Annual dynamics of antimicrobials and resistance determinants in flocculent and aerobic granular sludge treatment systems

Biostimulation with oxygen and electron donors supports micropollutant biodegradation in an experimentally simulated nitrate-reducing aquifer

The availability of suitable electron donors and acceptors limits micropollutant natural attenuation in oligotrophic groundwater. This study investigated how electron donors with different biodegradability (humics, dextran, acetate, and ammonium), and different oxygen concentrations affect the biodegradation of 15 micropollutants (initial concentration of each micropollutant = 50 μg/L) in simulated nitrate reducing aquifers. Tests mimicking nitrate reducing field conditions showed no micropollutant biodegradation, even with electron donor amendment. However, 2,4-dichlorophenoxyacetic acid and mecoprop were biodegraded under (micro)aerobic conditions with and without electron donor addition. The highest 2,4-dichlorophenoxyacetic acid and mecoprop biodegradation rates and removal efficiencies were obtained under fully aerobic conditions with amendment of an easily biodegradable electron donor. Under microaerobic conditions, however, amendment with easily biodegradable dissolved organic carbon (DOC) inhibited micropollutant biodegradation due to competition between micropollutants and DOC for the limited oxygen available. Microbial community composition was dictated by electron acceptor availability and electron donor amendment, not by micropollutant biodegradation. Low microbial community richness and diversity led to the absence of biodegradation of the other 13 micropollutants (such as bentazon, chloridazon, and carbamazepine). Finally, adaptation and potential growth of biofilms interactively determined the location of the micropollutant removal zone relative to the point of amendment. This study provides new insight on how to stimulate in situ micropollutant biodegradation to remediate oligotrophic groundwaters as well as possible limitations of this process.

When aerobic granular sludge faces emerging contaminants: A review

The evolution of emerging contaminants (ECs) has caused greater requirements and challenges to the current biological wastewater treatment technology. As one of the most promising biological treatment technologies, the aerobic granular sludge (AGS) process also faces the challenge of ECs. This study summarizes the recent progress and characteristics of several representative ECs (persistent organic pollutants, endocrine disrupting chemicals, antibiotics, and microplastics) in AGS systems that have garnered widespread attention. Additionally, the biodegradation and adsorption mechanisms of ECs were discussed, and the interactions between various ECs and AGS was elucidated. The importance of extracellular polymeric substances for the stabilization of AGS and the removal of ECs is also discussed. Knowledge gaps and future research directions that may enable the practical application of AGS are highlighted. Overall, AGS processes show great application potential and this review provides guidance for the future implementation of AGS technology as well as elucidating the mechanism of its interaction with ECs.

Effect of dissolved organic carbon on micropollutant biodegradation by aquifer and soil microbial communities

Groundwater, a major source of drinking water worldwide, is often contaminated with micropollutants. Although microbial communities in aquifers and soils have the capability to biodegrade some micropollutants, this process is limited in situ. Biostimulation with dissolved organic carbon (DOC) is known to promote micropollutant biodegradation, but the role of DOC biodegradability is still poorly understood. This study investigated how three DOC types with different biodegradability (humics, dextran and acetate) affect the biodegradation of 15 micropollutants by aquifer and soil microbial communities under aerobic and nitrate reducing conditions. Although originating from different environments, both communities were able to biodegrade the same 4 micropollutants under aerobic conditions - 2,4-D, MCPP, chloridazon (CLZ) and chloridazon-desphenyl. However, DOC addition only affected MCPP biodegradation, promoting MCPP biodegradation regardless of DOC biodegradability. Biodegradation of 2,4-D, MCPP and CLZ under aerobic conditions was observed after a lag phase, whose duration differed per compound. 2,4-D was biodegraded first and fully. Aquifer community was able to degrade about half of the initial MCPP concentration (removal efficiency of 49.3 ± 11.7%). CLZ was fully biodegraded by the aquifer community, but not by the soil community, possibly due to substrate competition with organics originating from the inoculum. Therefore, the natural organic carbon present in the inocula and in environmental systems can influence micropollutant biodegradation. Under nitrate reducing conditions micropollutant biodegradation was not observed nor biostimulated by DOC addition. The results also highlight the importance of sufficient exposure time to trigger in situ micropollutant biodegradation.

Unraveling the Role of Microalgae in Mitigating Antibiotics and Antibiotic Resistance Genes in Photogranules Treating Antibiotic Wastewater

Harnessing the potential of specific antibiotic-degrading microalgal strains to optimize microalgal-bacterial granular sludge (MBGS) technology for sustainable antibiotic wastewater treatment and antibiotic resistance genes (ARGs) mitigation is currently limited. This article examined the performance of bacterial granular sludge (BGS) and MBGS (of Haematococcus pluvialis, an antibiotic-degrading microalga) systems in terms of stability, nutrient and antibiotic removal, and fate of ARGs and mobile genetic elements (MGEs) under multiclass antibiotic loads. The systems exhibited excellent performance under none and 50 μg/L mixed antibiotics and a decrease in performance at a higher concentration. The MBGS showed superior potential, higher nutrient removal, 53.9 mg/L/day higher chemical oxygen demand (COD) removal, and 5.2-8.2% improved antibiotic removal, notably for refractory antibiotics, and the system removal capacity was predicted. Metagenomic analysis revealed lower levels of ARGs and MGEs in effluent and biomass of MBGS compared to the BGS bioreactor. Particle association niche and projection pursuit regression models indicated that microalgae in MBGS may limit gene transfers among biomass and effluent, impeding ARG dissemination. Moreover, a discrepancy was found in the bacterial antibiotic-degrading biomarkers of BGS and MBGS systems due to the microalgal effect on the microcommunity. Altogether, these findings deepened our understanding of the microalgae's value in the MBGS system for antibiotic remediation and ARG propagation control.

Antimicrobials and antimicrobial resistance genes in a one-year city metabolism longitudinal study using wastewater-based epidemiology

This longitudinal study tests correlations between antimicrobial agents (AA) and corresponding antimicrobial resistance genes (ARGs) generated by a community of >100 k people inhabiting one city (Bath) over a 13 month randomised monitoring programme of community wastewater. Several AAs experienced seasonal fluctuations, such as the macrolides erythromycin and clarithromycin that were found in higher loads in winter, whilst other AA levels, including sulfamethoxazole and sulfapyridine, stayed consistent over the study period. Interestingly, and as opposed to AAs, ARGs prevalence was found to be less variable, which indicates that fluctuations in AA usage might either not directly affect ARG levels or this process spans beyond the 13-month monitoring period. However, it is important to note that weekly positive correlations between individual associated AAs and ARGs were observed where seasonal variability in AA use was reported: ermB and macrolides CLR-clarithromycin and dmCLR-N-desmethyl clarithromycin, aSPY- N-acetyl sulfapyridine and sul1, and OFX-ofloxacin and qnrS. Furthermore, ARG loads normalised to 16S rRNA (gene load per microorganism) were positively correlated to the ARG loads normalised to the human population (gene load per capita), which indicates that the abundance of microorganisms is proportional to the size of human population and that the community size, and not AA levels, is a major driver of ARG levels in wastewater. Comparison of hospital and community wastewater showed higher number of AAs and their metabolites, their frequency of occurrence and concentrations in hospital wastewater. Examples include: LZD-linezolid (used only in severe bacterial infections) and AMX-amoxicillin (widely used, also in community but with very low wastewater stability) that were found only in hospital wastewater. CIP-ciprofloxacin, SMX-sulfamethoxazole, TMP-trimethoprim, MTZ-metronidazole and macrolides were found at much higher concentrations in hospital wastewater while TET-tetracycline and OTC-oxytetracycline, as well as antiretrovirals, had an opposite trend. In contrast, comparable concentrations of resistant genes were observed in both community and hospital wastewater. This supports the hypothesis that AMR levels are more of an endemic nature, developing over time in individual communities. Both hospital and community wastewater had AAs that exceeded PNEC values (e.g. CLR-clarithromycin, CIP-ciprofloxacin). In general, though, hospital effluents had a greater number of quantifiable AAs exceeding PNECs (e.g. SMX-sulfamethoxazole, ERY-erythromycin, TMP-trimethoprim). Hospitals are therefore an important consideration in AMR surveillance as could be high risk areas for AMR.

Synergistic removal of pharmaceuticals and antibiotic resistance from ultrafiltered WWTP effluent: Free-floating ARGs exceptionally susceptible to degradation

To protect the environment and human health, antibiotic resistance genes (ARGs) and persistent pharmaceuticals need to be removed from WWTP effluent prior to its reuse. However, an efficient process for removing free-floating extracellular DNA (exDNA) in combination with a wide range of pharmaceuticals is yet to be reported for real process conditions. As a possible solution, we treated real ultrafiltered WWTP effluent with UV/H₂O₂ and combined GAC and zeolite sorption. In terms of exDNA, sequencing and high-throughput quantitative PCR (HT-qPCR) showed that exDNA is a potent carrier of numerous ARGs in ultrafiltered WWTP effluent (123 ARGs), including multi-drug efflux pump mexF that became the dominant exARG in GAC effluent over time. Due to the exposure to degradation agents, exDNA was reduced more efficiently than intracellular DNA, and overall levels of ARGs were substantially lowered. Moreover, GAC sorption was particularly effective in the removal of almost all the 85 detected pharmaceutical residues, with fresh GAC demonstrating an efficiency of up to 100%. However, zeolite (Si/Al 0.8) addition was needed to enhance the removal of persistent pollutants such as gabapentin and diclofenac to 57% and up to 100%, respectively. Our combined approach eminently decreases the hazardous effects of pharmaceuticals and antibiotic resistance in the ultrafiltered WWTP effluent, producing effluent suitable for multiple reuse options according to the latest legislation. In addition, we provided similarly promising but less extensive data for surface water and treated greywater.

Degradation of Antibiotic Resistance Genes by VADER with CRISPR-Cas Immunity

The evolution and dissemination of antibiotic resistance genes (ARGs) are prompting severe health and environmental issues. While environmental processes, e.g., biological wastewater treatment, are key barriers to prevent the spread of ARGs, they are often sources of ARGs at the same time, requiring upgraded biotechnology. Here, we present VADER, a synthetic biology system for the degradation of ARGs based on CRISPR-Cas immunity, an archaeal and bacterial immune system for eliminating invading foreign DNAs, to be implemented for wastewater treatment processes. Navigated by programmable guide RNAs, VADER targets and degrades ARGs depending on their DNA sequences, and by employing an artificial conjugation machinery, IncP, it can be delivered via conjugation. The system was evaluated by degrading plasmid-borne ARGs in Escherichia coli and further demonstrated via the elimination of ARGs on the environmentally relevant RP4 plasmid in Pseudomonas aeruginosa. Next, a prototype conjugation reactor at a 10-mL scale was devised, and 100% of the target ARG was eliminated in the transconjugants receiving VADER, giving a proof of principle for the implementation of VADER in bioprocesses. By generating a nexus of synthetic biology and environmental biotechnology, we believe that our work is not only an enterprise for tackling ARG problems but also a potential solution for managing undesired genetic materials in general in the future. IMPORTANCE Antibiotic resistance has been causing severe health problems and has led to millions of deaths in recent years. Environmental processes, especially those of the wastewater treatment sector, are an important barrier to the spread of antibiotic resistance from the pharmaceutical industry, hospitals, or civil sewage. However, they have been identified as a nonnegligible source of antibiotic resistance at the same time, as antibiotic resistance with its main cause, antibiotic resistance genes (ARGs), may accumulate in biological treatment units. Here, we transplanted the CRISPR-Cas system, an immune system via programmable DNA cleavage, to tackle the antibiotic resistance problem raised in wastewater treatment processes, and we propose a new sector specialized in ARG removal with a conjugation reactor to implement the CRISPR-Cas system. Our study provides a new angle for resolving public health issues via the implementation of synthetic biology in environmental contexts at the process level.

Geo-referenced simulations of E. coli in a sub-catchment of the Vecht River using a probabilistic approach

The proportion of wild swimmers at non-official bathing sites has increased during the Covid-19 pandemic. Bathing water quality at designated sites is monitored through analysis of the concentration of fecal indicator bacteria such as E. coli. However, non-official sites are generally not monitored. In a previous work, steady state modelling of E. coli was achieved at catchment scale, enabling a comparison of expected concentrations along an entire catchment for longtime average. However, E. coli concentrations can vary over several orders of magnitude at the same monitoring site throughout the year. To capture the temporal variability of E. coli concentrations on the catchment scale, we extended the existing deterministic E. coli sub-module of the GREAT-ER (Geo-referenced Exposure Assessment tool for European Rivers) model for probabilistic Monte-Carlo simulations. Here, selected model parameters are represented by probability distributions instead of fixed values. Wastewater treatment plant (WWTP) emissions and diffuse emissions were parameterized using selected data from a previous monitoring campaign (calibration data set) and in-stream processes were modeled using literature data. Comparison of simulation results with monitoring data (evaluation data set) indicates that predicted E. coli concentrations well-represent median measured concentrations, although the range of predicted concentrations is slightly larger than the observed concentration variability. The parameters with the largest influence on the range of predicted concentrations are flow rate and E. coli removal efficiency in WWTPs. A comparison of predicted 90th percentiles with the threshold for sufficient bathing water quality (according to the EU Bathing Water Directive) indicates that year-round swimming at sites influenced by WWTP effluents is advisable almost nowhere in the study area. A refinement of the model can be achieved if quantitative relationships between the WWTP removal efficiency and both, the treatment technologies as well as the operating parameters are further established.

Antibiotic resistance genes in landfill leachates from seven municipal solid waste landfills: Seasonal variations, hosts, and risk assessment

Landfills are reservoir of antibiotics and antibiotic resistance. Antibiotic resistance would transport to the environment through landfill leachate, posing threaten to the environment. However, long term monitoring on antibiotic resistance genes in landfill leachate transportation is limited. Furthermore, antibiotic resistance gene hosts and their risk assessment are lacking. In this study, we investigated the seasonal variation of ARGs sulI, tetO and tetW in seven Chinese municipal solid waste landfill leachates over two years (2017-2018) by quantitative polymerase chain reaction. We also evaluated the associated bacterial hosts and their risk levels based on metagenomics and omics-based framework for assessing the health risk of antimicrobial resistance genes, respectively. Because sulI, tetO and tetW are abundant and the most frequently detected ARGs in global landfill system, they are selected as target ARGs. Results showed that the relative content of target ARGs in 2017 was 100 times higher than that in 2018, suggesting ARGs attenuation. The hosts of sulI were phyla of Lentisphaerae and Proteobacteria, whereas the hosts of tetO and tetW were Bacteroidetes and Firmicutes. Remarkably, the host species include pathogenic bacterium (Salmonella enterica, Labilibaculum filiforme, Bacteroidales bacterium, Anaeromassilibacillus senegalensis, and Pseudochrobactrum sp. B5). ARGs tetO and tetW belong to the Rank II level with characters of enrichment in the human-associated environment and gene mobility, and sulI ranked as Rank VI. In addition, among 1210 known ARGs in the landfill leachate, 78 ARGs belonged to risk Rank I (enrichment in human-associated environment, gene mobility and pathogenicity), demonstrating high health risk of landfill system. These results demonstrate that antibiotic resistance in landfill and landfill leachate have high health risk and the kind of ARGs with high abundance in human-associated environment, gene mobility and pathogenicity should be paid more attention.

(Antibiotic-Resistant) E. coli in the Dutch-German Vecht Catchment─Monitoring and Modeling

Fecally contaminated waters can be a source for human infections. We investigated the occurrence of fecal indicator bacteria (E. coli) and antibiotic-resistant E. coli, namely, extended spectrum beta-lactamase (ESBL)-producing E. coli (ESBL-EC) and carbapenemase-producing E. coli (CP-EC) in the Dutch-German transboundary catchment of the Vecht River. Over the course of one year, bacterial concentrations were monitored in wastewater treatment plant (WWTP) influents and effluents and in surface waters with and without WWTP influence. Subsequently, the GREAT-ER model was adopted for the prediction of (antibiotic-resistant) E. coli concentrations. The model was parametrized and evaluated for two distinct scenarios (average flow scenario, dry summer scenario). Statistical analysis of WWTP monitoring data revealed a significantly higher (factor 2) proportion of ESBL-EC among E. coli in German compared to Dutch WWTPs. CP-EC were present in 43% of influent samples. The modeling approach yielded spatially accurate descriptions of microbial concentrations for the average flow scenario. Predicted E. coli concentrations exceed the threshold value of the Bathing Water Directive for a good bathing water quality at less than 10% of potential swimming sites in both scenarios. During a single swimming event up to 61 CFU of ESBL-EC and less than 1 CFU of CP-EC could be taken up by ingestion.

Removal of organic micropollutants from municipal wastewater by aerobic granular sludge and conventional activated sludge

Removal performances of organic micropollutants by conventional activated sludge (CAS) and aerobic granular sludge (AGS) were investigated at a full-scale wastewater treatment plant. Lab-scale kinetic experiments were performed to assess the micropollutant transformation rates under oxic and anoxic conditions. Transformation rates were used to model the micropollutant removal in the full-scale processes. Metagenomic sequencing was used to compare the microbial communities and antimicrobial resistance genes of the CAS and AGS systems. Higher transformation ability was observed for CAS compared to AGS for most compounds, both at the full-scale plant and in the complementary batch experiments. Oxic conditions supported the transformation of several micropollutants with faster and/or comparable rates compared to anoxic conditions. The estimated transformation rates from batch experiments adequately predicted the removal for most micropollutants in the full-scale processes. While the compositions in microbial communities differed between AGS and CAS, the full-scale biological reactors shared similar resistome profiles. Even though granular biomass showed lower potential for micropollutant transformation, AGS systems had somewhat higher gene cluster diversity compared to CAS, which could be related to a higher functional diversity. Micropollutant exposure to biomass or mass transfer limitations, therefore played more important roles in the observed differences in OMP removal.

Research needs for optimising wastewater-based epidemiology monitoring for public health protection

Wastewater-based epidemiology (WBE) is an unobtrusive method used to observe patterns in illicit drug use, poliovirus, and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The pandemic and need for surveillance measures have led to the rapid acceleration of WBE research and development globally. With the infrastructure available to monitor SARS-CoV-2 from wastewater in 58 countries globally, there is potential to expand targets and applications for public health protection, such as other viral pathogens, antimicrobial resistance (AMR), pharmaceutical consumption, or exposure to chemical pollutants. Some applications have been explored in academic research but are not used to inform public health decision-making. We reflect on the current knowledge of WBE for these applications and identify barriers and opportunities for expanding beyond SARS-CoV-2. This paper critically reviews the applications of WBE for public health and identifies the important research gaps for WBE to be a useful tool in public health. It considers possible uses for pathogenic viruses, AMR, and chemicals. It summarises the current evidence on the following: (1) the presence of markers in stool and urine; (2) environmental factors influencing persistence of markers in wastewater; (3) methods for sample collection and storage; (4) prospective methods for detection and quantification; (5) reducing uncertainties; and (6) further considerations for public health use.

Differential variations of intracellular and extracellular antibiotic resistance genes between treatment units in centralized sewage sludge treatment plants

Centralized sludge treatment plants (CSTPs) are implicated as strong hotspots of antibiotic resistance genes (ARGs). However, the knowledge gap on the fate of intracellular and extracellular ARGs (iARGs and eARGs), and the functionality of resistant hosts limit risk assessment and management of CSTP resistome. Here, the flow of iARGs and eARGs across treatment units and analyses of ARG hosts were systematically explored in three full-scale CSTPs using quantitative metagenomic approaches. We found that 29% of sludge ARGs could be removed, with iARGs being dominant in the produced biosolids. The treatment process significantly affected the variations of iARG and eARG abundance while no significant difference in composition between iARGs and eARGs was observed in CSTPs. 15% of 295 recovered genomes were identified as antibiotic-resistant hosts, among which Actinobacteriota tended to encode multiple resistance. The key functions of ARG hosts were relative to the biological organic removal (e.g., carbohydrates). There also existed relationships between certain resistance mechanisms and functional traits, indicating that ARGs might take part in the physiological process of microorganisms in the sludge treatment. These findings provide important insight into the differential resistome variations and host functionality, which would be crucial in the management of antibiotic resistance in CSTPs.

Seasonal distribution of antibiotic resistance genes under the influence of land-ocean interaction in a semi-enclosed bay

The irrational use of antibiotics has given rise to the proliferation of antibiotic resistance genes (ARGs) in coastal bays. There were few reports on the seasonal distribution of ARGs under the influence of land-ocean interaction in coastal bay. This work studied the seasonal and spatial proliferation of ARGs under the influences of land-ocean interaction in the Sishili Bay. Ten ARGs including tetB, tetG, tetX, sul1, sul2, qnrA, qnrB, qnrS, ermF, ermT and class 1 integron-integrase gene (intI1) were detected and quantified. The relative abundances of intI1 and most of ARGs were in orders of magnitude of 1 × 10^-7-2 copies/16S rRNA copies. The abundances of total ARGs in autumn and summer were much higher than those in the other seasons. Estuary, port and aquaculture farms were important reservoirs of ARGs in the bay. The nutrient levels in coastal water were positively associated with most of the ARGs and intI1, indicating that the water quality was an important driver of ARGs and their transmission. The land-based discharge and seawater stratification were proved to be the dominant driving factors for the seasonal distribution of ARGs in the coastal bay. The land-based discharge and seawater stratification were enhanced from spring to summer, which led to the sharp increase in ARGs in the surface water of the bay.

The balance between treatment efficiency and receptor quality determines wastewater impacts on the dissemination of antibiotic resistance

This study investigated the balance between treatment efficiency and impact caused by urban wastewater treatment plants (UWTPs) on the dissemination of antibiotic resistance. Four full-scale UWTPs (PT1-PT4) and the receiving river were sampled over four campaigns. The 16 S rRNA gene, two mobile genetic elements (MGEs), eight antibiotic resistance genes (ARGs), and culturable bacteria were monitored over different treatment stages and in hospital effluent. The bacterial and antibiotic resistance load was not significantly different in the inflow of the four UWTPs (p > 0.01). Biological treatment promoted ARGs reduction values up to 2.5 log-units/mL, while UV (PT1, PT2) or sand filtration/ozonation (PT3) led to removal values < 0.6 log-units/mL. The final effluent of PT3, with the highest removal rates and significantly lower ARGs abundance, was not significantly different from the receiving water body. Emerging ARGs (e.g., bla_VIM, bla_OXA-48, and bla_KPC) were sporadically detected in the river, although more frequent downstream. Hospital effluent might contribute for the occurrence of some, but not all these ARGs in the river. A major conclusion was that the impact of the UWTPs on the river was not only determined by treatment efficiency and final effluent quality, but also by the background contamination of the river and/or dilution rate.

Metagenomic profiling and transfer dynamics of antibiotic resistance determinants in a full-scale granular sludge wastewater treatment plant

In the One Health context, wastewater treatment plants (WWTPs) are central to safeguarding water resources. Nonetheless, many questions remain about their effectiveness in preventing antimicrobial resistance (AMR) dissemination. Most surveillance studies monitor the levels and removal of selected antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in intracellular DNA (iDNA) extracted from WWTP influents and effluents. The role of extracellular free DNA (exDNA) in wastewater is mostly overlooked. This study analyzed the transfer of ARGs and MGEs in a full-scale Nereda® reactor removing nutrients with aerobic granular sludge. We tracked the composition and fate of the iDNA and exDNA pools of influent, sludge, and effluent samples. Metagenomics was used to profile the microbiome, resistome, and mobilome signatures of iDNA and exDNA extracts. Selected ARGs and MGEs were analyzed by qPCR. From 2,840 ARGs identified, the genes arr-3 (2%), tetC (1.6%), sul1 (1.5%), oqxB (1.2%), and aph(3")-Ib (1.2%) were the most abundant among all sampling points and bioaggregates. Pseudomonas, Acinetobacter, Aeromonas, Acidovorax, Rhodoferax, and Streptomyces populations were the main potential hosts of ARGs in the sludge. In the effluent, 478 resistance determinants were detected, of which 89% were from exDNA potentially released by cell lysis during aeration in the reactor. MGEs and multiple ARGs were co-localized on the same extracellular genetic contigs. Total intracellular ARGs decreased 3-42% due to wastewater treatment. However, the ermB and sul1 genes increased by 2 and 1 log gene copies mL^-1, respectively, in exDNA from influent to effluent. The exDNA fractions need to be considered in AMR surveillance, risk assessment, and mitigation strategies.

Migration, Transformation and Removal of Macrolide Antibiotics in The Environment: A Review

Macrolide antibiotics (MAs), as a typical emerging pollutant, are widely detected in environmental media. When entering the environment, MAs can interfere with the growth, development and reproduction of organisms, which has attracted extensive attention. However, there are few reviews on the occurrence characteristics, migration and transformation law, ecotoxicity and related removal technologies of MAs in the environment. In this work, combined with the existing relevant research, the migration and transformation law and ecotoxicity characteristics of MAs in the environment are summarized, and the removal mechanism of MAs is clarified. Currently, most studies on MAs are based on laboratory simulation experiments, and there are few studies on the migration and transformation mechanism between multiphase states. In addition, the cost of MAs removal technology is not satisfactory. Therefore, the following suggestions are put forward for the future research direction. The migration and transformation process of MAs between multiphase states (such as soil-water-sediment) should be focused on. Apart from exploring the new treatment technology of MAs, the upgrading and coupling of existing MAs removal technologies to meet emission standards and reduce costs should also be concerned. This review provides some theoretical basis and data support for understanding the occurrence characteristics, ecotoxicity and removal mechanism of MAs.

Metatranscriptomic insight into the effects of antibiotic exposure on performance during anaerobic co-digestion of food waste and sludge

Antibiotics are inevitably entered into anaerobic co-digestion (AcoD) system of food waste (FW) and sludge along with the addition of abundant antibiotic-containing activated sludge. However, the in-depth insights into antibiotics affecting AcoD performance have not comprehensively studied. In present study, the results showed that tetracycline (TC), sulfamethoxazole (SMZ) and erythromycin (ERY) inhibited and delayed methane production except for 5 mg/L ERY. By comparison, TC and SMZ significantly inhibited the cumulative methane yields (one-way ANOVA, p < 0.01), and the inhibition effects were magnified as the antibiotic level increased. Physicochemical and methane yield analysis indicated antibiotics inhibited hydrolysis process and delayed methanogenesis process, which was in line with the declined abundance of acetogenic Proteiniphilum and hydrogenotrophic Methanobacterium during AcoD. Furthermore, metatranscriptomic analysis demonstrated the microbial activities of major organic and energy metabolism were down-regulated under antibiotics exposure, thereby down-regulating the expressions of key coenzymes (coenzymes M, F420, methanofuran) biosynthesis for methanogenesis and methane metabolism. The declined methanogenesis activity was completely consistent with the inhibited activity of dominant Methanosarcina and methane production, proving the importance of Methanosarcina on methane production. This study provides new metatranscriptomic evidence into the effects of antibiotics on methanogenesis during AcoD.

Natural recreational waters and the risk that exposure to antibiotic resistant bacteria poses to human health

Antimicrobial resistance (AMR) is widely recognised as a considerable threat to human health, wellbeing and prosperity. Many clinically important antibiotic resistance genes are understood to have originated in the natural environment. However, the complex interactions between humans, animals and the environment makes the health implications of environmental AMR difficult to quantify. This narrative review focuses on the current state of knowledge regarding antibiotic resistant bacteria (ARB) in natural bathing waters and implications for human health. It considers the latest research focusing on the transmission of ARB from bathing waters to humans. The limitations of existing evidence are discussed, as well as research priorities. The authors are of the opinion that future studies should include faecally contaminated bathing waters and people exposed to these environments to accurately parameterise environment-to-human transmission.

Spatiotemporal profiling of antibiotics and resistance genes in a river catchment: Human population as the main driver of antibiotic and antibiotic resistance gene presence in the environment

Studies to understand the role wastewater treatment plants (WWTPs) play in the dissemination of antibiotics (ABs), and in the emergence of antibiotic resistance (ABR), play an important role in tackling this global crisis. Here we describe the abundance and distribution of 16 ABs, and 4 corresponding antibiotic resistance genes (ARGs), sampled from the influent to five WWTPs within a single river catchment. We consider four classes of antibiotics: fluroquinolones, macrolides, sulfamethoxazole and chloramphenicol, as well the corresponding antibiotic resistance genes qnrS, ermB, sul1 and catA. All antibiotics, apart from four fluroquinolones (besifloxacin, lomefloxacin, ulifloxacin, prulifloxacin), were detected within all influent wastewater from the 5 cities (1 city = 1 WWTP), as were the corresponding antibiotic resistance genes (ARGs). Strong correlations were observed between the daily loads of ABs and ARGs versus the size of the population served by each WWTP, as well as between AB and ARG loads at a single site. The efficiency of ABs and ARGs removal by the WWTPs varied according to site (and treatment process utilized) and target, although strong correlations were maintained between the population size served by WWTPs and daily loads of discharged ABs and ARGs into the environment. We therefore conclude that population size is the main determinant of the magnitude of AB and ARG burden in the environment.

Temperature and Nutrient Limitations Decrease Transfer of Conjugative IncP-1 Plasmid pKJK5 to Wild Escherichia coli Strains

Plasmid-mediated dissemination of antibiotic resistance among fecal Enterobacteriaceae in natural ecosystems may contribute to the persistence of antibiotic resistance genes in anthropogenically impacted environments. Plasmid transfer frequencies measured under laboratory conditions might lead to overestimation of plasmid transfer potential in natural ecosystems. This study assessed differences in the conjugative transfer of an IncP-1 (pKJK5) plasmid to three natural Escherichia coli strains carrying extended-spectrum beta-lactamases, by filter mating. Matings were performed under optimal laboratory conditions (rich LB medium and 37°C) and environmentally relevant temperatures (25, 15 and 9°C) or nutrient regimes mimicking environmental conditions and limitations (synthetic wastewater and soil extract). Under optimal nutrient conditions and temperature, two recipients yielded high transfer frequencies (5 × 10-1) while the conjugation frequency of the third strain was 1000-fold lower. Decreasing mating temperatures to psychrophilic ranges led to lower transfer frequencies, albeit all three strains conjugated under all the tested temperatures. Low nutritive media caused significant decreases in transconjugants (-3 logs for synthetic wastewater; -6 logs for soil extract), where only one of the strains was able to produce detectable transconjugants. Collectively, this study highlights that despite less-than-optimal conditions, fecal organisms may transfer plasmids in the environment, but the transfer of pKJK5 between microorganisms is limited mainly by low nutrient conditions.