Occurrence and persistence of antibiotic resistance genes in river biofilms after wastewater inputs in small rivers

Environmental Concentrations of Sulfonamides Can Alter Bacterial Structure and Induce Diatom Deformities in Freshwater Biofilm Communities

Since the early 1920s, the intensive use of antibiotics has led to the contamination of the aquatic environment through diffuse sources and wastewater effluents. The antibiotics commonly found in surface waters include sulfamethoxazole (SMX) and sulfamethazine (SMZ), which belong to the class of sulfonamides, the oldest antibiotic class still in use. These antibiotics have been detected in all European surface waters with median concentrations of around 50 ng L^–1 and peak concentrations of up to 4–6 μg L^–1. Sulfonamides are known to inhibit bacterial growth by altering microbial production of folic acid, but sub-lethal doses may trigger antimicrobial resistance, with unknown consequences for exposed microbial communities. We investigated the effects of two environmentally relevant concentrations (500 and 5,000 ng L^–1) of SMZ and SMX on microbial activity and structure of periphytic biofilms in stream mesocosms for 28 days. Measurement of sulfonamides in the mesocosms revealed contamination levels of about half the nominal concentrations. Exposure to sulfonamides led to slight, transitory effects on heterotrophic functions, but persistent effects were observed on the bacterial structure. After 4 weeks of exposure, sulfonamides also altered the autotrophs in periphyton and particularly the diversity, viability and cell integrity of the diatom community. The higher concentration of SMX tested decreased both diversity (Shannon index) and evenness of the diatom community. Exposure to SMZ reduced diatom species richness and diversity. The mortality of diatoms in biofilms exposed to sulfonamides was twice that in non-exposed biofilms. SMZ also induced an increase in diatom teratologies from 1.1% in non-exposed biofilms up to 3% in biofilms exposed to SMZ. To our knowledge, this is the first report on the teratological effects of sulfonamides on diatoms within periphyton. The increase of both diatom growth rate and mortality suggests a high renewal of diatoms under sulfonamide exposure. In conclusion, our study shows that sulfonamides can alter microbial community structures and diversity at concentrations currently present in the environment, with unknown consequences for the ecosystem. The experimental set-up presented here emphasizes the interest of using natural communities to increase the ecological realism of ecotoxicological studies and to detect potential toxic effects on non-target species.

Quantifying the occurrence and transformation potential of extracellular polymeric substances (EPS)-associated antibiotic resistance genes in activated sludge

Antibiotic resistance has been regarded as a global concern and biological wastewater treatment plants (WWTPs) are ideal hotbeds for the emergence and propagation of antibiotic resistance genes (ARGs). Extracellular polymeric substances (EPS), one of the primary components of activated sludge, might affect the distribution of extracellular ARGs in supernatant and EPS matrix, and thus alter their uptake potential by microbial cells. Herein, the presence and significance of EPS-associated ARGs in activated sludge from four WWTPs were assessed. Seven typical ARGs (sulI, sulII, bla_TEM-1, tetA, tetO, tetQ, tetW) and class I integron (intI1) in EPS-associated, cell-free, and intracellular DNA were quantified. Results show that the absolute abundances of EPS-associated, cell-free, and intracellular ARGs were 5.90 × 10⁶-6.45 × 10⁹, 5.53 × 10⁴-4.58 × 10⁶, and 2.68 × 10⁸-1.79 × 10¹¹ copies/g-volatile suspended solids, respectively. The absolute abundances of EPS-associated ARGs were 0.2-4.6 orders of magnitude higher than those of the corresponding cell-free ARGs. Considering the higher DNA contents in EPS, the transformation abilities of EPS-associated ARGs were 3.3-236.3 folds higher than those of cell-free ARGs. Therefore, EPS-associated ARGs are an important source of extracellular ARGs, and it may play a crucial role in horizontal gene transfer via transformation in WWTPs.

Micropollutant biotransformation and bioaccumulation in natural stream biofilms

Micropollutants are ubiquitously found in natural surface waters and pose a potential risk to aquatic organisms. Stream biofilms, consisting of bacteria, algae and other microorganisms potentially contribute to bioremediating aquatic environments by biotransforming xenobiotic substances. When investigating the potential of stream biofilms to remove micropollutants from the water column, it is important to distinguish between different fate processes, such as biotransformation, passive sorption and active bioaccumulation. However, due to the complex nature of the biofilm community and its extracellular matrix, this task is often difficult. In this study, we combined biotransformation experiments involving natural stream biofilms collected up- and downstream of wastewater treatment plant outfalls with the QuEChERS extraction method to distinguish between the different fate processes. The QuEChERS extraction proved to be a suitable method for a broad range of micropollutants (> 80% of the investigated compounds). We found that 31 out of 63 compounds were biotransformed by the biofilms, with the majority being substitution-type biotransformations, and that downstream biofilms have an increased biotransformation potential towards specific wastewater-relevant micropollutants. Overall, using the experimental and analytical strategy developed, stream biofilms were demonstrated to have a broad inherent micropollutant biotransformation potential, and to thus contribute to bioremediation and improving ecosystem health.

The Effect of the Effluent from a Small-Scale Conventional Wastewater Treatment Plant Treating Municipal Wastewater on the Composition and Abundance of the Microbial Community, Antibiotic Resistome, and Pathogens in the Sediment and Water of a Receiving Stream

The effluents of wastewater treatment plants (WWTPs) are major contributors of nutrients, microbes—including those carrying antibiotic resistance genes (ARGs)—and pathogens to receiving waterbodies. The effect of the effluent of a small-scale activated sludge WWTP treating municipal wastewater on the composition and abundance of the microbial community as well as the antibiotic resistome and pathogens in the sediment and water of the receiving stream and river was studied using metagenome sequencing and a quantitative approach. Elevated Bacteroidetes proportions in the prokaryotic community, heightened sulfonamide and aminoglycoside resistance determinants proportions, and an increase of up to three orders of magnitude of sul1–sul2–aadA–blaOXA2 gene cluster abundances were recorded in stream water and sediments 0.3 km downstream of a WWTP discharge point. Further downstream, a gradual recovery of affected microbial communities along a distance gradient from WWTP was recorded, culminating in the mostly comparable state of river water and sediment parameters 3.7 km downstream of WWTP and stream water and sediments upstream of the WWTP discharge point. Archaea, especially Methanosarcina, Methanothrix, and Methanoregula, formed a substantial proportion of the microbial community of WWTP effluent as well as receiving stream water and sediment, and were linked to the spread of ARGs. Opportunistic environmental-origin pathogens were predominant in WWTP effluent and receiving stream bacterial communities, with Citrobacter freundii proportion being especially elevated in the close vicinity downstream of the WWTP discharge point.

Early and differential bacterial colonization on microplastics deployed into the effluents of wastewater treatment plants

Microbial colonization of microplastics (MPs) in aquatic ecosystems is a well-known phenomenon; however, there is insufficient knowledge of the early colonization phase. Wastewater treatment plant (WWTP) effluents have been proposed as important pathways for MPs entry and transport in aquatic environments and are hotspots of bacterial pathogens and antibiotic resistance genes (ARGs). This study aimed at characterizing bacterial communities in the early stage of biofilm formation on seven different types of MPs deployed in two different WWTPs effluents as well as measuring the relative abundance of two ARGs (sulI and tetM) on the tested MPs. Illumina Miseq sequencing of the 16S rRNA showed significant higher diversity of bacteria on MPs in comparison with free-living bacteria in the WWTP effluents. β-diversity analysis showed that the in situ environment (sampling site) and hydrophobicity, to a lesser extent, had a role in the early bacterial colonization phase. An early colonization phase MPs-core microbiome could be identified. Furthermore, specific core microbiomes for each type of polymer suggested that each type might select early attachment of bacteria. Although the tested WWTP effluent waters contained antibiotic resistant bacteria (ARBs) harboring the sulI and tetM ARGs, MPs concentrated ARBs harboring the sulI gene but not tetM. These results highlight the relevance of the early attachment phase in the development of bacterial biofilms on different types of MP polymers and the role that different types of polymers might have facilitating the attachment of specific bacteria, some of which might carry ARGs.

New insights on the combined removal of antibiotics and ARGs in urban wastewater through the use of two configurations of vertical subsurface flow constructed wetlands

The occurrence and removal of 49 antibiotics and 11 selected antibiotic resistance genes (ARGs) were investigated in 2 vertical subsurface flow (VF) constructed wetlands (1.5 m² each): an unsaturated (UVF) unit and a partially saturated (SVF) unit (0.35 m saturated out of 0.8 m) operating in parallel and treating urban wastewater. Thirteen antibiotics were detected in influent wastewater, 6 of which were present in all samples. The SVF showed statistical significance on the removal of 4 compounds (namely ciprofloxacin, ofloxacin, pipemidic acid and azithromycin), suggesting that the wider range of pH and/or redox conditions of this configuration might promote the microbial degradation of some antibiotics. In contrast, the concentration of the latter (except pipemidic acid) and also clindamycin was higher in the effluent than in the influent of the UVF. Five ARGs were detected in influent wastewater, sul1 and sul2, bla_TEM, ermB and qnrS. All of them were detected also in the biofilm of both wetlands, except qnrS. Average removal rates of ARGs showed no statistical differences between both wetland units, and ranged between 46 and 97% for sul1, 33 and 97% for sul2, 9 and 99% for ermB, 18 and 97% for qnrS and 11 and 98% for bla_TEM.

Metagenomic and network analyses decipher profiles and co-occurrence patterns of antibiotic resistome and bacterial taxa in the reclaimed wastewater distribution system

Metagenomic and network analyses were applied to decipher the profiles and co-occurrence of resistome and microbial taxa in the reclaimed wastewater distribution system, including reclaimed wastewater and two types of biofilms, i.e., surface layer biofilms and inner layer biofilms. The effects of chlorination, UV irradiation and no disinfection treatment on ARG relative abundance and composition were systemically investigated. The reclaimed wastewater possesses more diverse and abundant ARGs than biofilms and total ARG relative abundance followed the order of reclaimed wastewater samples > surface layer biofilms > inner layer biofilms. Multidrug, bacitracin, sulfonamide, aminoglycoside, beta-lactam, and macrolide-lincosamide-streptogramin resistance genes were the six most dominant ARG types and their sum accounted for 90.1 %-96.0 % of the total ARG relative abundance in different samples. Beta-lactam resistance gene was the discriminative ARG type for reclaimed wastewater. Bacitracin resistance gene and bacA were the discriminative ARG type and subtype for biofilms. Chlorination significantly reduced ARG relative abundance in the reclaimed wastewater. Nevertheless, it could not reduce ARG relative abundance in biofilms. Regarding to the total ARG profiles, there were no obvious increasing or decreasing trends over time during one year period. Co-occurrence results revealed twenty-six genera were deduced as the potential hosts of twenty-two ARG subtypes.

Antibiotic resistance genes in biofilms on plastic wastes in an estuarine environment

Plastic wastes are ubiquitous in aquatic environment. Biofilms, which are often formed on the surface of plastic waste, may contain antibiotic resistance genes (ARGs). This study focused on the occurrence and distribution of ARGs, metal resistance genes (MRGs) and their associated microbial communities in biofilms formed on different types of plastic, in comparison to associated sediment and water samples taken from the Yangtze Estuary. The results showed that polypropylene (PP) and polyethylene (PE) with visible biofilms were highly abundant, and the average absolute abundance of most tested ARGs in the biofilms was higher than that in the sediment and water, indicating that biofilms on plastics can act as a reservoir for ARGs. Moreover, the biofilms on PE had a higher relative abundance of ARGs, compared to those on other plastics, and Firmicutes on PE may be potential hosts for these ARGs. Furthermore, Bacillus, Mycobacterium and Pseudomonas may be multi-resistance genera on plastics, and tetA and tetW may have more potential hosts on PET and PP. Metals, total phosphorus and salinity may be the major environmental factors regulating ARGs in biofilms formed on plastics. The results provide new insights into evaluating the risks caused by plastic wastes and ARGs in biofilms formed on plastics in estuarine environment.

Localized effect of treated wastewater effluent on the resistome of an urban watershed

Background

Wastewater treatment is an essential tool for maintaining water quality in urban environments. While the treatment of wastewater can remove most bacterial cells, some will inevitably survive treatment to be released into natural environments. Previous studies have investigated antibiotic resistance within wastewater treatment plants, but few studies have explored how a river’s complete set of antibiotic resistance genes (the “resistome") is affected by the release of treated effluent into surface waters.

Results

Here we used high-throughput, deep metagenomic sequencing to investigate the effect of treated wastewater effluent on the resistome of an urban river and the downstream distribution of effluent-associated antibiotic resistance genes and mobile genetic elements. Treated effluent release was found to be associated with increased abundance and diversity of antibiotic resistance genes and mobile genetic elements. The impact of wastewater discharge on the river’s resistome diminished with increasing distance from effluent discharge points. The resistome at river locations that were not immediately downstream from any wastewater discharge points was dominated by a single integron carrying genes associated with resistance to sulfonamides and quaternary ammonium compounds.

Conclusions

Our study documents variations in the resistome of an urban watershed from headwaters to a major confluence in an urban center. Greater abundances and diversity of antibiotic resistance genes are associated with human fecal contamination in river surface water, but the fecal contamination effect seems to be localized, with little measurable effect in downstream waters. The diverse composition of antibiotic resistance genes throughout the watershed suggests the influence of multiple environmental and biological factors.

Stream microbial communities and ecosystem functioning show complex responses to multiple stressors in wastewater

Multiple anthropogenic drivers are changing ecosystems globally, with a disproportionate and intensifying impact on freshwater habitats. A major impact of urbanization are inputs from wastewater treatment plants (WWTPs). Initially designed to reduce eutrophication and improve water quality, WWTPs increasingly release a multitude of micropollutants (MPs; i.e., synthetic chemicals) and microbes (including antibiotic-resistant bacteria) to receiving environments. This pollution may have pervasive impacts on biodiversity and ecosystem services. Viewed through multiple lenses of macroecological and ecotoxicological theory, we combined field, flume, and laboratory experiments to determine the effects of wastewater (WW) on microbial communities and organic-matter processing using a standardized decomposition assay. First, we conducted a mensurative experiment sampling 60 locations above and below WWTP discharges in 20 Swiss streams. Microbial respiration and decomposition rates were positively influenced by WW inputs via warming and nutrient enrichment, but with a notable exception: WW decreased the activation energy of decomposition, indicating a "slowing" of this fundamental ecosystem process in response to temperature. Second, next-generation sequencing indicated that microbial community structure below WWTPs was altered, with significant compositional turnover, reduced richness, and evidence of negative MP influences. Third, a series of flume experiments confirmed that although diluted WW generally has positive influences on microbial-mediated processes, the negative effects of MPs are "masked" by nutrient enrichment. Finally, transplant experiments suggested that WW-borne microbes enhance decomposition rates. Taken together, our results affirm the multiple stressor paradigm by showing that different aspects of WW (warming, nutrients, microbes, and MPs) jointly influence ecosystem functioning in complex ways. Increased respiration rates below WWTPs potentially generate ecosystem "disservices" via greater carbon evasion from streams and rivers. However, toxic MP effects may fundamentally alter ecological scaling relationships, indicating the need for a rapprochement between ecotoxicological and macroecological perspectives.

Stream microbial communities and ecosystem functioning show complex responses to multiple stressors in wastewater

Multiple anthropogenic drivers are changing ecosystems globally, with a disproportionate and intensifying impact on freshwater habitats. A major impact of urbanization are inputs from wastewater treatment plants (WWTPs). Initially designed to reduce eutrophication and improve water quality, WWTPs increasingly release a multitude of micropollutants (MPs; i.e., synthetic chemicals) and microbes (including antibiotic-resistant bacteria) to receiving environments. This pollution may have pervasive impacts on biodiversity and ecosystem services. Viewed through multiple lenses of macroecological and ecotoxicological theory, we combined field, flume, and laboratory experiments to determine the effects of wastewater (WW) on microbial communities and organic-matter processing using a standardized decomposition assay. First, we conducted a mensurative experiment sampling 60 locations above and below WWTP discharges in 20 Swiss streams. Microbial respiration and decomposition rates were positively influenced by WW inputs via warming and nutrient enrichment, but with a notable exception: WW decreased the activation energy of decomposition, indicating a "slowing" of this fundamental ecosystem process in response to temperature. Second, next-generation sequencing indicated that microbial community structure below WWTPs was altered, with significant compositional turnover, reduced richness, and evidence of negative MP influences. Third, a series of flume experiments confirmed that although diluted WW generally has positive influences on microbial-mediated processes, the negative effects of MPs are "masked" by nutrient enrichment. Finally, transplant experiments suggested that WW-borne microbes enhance decomposition rates. Taken together, our results affirm the multiple stressor paradigm by showing that different aspects of WW (warming, nutrients, microbes, and MPs) jointly influence ecosystem functioning in complex ways. Increased respiration rates below WWTPs potentially generate ecosystem "disservices" via greater carbon evasion from streams and rivers. However, toxic MP effects may fundamentally alter ecological scaling relationships, indicating the need for a rapprochement between ecotoxicological and macroecological perspectives.

The impact of WWTP size and sampling season on the prevalence of antibiotic resistance genes in wastewater and the river system

There is a growing concern about the fate of antibiotic resistance genes (ARGs) during wastewater treatment and their potential impacts on the receiving water bodies. We hypothesised that the quantity of ARGs in effluents may be related to the size of wastewater treatment plants (WWTPs) and sampling season. To date, only several attempts have been made to investigate the impact of the above factors at the catchment scale. Therefore, the goal of the present study was to explore possible differences in the quantity of ARGs in treated wastewater from small, medium-sized and large WWTPs in the catchment of the Pilica River (9258 km²). The impact of treated wastewater on the concentration of ARGs was also determined along the river continuum from upland to lowland segments to the point of confluence with the Vistula (342 km). Treated effluent was sampled in 17 WWTPs, and river water was sampled in 7 sampling sites in four seasons. The concentrations of bla_TEM, tet(A), ermF, sul1 and aac(6')-Ib-cr genes, the integrase gene intI1 and the 16S rRNA gene were analysed by quantitative PCR. The physical and chemical parameters and nutrient concentrations (23 various parameters) in the analysed samples were determined. The highest absolute concentrations of the studied genes were noted in effluent samples from small WWTPs (p < 0.01). The concentration of ARGs (gene copies/mL) peaked in winter and spring samples (p < 0.04). The results of statistical analyses indicate that in small WWTPs, the absolute concentration of ARGs can be predicted based on the biochemical oxygen demand, in routine water analyses. However, none of the studied parameters supported predictions of ARG abundance in medium-sized and large WWTPs or in river water.

The use of epilithic biofilms as bioaccumulators of pesticides and pharmaceuticals in aquatic environments

Biofilms are a consortium of communities of organisms that live in syntrophic relationships and present a higher organization level than that of individual cells. Biofilms dominate microbial life in streams and rivers, enable crucial ecosystem processes, contribute to global biogeochemical flows and represent the main active bacterial life form. Epilithic biofilms are the main biomass found in rivers; their exposure to contaminants can lead to changes in their structure and composition. The composition of these communities is influenced by physicochemical factors, temperature, light and prior exposure to pollutants, among other factors, and it can be used for water quality monitoring purposes. The heterogenous composition of biofilms enables them to accumulate compounds in an integrative manner. Moreover, the availability of several sorption sites and their likely saturation can contribute to bioaccumulation. In aquatic environments, biofilms are also susceptible to the acquisition of antibiotic resistance genes and participate in their dissemination. Anthropic pressure intensification processes continuously expose water resources and, consequently, biofilm communities to different contamination sources. Therefore, the use of biofilms to indicate environmental pollution is reinforced by the progress of studies on the subject. Biofilm communities' response to pollutants in aquatic environments can be mainly influenced by the presence of different organisms, which may change due to community development or age. The current research aims to review studies about biofilm contamination and highlight the importance of biofilm use to better evaluate and maintain the quality of water bodies.

Prevalence of antibiotic resistance in the tropical rivers of Sri Lanka and India

We evaluate the imprints of urbanization, landuse and lifestyle on the prevalence and provenance of antibiotic resistance in the tropical rivers of Sri Lanka (Kelani and Gin) and India (Sabarmati, and Brahmaputra River). The prevalence of E. coli in the Kelani, Sabarmati, and Brahmaputra Rivers was in the range of 10-27, 267-76,600, and <50 CFU ml^-1 respectively. Isolated E. coli colonies were subjected to six antibiotics to assess their resistance. We found higher resistance to old generation antibiotics like tetracycline (TC), and sulfamethoxazole (ST) transcends the resistance for fluoroquinolones like norfloxacin (NFX), ciprofloxacin (CIP), and levofloxacin (LVX). Interestingly, both Indian rivers had exhibited relatively higher resistance to TC and ST than the Kelani river or Gin River, implying that the Sri Lankan situation is relatively less critical. At genetic level the resistance for β-lactams, fluoroquinolones and sulphonamides, were detected in many samples, as reported globally. While the resistance genes for aac-(6')-1b-cr, qnrS and sul1 were detected in both Sri Lankan and Indian Rivers, bla_TEM and ampC were specific to the Indian Rivers only. Decoupling of the prevalence of metal contamination and antibiotic resistance has been noticed in India and Sri Lanka. Study implies that urbanization, landuse, and lifestyle (ULL) are the three most critical factors governing multidrug resistance (MDR) and fecal contamination.

Antibiotic-resistant Escherichia coli and Klebsiella spp. in greywater reuse systems and pond water used for agricultural irrigation in the West Bank, Palestinian Territories

Treating and reusing greywater for agricultural irrigation is becoming increasingly prevalent in water-scarce regions such as the Middle East. However, the potential for antibiotic-resistant bacteria to be introduced into food systems or the environment via greywater reuse is a potential area of concern. It is known that off-grid treated greywater often has elevated levels of bacteria, however, little is known regarding the prevalence of antibiotic-resistant bacteria in this water source. To address this knowledge gap, samples (n = 61) of off-grid, household greywater (influent), treated greywater effluent, and irrigation pond water were collected between October 2017 and June 2018 from four farms in the West Bank, Palestinian Territories. Samples were tested for pH, turbidity, dissolved oxygen, electrical conductivity, and oxidation reduction potential. Standard membrane filtration was used to enumerate presumptive Escherichia coli, and isolates (n = 88) were purified, confirmed using 16S rRNA sequencing, and subjected to antimicrobial susceptibility testing using microbroth dilution. The majority of influent (76.5%) and effluent (70.6%) samples had detectable presumptive E. coli. Interestingly, the majority of the isolates were confirmed as Klebsiella sp. (n = 37), followed by E. coli (n = 32), and the remainder were classified as other Enterobacteriaceae (n = 19). A higher percentage of effluent isolates were fully susceptible to all tested antibiotics when compared to influent isolates (28.6% vs 18.6%). Resistance was most commonly observed against ampicillin (69.3% of all isolates), trimethoprim-sulfamethoxazole (11.4%), tetracycline (9.1%), and cefazolin (7.9%), and 7.9% of isolates were observed to be multidrug-resistant. While most water quality parameters were within Israeli and Palestinian wastewater reuse requirements, E. coli levels in effluent violated available standards. These findings suggest that, despite observed decreases in bacteria and an overall decrease in isolates expressing antibiotic resistance from influent to effluent, off-grid greywater treatment systems are still a potential source of both susceptible and antibiotic-resistant bacteria in the agricultural environment.

The incidence of antibiotic resistance within and beyond the agricultural ecosystem: A concern for public health

The agricultural ecosystem creates a platform for the development and dissemination of antimicrobial resistance, which is promoted by the indiscriminate use of antibiotics in the veterinary, agricultural, and medical sectors. This results in the selective pressure for the intrinsic and extrinsic development of the antimicrobial resistance phenomenon, especially within the aquaculture‐animal‐manure‐soil‐water‐plant nexus. The existence of antimicrobial resistance in the environment has been well documented in the literature. However, the possible transmission routes of antimicrobial agents, their resistance genes, and naturally selected antibiotic‐resistant bacteria within and between the various niches of the agricultural environment and humans remain poorly understood. This study, therefore, outlines an overview of the discovery and development of commonly used antibiotics; the timeline of resistance development; transmission routes of antimicrobial resistance in the agro‐ecosystem; detection methods of environmental antimicrobial resistance determinants; factors involved in the evolution and transmission of antibiotic resistance in the environment and the agro‐ecosystem; and possible ways to curtail the menace of antimicrobial resistance.

Effects of freshwater sponge Ephydatia fluviatilis on conjugative transfer of antimicrobial resistance in Enterococcus faecalis strains in aquatic environments

Filter feeding is a biotic process that brings waterborne bacteria in close contact with each other and may thus support the horizontal transfer of their antimicrobial resistance genes. This laboratory study investigated whether the freshwater sponge Ephydatia fluviatilis supported the transfer of vancomycin resistance between two Enterococcus faecalis strains that we previously demonstrated to exhibit pheromone responsive plasmid conjugation. Microcosm experiments exposed live and dead colonies of laboratory-grown sponges to a vancomycin-resistant donor strain and a rifampicin-resistant recipient strain of Ent. faecalis. Enterococci with both resistance phenotypes were detected on double selection plates. In comparison to controls, abundance of these presumed transconjugants increased significantly in water from sponge microcosms. Homogenized suspensions of sponge cells also yielded presumed transconjugants; however, there was no significant difference between samples from live or dead sponges. Fluorescent in situ hybridization analysis of the sponge cell matrix using species-specific probes revealed the presence of enterococci clusters with cells adjacent to each other. The results demonstrated that sponge colonies can support the horizontal transfer of antimicrobial resistance although the mechanism underlying this process, such as binding of the bacteria to the sponge collagen matrix, has yet to be fully elucidated.

Propagation of antibiotic resistance genes in an industrial recirculating aquaculture system located at northern China

The increasing prevalence and spread of antibiotic resistance genes (ARGs) in intensive aquaculture environments are of great concern to food safety and public health. However, the level of ARGs and their potential propagation factors in an industrial recirculating aquaculture system (RAS) have not previously been comprehensive explored. In this study, the levels of 14 different ARG markers and 2 kinds of mobile genetic elements (MGEs) were investigated in a RAS (including water, fish, feces, pellet feed meal, and biofilm samples) located northern China. qnrA, qnrB, qnrS, qepA, aac(6')-Ib, and floR were dominant ARGs, which average concentration levels were presented at 4.51-7.74 copies/L and 5.36-13.07 copies/g, respectively, suggesting that ARGs were prevalent in RAS with no recorded history of antibiotic use. Elevated level of ARGs was found in water of RAS even after the final UV treatment compared with its influent. In RAS, Proteobacteria, Verrucomicrobia, Bacteroidetes, and Planctomycetes were the predominant phyla. Notably, elevated levels of potential opportunistic pathogens were observed along with abundant ARGs suggesting an increasing risk of capturing ARGs and MGEs for human pathogens. This study has revealed for the first time that reared fish, their feces, pellet feed meal as the introduction sources and the selection roles of treatment units co-driven the ARG profile, and the co-selection of water environmental factors and their consequently induced bacterial community shifts formed by their influence are the determining drivers for the ARG propagation in RAS.

Cell-Free DNA: An Underestimated Source of Antibiotic Resistance Gene Dissemination at the Interface Between Human Activities and Downstream Environments in the Context of Wastewater Reuse

The dissemination of antimicrobial resistance (AMR) is one of the biggest challenges faced by mankind in the public health domains. It is currently favored by a lack of confinement between waste disposal and food production in the environmental compartment. To date, much effort has been devoted into the elucidation and control of cell-associated propagation of AMR. However, substantial knowledge gaps remain on the contribution of cell-free DNA to promote horizontal transfers of resistance genes in wastewater and downstream environments. Cell free DNA, which covers free extracellular DNA (exDNA) as well as DNA encapsulated in vesicles or bacteriophages, can persist after disinfection and promote gene transfer in the absence of physical and temporal contact between a donor and recipient bacteria. The increasing water scarcity associated to climatic change requires developing innovative wastewater reuse practices and, concomitantly, a robust evaluation of AMR occurrence by implementing treatment technologies able to exert a stringent control on AMR propagation in downstream environments exposed to treated or non-treated wastewater. This necessarily implies understanding the fate of ARGs on various forms of cell-free DNA, especially during treatment processes that are permissive to their formation. We propose that comprehensive approaches, investigating both the occurrence of ARGs and their compartmentalization in different forms of cellular or cell-free associated DNA should be established for each treatment technology. This should then allow selecting and tuning technologies for their capacity to limit the propagation of ARGs in any of their forms.

Antibiotic resistome associated with microbial communities in an integrated wastewater reclamation system

Antibiotic resistome is a raising concern around the world, especially considering treated wastewater for reclamation. A wastewater reclamation system (WWRS), composed by a treatment system (TS) and a reclaimed system (RS) with supplementation from the treated effluent and considered as an integrated system of treatment and reclamation, was selected in this study. High-throughput qPCR (HT-qPCR) was applied to profile 283 antibiotic resistance genes (ARGs) and 12 mobile genetic elements (MGEs) in the WWRS. A total of 251 ARG and 12 MGE subtypes were detected in the WWRS. The TS exhibited good performance for the removal of ARGs with the number, relative and absolute abundances of ARGs largely decreased (99.07% removal efficiency) in the final effluent, which might be ascribed to biosolid sedimentation. Enhancement of biosolids removal contributed the lessening of ARGs. In the RS, high quality effluent significantly reduced the number and abundance of ARGs along the flow to downstream. MGEs were less reduced in the treated effluent than that of the influent (R² = -0.16, p > 0.05), and exhibited close connections with ARGs. Arcobacter, Cloacibacterium, Cyanobacteria, Acinetobacter, Flavobacterium and Dechloromonas were the relatively abundant genera in the WWRS, and exhibited significantly correlations with ARGs. Microbial communities and MGEs contributed 65.64% to the changes of ARGs. These two factors may be the main drivers of ARG proliferation in the WWRS. Thus, attention should be paid to MGEs and those abundant genera when considering treated wastewater for reclamation.

Treatment enhances the prevalence of antibiotic-resistant bacteria and antibiotic resistance genes in the wastewater of Sri Lanka, and India

Wastewater treatment plants (WWTPs) are being debated for being the hot spots for the development of antibiotic resistance in pathogenic microbial communities. We observed the prevalence of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARG), and multidrug resistance (MDR) in two municipal WWTPs and one hospital WWTP in Western and Southern Sri Lanka, and compared the results with particular reference to Indian and the World scenario to trace the imprints of treatment on ARB and ARG. Result suggests that although wastewater treatment resulted in higher than 1.06 log Escherichia coli (E. coli) reduction at all WWTPs, yet the percent of E. coli resistant to most of the antibiotics increased from influent to effluent. Higher prevalence of ARB, ARG, and MDR were noted in hospital WWTP owing to the higher antibiotic concentrations used and excreted by the patients. With reference to India, the WWTPs in Sri Lanka showed more ARB and a consistent increase in its percentages after the treatment but were less resistant to Fluoroquinolone (FQ). E. coli strains isolated from each location of both countries showed multidrug resistance, which has increased after the treatment and was strongly correlated with FQ in every WWTP. Resistant genes for Fluoroquinolone (FQ) (aac-(6')-1b-cr, qnrB, qnrS), β-lactams (ampC), and sulphonamides (sul1) were common in all the wastewaters except additional parC gene in the hospital effluent of Sri Lanka, implying much higher resistance for quinolones, especially for Ciprofloxacin. Multivariate statistical treatments suggest that effluent showed higher loadings and association for MDR/ARB, where pH change and more extensive interaction with metals during the treatment processes seem to have profound effects.

Small-scale wastewater treatment plants as a source of the dissemination of antibiotic resistance genes in the aquatic environment

Wastewater treatment plants (WWTPs) are significant source of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), which can spread further in the environment by reaching rivers together with effluents discharged from WWTPs. In this study untreated and treated wastewater (UWW, TWW), upstream and downstream river water (URW, DRW) were collected from 4 WWTPs, in the winter and autumn seasons. The occurrence of ARB resistant to beta-lactams and tetracyclines as well as the presence of antibiotics from these classes were analysed in water and wastewater samples. Additionally, the amounts of 12 ARGs, 2 genes of mobile genetic elements (MGEs), gene uidA identifying E. coli and 16S rRNA were also determined. Resistance to beta-lactams prevailed among ARB in water and wastewater samples (constituting 82-88% of total counts of bacteria). The dominant genes in water and wastewater samples were bla_TEM, tetA, sul1. The gene bla_OXA demonstrated high variability of its concentration in samples collected in both seasons. Despite the high per cent reduction of ARB and ARGs concentration observed during the wastewater treatment processes, their large quantities are still transmitted into the environment. The research focuses on WWTPs' role in the dissemination of ARGs and MGEs in the aquatic environment.

Impacts on antibiotic-resistant bacteria and their horizontal gene transfer by graphene-based TiO2&Ag composite photocatalysts under solar irradiation

In recent years, photocatalysis has been considered as a promising method, which provides measures to environmental pollution. Antibiotic resistant bacteria (ARB) and their antibiotic resistance genes (ARGs), as the emerging environmental pollutants, are released into the environment, resulting in antibiotic resistance spread. TiO₂-based nanocomposites, as the most common photocatalytic material, may influence ARB and ARGs under photocatalytic conditions. However, the research on this aspect is rare. A novel nanocomposite synthesized from Ag, TiO₂ and graphene oxide (GO), was selected as a representative of nanomaterials for investigation. The experimental results indicated that TiO₂/Ag/GO nanocomposites significantly affected ARB vitality. 100 mg/L TiO₂/Ag/GO will reduce bacterial survival to 12.2% in 10 min under simulated sunlight irradiation. Chloramphenicol as the most representative antibiotic in the water, reduces the effect of ARB inactivation under photocatalytic conditions. The addition of TiO₂/Ag/GO could affect tetracycline antibiotic resistance. The level of bacterial tolerance to tetracycline had a significant reduction. The horizontal gene transfer was promoted from 1 to 2 folds with the addition of TiO₂/Ag/GO. Even high TiO₂/Ag/GO concentration (100 mg/L) sample had a limited promotion, suggesting that TiO₂/Ag/GO will not increase the risk of antibiotic resistance spread compared to other nano materials.

Emerging contaminants and antibiotic resistance in the different environmental matrices of Latin America

This review aims to gather and summarize information about the occurrence of emerging contaminants and antibiotic resistance genes in environmental matrices in Latin America. We aim to contribute to future research by compiling a list of priority pollutants adjusted to the needs and characteristics of Latin America, according to the data presented in this study. In order to perform a comprehensive research and secure a representative and unbiased amount of quality data concerning emerging contaminants in Latin America, the research was performed within the Scopus® database in a time frame from 2000 to July 2019. The countries with higher numbers of published articles were Brazil and México, while most studies were performed in the surroundings of Mexico City and in Southern and Southeastern Brazil. The main investigated environmental matrices were drinking water and surface water. The presence of antibiotic resistance was frequently reported, mainly in Brazil. Monitoring efforts should be performed in other countries in Latin America, as well as in other regions of Brazil and México. The suggested priority list for monitoring of emerging contaminants in Latin America covers: di(2-ethylhexyl) phthalate (DEHP), bisphenol-A (BP-A), 4-nonylphenol (4-NP), triclosan (TCS), estrone (E1), estradiol (E2), ethinylestradiol (EE2), tetracycline (TC), amoxicillin (AMOX), norfloxacin (NOR), ampicillin (AMP) and imipenem (IMP). We hope this list serves as a basis for the orientation of the future research and monitoring projects to better understand the distribution and concentration of the listed emerging substances.

Physicochemical quality of and Escherichia coli resistance profiles in urban surface waters

Aquatic ecosystems of urban rivers are contaminated through waste disposal, which poses a public health problem. The objective of this research was to evaluate the quality of water used for recreation and public supply of six rivers in the city of Cascavel - Paraná, including Cascavel, Quati, Bezerra, Antas, Clarito and Amambay. Samples were collected every 4 months in 2017, and their physicochemical and microbiological parameters, as well as resistance profiles of strains of Escherichia coli to antimicrobials distributed by pharmacies of the primary healthcare network, were evaluated. Parameters such as water temperature, turbidity, total nitrogen, total phosphorus, total coliforms and thermotolerant coliforms showed significant differences. The allowed limit for thermotolerant coliforms, which was set by National Environment Council, Resolution 357/2005, was exceeded in all of the six analyzed rivers. It was determined that 48.1% of E. coli strains showed resistance to nine antimicrobial tested. The highest levels of resistance were found for ampicillin (27.7%), tetracycline (27.7%) and amoxicillin (24.0%). The results of this study contribute to the understanding of the hazards associated with the contamination of springs in urban centers with wastewater containing resistant bacteria. Therefore, recovery work is necessary in these areas because of the importance of these water sources for the entire western region of Paraná state.

Distribution and co-occurrence of antibiotic and metal resistance genes in biofilms of an anthropogenically impacted stream

Urban stream biofilms are potential hotspots for resistomes and antibiotic resistance genes (ARGs). Biofilm communities that harbor resistance genes may be influenced by contaminant input (e.g., metals and antibiotics) from urban drainage (i.e., Wastewater Treatment Plant effluent and stormwater runoff); understanding the ecology of these communities and their resistome is needed. Given the potential importance of the co-occurrence of ARGs and metal resistance genes (MRGs), we investigated the spatial and temporal distribution of three ARGs (tetracycline [tetW] and sulfonamides [sulI and sulII]), four MRGs (lead [pbrT], copper [copA], and cadmium/cobalt/zinc [czcA and czcC]) via quantitative PCR and biofilm bacterial community composition via MiSeq 16S sequencing at four time points along an urbanization gradient (i.e., developed, agriculture, and forested sites) in a stream's watershed. Our results revealed that ARG and MRG abundances were significantly affected by land use-time interaction, with greater resistance abundances occurring in more urban locations during particular times of the year. It was also observed that changes in ARG and MRG profiles were influenced by differences in community composition among land use types, and that these differences were in response to changes in stream physicochemical parameters (pH, redox, temperature, nutrient availability, and metal concentration) that were driven by sub-watershed land use. Moreover, the dynamics between ARGs and MRGs within these communities correlated strongly and positively with one another. Taken altogether, our results demonstrate that changes in environmental properties due to human activity may drive the ARG-MRG profiles of biofilm communities by modulating community structure over time and space.

State of the art of tertiary treatment technologies for controlling antibiotic resistance in wastewater treatment plants

Antibiotic resistance genes (ARGs) have been considered as emerging contaminants of concern nowadays. There are no special technologies designed to directly remove ARGs in wastewater treatment plants (WWTPs). In order to reduce the risk of ARGs, it is vital to understand the efficiency of advanced treatment technologies in removing antibiotic resistance genes in WWTPs. This review highlights the application and efficiency of tertiary treatment technologies on the elimination of ARGs, s, based on an understanding of their occurrence and fate in WWTPs. These technologies include chemical-based processes such as chlorination, ozonation, ultraviolet, and advanced oxidation technology, as well as physical separation processes, biological processes such as constructed wetland and membrane bioreactor, and soil aquifer treatment. The merits, limitations and ameliorative measures of these processes are discussed, with the view to optimizing future treatment strategies and identifying new research directions.

Antibiotic microbial resistance (AMR) removal efficiencies by conventional and advanced wastewater treatment processes: A review

The World Health Organization (WHO) has identified the spread of antibiotic resistance as one of the major risks to global public health. An important transfer route into the aquatic environment is the urban water cycle. In this paper the occurrence and transport of antibiotic microbial resistance in the urban water cycle are critically reviewed. The presence of antibiotic resistance in low impacted surface water is being discussed to determine background antibiotic resistance levels, which might serve as a reference for treatment targets in the absence of health-based threshold levels. Different biological, physical and disinfection/oxidation processes employed in wastewater treatment and their efficacy regarding their removal of antibiotic resistant bacteria and antibiotic resistance geness (ARGs) were evaluated. A more efficient removal of antibiotic microbial resistance abundances from wastewater effluents can be achieved by advanced treatment processes, including membrane filtration, ozonation, UV-irradiation or chlorination, to levels typically observed in urban surface water or low impacted surface water.

Longitudinal Comparison of Bacterial Diversity and Antibiotic Resistance Genes in New York City Sewage

Urban sewage or wastewater is a diverse source of bacterial growth, as well as a hot spot for the development of environmental antibiotic resistance, which can in turn influence the health of the residents of the city. As part of a larger study to characterize the urban New York City microbial metagenome, we collected raw sewage samples representing three seasonal time points spanning the five boroughs of NYC and went on to characterize the microbiome and the presence of a range of antibiotic resistance genes. Through this study, we have established a baseline microbial population and antibiotic resistance abundance in NYC sewage which can prove to be very useful in studying the load of antibiotic usage, as well as for developing effective measures in antibiotic stewardship.

Bacterial resistance to antibiotics is a pressing health issue around the world, not only in health care settings but also in the community and environment, particularly in crowded urban populations. The aim of our work was to characterize the microbial populations in sewage and the spread of antibiotic resistance within New York City (NYC). Here, we investigated the structure of the microbiome and the prevalence of antibiotic resistance genes in raw sewage samples collected from the fourteen NYC Department of Environmental Protection wastewater treatment plants, distributed across the five NYC boroughs. Sewage, a direct output of anthropogenic activity and a reservoir of microbes, provides an ecological niche to examine the spread of antibiotic resistance. Taxonomic diversity analysis revealed a largely similar and stable bacterial population structure across all the samples, which was found to be similar over three time points in an annual cycle, as well as in the five NYC boroughs. All samples were positive for the presence of the seven antibiotic resistance genes tested, based on real-time quantitative PCR assays, with higher levels observed for tetracycline resistance genes at all time points. For five of the seven genes, abundances were significantly higher in May than in February and August. This study provides characteristics of the NYC sewage resistome in the context of the overall bacterial populations.

IMPORTANCE Urban sewage or wastewater is a diverse source of bacterial growth, as well as a hot spot for the development of environmental antibiotic resistance, which can in turn influence the health of the residents of the city. As part of a larger study to characterize the urban New York City microbial metagenome, we collected raw sewage samples representing three seasonal time points spanning the five boroughs of NYC and went on to characterize the microbiome and the presence of a range of antibiotic resistance genes. Through this study, we have established a baseline microbial population and antibiotic resistance abundance in NYC sewage which can prove to be very useful in studying the load of antibiotic usage, as well as for developing effective measures in antibiotic stewardship.

In vitro activity of antimicrobial-impregnated catheters against biofilms formed by KPC-producing Klebsiella pneumoniae

AIM

To evaluate the activity and effectiveness of impregnated central venous catheters (CVC) against Klebsiella pneumoniae biofilms.

METHODS AND RESULTS

The antimicrobial activity and durability of impregnated-CVCs were evaluated over time and the size of zones of inhibition (ZI) was measured. Biofilm formation was observed by quantitative culture and also by scanning electron microscopy. The catheters impregnated with chlorhexidine/silver sulfadiazine (CHX/SS) reduced bacteria counts by 0·3 log and were most effective (P < 0·01) against Klebsiella pneumoniae biofilms N-acetylcysteine/levofloxacin (NAC/LEV) catheters. It was observed that the catheter impregnated with NAC/LEV had initially the largest average ZI size being statistically significant (P < 0·01). The NAC/LEV combination remained active until day 30, whereas the combination of CHX/SS was completely inactivated from day 15 on.

CONCLUSIONS

The NAC/LEV combination showed greater durability on the catheters, but it was the CHX/SS combination that had the greater initial efficacy in bacterial inhibition. It was also observed that NAC/LEV-impregnated catheters do not prevent the emergence of resistant subpopulations inside the inhibition halos during antimicrobial susceptibility tests.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results highlighted that the in vitro efficacy of antimicrobial-impregnated CVCs is limited by time and that their colonization occurred earlier than expected. Our data also demonstrated that NAC/LEV remained active until day 30 of evaluation and CHX/SS combination was completely inactivated from day 15 on. Our findings suggested that implantable devices should be carefully used by medical community.

Antibiotic resistance in drinking water systems: Occurrence, removal, and human health risks

In recent years, there has been a growing interest on the occurrence of antibiotic-resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in treated and untreated drinking water. ARB and ARGs pose a public health concern when they transfer antibiotic resistance (AR) to human pathogens. However, it is still unclear whether the presence of environmental ARB and ARGs in source water, drinking water treatment plants, and drinking water distribution systems has any significant impact on human exposure to pathogenic ARB. In this review, we critically examine the occurrence of AR in groundwater, surface water, and treated distributed water. This offered a new perspective on the human health threat posed by AR in drinking water and helped in crafting a strategy for monitoring AR effectively. Using existing data on removal of ARB and ARGs in drinking water treatment plants, presence and proliferation of AR in drinking water distribution systems, and mechanisms and pathways of AR transfer in drinking water treatment plants, we conclude that combining UV-irradiation with advanced oxidative processes (such as UV/chlorine, UV/H₂O₂, and H₂O₂/UV/TiO₂) may enhance the removal of ARB and ARGs, while disinfection may promote horizontal gene transfer from environmental ARB to pathogens. The potential human health risks of AR were determined by examining human exposure to antibiotic resistant human pathogens and re-evaluating waterborne disease outbreaks and their links to environmental AR. We concluded that integrating disease outbreak analysis, human exposure modelling, and clinical data could provide critical information that can be used to estimate the dose-response relationships of pathogenic ARB in drinking water, which is required for accurate risk assessments.

Characterization of wastewater effluents in the Danube River Basin with chemical screening, in vitro bioassays and antibiotic resistant genes analysis

Averaged 7-day composite effluent wastewater samples from twelve wastewater treatment plants (WWTPs) in nine countries (Romania, Serbia, Hungary, Slovenia, Croatia, Slovakia, Czechia, Austria, Germany) in the Danube River Basin were collected. WWTPs' selection was based on countries' dominant technology and a number of served population with the aim to get a representative holistic view of the pollution status. Samples were analyzed for 2248 chemicals of emerging concern (CECs) by wide-scope target screening employing LC-ESI-QTOF-MS. 280 compounds were detected at least in one sample and quantified. Spatial differences in the concentrations and distribution of the compounds classes were discussed. Additionally, samples were analyzed for the possible agonistic/antagonistic potencies using a panel of in vitro transactivation reporter gene CALUX® bioassays including ERα (estrogenics), anti-AR (anti-androgens), GR (glucocorticoids), anti-PR (anti-progestins), PPARα and PPARγ (peroxisome proliferators) and PAH assays. The potency of the wastewater samples to cause oxidative stress and induce xenobiotic metabolism was determined using the Nrf2 and PXR CALUX® bioassays, respectively. The signals from each of the bioassays were compared with the recently developed effect-based trigger values (EBTs) and thus allowed for allocating the wastewater effluents into four categories based on their measured toxicity, proposing a putative action plan for wastewater operators. Moreover, samples were analyzed for antibiotics and 13 antibiotic-resistant genes (ARGs) and one mobile genetic element (intl1) with the aim to assess the potential for antibiotic resistance. All data collected from these various types of analysis were stored in an on-line database and can be viewed via interactive map at https://norman-data.eu/EWW_DANUBE.

Transfer of antibiotic resistance genes between Enterococcus faecalis strains in filter feeding zooplankton Daphnia magna and Daphnia pulex

Antibiotic resistant bacteria from faecal pollution sources are pervasive in aquatic environments. A facilitating role for the emergence of waterborne, multi-drug resistant bacterial pathogens has been attributed to biofiltration but had not yet been substantiated. This study investigated the effect of filtration and gut passage in Daphnia spp. on conjugal transfer of resistance genes in Enterococcus faecalis. In vivo conjugation experiments involved a vancomycin-resistant donor strain bearing a plasmid-borne vanA resistance gene, and two vancomycin-susceptible and rifampicin-resistant recipient strains in the presence of Daphnia magna or Daphnia pulex. Results showed successful transfer of the vanA resistance gene from donor to recipient; gene identity was confirmed by PCR and DNA sequencing. There was no significant difference in the number of transconjugants recovered from D. magna and D. pulex. However, transconjugant numbers differed by one order of magnitude between recipient strains. Transconjugant numbers from D. magna were also significantly different between treatments with ingestion of individual phytoplankton species before filtration of bacteria. The highest transfer efficiency calculated from excreted transconjugants was 2.5 × 10^-6. This proof of concept for facilitation of horizontal gene transfer by a filter feeding organism provides evidence that Daphnia can disseminate antibiotic resistant transconjugants in the environment.

Sorption removal of phthalate esters and bisphenols to biofilms from urban river: From macroscopic to microcosmic investigation

River biofilms play fundamental roles in shaping the architecture of aquatic systems. Sorption to biofilms was thought to be a crucial mechanism controlling the fate and transport of trace emerging contaminants. This study focused on the role of in situ colonized river biofilms in the early fate of phthalate esters (PAEs) and bisphenols (BPs) at trace concentrations in a representative urban river. PAEs and BPs were readily sorbed to biofilms with uptakes of 38.2-162.5 μg/g for PAEs and 1787.7-4425.6 μg/g for BPs, respectively. The total mass and characteristics of the colonized biofilms varied in response to seasons and water qualities. The biofilm colonized in the downstream of a wastewater treatment plant exhibited the highest sorption capacity among the tested sites, possibly attributed to the higher organic contents of biofilms owing to the elevated availability of nutrients. Correlation analysis indicates that certain water qualities, e.g., TN and NH₃N, and biofilm properties, e.g., organic and polysaccharide fractions could be selected to predict the sorption capacities of river biofilms. Hydrophobic partitioning into organic matter appears to be the dominant sorption mechanism and biofilm polysaccharides were probably responsible for the adhesion of tested compounds. The contaminant partitioning into biofilm and sediment at mass/volume ratios typical for small rivers suggests that the biofilm could serve as an important sorbing matrix for the trace organic contaminants as compared to the sediments. Our work yields new insights into the early uptake and accumulation of trace plasticizers by natural biofilms, which is of significance in understanding the subsequent transport of trace organic contaminants in fluvial systems.

Impact of the particulate matter from wastewater discharge on the abundance of antibiotic resistance genes and facultative pathogenic bacteria in downstream river sediments

Wastewater treatment plants (WWTPs) are point sources for both, the release of antibiotic resistance genes (ARGs) and the discharge of antibiotics (ABs) into the environment. While it is well established that ARGs emission by WWTPs leads to an ARGs increase in receiving rivers, also the role of sub-inhibitory AB concentrations in this context is being discussed. However, the results obtained in this study suggest that, at environmental concentrations, ABs do not have an effect on resistance selection. Instead, we emphasize the significance of ARG transport and, in that respect, highlight the relevance of wastewater particles and associated microorganisms. We can show that ARGs (ermB, bla_TEM,tetM, qnrS) as well as facultative pathogenic bacteria (FPB) (enterococci, Pseudomonas aeruginosa, Acinetobacter baumannii) inside the particulate fraction of WWTP effluent are very likely to remain in the riverbed of the receiving water due to sedimentation. Moreover, ARG and FPB abundances measured in the particulate fraction strongly correlated with the delta ARG and FPB abundances measured in the receiving river sediment (downstream compared to upstream) (R² = 0.93, p < 0.05). Apparently, the sheer amount of settleable ARGs and FPB from WWTP effluent is sufficient, to increase abundances in the receiving riverbed by 0.5 to 2 log units.

Occurrence and distribution of trace levels of antibiotics in surface waters and soils driven by non-point source pollution and anthropogenic pressure

Antibiotics in surface waters and soils are growing public health concerns and treated wastewater has often been identified as the main source of antibiotics. However, few studies have been conducted to evaluate the occurrence and concentrations of antibiotics in coastal cities without direct impact of wastewater discharge. In this study, the occurrence of 14 antibiotics including four macrolides, three sulfonamides, three β-lactams, lincomycin, chloramphenicol, furazolidon, and monensin in surface waters and soils in Singapore were analyzed with SPE-LC-ESI-MS/MS. The detected concentrations of antibiotics were all below 82.5 ng/L in surface waters and below 80.6 ng/g dry wt in soils. These concentrations were significantly lower than other cities that were under the impact of treated wastewater discharge, suggesting that reduction of treated wastewater discharge reduces occurrence of antibiotics in the environment. However, the wide occurrence of trace levels of antibiotics suggest that other factors may have contributed to detected environmental antibiotics. Population density was positively correlated with concentrations of clarithromycin, lincomycin, azithromycin, and sulfamethoxazole in surface waters, suggesting that non-point source pollution due to anthropogenic pressure may contribute to the wide detection of trace levels of antibiotics. The potential impact of antibiotic use, natural production, and half-lives of antibiotics were further discussed. Further studies are needed to evaluate how anthropogenic activities other than wastewater discharge may contribute to the occurrence of trace level antibiotics and their associated health risks in urban environments.

The Quest for Novel Antimicrobial Compounds: Emerging Trends in Research, Development, and Technologies

Pathogenic antibiotic resistant bacteria pose one of the most important health challenges of the 21st century. The overuse and abuse of antibiotics coupled with the natural evolutionary processes of bacteria has led to this crisis. Only incremental advances in antibiotic development have occurred over the last 30 years. Novel classes of molecules, such as engineered antibodies, antibiotic enhancers, siderophore conjugates, engineered phages, photo-switchable antibiotics, and genome editing facilitated by the CRISPR/Cas system, are providing new avenues to facilitate the development of antimicrobial therapies. The informatics revolution is transforming research and development efforts to discover novel antibiotics. The explosion of nanotechnology and micro-engineering is driving the invention of antimicrobial materials, enabling the cultivation of "uncultivable" microbes and creating specific and rapid diagnostic technologies. Finally, a revival in the ecological aspects of microbial disease management, the growth of prebiotics, and integrated management based on the "One Health" model, provide additional avenues to manage this health crisis. These, and future scientific and technological developments, must be coupled and aligned with sound policy and public awareness to address the risks posed by rising antibiotic resistance.

The Prevalence of Colistin Resistant Strains and Antibiotic Resistance Gene Profiles in Funan River, China

Anthropogenic activities near urban rivers may have significantly increased the acquisition and dissemination of antibiotic resistance. In this study, we investigated the prevalence of colistin resistant strains in the Funan River in Chengdu, China. A total of 18 mcr-1-positive isolates (17 Escherichia coli and 1 Enterobacter cloacae) and 6 mcr-3-positive isolates (2 Aeromonas veronii and 4 Aeromonas hydrophila) were detected, while mcr-2, mcr-4 and mcr-5 genes were not detected in any isolates. To further explore the overall antibiotic resistance in the Funan River, water samples were assayed for the presence of 15 antibiotic resistance genes (ARGs) and class 1 integrons gene (intI1). Nine genes, sul1, sul2, intI1, aac(6')-Ib-cr, bla _CTX-M, tetM, ermB, qnrS, and aph(3')-IIIa were found at high frequencies (70-100%) of the water samples. It is worth noting that mcr-1, bla _KPC, bla _NDM and vanA genes were also found in water samples, the genes that have been rarely reported in natural river systems. The absolute abundance of selected antibiotic resistance genes [sul1, aac(6')-Ib-cr, ermB, bla_CTX-M, mcr-1, and tetM] ranged from 0 to 6.0 (log₁₀ GC/mL) in water samples, as determined by quantitative polymerase chain reaction (qPCR). The sul1, aac(6')-Ib-cr, and ermB genes exhibited the highest absolute abundances, with 5.8, 5.8, and 6.0 log₁₀ GC/mL, respectively. The absolute abundances of six antibiotic resistance genes were highest near a residential sewage outlet. The findings indicated that the discharge of resident sewage might contribute to the dissemination of antibiotic resistant genes in this urban river. The observed high levels of these genes reflect the serious degree of antibiotic resistant pollution in the Funan River, which might present a threat to public health.

Hot spots of antibiotic tolerant and resistant bacterial subpopulations in natural freshwater biofilm communities due to inevitable urban drainage system overflows

Antibiotic resistant bacteria are a threat to human life. Recently, sewers have been identified as potential reservoirs. The intermittent injection of sewage into adjacent surface waters is inevitable, due to capacity limitations of the urban drainage system. Information regarding the effect to natural freshwater biofilms (NFB) due to the intermittent contaminations are scarce. Therefore, a fundamental screening is necessary. In April, we placed NFB-attachment constructions in a brook upstream and downstream from urban drainage overflow constructions. In meanwhile two sampling campaigns were conducted. The sewage and the brook water were collected to gather information about antibiotic background exposure of ciprofloxacin (CIP), clarithromycin (CLA) and doxycycline (DOX). Six months later we experimentally determined the oxygen uptake rate (OUR) of the NFB-communities after a 24 h lasting exposure with additionally dosed antibiotics. Concentrations of 0.1, 1.0 and 10.0 mg L^-1 were selected. CIP, CLA and DOX were individually dosed, and also in mixtures. The mean antibiotic background concentration in sewage was in a range of 575.5-1289.1 ng L^-1, which mainly exceeded the concentrations published in literature. The determined mean concentration in the brook was in a range of 4.6-539.0 ng L^-1. The first significant inhibition of the OUR with individually dosed antibiotics started mainly at a concentration of 1.0 mg L^-1. Antibiotics in a mixture with concentrations of 0.1 and 1.0 mg L^-1 were as effective as single dosed antibiotics with a concentration of 10.0 mg L^-1. The increased antibiotic tolerance and resistance of NFB-communities downstream of the combined sewer overflow (CSO) structure was a consequence of a severe impact due to urban drainage overflows. Hence, NFB-communities downstream of CSO-constructions are hot spots of antibiotic tolerant and resistant subpopulations and access restrictions should be announced, if an infection risk is present.

Prokaryotic horizontal gene transfer within the human holobiont: ecological-evolutionary inferences, implications and possibilities

The ubiquity of horizontal gene transfer in the living world, especially among prokaryotes, raises interesting and important scientific questions regarding its effects on the human holobiont i.e., the human and its resident bacterial communities considered together as a unit of selection. Specifically, it would be interesting to determine how particular gene transfer events have influenced holobiont phenotypes in particular ecological niches and, conversely, how specific holobiont phenotypes have influenced gene transfer events. In this synthetic review, we list some notable and recent discoveries of horizontal gene transfer among the prokaryotic component of the human microbiota, and analyze their potential impact on the holobiont from an ecological-evolutionary viewpoint. Finally, the human-Helicobacter pylori association is presented as an illustration of these considerations, followed by a delineation of unresolved questions and avenues for future research.

Sources of Antibiotic Resistance Genes in a Rural River System

The increasing prevalence of antibiotic resistance genes (ARGs) in the environment is problematic due to the risk of horizontal gene transfer and development of antibiotic resistant pathogenic bacteria. Using a suite of monitoring tools, this study aimed to investigate the sources of ARGs in a rural river system in Nova Scotia, Canada. The monitoring program specifically focused on the relative contribution of ARGs from a single tertiary-level wastewater treatment plant (WWTP) in comparison to contributions from the upgradient rural, sparsely developed, watershed. The overall gene concentration significantly ( < 0.05) increased downstream from the WWTP, suggesting that tertiary-level treatment still contributes ARGs to the environment. As a general trend, ARG concentrations upstream were found to decrease as proximity to human-impacted areas decreased; however, many ARGs remained above detection limits in headwater river samples, which suggested their ubiquitous presence in this watershed in the absence of obvious pollution sources. Significant correlations with ARGs were found for human fecal marker, and some antibiotics, suggesting that these markers may be useful for prediction and understanding of ARG levels and sources in rural rivers.

Antibiotic resistance in urban and hospital wastewaters and their impact on a receiving freshwater ecosystem

The main objective of this study was to investigate the antibiotic resistance (AR) levels in wastewater (WW) and the impact on the receiving river. Samples were collected once per season over one year in the WW of a hospital, in the raw and treated WW of two wastewater treatment plants (WWTPs), as well as upstream and downstream from the release of WWTPs effluents into the Zenne River (Belgium). Culture-dependent methods were used to quantify Escherichia coli and heterotrophic bacteria resistant to amoxicillin, sulfamethoxazole, nalidixic acid and tetracycline. Six antibiotic resistance genes (ARGs) were quantified in both particle-attached (PAB) and free-living (FLB) bacteria. Our results showed that WWTPs efficiently removed antibiotic resistant bacteria (ARB) regardless of its AR profile. The ARGs levels were the highest in the hospital WW and were significantly reduced in both WWTPs. However, ARB and ARGs abundances significantly increased into the Zenne River downstream from the WWTPs outfalls. The variation in the relative abundance of ARGs through WW treatment differed depending on the WWTP, fraction, and gene considered. The sul1 and sul2 genes in PAB fraction showed significantly higher relative abundances in the effluent compared to the influent of both WWTPs. This study demonstrated that WWTPs could be hotspots for AR spread with significant impacts on receiving freshwater ecosystems. This was the first comprehensive study investigating at the same time antibiotics occurrence, fecal bacteria indicators, heterotrophic bacterial communities, and ARGs (distinguishing PAB and FLB) to assess AR levels in WW and impacts on the receiving river.

Identification of Pharmaceuticals in The Aquatic Environment Using HPLC-ESI-Q-TOF-MS and Elimination of Erythromycin Through Photo-Induced Degradation

Monitoring pharmaceuticals throughout the water cycle is becoming increasingly important for the aquatic environment and eventually for human health. Targeted and non-targeted analysis are today's means of choice. Although targeted analysis usually conducted with the help of a triple quadrupole mass spectrometer may be more sensitive, only compounds previously selected can be identified. The most powerful non-targeted analysis is performed through time of flight mass spectrometers (TOF-MS) extended by a quadrupole mass analyzer (Q), as used in this study. Preceded by solid phase extraction and high-performance liquid chromatography (HPLC), the non-targeted approach allows to detect all ionizable substances with high sensitivity and selectivity. Taking full advantage of the Q-TOF-MS instrument, tandem mass spectrometry (MS/MS) experiments accelerate and facilitate the identification while a targeted MS method enhances the sensitivity but relies on reference standards for identification purposes. The identification of four pharmaceuticals from Rhine river water is demonstrated. The Rhine river originates in Tomasee, Graubünden, Switzerland and flows into the North Sea, near Southern Bight, The Netherlands. Its length amounts to 1232.7 km. Since it is of prime interest to effectively eliminate pharmaceuticals from the water cycle, the effect UV-C irradiation is demonstrated on a laboratory scale. This method allows fast degradation of pharmaceuticals, which is exemplarily shown for the macrolide antibiotic erythromycin. Using the above HPLC-Q-TOF-MS method, concentration-time diagrams are obtained for the parent drug and their photodegradation products. After establishing the equations for first-order sequential reactions, computational fitting allows the determination of kinetic parameters, which might help to predict irradiation times and conditions when potentially considered as fourth stage within wastewater treatment.

Occurrence and ecological risk assessment of 22 emerging contaminants in the Jilin Songhua River (Northeast China)

Rivers may receive pharmaceuticals, personal care products, and environment estrogens, which are emerging concerns, from various sources. Understanding the fate of these emerging contaminants (ECs) from the sources to their receiving river is important for assessing their ecosystem risk. Here, the occurrence, seasonal variation, spatial distribution, and ecological risk of 22 ECs in water and sediments from the Jilin Songhua River, as well as in the effluents from the riverside Jilin wastewater treatment plant (WWTP) were investigated. Results indicated that estriol with the highest median concentration of 21.5 ng L^-1 in the river water and with the highest median concentration of 481.5 ng g^-1 in the sediments, and methylparaben with the highest concentration of 29.6 ± 2.9 ng L^-1 in the WWTP effluents were the predominant contaminants. The total concentration of ECs in the river water in the dry season was about 1.5 times higher than that in the wet season. The concentrations of these ECs close to the contaminated tributary and the WWTP were relatively high. Risk assessment showed that the maximum risk quotient value of estrone was 1.07 in the river water and estriol was 2.10 in the effluents. In addition, erythromycin posed generally medium risk in the river water and WWTP effluents. It should be paid attention to the prior control of the three contaminants in the river region.

Evaluation of attenuation of pharmaceuticals, toxic potency, and antibiotic resistance genes in constructed wetlands treating wastewater effluents

The performance of constructed wetlands (CWs) in the removal of pharmaceutically active compounds (PhACs) is generally evaluated on the basis of chemical analysis. In this work, we used a combination of chemical, toxicological, and molecular analyses to assess the attenuation of PhACs, toxic potency and antibiotic resistance genes (ARGs) in a field study of three CWs serving as tertiary treatment of wastewater treatment plants. First, 17 PhACs were analysed chemically, of which 14 were detected and seven at concentrations >0.1μg/l. Even though some of the individual PhACs were moderately or highly removed in the CWs investigated, median removal of overall PhACs was approximately 50% in the vertical subsurface flow CW (VSF-CW) with a lower hydraulic loading rate while the removal in the other two free water surface flow CWs (SF-CWs) was negligible. Second, toxic potency of wastewater extracts was assessed in a range of bioassays. Estrogenicity was overall attenuated in CWs, while the neurotoxic potency of wastewater extracts did not decrease after passage through the two CWs investigated. Third, the VSF-CW and one of the SF-CW showed a positive removal of an integrase gene and three ARGs tested. The increased concentrations of ARGs in the other SF-CW, as well as the increase of total bacteria in all CWs, may relate to regrowth of resistance-carrying bacteria. Finally, multivariate analysis shows that most PhACs are positively correlated to the observed toxic potency. Additionally, low removal of organics and nutrients seems to parallel with low removal of PhACs. ARGs positively correlated with organics, nutrients and some PhACs, and the integrase gene but not to the respective antibiotics. The insufficient removal of PhACs, toxic potency, and ARGs indicates the need of an optimal design of CWs as tertiary treatment facilities.

Antibiotic resistance along an urban river impacted by treated wastewaters

Urban rivers are impacted ecosystems which may play an important role as reservoirs for antibiotic-resistant (AR) bacteria. The main objective of this study was to describe the prevalence of antibiotic resistance along a sewage-polluted urban river. Seven sites along the Zenne River (Belgium) were selected to study the prevalence of AR Escherichia coli and freshwater bacteria over a 1-year period. Culture-dependent methods were used to estimate E. coli and heterotrophic bacteria resistant to amoxicillin, sulfamethoxazole, nalidixic acid and tetracycline. The concentrations of these four antibiotics have been quantified in the studied river. The antibiotic resistance genes (ARGs), sul1, sul2, tetW, tetO, blaTEM and qnrS were also quantified in both particle-attached (PAB) and free-living (FLB) bacteria. Our results showed an effect of treated wastewaters release on the spread of antibiotic resistance along the river. Although an increase in the abundance of both AR E. coli and resistant heterotrophic bacteria was observed from upstream to downstream sites, the differences were only significant for AR E. coli. A significant positive regression was also found between AR E. coli and resistant heterotrophic bacteria. The concentration of ARGs increased from upstream to downstream sites for both particle-attached (PAB) and free-living bacteria (FLB). Particularly, a significant increase in the abundance of four among six ARGs analyzed was observed after crossing urban area. Although concentrations of tetracycline significantly correlated with tetracycline resistance genes, the antibiotic levels were likely too low to explain this correlation. The analysis of ARGs in different fractions revealed a significantly higher abundance in PAB compared to FLB for tetO and sul2 genes. This study demonstrated that urban activities may increase the spread of antibiotic resistance even in an already impacted river.

Use of prospective and retrospective risk assessment methods that simplify chemical mixtures associated with treated domestic wastewater discharges

A framework is presented that is intended to facilitate the evaluation of potential aquatic ecological risks resulting from discharges of down-the-drain chemicals. A scenario is presented using representatives of many of the types of chemicals that are treated domestically. Predicted environmental chemical concentrations are based on reported loading rates and routine removal rates for 3 types of treatment: trickling filter, activated sludge secondary treatment, and activated sludge plus advanced oxidation process as well as instream effluent dilution. In tier I, predicted effluent concentrations were compared with the lowest predicted-no-effect concentration (PNEC) obtained from the literature using safety factors as needed. A cumulative risk characterization ratio (cumRCR) < 1.0 indicates that risk is unlikely and no further action is needed. Otherwise, a tier 2 assessment is used, in which PNECs are based on trophic level. If tier 2 indicates a possible risk, then a retrospective assessment is recommended. In tier 1, the cumRCR was > 1.0 for all 3 treatment types in our scenario, even though no chemical exceeded a hazard quotient of 1.0 in activated sludge or advanced oxidation process. In tier 2, activated sludge yielded a lower cumRCR than trickling filter because of higher removal rates, and the cumRCR in the advanced oxidation process was << 1.0. Based on the maximum cumulative risk ratio (MCR), more than one-third of the predicted risk was accounted for by one chemical, and at least 90% was accounted for by 3 chemicals, indicating that few chemicals influenced the mixture risk in our scenario. We show how a retrospective assessment can test whether certain chemicals hypothesized as potential drivers in the prospective assessment could have, or are having, deleterious effects on aquatic life. Environ Toxicol Chem 2018;37:690-702. © 2017 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Biofilms as a sink for antibiotic resistance genes (ARGs) in the Yangtze Estuary

Biofilms are ubiquitous throughout aquatic environments and they are thought to promote the acquisition and dissemination of antibiotic resistant genes (ARGs). This study focused on the occurrence and distribution of five types of ARG in naturally-occurring biofilms, in comparison to associated sediment and water samples, from the Yangtze Estuary, which borders the meta-city of Shanghai, China. The detection frequency and abundances of most ARGs showed the following order: biofilm > sediment > water, which can be attributed to a high level of antibiotics and metals that can accelerate the generation and propagation of ARGs in biofilms. Most of ARG abundances were contributed by extracellular DNA (eDNA) in biofilm and sediment samples. ARGs (sul1, sul2, tetA and tetW) in eDNA were significantly correlated with TOC in both biofilm and sediment samples. Furthermore, both intracellular DNA-associated ARGs per gram of microbial biomass carbon (MBC) and eDNA-associated ARGs per gram of non-MBC and were higher in biofilms than sediments, and the partitioning coefficients of ARGs in eDNA between biofilm and water were higher than those between sediment and water. Our results provide new insight for evaluating the occurrence and abundance of ARGs in aquatic environments, confirming that biofilms are a significant sink for ARGs in the estuarine environment.

Cell-free DNA: A Neglected Source for Antibiotic Resistance Genes Spreading from WWTPs

Cell-associated ARGs in wastewater treatment plants (WWTPs) has been concerned, however, cell-free ARGs in WWTPs was rarely studied. In this study, the abundances of four representative ARGs, sulII, tetC, bla_PSE-1, and ermB, in a large municipal WWTP were investigated in both cell-associated and cell-free fractions. Cell-associated ARGs was the dominant ARGs fraction in the raw wastewater. After biological treatment, sludge settling, membrane filtration, and disinfection, cell-associated ARGs were substantially reduced, though the ratios of ARG/16S rRNA gene were increased with disinfection. Cell-free ARGs persisted in the WWTP with a removal of 0.36 log to 2.68 logs, which was much lower than the removal of cell-associated ARGs (3.21 logs to 4.14 logs). Therefore, the abundance ratio of cell-free ARGs to cell-associated ARGs increased from 0.04-1.59% to 2.00-1895.08% along the treatment processes. After 25-day-storage, cell-free ARGs in both biological effluent and disinfection effluent increased by 0.14 log to 1.99 logs and 0.12 log to 1.77 logs respectively, reflecting the persistence and low decay rate of cell-free ARGs in the discharge water. Therefore, cell-free ARGs might be a kind of important but previously neglected pollutant from WWTPs, which added potential risks to the effluent receiving environments.