarified in future studies.

Community analysis of arbuscular mycorrhizal fungi and bacteria in the maize mycorrhizosphere in a long-term fertilization trial.

In this study, we investigated the impact of organic and mineral fertilizers on the community composition of arbuscular mycorrhizal (AM) fungi and bacteria in the mycorrhizosphere of maize in a field experiment established in 1956, in south-east Sweden. Roots and root-associated soil aggregates were sampled four times during the growing season in 2005, in control plots and in plots amended with calcium nitrate, ammonium sulphate, green manure, farmyard manure or sewage sludge. Fungi in roots were identified by cloning and sequencing, and bacteria in soil aggregates were analysed by terminal-restriction fragment length polymorphism, cloning and sequencing. The community composition of AM fungi and bacteria was significantly influenced by the different fertilizers. Changes in microbial community composition were mainly correlated with changes in pH induced by the fertilization regime. However, other factors, including phosphate and soil carbon content, also contributed significantly to these changes. Changes in bacterial community composition and a reduction in bacterial taxon richness throughout the growing season were also manifest. The results of this study highlight the importance and significant effects of the long-term application of different fertilizers on edaphic factors and specific groups of fungi and bacteria playing a key role in arable soils.

Influence of arbuscular mycorrhizal mycelial exudates on soil bacterial growth and community structure.

Plant root systems colonized by arbuscular mycorrhizal (AM) fungi have previously been shown to influence soil bacterial populations; however, the direct influence of the AM extraradical mycelium itself on bacterial growth and community composition is not well understood. In this study, we investigated the effects of exudates produced by AM extraradical mycelia on the growth and development of an extracted soil bacterial community in vitro. The chemical composition of the mycelial exudates was analysed using proton nuclear magnetic resonance spectrometry. Following the addition of exudates to a bacterial community extracted from soil, bacterial growth and vitality were determined using a bacterial vitality stain and fluorescence microscopy. Changes in community composition were also analysed at various times over the course of 3 days by terminal restriction fragment length polymorphism analysis, in combination with cloning and sequencing of 16S rRNA genes. Mycelial exudates increased bacterial growth and vitality and changed bacterial community composition. Several Gammaproteobacteria, including a taxon within the Enterobacteriaceae, increased in frequency of occurrence in response to AM mycelial exudates. This study is the first attempt to identify carbohydrates from the extraradical mycelium of an AM fungus, and demonstrates the direct effects of mycelial exudates on a soil bacterial community.

Species composition of an ectomycorrhizal fungal community along a local nutrient gradient in a boreal forest.

Soil abiotic factors are considered to be important in determining the distribution of ectomycorrhizal (ECM) fungal species; however, there are few field data to support this. Here, we relate ECM species distributions to changes in soil chemistry along a short (90-m), natural nutrient gradient. The ECM community was characterized, using morphological and molecular techniques, in soil samples collected at 10-m intervals. There were pronounced changes in ECM fungal community structure along the transect, with many taxa showing discrete distributions. Although there was a change of host from Pinus to Picea along the gradient, host-specific fungi did not account for the observed change in community structure. Ordination analyses showed that community structure was strongly correlated with soil characteristics, in particular extractable ammonium and base saturation. However, autocorrelation among soil parameters makes it difficult to isolate the effects of individual parameters. The distinctive changes in soil and vegetation along the transect used in this study provided an exceptional opportunity to examine the local-scale impact of natural spatial heterogeneity on an ECM fungal community.

Attachment of different soil bacteria to arbuscular mycorrhizal fungal extraradical hyphae is determined by hyphal vitality and fungal species.

Attachment of certain bacteria to living arbuscular mycorrhizal fungal extraradical hyphae may be an important prerequisite for interactions between these microorganisms, with implications for nutrient supply and plant health. The attachment of five different strains of gfp-tagged soil bacteria (Paenibacillus brasilensis PB177 (pnf8), Bacillus cereus VA1 (pnf8), Pseudomonas fluorescens SBW25 :: gfp/lux, Arthrobacter chlorophenolicus A6G, and Paenibacillus peoriae BD62 (pnf8)) to vital and nonvital extraradical hyphae of the arbuscular mycorrhizal fungi Glomus sp. MUCL 43205 and Glomus intraradices MUCL 43194 was examined. Arthrobacter chlorophenolicus did not attach to hyphae, whereas the other bacterial strains did to a varying degree. Only P. brasilensis showed greater attachment to vital hyphae than nonvital hyphae of both Glomus species tested. Pseudomonas fluorescens showed a higher attachment to vital compared with nonvital Glomus sp. MUCL 43205 hyphae, whereas this relationship was opposite for attachment to G. intraradices. Both B. cereus and P. peoriae showed higher attachment to nonvital hyphae. This study provides novel evidence that under laboratory conditions soil bacteria differ in their ability to colonize vital and nonvital hyphae and that this can also be influenced by the arbuscular mycorrhizal fungal species involved. The significance of bacterial attachment to mycorrhizal fungal extraradical hyphae is discussed.