Metagenomic Characterization of Antibiotic Resistance Genes in Full-Scale Reclaimed Water Distribution Systems and Corresponding Potable Systems

Effect of UV pretreatment on the source control of floR during subsequent biotreatment of florfenicol wastewater

UV photolysis has been recommended as an alternative pretreatment method for the elimination of antibacterial activity of antibiotics against the indicator strain, but the pretreated antibiotic intermediates might not lose their potential to induce antibiotic resistance genes (ARGs) proliferation during subsequent biotreatment processes. The presence of florfenicol (FLO) in wastewater seriously inhibits the metabolic performance of anaerobic sludge microorganisms, especially the positive correlation between UV irradiation doses and ATP content, while it did not significantly affect the organics utilization ability and protein biosynthetic process of aerobic microorganisms. After sufficient UV pretreatment, the relative abundances of floR from genomic or plasmid DNA in subsequent aerobic and anaerobic biotreatment processes both decreased by two orders of magnitude, maintained at the level of the groups without FLO selective pressure. Meanwhile, the abundances of floR under anaerobic condition were always lower than that under aerobic condition, suggesting that anaerobic biotreatment systems might be more suitable for the effective control of target ARGs. The higher abundance of floR in plasmid DNA than in genome also indicated that the potential transmission risk of mobile ARGs should not be ignored. In addition, the relative abundance of intI1 was positively correlated with floR in its corresponding genomic or plasmid DNA (p < 0.05), which also increased the potential horizontal transfer risk of target ARGs. This study provides new insights into the effect of preferential UV photolysis as a pretreatment method for the enhancement of metabolic performance and source control of target ARGs in subsequent biotreatment processes. KEY POINTS: • Sufficient UV photolytic pretreatment efficiently controlled the abundance of floR • A synchronous decrease in abundance of intI1 reduced the risk of horizontal transfer • An appreciable abundance of floR in plasmid DNA was a potential source of total ARGs.

Aspirin altered antibiotic resistance genes response to sulfonamide in the gut microbiome of zebrafish

Pharmaceuticals are widespread in aquatic environments and might contribute to the prevalence of antibiotic resistance. However, the co-effect of antibiotics and non-antibiotic pharmaceuticals on the gut microbiome of fish is poorly understood. In this study, we characterized the variation of the zebrafish gut microbiome and resistome after exposure to sulfamethoxazole (SMX) and aspirin under different treatments. SMX contributed to the significant increase in the antibiotic resistance genes (ARGs) richness and abundance with 46 unique ARGs and five mobile genetic elements (MGEs) detected. Combined exposure to SMX and aspirin enriched total ARGs abundance and rearranged microbiota under short-term exposure. Exposure time was more responsible for resistome and the gut microbiome than exposure concentrations. Perturbation of the gut microbiome contributed to the functional variation related to RNA processing and modification, cell motility, signal transduction mechanisms, and defense mechanisms. A strong significant positive correlation (R = 0.8955, p < 0.001) was observed between total ARGs and MGEs regardless of different treatments revealing the key role of MGEs in ARGs transmission. Network analysis indicated most of the potential ARGs host bacteria belonged to Proteobacteria. Our study suggested that co-occurrence of non-antibiotics and antibiotics could accelerate the spread of ARGs in gut microbial communities and MGEs played a key role.

To what extent do water reuse treatments reduce antibiotic resistance indicators? A comparison of two full-scale systems

Water reuse is an essential strategy for reducing water demand from conventional sources, alleviating water stress, and promoting sustainability, but understanding the effectiveness of associated treatment processes as barriers to the spread of antibiotic resistance is an important consideration to protecting human health. We comprehensively evaluated the reduction of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in two field-operational water reuse systems with distinct treatment trains, one producing water for indirect potable reuse (ozone/biologically-active carbon/granular activated carbon) and the other for non-potable reuse (denitrification-filtration/chlorination) using metagenomic sequencing and culture. Relative abundances of total ARGs/clinically-relevant ARGs and cultured ARB were reduced by several logs during primary and secondary stages of wastewater treatment, but to a lesser extent during the tertiary water reuse treatments. In particular, ozonation tended to enrich multi-drug ARGs. The effect of chlorination was facility-dependent, increasing the relative abundance of ARGs when following biologically-active carbon filters, but generally providing a benefit in reduced bacterial numbers and ecological and human health resistome risk scores. Relative abundances of total ARGs and resistome risk scores were lowest in aquifer samples, although resistant Escherichia coli and Klebsiella pneumoniae were occasionally detected in the monitoring well 3-days downgradient from injection, but not 6-months downgradient. Resistant E. coli and Pseudomonas aeruginosa were occasionally detected in the nonpotable reuse distribution system, along with increased levels of multidrug, sulfonamide, phenicol, and aminoglycoside ARGs. This study illuminates specific vulnerabilities of water reuse systems to persistence, selection, and growth of ARGs and ARB and emphasizes the role of multiple treatment barriers, including aquifers and distribution systems.

NO3- as an electron acceptor elevates antibiotic resistance gene and human bacterial pathogen risks in managed aquifer recharge (MAR): A comparison with O2

Managed aquifer recharge (MAR) stands out as a promising strategy for ensuring water resource sustainability. This study delves into the comparative impact of nitrate (NO3-) and oxygen (O2) as electron acceptors in MAR on water quality and safety. Notably, NO3-, acting as an electron acceptor, has the potential to enrich denitrifying bacteria, serving as hosts for antibiotic resistance genes (ARGs) and enriching human bacterial pathogens (HBPs) compared to O2. However, a direct comparison between NO3- and O2 remains unexplored. This study assessed risks in MAR effluent induced by NO3- and O2, alongside the presence of the typical refractory antibiotic sulfamethoxazole. Key findings reveal that NO3- as an electron acceptor resulted in a 2 times reduction in dissolved organic carbon content compared to O2, primarily due to a decrease in soluble microbial product production. Furthermore, NO3- significantly enriched denitrifying bacteria, the primary hosts of major ARGs, by 747%, resulting in a 66% increase in the overall abundance of ARGs in the effluent of NO3- MAR compared to O2. This escalation was predominantly attributed to horizontal gene transfer mechanisms, as evidenced by a notable 78% increase in the relative abundance of mobile ARGs, alongside a minor 27% rise in chromosomal ARGs. Additionally, the numerous denitrifying bacteria enriched under NO3- influence also belong to the HBP category, resulting in a significant 114% increase in the abundance of all HBPs. The co-occurrence of ARGs and HBPs was also observed to intensify under NO3- influence. Thus, NO3- as an electron acceptor in MAR elevates ARG and HBP risks compared to O2, potentially compromising groundwater quality and safety.

Assessing the impact of low organic loading on effluent safety in wastewater treatment: Insights from an activated sludge reactor study

In this study, an organic loading (OL) of 300 mg/(L d) was set as the relative normal condition (OL-300), while 150 mg/(L d) was chosen as the condition reflecting excessively low organic loading (OL-150) to thoroughly assess the associated risks in the effluent of the biological wastewater treatment process. Compared with OL-300, OL-150 did not lead to a significant decrease in dissolved organic carbon (DOC) concentration, but it did improve dissolved organic nitrogen (DON) levels by ∼63 %. Interestingly, the dissolved organic matter (DOM) exhibited higher susceptibility to transformation into chlorinated disinfection by-products (Cl-DBPs) in OL-150, resulting in an increase in the compound number of Cl-DBPs by ∼16 %. Additionally, OL-150 induced nutrient stress, which promoted engendered human bacterial pathogens (HBPs) survival by ∼32 % and led to ∼51 % increase in the antibiotic resistance genes (ARGs) abundance through horizontal gene transfer (HGT). These findings highlight the importance of carefully considering the potential risks associated with low organic loading strategies in wastewater treatment processes.

Antibiotic resistance genes alterations in murine guts microbiome are associated with different types of drinking water

Antibiotic resistance genes (ARGs) are emerging contaminants threatening public health and commonly found in drinking water. However, the effect of different types of drinking water on ARG alterations in the gut microbiome is unclear. This study examines this issue in murine models in three phases (phase I: acclimation using ddH2O; phase II: treatment using different types of water, i.e. river water (RW), tap water (TW) and commercial bottled water (CBW); and phase III: recovery using ddH2O) using high-throughput qPCR and 16S rRNA amplicon sequencing. Results reveal that exposure to different types of drinking water could lead to significant changes in the gut microbiome, mobile genetic elements (MGEs), and ARGs. In phase II, treatment of RW and TW significantly increased the abundance of aminoglycoside and tetracycline resistance genes in mice guts (P < 0.01). In the recovery phase, consuming distilled water was found to restore ARG profiles to a certain extent in mice guts. Procrustes, network, redundancy and variation partitioning analysis indicated that ARG alterations in mice guts might relate to MGEs and bacterial communities. Our work suggests that the type of drinking water consumed may play a crucial role in shaping ARGs in gut microbiomes, emphasizing the urgent need for access to clean drinking water to mitigate the growing threat of antimicrobial resistance.

Revealing the response characteristics of periphyton biomass and community structure to sulfamethoxazole exposure in aquaculture water: The perspective of microbial network relationships

The widespread application of sulfonamide antibiotics in aquaculture has raised concerns about their adverse environmental impacts. Periphyton plays a crucial role in the aquatic ecosystem. In this study, we examined sulfamethoxazole (SMX) effects on the community structure and interactions of periphyton in simulated aquaculture water. Our findings indicated that the total biomass of periphyton decreased, while the biomass of periphytic algae and the secretion of extracellular polymeric substances (EPS) increased at 0.7 × 10-3 mg/L. Under higher SMX concentrations (5 mg/L and 10 mg/L), periphyton growth was severely inhibited, the microbial community structure of periphyton were sharply altered, characterized by the cyanobacteria growth suppression and decrease in the diversity index of community. Furthermore, elevated SMX concentrations (5 mg/L and 10 mg/L) increased the ratio of negative relationships from 45.4% to 49.4%, which suggested that high SMX concentrations promoted potential competition among microbes and disrupted the microbial food webs in periphyton. The absolute abundance of sul1 and sul2 genes in T2 and T3 groups were 2-3 orders of magnitude higher than those in control group after 30 days of SMX exposure, which elevated the risk of resistance gene enrichment and dissemination in the natural environment. The study contributes to our understanding of the detrimental effects of antibiotic pollution, which can induce changes in the structure and interaction relationship of microbial communities in aquaculture water.

Comparison of concentration and extraction workflows for qPCR quantification of intI1 and vanA in untreated wastewater

Quantitative polymerase chain reaction (qPCR) measurement of antibiotic resistance genes (ARGs) in untreated municipal wastewater may prove useful in combating the antimicrobial resistance crisis. However, harmonizing and optimizing qPCR-based workflows is essential to facilitate comparisons across studies, and includes achieving highly-effective ARG capture through efficient concentration and extraction procedures. In the current study, combinations of sample volume, membrane types and DNA extraction kits within filtration and centrifugation-based workflows were used to quantify 16S ribosomal RNA (16S rRNA), class 1 integron-integrase gene (intI1) and an ARG encoding resistance to vancomycin (vanA) in untreated wastewater sampled from three wastewater treatment plants (WWTPs). Highly abundant 16S rRNA and intI1 were detected in 100 % of samples from all three WWTPs using both 2 and 20 mL sample volumes, while lower prevalence vanA was only detected when using the 20 mL volume. When filtering 2 mL of wastewater, workflows with 0.20-/0.40-μm polycarbonate (PC) membranes generally yielded greater concentrations of the three targets than workflows with 0.22-/0.45-μm mixed cellulose ester (MCE) membranes. The improved performance was diminished when the sample volume was increased to 20 mL. Consistently greater concentrations of 16S rRNA, intI1 and vanA were yielded by filtration-based workflows using PC membranes combined with a DNeasy PowerWater (DPW) Kit, regardless of the sample volume used, and centrifugation-based workflows with DNeasy Blood & Tissue Kit for 2-mL wastewater extractions. Within the filtration-based workflows, the DPW kit yielded more detection and quantifiable results for less abundant vanA than the DNeasy PowerSoil Pro Kit and FastDNA™ SPIN Kit for Soil. These findings indicate that the performance of qPCR-based workflows for surveillance of ARGs in wastewater varies across targets, sample volumes, concentration methods and extraction kits. Workflows must be carefully considered and validated considering the target ARGs to be monitored.

The interaction between extracellular polymeric substances and corrosion products in pipes shaped different bacterial communities and the effects of micropollutants

There are growing concerns over the effects of micropollutants on biofilms formation and antibiotic resistance gene (ARGs) transmission in drinking water distribution pipes. However, there was no reports about the influence of the interaction between extracellular polymeric substances (EPS) and corrosion products on biofilms formation. Our results indicated that the abundance of quorum sensing (QS)-related genes, polysaccharide and amino acids biosynthesis genes of EPS was 6747-8055 TPM, 2221-2619 TPM, and 1461-1535 TPM in biofilms of cast iron pipes, respectively, which were higher than that of stainless steel pipes. The two-dimensional correlation spectroscopy (2D-COS) analysis of attenuated total reflectance-Fourier transform infrared spectrometry (ATR-FTIR) results indicated that polysaccharide of EPS was more easily adsorbed onto the corrosion products of cast iron pipes. Therefore, more human pathogenic bacteria (HPB) carrying ARGs were formed in biofilms of cast iron pipes. The amide I and amide II components and phosphate moieties of EPS were more susceptible to the corrosion products of stainless steel pipes. Thus, more bacteria genera carrying mobile genetic elements (MGE)-ARG were formed in biofilms of stainless steel pipes due to more abundance of QS-related genes, amino acids biosynthesis genes of EPS and the functional genes related to lipid metabolism. The enrichment of dimethyl phthalate (DMP), perfluorooctanoic acid (PFOA) and sulfadiazine (SUL) in corrosion products induced upregulation of QS and EPS-related genes, which promoted bacteria carrying different ARGs growth in biofilms, inducing more microbial risks.

The perfluoroalkyl substances influenced the distribution of bacterial communities and their functions from source water to tap water

Perfluoroalkyl substances (PFASs) and antibiotic resistance genes (ARGs) in drinking water are environmental issues that require special attention. The objective of this study was to know the effects of PFASs on microbial communities and their functional genes from source water to tap water. PFASs were detected by mass-labeled internal standards method, and the microbial communities and functional genes were analyzed by metagenomics. Our results indicated that the concentration of total PFASs in the water ranged from 47.7 to 171.4 ng/L, with perfluorobutanoic acid (PFBA) and perfluorooctanoic acid (PFOA) being the dominant types. The PFASs concentration decreased slowly from source to tap water in some months. PFBA, PFOA, perfluorooctane sulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) influenced the functional genes related to two-component system, bacterial secretion system and flagellar assembly of Aquabacterium, Methylobacterium, and Curvibacter, which contributed significantly to macB and evgS. Therefore, the bacterial communities enhanced adaptation to fluctuating environments by upregulating some functional genes under the PFASs stress, with concomitant changes in the expression of ARGs. Moreover, PFASs also promoted the expression of functional genes associated with human diseases, such as shigellosis and tuberculosis, which increased the risk of human pathogenicity. The bench scale experiment results also suggested that PFOA and PFOS in drinking water can promote the ARGs proliferation and induce microbial risk. Therefore, it is necessary to take measures to prevent the risks caused by PFASs and ARGs in drinking water.

Impact of corrosion inhibitors on antibiotic resistance, metal resistance, and microbial communities in drinking water

Corrosion inhibitors, including zinc orthophosphate, sodium orthophosphate, and sodium silicate, are commonly used to prevent the corrosion of drinking water infrastructure. Metals such as zinc are known stressors for antibiotic resistance selection, and phosphates can increase microbial growth in drinking water distribution systems (DWDS). Yet, the influence of corrosion inhibitor type on antimicrobial resistance in DWDS is unknown. Here, we show that sodium silicates can decrease antibiotic resistant bacteria (ARB) and antibiotic-resistance genes (ARGs), while zinc orthophosphate increases ARB and ARGs in source water microbial communities. Based on controlled bench-scale studies, zinc orthophosphate addition significantly increased the abundance of ARB resistant to ciprofloxacin, sulfonamides, trimethoprim, and vancomycin, as well as the genes sul1, qacEΔ1, an indication of resistance to quaternary ammonium compounds, and the integron-integrase gene intI1. In contrast, sodium silicate dosage at 10 mg/L resulted in decreased bacterial growth and antibiotic resistance selection compared to the other corrosion inhibitor additions. Source water collected from the drinking water treatment plant intake pipe resulted in less significant changes in ARB and ARG abundance due to corrosion inhibitor addition compared to source water collected from the pier at the recreational beach. In tandem with the antibiotic resistance shifts, significant microbial community composition changes also occurred. Overall, the corrosion inhibitor sodium silicate resulted in the least selection for antibiotic resistance, which suggests it is the preferred corrosion inhibitor option for minimizing antibiotic resistance proliferation in DWDS. However, the selection of an appropriate corrosion inhibitor must also be appropriate for the water chemistry of the system (e.g., pH, alkalinity) to minimize metal leaching first and foremost and to adhere to the lead and copper rule. IMPORTANCE Antibiotic resistance is a growing public health concern across the globe and was recently labeled the silent pandemic. Scientists aim to identify the source of antibiotic resistance and control points to mitigate the spread of antibiotic resistance. Drinking water is a direct exposure route to humans and contains antibiotic-resistant bacteria and associated resistance genes. Corrosion inhibitors are added to prevent metallic pipes in distribution systems from corroding, and the type of corrosion inhibitor selected could also have implications on antibiotic resistance. Indeed, we found that sodium silicate can minimize selection of antibiotic resistance while phosphate-based corrosion inhibitors can promote antibiotic resistance. These findings indicate that sodium silicate is a preferred corrosion inhibitor choice for mitigation of antibiotic resistance.

Metagenomic investigation reveals bacteriophage-mediated horizontal transfer of antibiotic resistance genes in microbial communities of an organic agricultural ecosystem

IMPORTANCE

Antibiotic resistance has become a serious health concern worldwide. The potential impact of viruses, bacteriophages in particular, on spreading antibiotic resistance genes is still controversial due to the complexity of bacteriophage-bacterial interactions within diverse environments. In this study, we determined the microbiome profiles and the potential antibiotic resistance gene (ARG) transfer between bacterial and viral populations in different agricultural samples using a high-resolution analysis of the metagenomes. The results of this study provide compelling genetic evidence for ARG transfer through bacteriophage-bacteria interactions, revealing the inherent risks associated with bacteriophage-mediated ARG transfer across the agricultural microbiome.

Prevalence of antimicrobial resistance in a full-scale drinking water treatment plant

Antibiotic resistance in drinking water has received increasing attention in recent years. In this study, the occurrence and abundance of antibiotic resistance genes (ARGs) in a drinking water treatment plant (DWTP) was comprehensively investigated using metagenomics. Bioinformatics analysis showed that 381 ARG subtypes belonging to 15 ARG types were detected, and bacitracin had the highest abundance (from 0.26 × 10-2 to 0.86 copies/cell), followed by multidrug (from 0.57 × 10-1 to 0.47 copies/cell) and sulfonamide (from 0.83 × 10-2 to 0.35 copies/cell). Additionally, 933 ARG-carrying contigs (ACCs) were obtained from the metagenomic data, among which 153 contigs were annotated as pathogens. The most abundant putative ARG host was Staphylococcus (7.9%), which most frequently carried multidrug ARGs (43.2%). Additionally, 38 high-quality metagenome-assembled genomes (MAGs) were recovered, one of which was identified as Staphylococcus aureus (Bin.624) and harboured the largest number of ARGs (n = 16). Using the cultivation technique, 60 isolates were obtained from DWTP samples, and Staphylococcus spp. (n = 11) were found to be dominant in all isolates, followed by Bacillus spp. (n = 17). Antimicrobial susceptibility testing showed that most Staphylococcus spp. were multidrug resistant (MDR). These results deepen our understanding of the distribution profiles of ARGs and antibiotic resistant bacteria (ARB) in DWTPs for potential health risk evaluation. Our study also highlights the need for new and efficient water purification technologies that can be introduced and applied in DWTPs.

Metagenomic evidence for antibiotics-driven co-evolution of microbial community, resistome and mobilome in hospital sewage

Overconsumption of antibiotics is an immediate cause for the emergence of antimicrobial resistance (AMR) and antibiotic resistant bacteria (ARB), though its environmental impact remains inadequately clarified. There is an urgent need to dissect the complex links underpinning the dynamic co-evolution of ARB and their resistome and mobilome in hospital sewage. Metagenomic and bioinformatic methods were employed to analyze the microbial community, resistome and mobilome in hospital sewage, in relation to data on clinical antibiotic use collected from a tertiary-care hospital. In this study, resistome (1,568 antibiotic resistance genes, ARGs, corresponding to 29 antibiotic types/subtypes) and mobilome (247 types of mobile genetic elements, MGEs) were identified. Networks connecting co-occurring ARGs with MGEs encompass 176 nodes and 578 edges, in which over 19 types of ARGs had significant correlations with MGEs. Prescribed dosage and time-dependent antibiotic consumption were associated with the abundance and distributions of ARGs, and conjugative transfer of ARGs via MGEs. Variation partitioning analyses show that effects of conjugative transfer were most likely the main contributors to transient propagation and persistence of AMR. We have presented the first evidence supporting idea that use of clinical antibiotics is a potent driving force for the development of co-evolving resistome and mobilome, which in turn supports the growth and evolution of ARB in hospital sewage. The use of clinical antibiotics calls for greater attention in antibiotic stewardship and management.

Metagenomic next generation sequencing for studying antibiotic resistance genes in the environment

Bacterial antimicrobial resistance (AMR) is a persisting and growing threat to human health. Characterization of antibiotic resistance genes (ARGs) in the environment is important to understand and control ARG-associated microbial risks. Numerous challenges exist in monitoring ARGs in the environment, due to the extraordinary diversity of ARGs, low abundance of ARGs with respect to the complex environmental microbiomes, difficulties in linking ARGs with bacterial hosts by molecular methods, difficulties in achieving quantification and high throughput simultaneously, difficulties in assessing mobility potential of ARGs, and difficulties in determining the specific AMR determinant genes. Advances in the next generation sequencing (NGS) technologies and related computational and bioinformatic tools are facilitating rapid identification and characterization ARGs in genomes and metagenomes from environmental samples. This chapter discusses NGS-based strategies, including amplicon-based sequencing, whole genome sequencing, bacterial population-targeted metagenome sequencing, metagenomic NGS, quantitative metagenomic sequencing, and functional/phenotypic metagenomic sequencing. Current bioinformatic tools for analyzing sequencing data for studying environmental ARGs are also discussed.

Seasonal and spatial variations of antibiotic resistance genes and bacterial biodiversity in biofilms covering the equipment at successive stages of drinking water purification

The presence of ARGs (antibiotic resistance genes) in the aquatic environment is a serious threat to public health especially in environmental biofilms as natural reservoirs of ARGs in water treatment plants (WTP). It has been shown that the treatment technology and source of water have a significant impact on the abundance and type of genes determining antibiotic resistance. The following indicator genes were proposed that should absolutely be controlled in environmental biofilms: intl1, sul2, sul1, tetA, blaOXA, and blaTEM. In both studied WTPs, the highest number of copies was determined for the intI1 gene. Among the tested ARGs, the highest values were obtained for genes sul1 and tetA. The qPCR analysis also revealed that the amounts of determined ARGs decreased in the following order: sulphonamides>carbapenems >tetracyclines > β-lactams >macrolides. The dominant bacterial types in all analysed samples were Proteobacteria and Bacteroidetes. Both ARGs and bacterial biodiversity was determined rather by sampling site (spatial variation) than seasonality. The obtained results show that biofilms are reservoirs of ARGs. This may affect the microbiological quality of water entering the water system. It is therefore necessary to include their analysis in the classical studies of water quality.

Machine learning-guided determination of Acinetobacter density in waterbodies receiving municipal and hospital wastewater effluents

A smart artificial intelligent system (SAIS) for Acinetobacter density (AD) enumeration in waterbodies represents an invaluable strategy for avoidance of repetitive, laborious, and time-consuming routines associated with its determination. This study aimed to predict AD in waterbodies using machine learning (ML). AD and physicochemical variables (PVs) data from three rivers monitored via standard protocols in a year-long study were fitted to 18 ML algorithms. The models' performance was assayed using regression metrics. The average pH, EC, TDS, salinity, temperature, TSS, TBS, DO, BOD, and AD was 7.76 ± 0.02, 218.66 ± 4.76 µS/cm, 110.53 ± 2.36 mg/L, 0.10 ± 0.00 PSU, 17.29 ± 0.21 °C, 80.17 ± 5.09 mg/L, 87.51 ± 5.41 NTU, 8.82 ± 0.04 mg/L, 4.00 ± 0.10 mg/L, and 3.19 ± 0.03 log CFU/100 mL respectively. While the contributions of PVs differed in values, AD predicted value by XGB [3.1792 (1.1040-4.5828)] and Cubist [3.1736 (1.1012-4.5300)] outshined other algorithms. Also, XGB (MSE = 0.0059, RMSE = 0.0770; R² = 0.9912; MAD = 0.0440) and Cubist (MSE = 0.0117, RMSE = 0.1081, R² = 0.9827; MAD = 0.0437) ranked first and second respectively, in predicting AD. Temperature was the most important feature in predicting AD and ranked first by 10/18 ML-algorithms accounting for 43.00-83.30% mean dropout RMSE loss after 1000 permutations. The two models' partial dependence and residual diagnostics sensitivity revealed their efficient AD prognosticating accuracies in waterbodies. In conclusion, a fully developed XGB/Cubist/XGB-Cubist ensemble/web SAIS app for AD monitoring in waterbodies could be deployed to shorten turnaround time in deciding microbiological quality of waterbodies for irrigation and other purposes.

Critical review of phytoremediation for the removal of antibiotics and antibiotic resistance genes in wastewater

Antibiotics in wastewater are a growing environmental concern. Increased prescription and consumption rates have resulted in higher antibiotic wastewater concentration. Conventional wastewater treatment methods are often ineffective at antibiotic removal. Given the environmental risk of antibiotics and associated antibiotic resistant genes (ARGs), finding methods of improving antibiotic removal from wastewater is of great importance. Phytoremediation of antibiotics in wastewater, facilitated through constructed wetlands, has been explored in a growing number of studies. To assess the removal efficiency and treatment mechanisms of plants and microorganisms within constructed wetlands for specific antibiotics of major antibiotic classes, the present review paper considered and evaluated data from the most recent published research on the topics of bench scale hydroponic, lab and pilot scale constructed wetland, and full scale constructed wetland antibiotic remediation. Additionally, microbial and enzymatic antibiotic degradation, antibiotic-ARG correlation, and plant effect on ARGs were considered. It is concluded from the present review that plants readily uptake sulfonamide, macrolide, tetracycline, and fluoroquinolone antibiotics and that constructed wetlands are an effective applied phytoremediation strategy for the removal of antibiotics from wastewater through the mechanisms of microbial biodegradation, root sorption, plant uptake, translocation, and metabolization. More research is needed to better understand the effect of plants on microbial community and ARGs. This paper serves as a synthesis of information that will help guide future research and applied use of constructed wetlands in the field antibiotic phytoremediation and wastewater treatment.

Functional Characterization of a Novel SMR-Type Efflux Pump RanQ, Mediating Quaternary Ammonium Compound Resistance in Riemerella anatipestifer

Riemerella anatipestifer (R. anatipestifer) is a multidrug-resistant bacterium and an important pathogen responsible for major economic losses in the duck industry. Our previous study revealed that the efflux pump is an important resistance mechanism of R. anatipestifer. Bioinformatics analysis indicated that the GE296_RS02355 gene (denoted here as RanQ), a putative small multidrug resistance (SMR)-type efflux pump, is highly conserved in R. anatipestifer strains and important for the multidrug resistance. In the present study, we characterized the GE296_RS02355 gene in R. anatipestifer strain LZ-01. First, the deletion strain RA-LZ01ΔGE296_RS02355 and complemented strain RA-LZ01cΔGE296_RS02355 were constructed. When compared with that of the wild-type (WT) strain RA-LZ01, the mutant strain ΔRanQ showed no significant influence on bacterial growth, virulence, invasion and adhesion, morphology biofilm formation ability, and glucose metabolism. In addition, the ΔRanQ mutant strain did not alter the drug resistance phenotype of the WT strain RA-LZ01 and displayed enhanced sensitivity toward structurally related quaternary ammonium compounds, such as benzalkonium chloride and methyl viologen, which show high efflux specificity and selectivity. This study may help elucidate the unprecedented biological functions of the SMR-type efflux pump in R. anatipestifer. Thus, if this determinant is horizontally transferred, it could cause the spread of quaternary ammonium compound resistance among bacterial species.

Metagenomic analysis revealed sources, transmission, and health risk of antibiotic resistance genes in confluence of Fenhe, Weihe, and Yellow Rivers

Rivers are important vectors and reservoirs of antibiotics resistance genes (ARGs). Information regarding transmission and health risk of ARGs in river confluence is still lacking. In this study, metagenomics was used to distinguish contributions of human activities on ARGs and human pathogenic bacteria (HPB) in confluence of Fenhe, Weihe, and Yellow Rivers. Bacitracin resistance gene and bacA were the highest in all rivers, with 1.86 × 10^-2-7.26 × 10^-2 and 1.79 × 10^-2-9.12 × 10^-2 copies/16S rRNA copies, respectively. River confluence significantly increased the abundance of ARGs, especially at the confluence of three rivers with the highest 1.53 × 10^-1 copies/16S rRNA copies. Antibiotic efflux and antibiotic target alteration were the dominant resistant mechanisms in three rivers. ARGs profiles were influenced by multiple factors, with the contributions of various factors ranked as microbial communities > physicochemical factors > human activities > mobile genetic elements (MGEs). Notably, human activities and animal feces were important potential contributors of ARGs in the Weihe River and Yellow River. Transposons, as the main MGEs in three rivers, played important roles in ARGs transfer. The confluence of three rivers had the highest abundance of MGEs with the greatest transfer potentials, and therefore exhibiting the largest exposure risk of ARGs with 232.4 copies/cap·d. Furthermore, correlations of ARGs, MGEs, and HPB in different rivers were constructed via co-occurrence modes to systematically illustrate the health risks of ARGs. This study firstly unveiled the transmission and health risk of ARGs in river confluence, providing supports for ARGs control in watershed.

Data-driven discoveries on widespread contamination of freshwater reservoirs by dominant antibiotic resistance genes

The propagation of antibiotic resistance genes (ARGs) in freshwater reservoirs threatens ecosystem security and human health, and has attracted increasing attention. A series of recent research articles on ARGs provides a unique opportunity for data-driven discoveries in this emerging field. Here, we mined data from a total of 290 samples from 60 reservoirs worldwide with a data-driven framework (DD) developed to discover geographical distribution, influencing factors and pollution hotspots of ARGs in freshwater reservoirs. Most data came from Asia and Europe where nine classes of ARGs were most frequently detected in reservoirs with multi-drug resistance and sulfonamide resistance genes prevailing. Factors driving distribution of reservoir ARGs differed between reservoir waters and sediments, and interactions among these factors had linear or nonlinear enhancement effects on the explanatory power of ARG distribution. During the cold season, small-sized reservoir waters rich in organic carbon, mobile genetic elements (MGEs) and antibiotics had a higher pollution potential of ARGs; during the spring drought, sediments in large reservoirs located in densely populated areas were more conducive to dissemination of ARGs due to their richness in antibiotics and MGEs. Thus, distribution pattern of ARG pollution hotspots in reservoir waters and sediments varies greatly depending on the differences of internal and external factors. From the "One Health" perspective, this widespread contamination of freshwater reservoirs by ARGs we discovered through the DD framework should be a push to promote integrated research across regions and disciplines. Especially the human - food-chain - ecosystem interface needs an improved understanding of ARG contamination mechanisms and targeted monitoring and evaluation systems should be developed to maintain all ecosystem services in freshwater reservoirs as well as to safeguard human health.

Growth and prevalence of antibiotic-resistant bacteria in microplastic biofilm from wastewater treatment plant effluents

It is accepted that Microplastic (MP) biofilms accumulates antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) in water. ARB/ARGs and MPs are emerging pollutants of concern due to various associated health risks. The objective of this study was to 1) investigate the ARB community in a pilot-scale wastewater treatment plant (WWTP) effluent, 2) to study and visualize the ARB/ARGs in MP biofilm grown in WWTP effluent and tap water, and 3) to analyze microplastic adherent ARB/ARGs in the biofilm and planktonic ARB/ARGs in the filtrate under controlled conditions. Results indicated the dominance of Pseudomonas, Aeromonas, and Bacillus among isolated ARB in WWTP effluent. Representative resistance strains were incubated in 300 mL water containing commercial polystyrene beads of 300550 μm diameter (MP) in a series of batch experiments. Microbiological, molecular, and microscopic analyses were performed by enumeration, 16srRNA, real-time polymerase chain reaction (qPCR), and Field Emission-Scanning Electron Microscopy (FEG-SEM) techniques. The analyzed viable ARB indicated an increasing trend in MP biofilms between days 3 and 5. It further decreased on days 7 and 9. The prevalence of ARB in the filtrate and MP biofilm varied as a function of time and TOC level, while no significant impacts were observed for minor temperature variation, low antibiotic pressure, and increased MP mass with few exceptions. Relative abundance of ARGs (vanA, sul1) and integron integrase gene (intl1) in MP biofilm were significantly different across different TOC levels, time, and antibiotic pressure. ARGs and intl1 were detected in the MP biofilm in tap water and WWTP effluent on day 30.

Unraveling the influence of human fecal pollution on antibiotic resistance gene levels in different receiving water bodies using crAssphage indicator gene

Discharged wastewater treatment plant (WWTP) effluents can contaminate receiving water bodies with human feces and alter the abundance of antibiotic resistance genes (ARGs). In this study, we examined the co-occurrence of ARGs, human fecal pollution indicator crAssphage, and antibiotics in human feces and a series of connected receiving water bodies affected by human feces, including water from different treatment units of a WWTP, river, lake, and tap waters. Results showed that crAssphage was detected in 68.2 % of the studied water bodies, confirming widespread human fecal contamination. Both ARG and crAssphage abundances exhibited a distance-decay effect from the emission source to the receiving environment. Interestingly, the detected ARG abundance in the water bodies was significantly correlated with crAssphage abundance but not with the residual antibiotic concentration, demonstrating that the presence of ARG could largely be explained by the extent of fecal pollution, with no clear signs of antibiotic selection. In addition, 14 ARGs co-shared by human feces and water bodies were significantly correlated with crAssphage. Furthermore, a close evolutionary relationship was observed between the bla_TEM-1 gene from human feces and aquatic environments. These results imply a potential ARG exchange between human feces and receiving water bodies. Overall, this study provides important insights into the distribution and sources of ARGs in water bodies affected by human fecal contamination.

A proposed framework for the identification of indicator genes for monitoring antibiotic resistance in wastewater: Insights from metagenomic sequencing

Antibiotic resistance is one of the greatest threats to global human and animal health of our time. Municipal wastewater has been identified as a hotspot of antibiotic resistance contamination to water bodies. However, there are numerous potential antibiotic resistant pathogens and their associated antibiotic resistance genes (ARGs), making it difficult to implement routine monitoring that addresses the breadth of the problem. The objective of this study was to identify candidate indicator ARGs for monitoring antibiotic resistance in wastewater and receiving water bodies. We developed a framework to identify indicator ARGs that incorporated clinical relevance, abundance in wastewater, geographic ubiquity, environmental relevance, ARG mobility, associations with mobile genetic elements, and the availability of quantitative analytical methods. To identify indicator ARGs, published metagenomic sequencing data from 191 wastewater samples originating from 64 countries across the world were obtained from online public repositories. Through ARG annotation and network analysis, this framework revealed 56 candidate indicator ARGs distributed across four modules of strongly correlated ARGs, with one ARG from each module (oqxA, ermB, sul1, and mexE) proposed as a minimally redundant monitoring target. The results of this study provide the basis for antibiotic resistance surveillance and monitoring framework in wastewater and contaminated waterways.

Seasonal dissemination of antibiotic resistome from livestock farms to surrounding soil and air: Bacterial hosts and risks for human exposure

Feces in livestock farms is a reservoir of antibiotic resistance genes (ARGs), which can disseminate into surrounding soil and air, bringing risks to human health. In this study, seasonal dissemination of ARGs in a livestock farm and implications for human exposure was explored. The experimental results showed that ARGs abundance basically ranked as feces > soil > air, and significant seasonal dependence was observed. The total ARGs in pig feces was relatively higher in autumn (10^9.7 copies g^-1) and winter (10^10.0 copies g^-1), and lower in summer (10^5.0 copies g^-1). Similarly, the lowest total ARGs in soil and air were also observed in summer. There were correlations among ARGs, integron intI1, and bacterial community. Total organic carbon was an important factor affecting ARGs distribution in the feces, and pH and moisture content significantly affected soil ARGs. The daily intakes of integron intI1 and ARGs from air were 10°^.5 copies h^-1 and 10^2.3 copies h^-1 for human exposure, respectively. Pseudomonas was a potential pathogenic host of bla_TEM-1 in feces, Pseudomonas and Acinetobacter were potential pathogenic hosts of multiple ARGs in soil, while ARGs in air did not migrate into pathogens.

Metagenomic-based surveillance systems for antibiotic resistance in non-clinical settings

The success of antibiotics as a therapeutic agent has led to their ineffectiveness. The continuous use and misuse in clinical and non-clinical areas have led to the emergence and spread of antibiotic-resistant bacteria and its genetic determinants. This is a multi-dimensional problem that has now become a global health crisis. Antibiotic resistance research has primarily focused on the clinical healthcare sectors while overlooking the non-clinical sectors. The increasing antibiotic usage in the environment - including animals, plants, soil, and water - are drivers of antibiotic resistance and function as a transmission route for antibiotic resistant pathogens and is a source for resistance genes. These natural compartments are interconnected with each other and humans, allowing the spread of antibiotic resistance via horizontal gene transfer between commensal and pathogenic bacteria. Identifying and understanding genetic exchange within and between natural compartments can provide insight into the transmission, dissemination, and emergence mechanisms. The development of high-throughput DNA sequencing technologies has made antibiotic resistance research more accessible and feasible. In particular, the combination of metagenomics and powerful bioinformatic tools and platforms have facilitated the identification of microbial communities and has allowed access to genomic data by bypassing the need for isolating and culturing microorganisms. This review aimed to reflect on the different sequencing techniques, metagenomic approaches, and bioinformatics tools and pipelines with their respective advantages and limitations for antibiotic resistance research. These approaches can provide insight into resistance mechanisms, the microbial population, emerging pathogens, resistance genes, and their dissemination. This information can influence policies, develop preventative measures and alleviate the burden caused by antibiotic resistance.

Short-term inhalation exposure evaluations of airborne antibiotic resistance genes in environments

Antibiotic resistance is a sword of Damocles that hangs over humans. In regards to airborne antibiotic resistance genes (AARGs), critical knowledge gaps still exist in the identification of hotspots and quantification of exposure levels in different environments. Here, we have studied the profiles of AARGs, mobile genetic elements (MGEs) and bacterial communities in various atmospheric environments by high throughput qPCR and 16S rRNA gene sequencing. We propose a new AARGs exposure dose calculation that uses short-term inhalation (STI). Swine farms and hospitals were high-risk areas where AARGs standardised abundance was more abundant than suburbs and urban areas. Additionally, resistance gene abundance in swine farm worker sputum was higher than that in healthy individuals in other environments. The correlation between AARGs with MGEs and bacteria was strong in suburbs but weak in livestock farms and hospitals. STI exposure analysis revealed that occupational intake of AARGs (via PM₁₀) in swine farms and hospitals were 110 and 29 times higher than in suburbs, were 1.5 × 10⁴, 5.6 × 10⁴ and 5.1 × 10² copies, i.e., 61.9%, 75.1% and 10.7% of the overall daily inhalation intake, respectively. Our study comprehensively compares environmental differences in AARGs to identify high-risk areas, and forwardly proposes the STI exposure dose of AARGs to guide risk assessment.

Source prevention of halogenated antibiotic resistance genes proliferation: UV/sulfite advanced reduction process achieved accurate and efficient elimination of florfenicol antibacterial activity

The production and consumption of halogenated antibiotics, such as florfenicol (FLO), remain high, accompanied by a large amount of antibiotic-containing wastewater, which would induce the potential proliferation and transmission of antibiotic resistance genes (ARGs) in conventional biological systems. This study revealed that the introduction of reductive species (mainly H) by adding sulfite during UV irradiation process accelerated the decomposition rate of FLO, increasing from 0.1379 min^-1 in the single UV photolytic system to 0.3375 min^-1 in the UV/sulfite system. The enhanced photodecomposition in UV/sulfite system was attributed to the improved dehalogenation performance and additional removal of sulfomethyl group at the site of the benzene ring, which were the representative structures consisting of FLO antibacterial activity. Compared with single UV photolysis, UV/sulfite advanced reduction process saved the light energy requirement by 40 % for the evolutionary suppression of floR, and its corresponding class of ARGs in subsequent biotreatment system was controlled at the level of the negative group. Compared with UV/H₂O₂ and UV/persulfate systems, the decomposition rate of FLO in the UV/S system was the highest and preserved the corresponding carbon source of the coexisting organic compounds for the potential utilization of microbial metabolism in subsequent biotreatment process. These results demonstrated that UV/sulfite advanced reduction process could be adopted as a promising pretreatment option for the source prevention of representative ARGs proliferation of halogenated antibiotics in subsequent biotreatment process.

Application of Nucleotide-Based Kinetic Modeling Approaches to Predict Antibiotic Resistance Gene Degradation during UV- and Chlorine-Based Wastewater Disinfection Processes: From Bench- to Full-Scale

This study investigated antibiotic resistance gene (ARG) degradation kinetics in wastewaters during bench- and full-scale treatment with UV light and chlorine─with the latter maintained as free available chlorine (FAC) in low-ammonia wastewater and converted into monochloramine (NH₂Cl) in high-ammonia wastewater. Twenty-three 142-1509 bp segments (i.e., amplicons) of seven ARGs (blt, mecA, vanA, tet(A), ampC, bla_NDM, bla_KPC) and the 16S rRNA gene from antibiotic resistant bacteria (ARB) strains Bacillus subtilis, Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae were monitored as disinfection targets by qPCR. Rate constants for ARG and 16S rRNA gene amplicon degradation by UV, FAC, and NH₂Cl were measured in phosphate buffer and used to expand and validate several recently developed approaches to predict DNA segment degradation rate constants based solely on their nucleotide contents, which were then applied to model ARG degradation during bench-scale treatment in buffer and wastewater matrixes. Kinetics of extracellular and intracellular ARG degradation by UV and FAC were well predicted up to ∼1-2-log₁₀ elimination, although with decreasing accuracy at higher levels for intracellular genes, while NH₂Cl yielded minimal degradation under all conditions (agreeing with predictions). ARB inactivation kinetics varied substantially across strains, with intracellular gene degradation lagging cell inactivation in each case. ARG degradation levels observed during full-scale disinfection at two wastewater treatment facilities were consistent with bench-scale measurements and predictions, where UV provided ∼1-log₁₀ ARG degradation, and chlorination of high-ammonia wastewater (dominated by NH₂Cl) yielded minimal ARG degradation.

Variations in Bacterial Communities and Antibiotic Resistance Genes Across Diverse Recycled and Surface Water Irrigation Sources in the Mid-Atlantic and Southwest United States: A CONSERVE Two-Year Field Study

Reduced availability of agricultural water has spurred increased interest in using recycled irrigation water for U.S. food crop production. However, there are significant knowledge gaps concerning the microbiological quality of these water sources. To address these gaps, we used 16S rRNA gene and metagenomic sequencing to characterize taxonomic and functional variations (e.g., antimicrobial resistance) in bacterial communities across diverse recycled and surface water irrigation sources. We collected 1 L water samples (n = 410) between 2016 and 2018 from the Mid-Atlantic (12 sites) and Southwest (10 sites) U.S. Samples were filtered, and DNA was extracted. The V3-V4 regions of the 16S rRNA gene were then PCR amplified and sequenced. Metagenomic sequencing was also performed to characterize antibiotic, metal, and biocide resistance genes. Bacterial alpha and beta diversities were significantly different (p < 0.001) across water types and seasons. Pathogenic bacteria, such as Salmonella enterica, Staphylococcus aureus, and Aeromonas hydrophilia were observed across sample types. The most common antibiotic resistance genes identified coded against macrolides/lincosamides/streptogramins, aminoglycosides, rifampin and elfamycins, and their read counts fluctuated across seasons. We also observed multi-metal and multi-biocide resistance across all water types. To our knowledge, this is the most comprehensive longitudinal study to date of U.S. recycled water and surface water used for irrigation. Our findings improve understanding of the potential differences in the risk of exposure to bacterial pathogens and antibiotic resistance genes originating from diverse irrigation water sources across seasons and U.S. regions.

Antibiotic resistomes and their chemical residues in aquatic environments in Africa

The aquatic environment is a hotspot for the transfer of antibiotic resistance to humans and animals. Several reviews have put together research efforts on the presence and distribution of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and antibiotic chemical residue (ACRs) in food, hospital wastewater, and even in other aquatic environments. However, these reports are largely focused on data from developed countries, while data from developing countries and especially those in Africa, are only marginally discussed. This review is the first effort that distills information on the presence and distribution of ARGs and ACRs in the African aquatic environments (2012-2021). This review provides critical information on efforts put into the study of ARB, ARGs, and ACRs in aquatic environments in Africa through the lens of the different sub-regions in the continent. The picture provided is compared with those from some other continents in the world. It turns out that the large economies in Africa (South Africa, Nigeria, Tunisia, Kenya) all have a few reports of ARB and ARGs in their aquatic environment while smaller economies in the continent could barely provide reports of these in their aquatic environment (in most cases no report was found) even though they have some reports on resistomes from clinical studies. Interestingly, the frequency of these reports of ARB and ARGs in aquatic environments in Africa suggests that the continent is ahead of the South American continent but behind Europe and Asia in relation to providing information on these contaminants. Common ARGs found in African aquatic environment encode resistance to sulfonamide, tetracycline, β-lactam, and macrolide classes of antibiotics. The efforts and studies from African scientists in eliminating ARB and ARGs from the aquatic environment in Africa are also highlighted. Overall, this document is a ready source of credible information for scientists, policy makers, governments, and regional bodies on ARB, ARGs, and ACRs in aquatic environments in Africa. Hopefully, the information provided in this review will inspire some necessary responses from all stakeholders in the water quality sector in Africa to put in more effort into providing more scientific evidence of the presence of ARB, ARGs, and ACRs in their aquatic environment and seek more efficient ways to handle them to curtail the spread of antibiotic resistance among the population in the continent. This will in turn, put the continent on the right path to meeting the United Nations Sustainable Development Goals #3 and #6, which at the moment, appears to be largely missed by most countries in the continent.

Inactivation of biohazards in healthcare wastewater by E-Beam and Gamma irradiation: a comparative study

The main objective of this study is to evaluate the effect of irradiation by Gamma rays and Electron Beam (E-Beam) on naturally occurring microorganisms shed in healthcare wastewater issued from multi-specialties hospital. We examined the susceptibility of naturally occurring total indicator bacteriophages towards Gamma rays and E-Beam irradiation to evaluate their appropriateness as viral indicators for healthcare wastewater quality control. Results showed that healthcare wastewater is a rich matrix containing bacteriophages surrogates of pathogenic waterborne viruses (4.5 Log10 PFU/100 mL for SOMCPH and 2.3 Log10 PFU/100 mL for FRNAPH), antibiotic resistant bacteria (Mean concentrations from 2.3 to 5.5 Log10 CFU/100 mL), molds and yeasts (2.7 Log10 CFU/100 mL), and spores of Clostridium perfringens (Mean concentration of 3.3 Log10 CFU/100 mL). After E-Beam irradiation, naturally occurring bacteria in healthcare wastewater showed lower resistance patterns (D10 values ranging between 0.21 ± 0.005 and 0.59 ± 0.005) compared to those obtained after Gamma irradiation (D10 values ranging between 0.25 ± 0.015 and 0.70 ± 0.0001). Spores of Clostridium perfringens were the most resistant assayed microbes either after E-Beam (D10 values of 3.74 ± 0.005) or Gamma irradiation (D10 values of 4.77 ± 0.025) of collected samples. According to inactivation patterns, a dose of 10 kGy was sufficient for a complete inactivation of spores. Bacteriophages isolated from healthcare wastewater showed the same resistance patterns as those previously obtained in urban treated sewage and were inactivated using higher doses than waterborne bacteria (D10 values of SOMCPH 1.46 ± 0.057; D10 values of FRNAPH 1.03 ± 0.057). Their resistance to irradiation treatment in such complex matrix corroborates their use to survey the viral quality of healthcare wastewater before their discharge in the urban sanitation network. D10 value analysis showed that bacteria and bacteriophages inactivation by E-Beam irradiation required lower doses than those required for their inactivation using Gamma rays. According to inactivation patterns, a dose of 7 kGy was sufficient for total inactivation of both pathogenic bacteria and viruses. Thus, E-Beam irradiation seems to be an efficient physical pre-treatment process for healthcare wastewater treatment prior to its discharge in urban sanitation system to ensure compliance with environmental standards and protect public health.

Higher spreading risk of antibacterial biocide and heavy metal resistance genes than antibiotic resistance genes in aerobic granular sludge

Metagenomic approach was applied to simultaneously reveal the antibiotic resistance genes (ARGs) and antibacterial biocide & metal resistance genes (BMRGs), and the corresponding microbial hosts with high mobility during aerobic granular sludge (AGS) formation process. The results showed that the relative abundance of BMRGs was 88-123 times that of ARGs. AGS process was easier to enrich BMRGs, leading to a greater risk of drug resistance caused by BMRGs than that by ARGs. The enrichments of ARGs and BMRGs in AGS were closely related to several enhanced microbial metabolisms (i.e., cell motility, transposase and ATP-binding cassette transporters) and their corresponding regulatory genes. Several enhanced KEGG Orthologs (KO) functions, such as K01995, K01996, K01997 and K02002, might cause a positive impact on the spread of ARGs and BMRGs, and the main contributors were the largely enriched glycogens accumulating organisms. The first dominant ARGs (adeF) was carried by lots of microbial hosts, which might be enriched and propagated mainly through horizontal gene transfer. Candidatus Competibacter denitrificans simultaneously harbored ARG (cmx) and Cu related RGs (corR). Many enriched bacteria contained simultaneously multiple BMRGs (copR and corR) and mobile genetic elements (integrons and plasmids), granting them high mobility capabilities and contributing to the spread of BMRGs. This study might provide deeper understandings of the proliferation and mobility of ARGs and BMRGs, importantly, highlighted the status of BMRGs, which laid the foundation for the controlling widespread of resistance genes in AGS.

The elimination of cell-associated and non-cell-associated antibiotic resistance genes during membrane filtration processes: A review

With increasing water reuse as a sustainable water management strategy, antibiotic resistance genes (ARGs) which have been identified as emerging contaminants in wastewater are attracting global attentions. Given that wastewater treatment plants are now well-established as a sink and source of ARGs in both cell-associated and non-cell-associated forms, a need is acknowledged to reduce their proliferation and protect public health. Due to their different characteristics, cell-associated and non-cell-associated ARGs may have distinct responses to membrane filtration processes which are widely used as advanced treatment to the secondary effluent. This review improves the understanding of the abundance of cell-associated and non-cell-associated ARGs in wastewaters and the secondary effluents and compares the elimination of ARGs in cell-associated and non-cell-associated forms by low-pressure and high-pressure membrane filtration processes. The former process reduces the concentration of cell-associated ARGs by more than 2-logs on average. An increase of the retention efficiency of non-cell-associated ARGs is observed with decreasing molecular weight cut-offs in ultrafiltration. The high-pressure membrane filtration (i.e., nanofiltration and reverse osmosis) can effectively eliminate both cell-associated and non-cell-associated ARGs, with averagely more than 4.6-log reduction. In general, the two forms of ARGs can be removed from water by the membrane filtration processes via the effects of size exclusion, adsorption, and electrostatic repulsion. The size and conformation of cell-associated and non-cell-associated ARGs, characteristics of membranes, coexisting substances, and biofilm formation influence ARG retention. Accumulation and potential proliferation of cell-associated and non-cell-associated ARGs in foulants and concentrate and corresponding control strategies warrant future research.

Antimicrobial Resistance Monitoring of Water Environments: A Framework for Standardized Methods and Quality Control

Antimicrobial resistance (AMR) is a grand societal challenge with important dimensions in the water environment that contribute to its evolution and spread. Environmental monitoring could provide vital information for mitigating the spread of AMR; this includes assessing antibiotic resistance genes (ARGs) circulating among human populations, identifying key hotspots for evolution and dissemination of resistance, informing epidemiological and human health risk assessment models, and quantifying removal efficiencies by domestic wastewater infrastructure. However, standardized methods for monitoring AMR in the water environment will be vital to producing the comparable data sets needed to address such questions. Here we sought to establish scientific consensus on a framework for such standardization, evaluating the state of the science and practice of AMR monitoring of wastewater, recycled water, and surface water, through a literature review, survey, and workshop leveraging the expertise of academic, governmental, consulting, and water utility professionals.

Antimicrobial Resistance Monitoring of Water Environments: A Framework for Standardized Methods and Quality Control

Antimicrobial resistance (AMR) is a grand societal challenge with important dimensions in the water environment that contribute to its evolution and spread. Environmental monitoring could provide vital information for mitigating the spread of AMR; this includes assessing antibiotic resistance genes (ARGs) circulating among human populations, identifying key hotspots for evolution and dissemination of resistance, informing epidemiological and human health risk assessment models, and quantifying removal efficiencies by domestic wastewater infrastructure. However, standardized methods for monitoring AMR in the water environment will be vital to producing the comparable data sets needed to address such questions. Here we sought to establish scientific consensus on a framework for such standardization, evaluating the state of the science and practice of AMR monitoring of wastewater, recycled water, and surface water, through a literature review, survey, and workshop leveraging the expertise of academic, governmental, consulting, and water utility professionals.

A snapshot of the global drinking water virome: Diversity and metabolic potential vary with residual disinfectant use

Viruses are important drivers of microbial community ecology and evolution, influencing microbial mortality, metabolism, and horizontal gene transfer. However, the effects of viruses remain largely unknown in many environments, including in drinking water systems. Drinking water metagenomic studies have offered a whole community perspective of bacterial impacts on water quality, but have not yet considered the influences of viruses. In this study, we address this gap by mining viral DNA sequences from publicly available drinking water metagenomes from distribution systems in six countries around the world. These datasets provide a snapshot of the taxonomic diversity and metabolic potential of the global drinking water virome; and provide an opportunity to investigate the effects of geography, climate, and drinking water treatment practices on viral diversity. Both environmental conditions and differences in sample processing were found to influence the viral composition. Using free chlorine as the residual disinfectant was associated with clear differences in viral taxonomic diversity and metabolic potential, with significantly fewer viral populations and less even viral community structures than observed in distribution systems without residual disinfectant. Additionally, drinking water viruses carry antibiotic resistance genes (ARGs), as well as genes to survive oxidative stress and nitrogen limitation. Through this study, we have demonstrated that viral communities are diverse across drinking water systems and vary with the use of residual disinfectant. Our findings offer directions for future research to develop a more robust understanding of how virus-bacteria interactions in drinking water distribution systems affect water quality.

Triclosan enriched resistance genes more easily than copper in the presence of environmental tetracycline in aerobic granular sludge system

Triclosan (TCS) and copper (Cu²⁺) were exposed to aerobic granular sludge (AGS) system treating wastewater containing environmental tetracycline, respectively, to explore the different biochemical responses, more importantly, the fates of resistance genes (RGs) in AGS system. The results showed that TCS and Cu²⁺ could significantly inhibit the N and P removal in AGS system by reducing several key functional genes, including amoA gene of ammonia-oxidizing bacteria, Nitrospira and phosphorus accumulating organisms 16S rRNA genes. TCS caused higher degree of RGs' enrichment than Cu²⁺, which made the average total relative abundance of RGs of 1.38 ± 0.73 and 0.78 ± 0.24 in TCS and Cu system, respectively. Cu²⁺ could induce a wider range of horizontal gene transfer than TCS, leading to the detections of more potential hosts harboring RGs in Cu system. Cu system seemed to have stronger repair, immunity and defense ability than TCS system, which enabled it to have sufficient ability to trigger protection mechanism to realize self-protection, eventually the RGs also were controlled. Integron (intI1 and intI3) and plasmids (trb-C and IncQ) might cooperate with microorganisms and water quality parameters to enhance the enrichment of RGs in TCS system, however this interaction among various environmental factors was not obvious in Cu system, which might be responsible for the lower abundance of RGs. The increasing levels of TCS and Cu²⁺ in wastewater should be paid more attentions during the treatment of wastewater containing environmental tetracycline by AGS system. Especially for TCS, it had the ability to enrich RGs more easily than Cu²⁺, which should be prevented from entering wastewater treatment plants as far as possible, to avoid more serious proliferation and dissemination of various RGs.

Insights into nitrogen removal from seawater-based wastewater through marine anammox bacteria under ampicillin stress: Microbial community evolution and genetic response

Global spread of ampicillin (AMP) in the aquatic environment have attracted much attention recently. Marine anammox bacteria (MAB) have potentials in saline wastewater treatment due to their good salt tolerance. However, to date, the effect resulting from AMP on MAB is still unknown. Herein, the effect of AMP on MAB, involving microbial community evolution and genetic response, was investigated for the first time. A lab-scale reactor inoculated by MAB sludge was operated under saline condition (35 g/L) and AMP stress of different gradients. Within 200 cycles, nitrogen removal performance was monitored and sludge samples were withdrawn for high-throughput sequencing analyses and qPCR. The results confirmed that the nitrogen removal capacity of MAB declined with increasing AMP dosage, and almost collapsed at 300 mg/L AMP. The total nitrogen removal rate and specific anammox activity finally dropped to 0.17 kg N m^-3 d^-1 and 101.86 mg N g^-1VSS d^-1, respectively. Pseudoalteromonas (38.13%) dominated the reactor on Cycle 190, which formed a new symbiosis with MAB. And the emergence of oleophilic bacteria such as Colwellia (2.53%) was also observed. Moreover, antibiotic resistance genes were detected with increased abundance and diversity, indicating the AMP dosing significantly promoted microbial community evolution and genetic response.

Ancient Oriental Wisdom still Works: Removing ARGs in Drinking Water by Boiling as compared to Chlorination

Antibiotic resistance genes (ARGs) in municipal drinking water may not be effectively removed during centralized treatment. To reduce potential health risks, water disinfection at the point-of-use scale is warranted. This study investigated the performance of boiling, a prevalent household water disinfection means, in response to ARGs contamination. We found that boiling was more efficient in inactivating both Escherichia coli and environmental bacteria compared to chlorination and pasteurization. Boiling of environmental bacteria suspension removed a much broader spectrum of ARGs and mobile genetic elements (up to 141 genes) than chlorination (up to 13 genes), such better performance was largely attributed to a stronger inactivation of chlorine-tolerant bacteria including Acinetobacter and Bacillus. Accumulation of extracellular ARGs was found during low-temperature heating (≤ 80°C) and in the initial stage of chlorination (first 3 min when initial chlorine was 5 mg/L and first 12 min when initial chlorine was 1 mg/L). These extracellular ARGs as well as the intracellular ARGs got removed as the heating temperature increased or the chlorination time prolonged. Under the same treatment time (30 min), high-temperature heating (≥ 90.1°C) damaged the DNA structure more thoroughly than chlorination (5 mg/L). Taking into account the low transferability of ARGs after DNA melting, boiling may provide an effective point-of-use approach to attenuating bacterial ARGs in drinking water and is still worth promoting in the future.

Bioleaching rather than chemical conditioning using Fe[III]/CaO or polyacrylamide mitigates antibiotic resistance in sludge composting via pre-removing antibiotic resistance genes and limiting horizontal gene transfer

Conditioning can drastically improve the dewaterability of sewage sludge and is widely practiced in most wastewater treatment plants (WWTPs). Sludge conditioning was also reported as a crucial step in sludge treatment to attenuate antibiotic resistance, but it remains unclear whether the attenuated antibiotic resistance by conditioning treatments would guarantee low abundance of antibiotic resistance genes (ARGs) in the compost products of municipal sewage sludge. Herein, the impacts of three conditioning treatments, including bioleaching and chemical conditioning using Fe[III]/CaO or polyacrylamide (PAM), on the abundances of 20 ARGs and 4 mobile genetic elements (MGEs) during conventional aerobic composting of dewatered sludge were investigated. It was found that the absolute and relative abundances of total ARGs in compost product of bioleached sludge accounted for only 13.8%-28.8% of that in compost products of un-conditioned, Fe[III]/CaO-conditioned, or PAM-conditioned sludges. Besides, bioleaching conditioning resulted in the lowest abundances of ARG subtypes and ARG-associated bacteria in the sludge compost product. The shift of ARG profiles in the bioleached sludge composting can be mainly ascribed to the ARG-associated bacteria, while the MGEs drove the ARG profiles during conventional composting of un-conditioned sludge and the two chemically conditioned sludge. Thus, bioleaching conditioning is superior to the chemical conditioning using Fe[III]/CaO or PAM in mitigating antibiotic resistance in sludge compost products, which was contributed by the pre-removal of ARGs prior to composting treatment and the potential limitation of ARGs transfer during conventional composting.

A watershed impacted by anthropogenic activities: Microbial community alterations and reservoir of antimicrobial resistance genes

Water is the main resource for maintaining life. Anthropic activities influence the microbial epidemiological chain in watersheds, which can act as ways of disseminating microorganisms resistant to antimicrobial drugs, with impacts on human, animal, and environmental health. Here, we characterized aquatic microbial communities and their resistomes in samples collected along Rio das Ostras watershed during two seasons. Surface water samples were collected at eleven sites from the Jundiá, Iriry, and Rio das Ostras rivers in two seasons (dry and wet season). Microbial DNA was extracted, high-throughput sequenced and screened for antimicrobial resistance genetic (ARG) markers. The physicochemical characteristics and the microbiota data confirmed that Rio das Ostras watershed can be divided into three well defined portions: rural, urban, and marine. Rural areas were enriched by bacteria typically found in limnic environments and Patescibacteria phyla. The urban portion was characterized by sites with low pH and groups associated with iron oxidation. Some genera of clinical relevance were also identified, though in relatively low abundance. The marine site was enriched mainly by Cyanobacteria and bacteria that showed strong correlation with conductivity, salinity, and chloride. Twenty-six ARG markers were identified on the resistome, being found most frequently in the urban area, despite being present in rural sites. Among them were some related to classes of great clinical concern, such as genes coding for extended-spectrum beta-lactamase (bla_CTX-M and bla_TEM), resistance to carbapenems (bla_KPC) and to methicillin by Staphylococcus aureus (mecA). These results broaden our understanding of the microbial community of a watershed impacted by anthropogenic actions. The large number of ARGs detected along the Rio das Ostras watershed contrasts with the small number of microorganisms of clinical relevance observed, suggesting that antimicrobial resistance has arisen from non-clinical environments and microbes. Our results corroborate that freshwater acts as a reservoir of antimicrobial resistance genes.

The role of antibiotics and heavy metals on the development, promotion, and dissemination of antimicrobial resistance in drinking water biofilms

Antimicrobial resistance (AMR), as well as the development of biofilms in drinking water distribution systems (DWDSs), have become an increasing concern for public health and management. As bulk water travels from source to tap, it may accumulate contaminants of emerging concern (CECs) such as antibiotics and heavy metals. When these CECs and other selective pressures, such as disinfection, pipe material, temperature, pH, and nutrient availability interact with planktonic cells and, consequently, DWDS biofilms, AMR is promoted. The purpose of this review is to highlight the mechanisms by which AMR develops and is disseminated within DWDS biofilms. First, this review will lay a foundation by describing how DWDS biofilms form, as well as their basic intrinsic and acquired resistance mechanisms. Next, the selective pressures that further induce AMR in DWDS biofilms will be elaborated. Then, the pressures by which antibiotic and heavy metal CECs accumulate in DWDS biofilms, their individual resistance mechanisms, and co-selection are described and discussed. Finally, the known human health risks and current management strategies to mitigate AMR in DWDSs will be presented. Overall, this review provides critical connections between several biotic and abiotic factors that influence and induce AMR in DWDS biofilms. Implications are made regarding the importance of monitoring and managing the development, promotion, and dissemination of AMR in DWDS biofilms.

An Ohio State Scenic River Shows Elevated Antibiotic Resistance Genes, Including Acinetobacter Tetracycline and Macrolide Resistance, Downstream of Wastewater Treatment Plant Effluent

The entry of antibiotic resistance genes (ARGs) into aquatic systems has been documented for large municipal wastewater treatment plants (WWTPs), but there is less study of the impact of smaller plants that are situated on small rural rivers. We sampled water metagenomes for ARGs and taxa composition from the Kokosing River, a small rural river in Knox County, Ohio, which has been designated an Ohio State Scenic River for retention of natural character. Samples were obtained 1.0 km upstream, 120 m downstream, and 6.4 km downstream from the effluent release of the Mount Vernon WWTP. ARGs were identified in metagenomes using ShortBRED markers from the comprehensive antibiotic resistance database (CARD) screened against UniPROT. Through all seasons, the metagenome just downstream of the WWTP effluent showed a substantial elevation of at least 15 different ARGs, including 6 ARGs commonly associated with Acinetobacter baumannii, such as msrE, mphE (macrolide resistance), and tet(39) (tetracycline resistance). The ARGs most prevalent near the effluent pipe persisted 6.4 km downriver. Using metagenomic phylogenetic analysis (MetaPhlAn2) clade-specific marker genes, the taxa distribution near the effluent showed elevation of reads annotated as Acinetobacter species as well as gut-associated taxa, Bacteroides and Firmicutes. The ARG levels and taxa prevalence showed little dependence on seasonal chlorination of the effluent. Nitrogen and phosphorus were elevated near the effluent pipe but had no consistent correlation with ARG levels. We show that in a rural river microbiome, year-round wastewater effluent substantially elevates ARGs, including those associated with multidrug-resistant A. baumannii.

IMPORTANCE Antibiotic resistance is a growing problem worldwide, with frequent transmission between pathogens and environmental organisms. Rural rivers can support high levels of recreational use by people unaware of inputs from treated wastewater, while wastewater treatment plants (WWTPs) can generate a small but significant portion of flow volume into a river surrounded by forest and agriculture. There is little information on the rural impacts of WWTP effluent on the delivery and transport of antibiotic resistance genes. In our study, the river water proximal to wastewater effluent shows evidence for the influx of multidrug-resistant Acinetobacter baumannii, an opportunistic pathogen of concern for hospitals but also widespread in natural environments. Our work highlights the importance of wastewater effluent in management of environmental antibiotic resistance, even in high quality, rural river systems.

Towards risk assessment for antibiotic resistant pathogens in recycled water: a systematic review and summary of research needs

Risk assessment is critical for identifying target concentrations of antibiotic resistant pathogens necessary for mitigating potential harmful exposures associated with water reuse. However, there is currently limited available data characterizing the concentrations of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in recycled water to support robust efforts at risk assessment. The objective of this systematic review was to identify and synthesize the existing literature documenting the presence and abundance of ARB and ARGs in recycled water. In addition, this review identifies best practices and explores monitoring targets for studying ARB and ARGs in recycled water to guide future work and identifies key research needs aimed at better supporting quantitative microbial risk assessment focused on recycled water and antibiotic resistance. Future efforts to collect data about ARB and ARG prevalence in recycled water should report concentration data per unit volume. Sample metadata should also be provided, including a description of treatment approach, a description of planned water uses (e.g., potable, irrigation), methods for conveyance to the point of use, and available physicochemical water quality data. Additional research is needed aimed at identifying recommended ARB and ARG monitoring targets and for developing approaches to incorporate metagenomic data into risk assessment.

Dynamics of antibiotic resistance and its association with bacterial community in a drinking water treatment plant and the residential area

Drinking water treatment techniques are used globally in the context of water security and public health, yet they are not applicable to antibiotic resistance gene (ARG) contamination. Using high-throughput quantitative PCR, we analyzed the prevalence and diversity of ARGs and mobile genetic elements (MGEs) in water supplies. A total of 224 ARGs and MGEs were detected in all sampling sites. Absolute abundance and detected number of ARGs decreased significantly (P < 0.05) in sand filter water after drinking water treatment and increased thereafter at point-of-use (household tap water). Changes in the composition and diversity of the bacterial community were observed in water samples at different steps. A significant correlation (P < 0.001) between microbial communities and ARG profiles was observed, and variance in ARG profiles could be primarily attributed to community composition (11.9%), and interaction between community composition, environmental factors and MGEs (30.7%). A network analysis was performed, and the results showed eight bacterial phyla were significantly correlated with nine different classes of ARGs, suggesting the potential bacterial host for ARGs. This study suggested that although the absolute abundance of ARGs decreased after treatment of drinking water treatment plants (DWTPs), the rebounded of ARGs in the water distribution system should not be neglected.

Inactivation, removal, and regrowth potential of opportunistic pathogens and antimicrobial resistance genes in recycled water systems

With two thirds of the global population living in areas affected by water scarcity, wastewater reuse is actively being implemented or explored by many nations. There is a need to better understand the efficacy of recycled water treatment plants (RWTPs) for removal of human opportunistic pathogens and antimicrobial resistant microorganisms. Here, we used a suite of probe-based multiplex and SYBR green real-time PCR assays to monitor enteric opportunistic pathogens (EOPs; Acinetobacter baumannii, Arcobacter butzlieri, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Legionella spp., Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Enteritidis, Streptococcus spp.) and antimicrobial resistance genes (ARGs; qnrS, bla_SHV, bla_TEM, bla_GES, bla_KPC, bla_IMI, bla_SME, bla_NDM, bla_VIM, bla_IMP, bla_OXA-48-like, mcr-1 and mcr-3) of key concern from an antimicrobial resistance (AMR), waterborne and foodborne disease perspective. The class 1 integron-integrase gene (intl1) was quantified as a proxy for multi-drug resistance. EOPs, intl1 and ARGs absolute abundance (DNA and RNA) and metabolic activity (RNA) was assessed through three RWTPs with differing treatment trains. Our results indicate that RWTPs produced high quality recycled water for non-potable reuse by removing >95% of EOPs and ARGs, however, subpopulations of EOPs and ARGs survived disinfection and demonstrated potential to become actively growing members of the recycled water and distribution system microbiomes. The persistence of functional intl1 suggests that significant genetic recombination capacity remains in the recycled water, along with the likely presence of multi-drug resistant bacteria. Results provide new insights into the persistence and growth of EOPs, and prevalence and removal of ARGs in recycled water systems. These data will contribute towards the emerging evidence base of AMR risks in recycled water to inform quantitative risk-based policy development regarding water recycling schemes.

A Quantitative Metagenomic Sequencing Approach for High-Throughput Gene Quantification and Demonstration with Antibiotic Resistance Genes

Comprehensive microbial risk assessment requires high-throughput quantification of diverse microbial risks in the environment. Current metagenomic next-generation sequencing approaches can achieve high-throughput detection of genes indicative of microbial risks but lack quantitative capabilities. This study developed and tested a quantitative metagenomic next-generation sequencing (qmNGS) approach. Numerous xenobiotic synthetic internal DNA standards were used to determine the sequencing yield (Y_seq) of the qmNGS approach, which can then be used to calculate absolute concentration of target genes in environmental samples based on metagenomic sequencing results. The qmNGS approach exhibited excellent linearity as indicated by a strong linear correlation (r² = 0.98) between spiked and detected concentrations of internal standards. High-throughput capability of the qmNGS approach was demonstrated with artificial Escherichia coli mixtures and cattle manure samples, for which 95 ± 3 and 208 ± 4 types of antibiotic resistance genes (ARGs) were detected and quantified simultaneously. The qmNGS approach was further compared with quantitative real-time PCR (qPCR) and demonstrated comparable levels of accuracy and less variation for the quantification of six target genes (16S, tetO, sulI, tetM, ermB, and qnrS). IMPORTANCE Monitoring and comprehensive assessment of microbial risks in the environment require high-throughput gene quantification. The quantitative metagenomic NGS (qmNGS) approach developed in this study incorporated numerous xenobiotic and synthetic DNA internal standard fragments into metagenomic NGS workflow, which are used to determine a new parameter called sequencing yield that relates sequence base reads to absolute concentration of target genes in the environmental samples. The qmNGS approach demonstrated excellent method linearity and comparable performance as the qPCR approach with high-throughput capability. This new qmNGS approach can achieve high-throughput and accurate gene quantification in environmental samples and has the potential to become a useful tool in monitoring and comprehensively assessing microbial risks in the environment.

Effect of preferential UV photolysis on the source control of antibiotic resistome during subsequent biological treatment systems

The environmental spread of antibiotic resistance genes (ARGs) from the direct application of traditional biological treatment systems for antibiotics in water is a potential public health threat. UV photolysis has been proved to be an efficient pretreatment method for antibacterial activity elimination, but the fate of antibiotic resistome in subsequent bioreactors fed with pretreated florfenicol (FLO) in synthetic wastewater is still unknown. Antibacterial activity in synthetic wastewater was effectively eliminated by UV irradiation pretreatment, and the diversity and abundance of detected ARGs in both aerobic and anaerobic bioreactors were significantly lower than those without pretreatment. Meanwhile, UV irradiation pretreatment shaped the structure and composition of sludge microbial communities in the subsequent bioreactors closer to those of the FLO-free groups. The relative abundances of Pseudomonas and Escherichia-Shigella working as the potential hosts of ARGs were significantly reduced in aerobic and anaerobic bioreactors, respectively. The significantly positive correlation between floR and intI1 and the decrease of intI1 abundance in UV photolytic pretreatment groups indicated that the horizontal transfer of floR was decreased. The study provides new insights into the effect of preferential UV photolysis as a pretreatment method on the source control of antibiotic resistome in subsequent biological treatment process.

Comparative investigation on removal characteristics of tetracycline from water by modified wood membranes with different channel walls

The alkali-innocuous citric acid (CA) modified wood membranes (WMs) have been developed as facile, economical, and effective adsorption membranes to remove tetracycline (TC) from water. However, TC removal by modified WMs with different types of wood channel walls have rarely been compared. Therefore, in this study, modified WMs were prepared with pinewood (PW) and basswood (BW). The PW and BW WMs before and after modification were characterized by SEM, EDX, XRD, ATR-FTIR, TGA, contact angle and zeta potential. After modification, cellulose I in cellulose crystal structures of raw WM transformed to cellulose II and the contents of carboxylic groups for PW and BW were enhanced to make the hydrophilicity of WM surface increased. Compared with modified PW WMs, particles formed on the channel walls of modified BW WMs containing vessel pits to make more carboxylic groups introduced. The TC adsorption breakthrough curves showed that the 6 wt% alkali- CA modified BW had an effective filtration volume of 1968 bed volume (BV) compared with the 4 wt% alkali-CA modified PW of 1205 BV as the influent TC and breakthrough point were chosen at 2 and 0.5 mg/L, respectively. At low pH, TC complex with WM surfaces through Lewis acid-base interaction. Zwitterionic TC was shown to favor adsorption onto WM via hydrogen bonding at pH of around 5. With further increasing pH, TC adsorption efficiency decreased due to the electrostatic repulsion. The costs of modified BW and PW are about 0.0054-0.0126 US$/m³ and 0.01-0.024 US$/m³ for a low TC concentration effluent (0-0.5 mg/L), respectively. This work shed a new sight on how to develop economical and effective adsorption WMs for contaminants removal from water.