Antibiotic Resistance Genes In Wastewater Treatment Plants Research Articles

Comparative assessment of microbiome and resistome of influent and effluent of sewage treatment plant and common effluent treatment plant located in Delhi, India using shotgun approach

Antimicrobial resistance (AMR) is a significant threat that demands surveillance to identify and analyse trends of the emerging antibiotic resistance genes (ARGs) and potential microbial carriers. The influent of the wastewater treatment plants (WWTPs) reflects the microbes derived from the population and effluent being the source of dissemination of potential pathogenic microbes and AMR. The present study aimed to monitor microbial communities and antibiotic resistance genes in WWTPs employing a whole metagenome shotgun sequencing approach. The samples were collected from a sewage treatment plant (STP) and a common effluent treatment plant (CETP) in Delhi, India. The results showed the influent of STP to be rich in Bifidobacterium, Bacteroides, Escherichia, Arcobacter, and Pseudomonas residents of gut microbiota and known to cause diseases in humans and animals; whereas the CETP sample was abundant in Aeromonas, Escherichia, and Shewanella known to be involved in the degradation of different compounds. Interestingly, the effluent samples from both STPs and CETP were rich in microbial diversity, comprising organic and xenobiotic compound degrading and disease-causing bacteria, indicating the effluent being the source of dissemination of concerning bacteria to the environment. The functional profile at both sites displayed similarity with an abundance of housekeeping function genes as analyzed by Clusters of Orthologous Genes (COG), KEGG Orthology (KO), and subsystem databases. Resistome profiling by MEGARes showed the dominance of ARGs corresponding to beta-lactams having relative abundance ranging from 16% to 34% in all the metagenome datasets, followed by tetracycline (8% to16%), aminoglycosides (7% to 9%), multi-drug (5% to 9%), and rifampin (3% to 9%). Also, AMR genes oxa, ant3-DPRIME, and rpoB, which are of clinical importance were predominantly and most prevalently present in all the samples. The presence of AMR in effluents from both types of treatment plants indicates that wastewater from both sources contributes to the spread of pathogenic bacteria and resistance genes, increasing the environmental AMR burden and therefore requires tertiary treatment before discharge. This work will facilitate further research towards the identification of suitable biomarkers for monitoring antibiotic resistance.

Research progress on the origin, fate, impacts and harm of microplastics and antibiotic resistance genes in wastewater treatment plants

Previous studies reported microplastics (MPs), antibiotics, and antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). There is still a lack of research progress on the origin, fate, impact and hazards of MPs and ARGs in WWTPs. This paper fills a gap in this regard. In our search, we used “microplastics”, “antibiotic resistance genes”, and “wastewater treatment plant” as topic terms in Web of Science, checking the returned results for relevance by examining paper titles and abstracts. This study mainly explores the following points: (1) the origins and fate of MPs, antibiotics and ARGs in WWTPs; (2) the mechanisms of action of MPs, antibiotics and ARGs in sludge biochemical pools; (3) the impacts of MPs in WWTPs and the spread of ARGs; (4) and the harm inflicted by MPs and ARGs on the environment and human body. Contaminants in sewage sludge such as MPs, ARGs, and antibiotic-resistant bacteria enter the soil and water. Contaminants can travel through the food chain and thus reach humans, leading to increased illness, hospitalization, and even mortality. This study will enhance our understanding of the mechanisms of action among MPs, antibiotics, ARGs, and the harm they inflict on the human body.

Prevalence of antibiotics, antibiotic resistance genes, and their associations in municipal wastewater treatment plants along the Yangtze River basin, China

The overuse and misuse of antibiotics have resulted in the pollution of antibiotics and antibiotic resistance genes (ARGs) in municipal wastewater treatment plants (WWTPs), posing threats to ecological security and human health. Thus, a comprehensive investigation was conducted to assess the occurrence, removal efficiency, and ecological risk of antibiotics, along with the diversity, abundance, and co-occurrence of ARGs, and their correlations in 13 WWTPs along the Yangtze River Basin. Among 35 target antibiotics, 23 antibiotics within 6 categories were detected in all the samples. Amoxicillin (AMO), ofloxacin (OFL), and pefloxacin (PEF) were predominant in influents, while AMO exhibited dominance with the highest concentration of 1409 ng/L in effluents. Although antibiotic removal performance varied among different WWTPs, a significant decrease in each antibiotic category and overall antibiotics was observed in effluents compared with that in influents (p < 0.05). Remarkably, ecological risk assessment revealed high risks associated with AMO and ciprofloxacin (CIP) and medium risks linked to several antibiotics, notably including OFL, roxithromycin (ROX), clarithromycin (CLA), and tetracycline (TC). Furthermore, 96 ARG subtypes within 12 resistance types were detected in this study, and the total absolute abundance and diversity of ARGs were significantly decreased from influents to effluents (p < 0.05). Enrichment of 38 ARGs (e.g., blaNDM, ermA, vatA, mexA, and dfrA25) in effluents indicated potential health risks. Various mobile genetic elements (MGEs), exhibited significant correlations with a majority of ARGs in both influents and effluents, such as intⅠ1, tnpA1, tnpA5, and tp614, underscoring the important role of MGEs in contributing to the ARG dissemination. Many antibiotics displayed lower correlations with corresponding ARGs, but exhibited higher correlations with other ARGs, suggesting complex selective pressures influencing ARG propagation. Overall, the incomplete elimination of antibiotics and ARGs in WWTPs is likely to pose adverse impacts on aquatic ecosystems in the Yangtze River Basin.

Horizontal transfer potential of antibiotic resistance genes in wastewater treatment plants unraveled by microfluidic-based mini-metagenomics

Wastewater treatment plants (WWTPs) are known to harbor antibiotic resistance genes (ARGs), which can potentially spread to the environment and human populations. However, the extent and mechanisms of ARG transfer in WWTPs are not well understood due to the high microbial diversity and limitations of molecular techniques. In this study, we used a microfluidic-based mini-metagenomics approach to investigate the transfer potential and mechanisms of ARGs in activated sludge from WWTPs. Our results show that while diverse ARGs are present in activated sludge, only a few highly similar ARGs are observed across different taxa, indicating limited transfer potential. We identified two ARGs, ermF and tla-1, which occur in a variety of bacterial taxa and may have high transfer potential facilitated by mobile genetic elements. Interestingly, genes that are highly similar to the sequences of these two ARGs, as identified in this study, display varying patterns of abundance across geographic regions. Genes similar to ermF found are widely found in Asia and the Americas, while genes resembling tla-1 are primarily detected in Asia. Genes similar to both genes are barely detected in European WWTPs. These findings shed light on the limited horizontal transfer potential of ARGs in WWTPs and highlight the importance of monitoring specific ARGs in different regions to mitigate the spread of antibiotic resistance.

Metagenomic insight into the prevalence and driving forces of antibiotic resistance genes in the whole process of three full-scale wastewater treatment plants

The spread of antibiotic resistance genes (ARGs) is an emerging global health concern, and wastewater treatment plants (WWTPs), as an essential carrier for the occurrence and transmission of ARGs, deserves more attention. Based on the Illumina NovaSeq high-throughput sequencing platform, this study conducted a metagenomic analysis of 18 samples from three full-scale WWTPs to explore the fate of ARGs in the whole process (influent, biochemical treatment, advanced treatment, and effluent) of wastewater treatment. Total 70 ARG subtypes were detected, among which multidrug, aminoglycoside, tetracycline, and macrolide ARGs were most abundant. The different treatment processes used for three WWTPs were capable of reducing ARG diversity, but did not significantly reduce ARG abundance. Compared to that by denitrification filters, the membrane bioreactor (MBR) process was advantageous in controlling the prevalence of multidrug ARGs in WWTPs. Linear discriminant analysis Effect Size (LEfSe) suggested g_Nitrospira, g_Curvibacter, and g_Mycobacterium as the key bacteria responsible for differential ARG prevalence among different WWTPs. Meanwhile, adeF, sul1, and mtrA were the persistent antibiotic resistance genes (PARGs) and played dominant roles in the prevalence of ARGs. Proteobacteria and Actinobacteria were the host bacteria of majority ARGs in WWTPs, while Pseudomonas and Nitrospira were the most crucial host bacteria influencing the dissemination of critical ARGs (e.g., adeF). In addition, microbial richness was determined to be the decisive factor affecting the diversity and abundance of ARGs in wastewater treatment processes. Overall, regulating the abundance of microorganisms and key host bacteria by selecting processes with microbial interception, such as MBR process, may be beneficial to control the prevalence of ARGs in WWTPs.

Deciphering the antibiotic resistome and microbial community in municipal wastewater treatment plants at different elevations in eastern and western China

Antibiotic resistance genes (ARGs) as emerging environmental contaminants pose severe global risks to public health and ecosystems. Municipal wastewater treatment plants (WWTPs) are crucial transmitters for the dissemination and propagation of ARGs into receiving water bodies via mobile genetic elements (MGEs). However, the comprehensive and deep deciphering of the diversity, abundance, and potential hosts of ARGs in two distinct altitudinal WWTPs is scarce. In this work, we revealed the elevational distribution characteristics of the resistance genes and microbial community of six WWTPs from two distinct geographical zones: a low−elevation (LE) region (Shandong, 10–22 m above sea level) and a high−elevation (HE) region (Gansu, 1,520–1,708 m above sea level). Significant elevational variations in the diversity and relative abundance of resistance genes were observed. Wastewater treatment could significantly reduce the concentrations of ARGs and MGEs by about 1–2 and 2–3 orders of magnitude, respectively. However, above 69.95% of resistance genes were enriched in effluent. In particular, 24 ARG subtype, 3 MGE subtypes, and 59 bacterial genera were persistent in all samples. More potential hosts for ARGs in LE region and more abundant human gut microbiota in HE region were identified. This work provides helpful information for controlling the spread of ARGs for their management and assessment, thereby mitigating the risks of ARGs in WWTPs.

Clinically Relevant β-Lactam Resistance Genes in Wastewater Treatment Plants.

Antimicrobial resistance (AMR) is one of the largest global concerns due to its influence in multiple areas, which is consistent with One Health's concept of close interconnections between people, animals, plants, and their shared environments. Antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) circulate constantly in various niches, sediments, water sources, soil, and wastes of the animal and plant sectors, and is linked to human activities. Sewage of different origins gets to the wastewater treatment plants (WWTPs), where ARB and ARG removal efficiency is still insufficient, leading to their transmission to discharge points and further dissemination. Thus, WWTPs are believed to be reservoirs of ARGs and the source of spreading AMR. According to a World Health Organization report, the most critical pathogens for public health include Gram-negative bacteria resistant to third-generation cephalosporins and carbapenems (last-choice drugs), which represent β-lactams, the most widely used antibiotics. Therefore, this paper aimed to present the available research data for ARGs in WWTPs that confer resistance to β-lactam antibiotics, with a particular emphasis on clinically important life-threatening mechanisms of resistance, including extended-spectrum β-lactamases (ESBLs) and carbapenemases (KPC, NDM).

Horizontal transfer of the multidrug resistance plasmid RP4 inhibits ammonia nitrogen removal dominated by ammonia-oxidizing bacteria

Antibiotic resistance genes (ARGs) have become an important public health concern. Particularly, although several ARGs have been identified in wastewater treatment plants (WWTPs), very few studies have characterized their impacts on reactor performance. Therefore, our study sought to investigate the effect of a representative conjugative transfer plasmid (RP4) encoding multidrug resistance genes on ammonia oxidation. To achieve this, we established sequencing batch reactors (SBRs) and a conjugation model with E. coli donor strains carrying the RP4 plasmid and a typical ammonia-oxidating (AOB) bacterial strain (Nitrosomonas europaea ATCC 25978) as a recipient to investigate the effect of conjugative transfer of plasmid RP4 on AOB. Our findings demonstrated that the RP4 plasmid carried by the donor strains could be transferred to AOB in the SBR and to Nitrosomonas europaea ATCC 25978. In SBR treated with donor strains carrying the RP4 plasmid, ammonia removal efficiency continuously decreased to 71%. Once the RP4 plasmid entered N. europaea ATCC 25978 in the conjugation model, ammonia removal was significantly inhibited and nitrite generation was decreased. Furthermore, the expression of several functional genes related to ammonia oxidation in AOB was suppressed following the transfer of the RP4 plasmid, including amoA, amoC, hao, nirK, and norB. In contrast, the cytL gene encoding cytochrome P460 was upregulated. These results demonstrated the ecological risk of ARGs in WWTPs, and therefore measures must be taken to avoid their transfer.

The prevalence and removal of antibiotic resistance genes in full-scale wastewater treatment plants: Bacterial host, influencing factors and correlation with nitrogen metabolic pathway

This study investigated the prevalence of antibiotic resistance genes (ARGs) in the influent, effluent, and waste activated sludge (WAS) of eight full-scale municipal wastewater treatment plants (WWTPs) in Shanghai, China. A comprehensive understanding of the correlation between various influencing factors (characteristics of wastewater and WAS, antibiotics, metals, mobile genetic elements) and ARGs was explored. Among the eight full-scale WWTPs, the Unitank process was inefficient in removing typical ARGs compared with continuous-flow anaerobic-anoxic-aerobic and oxidation ditch processes. Antibiotic was identified as the most influential factor affecting the occurrence of ARGs in wastewater, followed by flow rate and nutrients. Positive correlations were observed between antibiotics and their corresponding ARGs in the influent, while this correlation disappeared in the WAS. Class I integron, wastewater characteristics (nitrogen and flow rate), antibiotics (ofloxacin, sulfamethazine, and erythromycin), metals (Mg, Al, Fe, and Mn) were identified as crucial factors comprehensively affecting the distribution of ARGs in WAS. Dissimilatory nitrate reduction profoundly influenced the fate of ARGs during wastewater treatment processes, and K04561 (norB), K02567 (napA), K00262 (gdhA), K00284 (gltS) were identified as the most significant genes in the nitrogen metabolism pathway (ko00910). This study provides a new perspective for comprehensively understanding the occurrence and dissemination of ARGs in WWTPs.

Extracellular polymeric substances (EPS) associated extracellular antibiotic resistance genes in activated sludge along the AAO process: Distribution and microbial secretors

Wastewater treatment plants (WWTPs) are important sources of antibiotic resistance genes (ARGs). Increasing attention has been paid to extracellular ARGs in cell-free form due to their horizontal gene transfer via transformation. However, the fate of the adsorbed form of extracellular ARGs that exist in extracellular polymeric substances (EPS) of activated sludge in WWTP remains largely unknown. Herein, seven EPS-associated ARGs along the anaerobic-anoxic-aerobic (AAO) process were quantified using quantitative polymerase chain reaction. Results show that the absolute abundances of EPS-associated ARGs were 0.69–4.52 logs higher than those of cell-free ARGs. There was no significant difference in the abundances of EPS-associated ARGs along the AAO process. Among these target genes, the abundances of EPS-associated sul genes were higher than those of EPS-associated tet and bla genes. Proteobacteria and Bacteroidetes were identified as the major secretors of EPS-associated ARGs, and they may play an important role in the proliferation of extracellular ARGs. Moreover, the transformation efficiencies of EPS-associated ARGs were 3.55–4.65 logs higher than those of cell-free ARGs, indicating that EPS-associated ARGs have higher environmental risks. These findings have advanced our understanding of EPS-associated ARGs and are useful for the control and risk assessment of ARGs in WWTPs.

A Review on Occurrence and Spread of Antibiotic Resistance in Wastewaters and in Wastewater Treatment Plants: Mechanisms and Perspectives.

This paper reviews current knowledge on sources, spread and removal mechanisms of antibiotic resistance genes (ARGs) in microbial communities of wastewaters, treatment plants and downstream recipients. Antibiotic is the most important tool to cure bacterial infections in humans and animals. The over- and misuse of antibiotics have played a major role in the development, spread, and prevalence of antibiotic resistance (AR) in the microbiomes of humans and animals, and microbial ecosystems worldwide. AR can be transferred and spread amongst bacteria via intra- and interspecies horizontal gene transfer (HGT). Wastewater treatment plants (WWTPs) receive wastewater containing an enormous variety of pollutants, including antibiotics, and chemicals from different sources. They contain large and diverse communities of microorganisms and provide a favorable environment for the spread and reproduction of AR. Existing WWTPs are not designed to remove micropollutants, antibiotic resistant bacteria (ARB) and ARGs, which therefore remain present in the effluent. Studies have shown that raw and treated wastewaters carry a higher amount of ARB in comparison to surface water, and such reports have led to further studies on more advanced treatment processes. This review summarizes what is known about AR removal efficiencies of different wastewater treatment methods, and it shows the variations among different methods. Results vary, but the trend is that conventional activated sludge treatment, with aerobic and/or anaerobic reactors alone or in series, followed by advanced post treatment methods like UV, ozonation, and oxidation removes considerably more ARGs and ARB than activated sludge treatment alone. In addition to AR levels in treated wastewater, it examines AR levels in biosolids, settled by-product from wastewater treatment, and discusses AR removal efficiency of different biosolids treatment procedures. Finally, it puts forward key-points and suggestions for dealing with and preventing further increase of AR in WWTPs and other aquatic environments, together with a discussion on the use of mathematical models to quantify and simulate the spread of ARGs in WWTPs. Mathematical models already play a role in the analysis and development of WWTPs, but they do not consider AR and challenges remain before models can be used to reliably study the dynamics and reduction of AR in such systems.

Release of Antibiotic-Resistance Genes from Hospitals and a Wastewater Treatment Plant in the Kathmandu Valley, Nepal

Hospitals and wastewater treatment plants (WWTPs) are high-risk point sources of antibiotic-resistance genes (ARGs) and antibiotic-resistant bacteria. This study investigates the occurrence of clinically relevant ARGs (sul1, tet(B), blaCTX-M, blaNDM-1, qnrS) and a class one integron (intI1) gene in urban rivers, hospitals, and municipal wastewater in the Kathmandu Valley, Nepal. Twenty-five water samples were collected from three rivers, six hospitals, and a wastewater treatment plant to determine the concentrations of ARGs and intI1 using quantitative polymerase chain reactions. From the results, all tested ARGs were detected in the river water; also, concentrations of ARGs in WWTP and hospital effluents varied from 6.2 to 12.5 log10 copies/L, highlighting the role of a WWTP and hospitals in the dissemination of ARGs. Except for blaNDM-1, significant positive correlations were found between intI1 and other individual ARGs (r = 0.71–0.96, p &lt; 0.05), indicating the probable implications of intI1 in the transfer of ARGs. Furthermore, this study supports the statement that the blaNDM-1 gene is most likely to be spread in the environment through untreated hospital wastewater. Due to the interaction of surface water and groundwater, future research should focus on ARGs and factors associated with the increase/decrease in their concentration levels in drinking water sources of the Kathmandu Valley.

A review of ARGs in WWTPs: Sources, stressors and elimination

Antibiotic resistance genes (ARGs) in aquatic environments, which seriously endanger human health and ecological safety, have become a worldwide concern due to their easy diffusion and proliferation. Wastewater treatment plants (WWTPs), which receive resistant bacteria and ARGs from a wide variety of sources (i.e., livestock farms, hospitals, antibiotic manufactures, and households), are regarded as important emission sources of aquatic ARGs. This review presents a quantitative profile of the majority sources of ARGs in the influent of WWTPs and discusses the potential factors that affect the concentration distribution of ARGs. Specifically, a noteworthy existence of ARGs, which ranged from 1E + 05 to 1E + 11 copies/mL, was detected in livestock breeding wastewater, and household wastewater (caused by the unlimited utilization of antibiotics) was determined to be the predominant contributor of ARGs in WWTPs. We summarized the selective pressure on ARGs and determined the positive correlation of the concentration of ARGs and the existence of many containments, including antibiotics, heavy metals (Zn and Cu were frequently reported), quaternary ammonium compounds, etc. In the last section, physical, chemical, and biological treatments for the removal of ARGs and their effluent in WWTPs are discussed and prospective future studies are summarized.

Exploration of the antibiotic resistome in a wastewater treatment plant by a nine-year longitudinal metagenomic study

The spread of antibiotic resistance genes (ARGs) is a growing global problem. Activated sludge (AS) in wastewater treatment plants (WWTPs) has been proposed as a hotspot for ARGs. However, few studies have been conducted to uncover the temporal dynamics of the resistome of AS in WWTPs by long-term longitudinal sampling. In this study, we quantified ARGs and identified their host microbiome in a Hong Kong WWTP in 97 monthly AS samples spanning 9 years. Throughout this analysis, we demonstrated that both the abundance and structures of the resistome changed significantly every two to three years, implying that there was a successive selection of resistomes in the AS system over the study period. The detection of genes of antibiotic-resistant pathogens that are emerging major threats to public health in the AS samples, including mcr, CRE (carbapenem-resistant Enterobacteriaceae) and MRSA (methicillin-resistant Staphylococcus aureus)-related genes, highlight the role of WWTPs as reservoirs of ARGs. In addition, the core resistome (abundant and persistent genes) in AS were found to overlap with those in other ecosystems such as urban sewage, livestock feces, and fishpond sediments, revealing the broad dissemination of ARGs in WWTPs and other environments. Annual variation of resistomes were explained via structural equation modeling (SEM), which deciphered the structural linkages of determining factors such as the operational parameters, microbial community composition and horizontal gene transfer (HGT). Specifically, potentially relevant antibiotic resistance bacteria (ARBs) were explored and discussed based on assembly-based analyses and network correlations. Moreover, consistent with the clear relationship between resistomes and mobile genetic elements (MGEs), it was found that there was a relatively high potential for gene exchange in AS in comparison with soil genomes, which could be explained by the engineering features of WWTPs. Based on these findings, longitudinal monitoring of WWTPs is warranted for risk assessment to reveal emerging ARGs, resistome evolution, correlations with ARBs, and the potential for spread in downstream environments and concomitant exposure risks for humans.

Metagenomic and metatranscriptomic analyses reveal activity and hosts of antibiotic resistance genes in activated sludge

Wastewater treatment plants (WWTPs) are a source and reservoir for subsequent spread of various antibiotic resistance genes (ARGs). However, little is known about the activity and hosts of ARGs in WWTPs. Here, we utilized both metagenomic and metatranscriptomic approaches to comprehensively reveal the diversity, abundance, expression and hosts of ARGs in activated sludge (AS) from three conventional WWTPs in Taiwan. Based on deep sequencing data and a custom-made ARG database, a total of 360 ARGs associated with 24 classes of antibiotics were identified from the three AS metagenomes, with an abundance range of 7.06 × 10−1–1.20 × 10−4 copies of ARG/copy of 16S rRNA gene. Differential coverage binning analysis revealed that >22 bacterial phyla were the putative hosts of the identified ARGs. Surprisingly, genus Mycobacterium and family Burkholderiaceae were observed as multi-drug resistant harboring 14 and 50 ARGs. Metatranscriptome analysis showed 65.8% of the identified ARGs were being expressed, highlighting that ARGs were not only present, but also transcriptionally active in AS. Remarkably, 110 identified ARGs were annotated as plasmid-associated and displayed a close to two-fold increased likelihood of being transcriptionally expressed compared to those ARGs found exclusively within bacterial chromosomes. Further analysis showed the transcript abundance of aminoglycoside, sulfonamide, and tetracycline resistance genes was mainly contributed by plasmid-borne ARGs. Our approach allowed us to specifically link ARGs to their transcripts and genetic context, providing a comprehensive insight into the prevalence, expression and hosts of ARGs in AS. Overall, results of this study enhance our understanding of the distribution and dissemination of ARGs in WWTPs, which benefits environmental risk assessment and management of ARB and ARGs.

Conjugative potential of antibiotic resistance plasmids to activated sludge bacteria from wastewater treatment plants

Wastewater treatment plants (WWTPs) have been considered as hotspots to spread antibiotic resistance genes (ARGs). However, the potential of activated sludge bacteria to disseminating ARGs in WWTPs has not been clearly understood. In this study, we investigated the conjugative potential of bacteria in five activated sludge samples from different WWTPs, by using Escherichia coli as donor of broad-host range IncP-1 plasmid pKJK5. The maximum transfer frequencies were in the range of 1 × 10−3–4.3 × 10−2 per recipient. Conjugative potentials were determined as the ratio of relative abundances in transconjuants to those in recipients. In all transconjugant pools, there were fifteen shared genera, which contained pathogenic bacteria in potential. The dominant shared genera included Aeromonas, Acinetobacter and Enterobacter, accounting for 65%–96% of the total abundance, with the conjugative potential in the range of 0.4–4.9. Gram-positive bacteria, Vagococcus and Kurthia, were also found in the transconjugants. Their relative abundances were in the range of 1.5%–7.2% and conjugative potentials were much higher (ranged from 2.1 to 48), deserving more attention to estimating the risks. Conjugative potential for certain genera were found diverse in different processes, implying possible correlation with process operation. This study can be helpful for ARG risk assessment and control in WWTPs.

Mercury/silver resistance genes and their association with antibiotic resistance genes and microbial community in a municipal wastewater treatment plant

Municipal wastewater treatment plants (WWTPs) are an important reservoir for heavy metal (e.g., Hg and Ag) resistance genes and antibiotic resistance genes (ARGs). However, current knowledge on Hg/Ag resistance genes and their association with ARGs in WWTPs remains largely unknown. In this study, the fates of five Hg/Ag resistance genes (merB, merD, merR, silE, and silR), five ARGs (sulI, sulII, tetO, tetQ, tetW), and class 1 integrase (intI1) in a WWTP were investigated. Results show that the absolute abundances of all target genes were greatly reduced through the treatment systems. The dynamics of merB, merD and silE were significantly correlated with tetW and sulII. Based on network analysis, Hg/Ag resistance genes might share the same microbial hosts with tetQ and tetW, implying the potential importance of Hg/Ag in ARGs evolution and spread. These findings advanced our understanding of the occurrence of Hg/Ag resistance genes and ARGs in WWTPs.

Distribution and Removal of Antibiotic Resistance Genes in Two Sequential Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) have been regarded as important point-sources of antibiotic resistance genes (ARGs) in aquatic environments. To investigate the distribution and removal of ARGs in WWTPs, a pharmaceutical wastewater treatment plant (PWWTP) and an integrated wastewater treatment plant (IWWTP) in a fine-chemical industrial park were chosen, and polymerase chain reaction (PCR) and real-time PCR techniques were used to determine the occurrence and abundances of ARGs along the treatment processes. Ten and fifteen ARGs were detected initially in the influents of PWWTP and IWWTP respectively, in which tetracycline and sulfonamide resistance genes were frequently reported, while dfrA13 was first reported in WWTPs. The most abundant ARGs in the influents were sul Ⅰ and sul Ⅱ, followed by dfrA13, tetQ, floR, tetO, and tetW. The total ARGs increased by 0.21 log after the treatment by PWWTP, whose effluent contributed 0.87% to the inflow yet 5.05% to the total ARGs of IWWTP. Finally the total ARGs removed by IWWTP was 1.03 log, with the remaining ARGs then transported within the final effluent to the nearby coastal area. The authors concluded that the environmental and other impacts from the spread of ARGs on the microbial communities of the coastal environment needed further study.

Antibiotic resistance genes show enhanced mobilization through suspended growth and biofilm-based wastewater treatment processes.

Wastewater treatment plants (WWTPs) are known to harbor antibiotic resistance genes (ARGs) that are disseminated into the environment via effluent. However, few studies have compared abundance, mobilization and selective pressures for ARGs in WWTPs as a function of variations in secondary treatment bioprocesses. We used shotgun metagenomics to provide a comprehensive analysis of ARG composition, relationship to mobile genetic elements and co-occurrences with antibiotic production genes (APGs) throughout two full-scale municipal WWTPs, one of which employs biofilm-based secondary treatment and another that uses a suspended growth system. Results showed that abundances of ARGs declined by over 90% per genome equivalent in both types of wastewater treatment processes. However, the fractions of ARGs associated with mobile genetic elements increased substantially between influent and effluent in each plant, indicating significant mobilization of ARGs throughout both treatment processes. Strong positive correlations between ARGs and APGs were found for the aminoglycoside antibiotic class in the suspended growth system and for the streptogramin antibiotic class in the biofilm system. The biofilm and suspended growth WWTPs exhibited similarities in ARG abundances, composition and mobilization trends. However, clear differences were observed for within-plant ARG persistence. These findings suggest that both biofilm and suspended growth-based WWTPs may promote genetic mobilization of persistent ARGs that are then disseminated in effluent to receiving water bodies.

Antibiotic resistance genes show enhanced mobilization through suspended growth and biofilm-based wastewater treatment processes.

Wastewater treatment plants (WWTPs) are known to harbor antibiotic resistance genes (ARGs) that are disseminated into the environment via effluent. However, few studies have compared abundance, mobilization and selective pressures for ARGs in WWTPs as a function of variations in secondary treatment bioprocesses. We used shotgun metagenomics to provide a comprehensive analysis of ARG composition, relationship to mobile genetic elements and co-occurrences with antibiotic production genes (APGs) throughout two full-scale municipal WWTPs, one of which employs biofilm-based secondary treatment and another that uses a suspended growth system. Results showed that abundances of ARGs declined by over 90% per genome equivalent in both types of wastewater treatment processes. However, the fractions of ARGs associated with mobile genetic elements increased substantially between influent and effluent in each plant, indicating significant mobilization of ARGs throughout both treatment processes. Strong positive correlations between ARGs and APGs were found for the aminoglycoside antibiotic class in the suspended growth system and for the streptogramin antibiotic class in the biofilm system. The biofilm and suspended growth WWTPs exhibited similarities in ARG abundances, composition and mobilization trends. However, clear differences were observed for within-plant ARG persistence. These findings suggest that both biofilm and suspended growth-based WWTPs may promote genetic mobilization of persistent ARGs that are then disseminated in effluent to receiving water bodies.