Agrochemicals indirectly increase survival of E. coli O157:H7 and indicator bacteria by reducing ecosystem services

Soil microbial community fragmentation reveals indirect effects of fungicide exposure mediated by biotic interactions between microorganisms

Fungicides are used worldwide to improve crop yields, but they can affect non-target soil microorganisms which are essential for ecosystem functioning. Microorganisms form complex communities characterized by a myriad of interspecies interactions, yet it remains unclear to what extent non-target microorganisms are indirectly affected by fungicides through biotic interactions with sensitive taxa. To quantify such indirect effects, we fragmented a soil microbial community by filtration to alter biotic interactions and compared the effect of the fungicide hymexazol between fractions in soil microcosms. We postulated that OTUs which are indirectly affected would exhibit a different response to the fungicide across the fragmented communities. We found that hymexazol primarily affected bacterial and fungal communities through indirect effects, which were responsible for more than 75% of the shifts in relative abundance of the dominant microbial OTUs after exposure to an agronomic dose of hymexazol. However, these indirect effects decreased for the bacterial community when hymexazol doses increased. Our results also suggest that N-cycling processes such as ammonia oxidation can be impacted indirectly by fungicide application. This work sheds light on the indirect impact of fungicide exposure on soil microorganisms through biotic interactions, which underscores the need for higher-tier risk assessment. ENVIRONMENTAL IMPLICATION: In this study, we used a novel approach based on the fragmentation of the soil microbial community to determine to which extent fungicide application could indirectly affect fungi and bacteria through biotic interactions. To assess off-target effects of fungicide on soil microorganisms, we selected hymexazol, which is used worldwide to control a variety of fungal plant pathogens, and exposed arable soil to the recommended field rate, as well as to higher rates. Our findings show that at least 75% of hymexazol-impacted microbial OTUs were indirectly affected, therefore emphasizing the importance of tiered risk assessment.

Enterococci pathways to coastal waters and implications of sea level rise

Highly urban coastal communities in low lying areas and with high water tables are vulnerable to sea-level rise and to corresponding increases in coastal groundwater levels. Stormwater conveyance systems are under increased risk. Rising groundwater levels affect the hydraulics of the stormwater system thereby increasing contaminant transport, for example the fecal indicator bacteria enterococci, to coastal waters. This study offers a unique opportunity to evaluate the impacts of increased contaminant transport on marine coastal environments. Here we assessed historic and recent coastal water quality, stormwater sampling data, groundwater monitoring and tidal elevations near the coastline, in the context of altered hydraulics within the system. Two pathways of enterococci to marine waters were identified. Direct discharge of contaminated stormwater runoff via the stormwater outfalls and tidally driven contaminated groundwater discharge. As sea level continues to rise, we hypothesize that a diminished unsaturated zone coupled with altered hydraulic conditions at the coastal groundwater zone will facilitate the transport of enterococci from urban sediments to the study site (Park View Waterway in Miami Beach, FL USA). We recommend improvements to the stormwater conveyance system, and maintenance of the sanitary sewer system to mitigate these impacts and minimize transport of enterococci, and other stormwater pollutants to coastal waters. The results of this study can be useful to interpret high enterococci levels in low lying coastal areas where groundwater is influenced by rising sea water levels.

Unraveling the effect of land use on the bacterioplankton community composition from highly impacted shallow lakes at a regional scale

Bacterioplankton communities play a crucial role in global biogeochemical processes and are highly sensitive to changes induced by natural and anthropogenic stressors in aquatic ecosystems. We assessed the influence of Land Use Land Cover (LULC), environmental, and geographic changes on the bacterioplankton structure in highly connected and impacted shallow lakes within the Salado River basin, Buenos Aires, Argentina. Additionally, we investigated how changes in LULC affected the limnological characteristics of these lakes at a regional scale. Our analysis revealed that the lakes were ordinated by sub-basins (upper and lower) depending on their LULC characteristics and limnological properties. In coincidence, the same ordination was observed when considering the Bacterioplankton Community Composition (BCC). Spatial and environmental predictors significantly explained the variation in BCC, although when combined with LULC the effect was also important. While the pure LULC effect did not explain a significant percentage of BCC variation, the presence of atrazine in water, an anthropogenic variable linked to LULC, directly influenced both the BCC and some Amplicon Sequence Variants (ASVs) in particular. Our regional-scale approach contributes to understanding the complexity of factors driving bacterioplankton structure and how LULC pervasively affect these communities in highly impacted shallow lake ecosystems from the understudied Southern Hemisphere.

From ecological functions to ecosystem services: linking coastal lagoons biodiversity with human well-being

In this review we highlight the relevance of biodiversity that inhabit coastal lagoons, emphasizing how species functions foster processes and services associated with this ecosystem. We identified 26 ecosystem services underpinned by ecological functions performed by bacteria and other microbial organisms, zooplankton, polychaetae worms, mollusks, macro-crustaceans, fishes, birds, and aquatic mammals. These groups present high functional redundancy but perform complementary functions that result in distinct ecosystem processes. Because coastal lagoons are located in the interface between freshwater, marine and terrestrial ecosystems, the ecosystem services provided by the biodiversity surpass the lagoon itself and benefit society in a wider spatial and historical context. The species loss in coastal lagoons due to multiple human-driven impacts affects the ecosystem functioning, influencing negatively the provision of all categories of services (i.e., supporting, regulating, provisioning and cultural). Because animals' assemblages have unequal spatial and temporal distribution in coastal lagoons, it is necessary to adopt ecosystem-level management plans to protect habitat heterogeneity and its biodiversity, ensuring the provision of services for human well-being to multi-actors in the coastal zone.

Decoupling pollution-agricultural growth and predicting climate change impacts on decoupling index using Bayesian network in different climatic regions

Applying the principles of healthy products through agriculture practices has become an important issue due to significant environmental impacts of agrochemicals application. The agrochemicals have been recognized as an essential component of modern agriculture, but they are also an important source of environmental pollution that threatens the human's health and are main sources of carbon emissions. Pesticides and fertilizers application are important in the process of Iran's food production. In Iran, intensifying the agricultural production has led to overuse of chemical fertilizers and pesticides. This work is the first effort to quantify and compare the decoupling index pollution from agricultural sector using Tapio decoupling indicator and predict climate change impacts on this index by using Bayesian network across the whole country of Iran. For this purpose, required annual data of predictor variables for the period of 2008 to 2018 was used to calculate the decoupling index. For projecting climate change impacts on this index by using Bayesian network, monthly mean values of climatic variables were used. While Iranian farmers are criticized for pesticide overuse, these study findings showed that during the period of 2008-2018, decoupling index for pesticides (agricultural pollution by using pesticide) and decoupling index for fertilizer (agricultural pollution by using fertilizer) in the selected provinces fluctuate between RD-SD, SD-SD, SD-SD, and RD-SD. Therefore, the decoupling states show that in most study years, there is a strong decoupling of agricultural growth in selected provinces. This means that in the selected provinces, pollutant emissions of chemical fertilizer and pesticides use for agricultural productions have decreased and it has been well controlled. Therefore, by expansion of agricultural sector, the situation of agricultural pollution in these provinces in most years has not been intensified. Control of agricultural pollution in these provinces has shown a positive and significant impact on public health. In selected provinces, the cleaner agricultural products and application of organic fertilizers have been increased. This study results also showed that the climate change will accelerate increment of pests population and thus pesticides application in different climatic regions.

Role of soil in the regulation of human and plant pathogens: soils' contributions to people

Soil and soil biodiversity play critical roles in Nature's Contributions to People (NCP) # 10, defined as Nature's ability to regulate direct detrimental effects on humans, and on human-important plants and animals, through the control or regulation of particular organisms considered to be harmful. We provide an overview of pathogens in soil, focusing on human and crop pathogens, and discuss general strategies, and examples, of how soils' extraordinarily diverse microbial communities regulate soil-borne pathogens. We review the ecological principles underpinning the regulation of soil pathogens, as well as relationships between pathogen suppression and soil health. Mechanisms and specific examples are presented of how soil and soil biota are involved in regulating pathogens of humans and plants. We evaluate how specific agricultural management practices can either promote or interfere with soil's ability to regulate pathogens. Finally, we conclude with how integrating soil, plant, animal and human health through a 'One Health' framework could lead to more integrated, efficient and multifunctional strategies for regulating detrimental organisms and processes. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.

The Atrazine Saga and its Importance to the Future of Toxicology, Science, and Environmental and Human Health

The herbicide atrazine is one of the most commonly used, well studied, and controversial pesticides on the planet. Much of the controversy involves the effects of atrazine on wildlife, particularly amphibians, and the ethically questionable decision making of members of industry, government, the legal system, and institutions of higher education, in most cases in an effort to "bend science," defined as manipulating research to advance economic, political, or ideological ends. In this Critical Perspective I provide a timeline of the most salient events in the history of the atrazine saga, which includes a multimillion-dollar smear campaign, lawsuits, investigative reporting, accusation of impropriety against the US Environmental Protection Agency, and a multibillion-dollar transaction. I argue that the atrazine controversy must be more than just a true story of cover-ups, bias, and vengeance. It must be used as an example of how manufacturing uncertainty and bending science can be exploited to delay undesired regulatory decisions and how greed and conflicts of interest-situations where personal or organizational considerations have compromised or biased professional judgment and objectivity-can affect environmental and public health and erode trust in the discipline of toxicology, science in general, and the honorable functioning of societies. Most importantly, I offer several recommendations that should help to 1) prevent the history of atrazine from repeating itself, 2) enhance the credibility and integrity of science, and 3) enrich human and environmental health. Environ Toxicol Chem 2021;40:1544-1558. © 2021 SETAC.

Influence of soil microbes on Escherichia coli O157:H7 survival in soil rinse and artificial soil

AIMS

This research investigated the influence of soil microbiota on Escherichia coli O157:H7 survival in soil rinse and artificial soil. Additionally, the influence of selected soil bacteria on E. coli O157:H7 in soil environments was determined.

METHODS AND RESULTS

Escherichia coli O157:H7 counts (log CFU per ml or g^-1 ) were determined by spread plating: (i) artificial soil amended with soil rinse (filter-sterilized and unfiltered) at 30°C; (ii) unfiltered soil rinse (50 ml) treated with cycloheximide (200 μg ml^-1 ), vancomycin (40 μg ml^-1 ), heat (80°C, 15 min) and no treatment (control) for 7 days at 30°C and (iii) filtered soil rinse with selected soil bacterial isolates over 7 days. There was a significant difference (P = 0·027) in E. coli O157:H7 counts after 35 days between artificial soils amended with filtered (4·45 ± 0·29) and non-filtered (1·83 ± 0·33) soil rinse. There were significant differences (P < 0·05) in E. coli O157:H7 counts after 3 days of incubation between soil rinse treatments (heat (7·04 ± 0·03), cycloheximide (6·94 ± 0·05), vancomycin (4·26 ± 0·98) and control (5·00 ± 0·93)). Lastly, a significant difference (P < 0·05) in E. coli O157:H7 counts was observed after 3 days of incubation at 30°C in filtered soil rinse when incubated with Paenibacillus alvei versus other soil bacterial isolates evaluated.

CONCLUSIONS

Soil microbiota isolated from Florida sandy soil influenced E. coli O157:H7 survival. Specifically, P. alvei reduced E. coli O157:H7 by over 3 log CFU per ml after 3 days of incubation at 30°C in filtered soil rinse.

SIGNIFICANCE AND IMPACT OF THE STUDY

This research identified soil bacterial isolates that may reduce E. coli O157:H7 in the soil environment and be used in future biocontrol applications.

The response of nitrogen cycling and bacterial communities to E. coli invasion in aquatic environments with submerged vegetation

The effects of exogenous Escherichia coli on nitrogen cycling (N-cycling) in freshwater remains unclear. Thus, seven ecosystems, six with submerged plants-Potamogeton crispus (PC) and Myriophyllum aquaticum (MA)-and one with no plants were set up. Habitats were assessed before and after E. coli addition (10⁷ colony-forming units/mL). E. coli colonization of freshwater ecosystems had significant effects on bacterial community structure in plant surface biofilms and surface sediments (ANOVA, P < 0.05). It reduced the relative abundance of nitrosification bacteria (-70.94 ± 26.17%) and nitrifiers (-47.86 ± 23.68%) in biofilms which lead to significant reduction of ammoxidation in water (P < 0.05). The N-cycling intensity from PC systems was affected more strongly by E. coli than were MA systems. Furthermore, the coupling coefficient of exogenous E. coli to indigenous N-cycling bacteria in sediments (6.061, average connectivity degree) was significantly weaker than that in biofilms (9.852). Additionally, at the genus level, E. coli were most-closely associated with N-cycling bacteria such as Prosthecobacter, Hydrogenophaga, and Bacillus in sediments and biofilms according to co-occurrence bacterial network (Spearman). E. coli directly changed their abundance, so that the variability of species composition of N-cycling bacterial taxa was triggered, as well. Overall, exogenous E. coli repressed ammoxidation, but promoted ammonification and denitrification. Our results provided new insights into how pathogens influence the nitrogen cycle in freshwater ecosystems.

Effect of difenoconazole fungicide on physiological responses and ultrastructural modifications in model organism Tetrahymena pyriformis

The continuous and extensive use of pesticides, particularly in the field of agriculture, leads to contamination of all ecosystems (water, soil, and atmosphere). Among pesticides, fungicides constitute a larger group whose impact on the environment are still poorly studied. Difenoconazole belongs to triazole group of fungicides having high photochemical stability and have low biodegradability, which makes them persistent in water bodies. The present study focuses on the physiological and cytotoxic impact of difenoconazole fungicide on ciliated protozoa, Tetrahymena pyriformis with reference to growth, morphology, behaviour and its generation time. Morphological studies showed changes in the shape and size of T. pyriformis. Our result showed an inhibitory effect on population growth of T. pyriformis and the IC₅₀ concentration was found to be 6.8 μg mL^-1.The numbers of generations decreased and generation time was found to be extended in a concentration and time dependent manner. Difenoconazole caused significant depletion in phagocytic activity and also ultra-structural changes were observed by Transmission electron microscopy (TEM) analysis. The results indicate that the Tetrahymena toxicity assay could be used as a complementary system to rapidly elucidate the cytotoxic potential of fungicide.

Fertilizer Use in China: The Role of Agricultural Support Policies

Using a decomposition method, this paper proposes an analytical framework to investigate the mechanisms by which agricultural support policies affect farmers’ use of fertilizers in agriculture in China. The mechanisms are decomposed into “three effects” (structural, scale, and technological effects). It is found that China’s agricultural support polices have significantly contributed to the increased use of agricultural fertilizers through encouraging farmers to bring more land under cultivation (the scale effect). Meanwhile, some policies have also helped reduce fertilizer consumption when farmers were motivated to increase the area of grains crops (the structural effect). The role of technological progress in affecting fertilizer consumption (the technological effect) appears to be minimal and uncertain. Compared to direct subsidies, indirect subsidies play a much greater role in affecting farmers’ production decision making and are more environmentally consequential. This paper argues that some of China’s agricultural support policies are not well aligned with one key objective of the country’s rural policies—improving environmental sustainability. It is recommended that the government takes measures to reform agricultural support policies and to reconcile agricultural and rural policies in order to achieve sustainable rural development.

Emerging human infectious diseases and the links to global food production

Infectious diseases are emerging globally at an unprecedented rate while global food demand is projected to increase sharply by 2100. Here, we synthesize the pathways by which projected agricultural expansion and intensification will influence human infectious diseases and how human infectious diseases might likewise affect food production and distribution. Feeding 11 billion people will require substantial increases in crop and animal production that will expand agricultural use of antibiotics, water, pesticides and fertilizer, and contact rates between humans and both wild and domestic animals, all with consequences for the emergence and spread of infectious agents. Indeed, our synthesis of the literature suggests that, since 1940, agricultural drivers were associated with >25% of all - and >50% of zoonotic - infectious diseases that emerged in humans, proportions that will likely increase as agriculture expands and intensifies. We identify agricultural and disease management and policy actions, and additional research, needed to address the public health challenge posed by feeding 11 billion people.

Fungicides: An Overlooked Pesticide Class?

Fungicides are indispensable to global food security and their use is forecasted to intensify. Fungicides can reach aquatic ecosystems and occur in surface water bodies in agricultural catchments throughout the entire growing season due to their frequent, prophylactic application. However, in comparison to herbicides and insecticides, the exposure to and effects of fungicides have received less attention. We provide an overview of the risk of fungicides to aquatic ecosystems covering fungicide exposure (i.e., environmental fate, exposure modeling, and mitigation measures) as well as direct and indirect effects of fungicides on microorganisms, macrophytes, invertebrates, and vertebrates. We show that fungicides occur widely in aquatic systems, that the accuracy of predicted environmental concentrations is debatable, and that fungicide exposure can be effectively mitigated. We additionally demonstrate that fungicides can be highly toxic to a broad range of organisms and can pose a risk to aquatic biota. Finally, we outline central research gaps that currently challenge our ability to predict fungicide exposure and effects, promising research avenues, and shortcomings of the current environmental risk assessment for fungicides.

A pesticide paradox: fungicides indirectly increase fungal infections

There are many examples where the use of chemicals have had profound unintended consequences, such as fertilizers reducing crop yields (paradox of enrichment) and insecticides increasing insect pests (by reducing natural biocontrol). Recently, the application of agrochemicals, such as agricultural disinfectants and fungicides, has been explored as an approach to curb the pathogenic fungus, Batrachochytrium dendrobatidis (Bd), which is associated with worldwide amphibian declines. However, the long-term, net effects of early-life exposure to these chemicals on amphibian disease risk have not been thoroughly investigated. Using a combination of laboratory experiments and analysis of data from the literature, we explored the effects of fungicide exposure on Bd infections in two frog species. Extremely low concentrations of the fungicides azoxystrobin, chlorothalonil, and mancozeb were directly toxic to Bd in culture. However, estimated environmental concentrations of the fungicides did not reduce Bd on Cuban tree frog (Osteopilus septentrionalis) tadpoles exposed simultaneously to any of these fungicides and Bd, and fungicide exposure actually increased Bd-induced mortality. Additionally, exposure to any of these fungicides as tadpoles resulted in higher Bd abundance and greater Bd-induced mortality when challenged with Bd post-metamorphosis, an average of 71 d after their last fungicide exposure. Analysis of data from the literature revealed that previous exposure to the fungicide itraconazole, which is commonly used to clear Bd infections, made the critically endangered booroolong frog (Litoria booroolongensis) more susceptible to Bd. Finally, a field survey revealed that Bd prevalence was positively associated with concentrations of fungicides in ponds. Although fungicides show promise for controlling Bd, these results suggest that, if fungicides do not completely eliminate Bd or if Bd recolonizes, exposure to fungicides has the potential to do more harm than good. To ensure that fungicide applications have the intended consequence of curbing amphibian declines, researchers must identify which fungicides do not compromise the pathogen resistance mechanisms of amphibians.

The pros and cons of ecological risk assessment based on data from different levels of biological organization

Ecological risk assessment (ERA) is the process used to evaluate the safety of manufactured chemicals to the environment. Here we review the pros and cons of ERA across levels of biological organization, including suborganismal (e.g., biomarkers), individual, population, community, ecosystem and landscapes levels. Our review revealed that level of biological organization is often related negatively with ease at assessing cause-effect relationships, ease of high-throughput screening of large numbers of chemicals (it is especially easier for suborganismal endpoints), and uncertainty of the ERA because low levels of biological organization tend to have a large distance between their measurement (what is quantified) and assessment endpoints (what is to be protected). In contrast, level of biological organization is often related positively with sensitivity to important negative and positive feedbacks and context dependencies within biological systems, and ease at capturing recovery from adverse contaminant effects. Some endpoints did not show obvious trends across levels of biological organization, such as the use of vertebrate animals in chemical testing and ease at screening large numbers of species, and other factors lacked sufficient data across levels of biological organization, such as repeatability, variability, cost per study and cost per species of effects assessment, the latter of which might be a more defensible way to compare costs of ERAs than cost per study. To compensate for weaknesses of ERA at any particular level of biological organization, we also review mathematical modeling approaches commonly used to extrapolate effects across levels of organization. Finally, we provide recommendations for next generation ERA, submitting that if there is an ideal level of biological organization to conduct ERA, it will only emerge if ERA is approached simultaneously from the bottom of biological organization up as well as from the top down, all while employing mathematical modeling approaches where possible to enhance ERA. Because top-down ERA is unconventional, we also offer some suggestions for how it might be implemented efficaciously. We hope this review helps researchers in the field of ERA fill key information gaps and helps risk assessors identify the best levels of biological organization to conduct ERAs with differing goals.

The Interplay Between Predation, Competition, and Nutrient Levels Influences the Survival of Escherichia coli in Aquatic Environments

Nutrient levels, competition from autochthonous microorganisms, and protozoan predation may all influence survival of fecal microorganisms as they transition from the gastrointestinal tract to aquatic habitats. Although Escherichia coli is an important indicator of waterborne pathogens, the effects of environmental stressors on its survival in aquatic environments remain poorly understood. We manipulated organic nutrient, predation, and competition levels in outdoor microcosms containing natural river water, sediments, and microbial populations to determine their relative contribution to E. coli survival. The activities of predator (protozoa) and competitor (indigenous bacteria) populations were inhibited by adding cycloheximide or kanamycin. We developed a statistical model of E. coli density over time that fits with the data under all experimental conditions. Predation and competition had significant negative effects on E. coli survival, while higher nutrient levels increased survival. Among the main effects, predation accounted for the greatest variation (40 %) compared with nutrients (25 %) or competition (15 %). The highest nutrient level mitigated the effect of predation on E. coli survival. Thus, elevated organic nutrients may disproportionately enhance the survival of E. coli, and potentially that of other enteric bacteria, in aquatic habitats.

The herbicide atrazine induces hyperactivity and compromises tadpole detection of predator chemical cues

The ability to detect chemical cues is often critical for freshwater organisms to avoid predation and find food and mates. In particular, reduced activity and avoidance of chemical cues signaling predation risk are generally adaptive behaviors that reduce prey encounter rates with predators. The present study examined the effects of the common herbicide atrazine on the ability of Cuban tree frog (Osteopilus septentrionalis) tadpoles to detect and respond to chemical cues from larval dragonfly (Libellulidae sp.) predators. Tadpoles exposed to an estimated environmental concentration of atrazine (calculated using US Environmental Protection Agency software; measured concentration, 178 μg/L) were significantly hyperactive relative to those exposed to solvent control. In addition, control tadpoles significantly avoided predator chemical cues, but tadpoles exposed to atrazine did not. These results are consistent with previous studies that have demonstrated that ecologically relevant concentrations of atrazine can induce hyperactivity and impair the olfactory abilities of other freshwater vertebrates. The authors call for additional studies examining the role of chemical contaminants in disrupting chemical communication and the quantification of subsequent impacts on the fitness and population dynamics of wildlife. Environ Toxicol Chem 2016;35:2239-2244. © 2016 SETAC.

A synthesis of the effects of pesticides on microbial persistence in aquatic ecosystems

Pesticides have a pervasive presence in aquatic ecosystems throughout the world. While pesticides are intended to control fungi, insects, and other pests, their mechanisms of action are often not specific enough to prevent unintended effects, such as on non-target microbial populations. Microorganisms, including algae and cyanobacteria, protozoa, aquatic fungi, and bacteria, form the basis of many food webs and are responsible for crucial aspects of biogeochemical cycling; therefore, the potential for pesticides to alter microbial community structures must be understood to preserve ecosystem services. This review examines studies that focused on direct population-level effects and indirect community-level effects of pesticides on microorganisms. Generally, insecticides, herbicides, and fungicides were found to have adverse direct effects on algal and fungal species. Insecticides and fungicides also had deleterious direct effects in the majority of studies examining protozoa species, although herbicides were found to have inconsistent direct effects on protozoans. Our synthesis revealed mixed or no direct effects on bacterial species among all pesticide categories, with results highly dependent on the target species, chemical, and concentration used in the study. Examination of community-level, indirect effects revealed that all pesticide categories had a tendency to reduce higher trophic levels, thereby diminishing top-down pressures and favoring lower trophic levels. Often, indirect effects exerted greater influence than direct effects. However, few studies have been conducted to specifically address community-level effects of pesticides on microorganisms, and further research is necessary to better understand and predict the net effects of pesticides on ecosystem health.

Comanaging fresh produce for nature conservation and food safety

In 2006, a deadly Escherichia coli O157:H7 outbreak in bagged spinach was traced to California's Central Coast region, where >70% of the salad vegetables sold in the United States are produced. Although no definitive cause for the outbreak could be determined, wildlife was implicated as a disease vector. Growers were subsequently pressured to minimize the intrusion of wildlife onto their farm fields by removing surrounding noncrop vegetation. How vegetation removal actually affects foodborne pathogens remains unknown, however. We combined a fine-scale land use map with three datasets comprising ∼250,000 enterohemorrhagic E. coli (EHEC), generic E. coli, and Salmonella tests in produce, irrigation water, and rodents to quantify whether seminatural vegetation surrounding farmland is associated with foodborne pathogen prevalence in California's Central Coast region. We found that EHEC in fresh produce increased by more than an order of magnitude from 2007 to 2013, despite extensive vegetation clearing at farm field margins. Furthermore, although EHEC prevalence in produce was highest on farms near areas suitable for livestock grazing, we found no evidence of increased EHEC, generic E. coli, or Salmonella near nongrazed, seminatural areas. Rather, pathogen prevalence increased the most on farms where noncrop vegetation was removed, calling into question reforms that promote vegetation removal to improve food safety. These results suggest a path forward for comanaging fresh produce farms for food safety and environmental quality, as federal food safety reforms spread across ∼4.5 M acres of US farmland.

LA35 Poultry Fecal Marker Persistence Is Correlated with That of Indicators and Pathogens in Environmental Waters

Disposal of fecally contaminated poultry litter by land application can deliver pathogens and fecal indicator bacteria (FIB) into receiving waters via runoff. While water quality is regulated by FIB enumeration, FIB testing provides inadequate information about contamination source and health risk. This microbial source tracking (MST) study compared the persistence of the Brevibacterium sp. strain LA35 16S rRNA gene (marker) for poultry litter with that of pathogens and FIB under outdoor, environmentally relevant conditions in freshwater, marine water, and sediments over 7 days. Salmonella enterica, Campylobacter jejuni, Campylobacter coli, Bacteroidales, and LA35 were enumerated by quantitative PCR (qPCR), and Enterococcus spp. and E. coli were quantified by culture and qPCR. Unlike the other bacteria, C. jejuni was not detectable after 48 h. Bacterial levels in the water column consistently declined over time and were highly correlated among species. Survival in sediments ranged from a slow decrease over time to growth, particularly in marine microcosms and for Bacteroidales. S. enterica also grew in marine sediments. Linear decay rates in water (k) ranged from -0.17 day(-1) for LA35 to -3.12 day(-1) for C. coli. LA35 levels correlated well with those of other bacteria in the water column but not in sediments. These observations suggest that, particularly in the water column, the fate of LA35 in aquatic environments is similar to that of FIB, C. coli, and Salmonella, supporting the hypothesis that the LA35 marker gene can be a useful tool for evaluating the impact of poultry litter on water quality and human health risk.

Protozoan predation is differentially affected by motility of enteric pathogens in water vs. sediments

Survival of enteric bacteria in aquatic habitats varies depending upon species, strain, and environmental pressures, but the mechanisms governing their fate are poorly understood. Although predation by protozoa is a known, top-down control mechanism on bacterial populations, its influence on the survival of fecal-derived pathogens has not been systematically studied. We hypothesized that motility, a variable trait among pathogens, can influence predation rates and bacterial survival. We compared the survival of two motile pathogens of fecal origin by culturing Escherichia coli O157 and Salmonella enterica Typhimurium. Each species had a motile and non-motile counterpart and was cultured in outdoor microcosms with protozoan predators (Tetrahymena pyriformis) present or absent. Motility had a significant, positive effect on S. enterica levels in water and sediment in the presence or absence of predators. In contrast, motility had a significant negative effect on E. coli O157 levels in sediment, but did not affect water column levels. The presence/absence of protozoa consistently accounted for a greater proportion of the variability in bacterial levels (>95 %) than in bacterial motility (<4 %) in the water column. In sediments, however, motility was more important than predation for both bacteria. Calculations of total CFU/microcosm showed decreasing bacterial concentrations over time under all conditions except for S. enterica in the absence of predation, which increased ∼0.5-1.0 log over 5 days. These findings underscore the complexity of predicting the survival of enteric microorganisms in aquatic habitats, which has implications for the accuracy of risk assessment and modeling of water quality.

Contamination of water resources by pathogenic bacteria

Water-borne pathogen contamination in water resources and related diseases are a major water quality concern throughout the world. Increasing interest in controlling water-borne pathogens in water resources evidenced by a large number of recent publications clearly attests to the need for studies that synthesize knowledge from multiple fields covering comparative aspects of pathogen contamination, and unify them in a single place in order to present and address the problem as a whole. Providing a broader perceptive of pathogen contamination in freshwater (rivers, lakes, reservoirs, groundwater) and saline water (estuaries and coastal waters) resources, this review paper attempts to develop the first comprehensive single source of existing information on pathogen contamination in multiple types of water resources. In addition, a comprehensive discussion describes the challenges associated with using indicator organisms. Potential impacts of water resources development on pathogen contamination as well as challenges that lie ahead for addressing pathogen contamination are also discussed.