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

Changes of composition and antibiotic resistance of fecal coliform bacteria in municipal wastewater treatment plant

The dynamics of the composition and antibiotic resistance of the fecal coliform bacteria (FCB) in a typical wastewater treatment plant (WWTP) were investigated concerning the seasonal changes. Results showed that WWTP could remove the FCB concentration by 3∼5 logs within the effluent of 104∼105 CFU/L, but the antibiotic resistant rate of FCB species increased significantly after WWTP. The dominant FCB changed from Escherichia coli in the influent (∼73.0%) to Klebsiella pneumoniae in the effluent (∼53.3%) after WWTP, where the Escherichia coli was removed the most, while Klebsiella pneumoniae was the most persistent. The secondary tank removed the most of FCB (by 3∼4 logs) compared to other processes, but increased all the concerned antibiotic resistant rate. The potential super bugs of FCB community showing resistance to all the target antibiotics were selected in the biological treatment unit of WWTP. The FCB showed the highest multiple antibiotic resistance (92.9%) in total which even increased to 100% in the effluent. Klebsiella has the highest antibiotic resistant rate in FCB, with a multiple antibiotic resistance rate of 98.4%. These indicated that the Klebsiella pneumoniae not just Escherichia coli should be specially emphasized after WWTP concerning the health risk associated with FCB community.

Unnoticed antimicrobial resistance risk in Tibetan cities unveiled by sewage metagenomic surveillance: Compared to the eastern Chinese cities

Sewage surveillance is a cost-effective tool for assessing antimicrobial resistance (AMR) in urban populations. However, research on sewage AMR in remote areas is still limited. Here, we used shotgun metagenomic sequencing to profile antibiotic resistance genes (ARGs) and ARG-carrying pathogens (APs) across 15 cities in Tibetan Plateau (TP) and the major cities in eastern China. Notable regional disparities in sewage ARG composition were found, with a significantly higher ARG abundance in TP (2.97 copies/cell). A total of 542 and 545 APs were identified in sewage from TP and the East, respectively, while more than 40 % carried mobile genetic elements (MGEs). Moreover, 65 MGEs-carrying APs were identified as World Health Organization (WHO) priority-like bacterial and fungal pathogens. Notably, a fungal zoonotic pathogen, Enterocytozoon bieneusi, was found for the first time to carry a nitroimidazole resistance gene (nimJ). Although distinct in AP compositions, the relative abundances of APs were comparable in these two regions. Furthermore, sewage in TP was found to be comparable to the cities in eastern China in terms of ARG mobility and AMR risks. These findings provide insights into ARGs and APs distribution in Chinese sewage and stress the importance of AMR surveillance and management strategies in remote regions.

Antibiotic resistance genes risks in relation to host pathogenicity and mobility in a typical hospital wastewater treatment process

Hospital wastewaters (HWWs) serve as critical reservoirs for disseminating antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB). However, the dynamics and noteworthy shifts of ARGs and their associated pathogenicity, mobility, and resistome risks during HWWs treatment processes remain poorly understood. Utilizing metagenomic sequencing and assembly, we identified 817 ARG subtypes conferring resistance to 20 classes of antibiotics across 18 HWW samples from influent to effluent. Genes encoding resistance to multidrug, aminoglycoside and beta_lactam were the most prevalent ARG types, reflecting patterns observed in clinical settings. On-site treatment efforts decreased the relative abundance of ARGs by 77.4% from influent to secondary sedimentation, whereas chlorine disinfection significantly increased their abundance in the final effluent. Deterministic processes primarily drove the taxonomic assembly, with Proteobacteria being the most abundant phylum and serving as the primary host for 15 ARG types. Contig-based analysis further revealed 114 pathogenic ARB, with Escherichia coli, Pseudomonas alcaligenes, and Pseudomonas aeruginosa exhibiting multidrug-resistant. The contributions of host bacteria and pathogenic ARB varied throughout wastewater treatment. In addition, 7.10%-31.0 % ARGs were flanked by mobile genetic elements (MGEs), predominantly mediated by transposase (74.1%). Notably, tnpA exhibited the highest potential for ARG dissemination, frequently co-occurring with beta-lactam resistance genes (35.2%). Considering ARG profiles, pathogenic hosts, and transferability, raw influent exhibited the highest antibiotic resistome risk index (ARRI), followed by the final effluent. Chlorine disinfection exacerbated resistome risks by inducing potential pathogenic ARB and mobile ARGs, posing threats to the receiving environment. This study delineates ARG occurrence patterns, highlights mechanisms of ARG carriage and horizontal gene transfer, and provides insights for assessing resistance risks and prioritizing interventions in clinical settings.

Increasing biomass concentration facilitates simultaneous nitrogen removal and sludge reduction under low C/N conditions

To overcome the issues of limited carbon source and high sludge production in partial denitrification/anammox (PD/A) process, the effects of mixed liquor suspended solids (MLSS) and carbon/nitrogen ratio (C/N) on PD/A were investigated through parallel experiments. Nitrogen removal efficiencies decreased significantly when C/N was reduced (1.5 → 0.75). When MLSS was doubled, the nitrogen removal efficiencies in the two parallel reactors increased from 75.3 %, 72.9 % to 86.9 %, 89.7 %, respectively, and sludge yields decreased obviously. Combining with in-situ test, it was speculated when MLSS increased, fermentation was enhanced, providing substrate for partial denitrification. Thauera, involved in partial denitrification, decreased obviously with reduced C/N, but increased from 9.93 % to 38.16 % when MLSS doubled, which could promote the PD/A process. Terrimonas and Ignavibacterium (fermentative bacteria) increased from 1.26 %, 5.22 % to 6.62 %, 6.30 %, respectively. These results proved that increasing MLSS under low C/N ratios promoted fermentation in PD/A system, facilitating efficient nitrogen removal and sludge reduction.

Spatiotemporal profiles and underlying mechanisms of the antibiotic resistome in two water-diversion lakes

Human-induced interventions have altered the local characteristics of the lake ecosystems through changes in hydraulic exchange, which in turn impacts the ecological processes of antibiotic resistance genes (ARGs) in the lakes. However, the current understanding of the spatiotemporal patterns and driving factors of ARGs in water-diversion lakes is still seriously insufficient. In the present study, we investigated antibiotic resistome in the main regulation and storage hubs, namely Nansi Lake and Dongping Lake, of the eastern part of the South-to-North Water Diversion project in Shandong Province (China) using a metagenomic-based approach. A total of 653 ARG subtypes belonging to 25 ARG types were detected with a total abundance of 0.125-0.390 copies/cell, with the dominance of bacitracin, multidrug, and macrolide-lincosamide streptogramin resistance genes. The ARG compositions were sensitive to seasonal variation and also interfered by artificial regulation structures along the way. Human pathogenic bacteria such as Acinetobacter calcoaceticus, Acinetobacter lwoffii, Klebsiella pneumoniae, along with the multidrug resistance genes they carried, were the focus of risk control in the two studied lakes, especially in summer. Plasmids were the key mobile genetic elements (MGEs) driving the horizontal gene transfer of ARGs, especially multidrug and sulfonamide resistance genes. The null model revealed that stochastic process was the main driver of ecological drift for ARGs in the lakes. The partial least squares structural equation model further determined that seasonal changes of pH and temperature drove a shift in the bacterial community, which in turn shaped the profile of ARGs by altering the composition of MGEs, antibacterial biocide- and metal-resistance genes (BMGs), and virulence factor genes (VFGs). Our results highlighted the importance of seasonal factors in determining the water transfer period. These findings can aid in a deeper understanding of the spatiotemporal variations of ARGs in lakes and their driving factors, offering a scientific basis for antibiotic resistance management.

Simultaneous efficient removal of tetracycline and mitigation of antibiotic resistance genes enrichment by a modified activated sludge process with static magnetic field

To address the increasing issue of antibiotic wastewater, this study applied a static magnetic field (SMF) to the activated sludge process to increase the efficiency of tetracycline (TC) removal from swine wastewater and to reveal its enhanced mechanisms. The results demonstrated that the SMF-modified activated sludge process could achieve almost complete TC removal at sludge loading rates of 0.3 mg TC/g MLSS/d. Analysis of zeta potential and extracellular polymeric substances composition of the activated sludge revealed that SMF increased electrostatic interactions between TC and activated sludge and made activated sludge has much more binding sites, finally resulting in the increased TC biosorption. Metagenomic analysis showed that SMF promoted the enrichment of ammonia-oxidizing bacteria, TC-degrading bacteria, and aromatic compounds-degrading bacteria; it also enhanced ammonia monooxygenase- and cytochrome P450-mediated TC metabolism while upregulating functional genes associated with oxidase, reductase, and dehydrogenase - all contributing to increased TC biodegradation. Additionally, SMF mitigated the enrichment and spread of antibiotic resistance genes (ARGs) by decreasing the abundance of potential hosts of ARGs and inhibiting the upregulation of genes encoding ABC transporters and putative transposase. Based on these findings, this study demonstrates that magnetic field is an enhancement strategy with great potential to relieve the harmful impacts of the growing antibiotic wastewater problem on human health and the ecosystem.

Trajectory of antibiotic resistome response to antibiotics gradients: A comparative study from pharmaceutical and associated wastewater treatment plants to receiving river

Pharmaceutical wastewater often contains significant levels of antibiotic residues, which continuously induce and promote antibiotic resistance during the sewage treatment process. However, the specific impact of antibiotics on the emergence of antibiotic resistance genes (ARGs), microbiomes, and mobile genetic elements (MGEs), as well as the dose-response relationship remain unclear. Herein, through metagenomic sequencing and analysis, we investigated the fate, transmission, and associated risk of ARGs over a ten-year period of exposure to a gradient of sulfonamide antibiotics at a pharmaceutical wastewater treatment plant (PWWTP), an associated wastewater treatment plant (WWTP), and the receiving river. Through abundance comparison and principal co-ordinates analysis (PCoA), our results revealed distinct ARG, microbiome, and MGE profiles across different antibiotic concentrations. Notably, there was a decreasing trend in the abundance of ARGs and MGEs as the antibiotic concentrations were attenuated (p < 0.05). Further partial least squares path modeling analysis, Procrustes analysis and network analysis indicated that variation in MGEs and microbiomes were the driving forces behind the distribution of ARGs. Based on these findings, we proposed an antibiotic-microbiome-MGE-ARG dissemination paradigm, in which integrons as key drivers were closely associated with prevalent ARGs such as sul1, sul2, and aadA. With a focus on human pathogenic bacteria and the associated health risks of ARGs, we conducted pathogen source analysis and calculated the antibiotic resistome risk index (ARRI). Our findings highlighted potential risks associated with the transition from PWWTP to WWTP, raising concerns regarding risk amplification due to the mixed treatment of antibiotic-laden industrial wastewater and domestic sewage. Overall, the results of our study provide valuable information for optimizing wastewater treatment practices to better manage antibiotic resistance.

Synergy between Nitrogen Removal and Fermentation Bacteria Ensured Efficient Nitrogen Removal of a Mainstream Anammox System at Low Temperatures

Simultaneous partial nitrification, anammox, denitrification, and fermentation (SNADF) is a novel process achieving simultaneous advanced sludge reduction and nitrogen removal. The influence of low temperatures on the SNADF reactor was explored to facilitate the application of mainstream anammox. When temperature decreased from 32 to 16 °C, efficient nitrogen removal was achieved, with a nitrogen removal efficiency of 81.9-94.9%. Microbial community structure analysis indicated that the abundance of Candidatus Brocadia (dominant anaerobic ammonia oxidizing bacteria (AnAOB) in the system) increased from 0.03% to 0.18%. The abundances of Nitrospira and Nitrosomonas increased from 1.6% and 0.16% to 2.5% and 1.63%, respectively, resulting in an increase in the ammonia-oxidizing bacteria (AOB) to nitrite-oxidizing bacteria (NOB) abundance ratio from 0.1 to 0.64. This ensured sufficient nitrite for AnAOB, promoting nitrogen removal. In addition, Candidatus Competibacter, which plays a role in partial denitrification, was the dominant denitrification bacteria (DNB) and provided more nitrite for AnAOB, facilitating AnAOB enrichment. Based on the findings from microbial correlation network analysis, Nitrosomonas (AOB), Thauera, and Haliangium (DNB), and A4b and Saprospiraceae (fermentation bacteria), were center nodes in the networks and therefore essential for the stability of the SNADF system. Moreover, fermentation bacteria, DNB, and AOB had close connections in substrate cooperation and resistance to adverse environments; therefore, they also played important roles in maintaining stable nitrogen removal at low temperatures. This study provided new suggestions for mainstream anammox application.

Spatiotemporal distribution of the planktonic microbiome and antibiotic resistance genes in a typical urban river contaminated by macrolide antibiotics

The widespread application of macrolide antibiotics has caused antibiotic resistance pollution, threatening the river ecological health. In this study, five macrolide antibiotics (azithromycin, clarithromycin, roxithromycin, erythromycin, and anhydro erythromycin A) were monitored in the Zao River across three hydrological periods (April, July, and December). Simultaneously, the changes in antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and planktonic bacterial communities were determined using metagenomic sequencing. A clear pollution gradient was observed for azithromycin and roxithromycin, with the concentrations in the dry season surpassing those in other seasons. The highest concentration was observed for azithromycin (1.36 μg/L). The abundance of MLS resistance genes increased along the Zao River during the dry season, whereas the opposite trend was obtained during the wet season. A significant correlation between the levels of MLS resistance genes and macrolide antibiotics was identified during the dry season. Notably, compared with the reference site, the abundance of transposase in the effluent from wastewater treatment plants (WWTPs) was significantly elevated in both dry and wet seasons, whereas the abundance of insertion sequences (IS) and plasmids declined during the dry season. The exposure to wastewater containing macrolide antibiotics altered the diversity of planktonic bacterial communities. The bacterial host for ARGs appeared to be Pseudomonas, primarily associated with multidrug subtypes. Moreover, the ARG subtypes were highly correlated with MGEs (transposase and istA). The partial least-squares path model (PLS-PM) demonstrated a positive correlation between the abundance of MGEs and ARGs, indicating the significance of horizontal gene transfer (HGT) in the dissemination of ARGs within the Zao River. Environmental variables, such as TN and NO3--N, were significantly correlated with the abundance of MGEs, ARGs, and bacteria. Collectively, our findings could provide insights into the shift patterns of the microbiome and ARGs across the contamination gradient of AZI and ROX in the river.

Effect of Stepwise Exposure to High-Level Erythromycin on Anaerobic Digestion

High-level erythromycin (ERY) fermentation wastewater will pose serious threats to lake environments. Anaerobic digestion (AD) has advantages in treating high-level antibiotic wastewater. However, the fate of antibiotic resistance genes (ARGs) and microbial communities in AD after stepwise exposure to high-level ERY remains unclear. In this study, an AD reactor was first exposed to 0, 5, 10, 50, 100 and 200 mg/L ERY and then re-exposed to 0, 50, 200 and 500 mg/L ERY to investigate the effect of ERY on AD. The results show that AD could adapt to the presence of high-level ERY (500 mg/L) and could maintain efficient CH4 production after domestication with low-level ERY (50 mg/L). The AD process could achieve higher removal of ERY (>94%), regardless of the initial ERY concentration. ErmB and mefA, conferring resistance through target alteration and efflux pumps, respectively, were dominant in the AD process. The first exposure to ERY stimulated an increase in the total ARG abundance, while the AD process seemed to discourage ARG maintenance following re-exposure to ERY. ERY inhibited the process of acetoclastic methanogenesis, but strengthened the process of hydrogenotrophic methanogenesis. This work provides useful information for treating high-level ERY fermentation wastewater by the AD process.

Strong suppression of silver nanoparticles on antibiotic resistome in anammox process

This study comprehensively deciphered the effect of silver nanoparticles (AgNPs) on anammox flocculent sludge, including nitrogen removal performance, microbial community structure, functional enzyme abundance, antibiotic resistance gene (ARGs) dissemination, and horizontal gene transfer (HGT) mechanisms. After long-term exposure to 0-2.5 mg/L AgNPs for 200 cycles, anammox performance significantly decreased (P < 0.05), while the relative abundances of dominant Ca. Kuenenia and anammox-related enzymes (hzsA, nirK) increased compared to the control (P < 0.05). For antibiotic resistome, ARG abundance hardly changed with 0-0.5 mg/L AgNPs but decreased by approximately 90% with 1.5-2.5 mg/L AgNPs. More importantly, AgNPs effectively inhibited MGE-mediated HGT of ARGs. Additionally, structural equation model (SEM) disclosed the underlying relationship between AgNPs, the antibiotic resistome, and the microbial community. Overall, AgNPs suppressed the anammox-driven nitrogen cycle, regulated the microbial community, and prevented the spread of ARGs in anammox flocs. This study provides a theoretical baseline for an advanced understanding of the ecological roles of nanoparticles and resistance elements in engineered ecosystems.

From disinfection to pathogenicity: Occurrence, resistome risks and assembly mechanism of biocide and metal resistance genes in hospital wastewaters

Hospital wastewaters (HWWs) represent critical reservoir for the accumulation and propagation of resistance genes. However, studies on biocide and metal resistance genes (BMRGs) and their associated resistome risks and driving mechanisms in HWWs are still in their infancy. Here, metagenomic assembly was firstly used to investigate host pathogenicity and transferability profiles of BMGRs in a typical HWWs system. As a result, genes conferring resistance to Ethidium Bromide, Benzylkonium Chloride, and Cetylpyridinium Chloride dominated biocide resistance genes (BRGs), whereas Cu resistance gene was the largest contributor of metal resistance genes (MRGs). Most BMRGs experienced significant reduction from anoxic-aerobic treatment to sedimentation stages but exhibited enrichment after chlorine disinfection. Network analysis indicated intense interactions between BMRGs and virulence factors (VFs). Polar_flagella, belonging to the adherence was identified to play important role in the network. Contig-based analysis further revealed noteworthy shifts in host associations along the treatment processes, with Pseudomonadota emerging as the primary carrier, hosting 91.1% and 85.3% of the BRGs and MRGs. A total of 199 opportunistic pathogens were identified to carry 285 BMRG subtypes, which mainly included Pseudomonas alcaligenes, Pseudomonas lundensis, and Escherichia coli. Notably, ruvB conferring resistance to Cr, Cetylpyridinium Chloride, and Dodine were characterized with the highest frequency carried by pathogens. Diverse co-occurrence patterns between BMRGs and mobile genetic elements (MGEs) were found from the raw influent to final effluent. Overall, 10.5% BRGs and 8.84% MRGs were mobile and among the 4 MGEs, transposase exhibited the greatest potential for the BMRGs dissemination. Furthermore, deterministic processes played a dominant role in bacterial communities and BMRGs assembly in HWWs. Bacterial communities contributed more than MGEs in shaping the resistome. Taken together, this work demonstrated widespread BMRGs pollution throughout the HWWs treatment system, emphasizing the potential for informing resistome risk and ecological mechanism in medical practice.

Dissolved organic nitrogen is a key to improving the biological treatment potential of landfill leachate

Biological treatment is one of the most promising efficient, low-carbon and affordable approaches for the treatment of recalcitrantly degradable wastewater, such as landfill leachate. However, even the macroscopic molecular level analysis of dissolved organic matter (DOM) is limiting to the enhancement of biological treatment efficacy, and there is an urgent need for deeper exploration of DOM to gain insights into the key constraining substances. In the present study targeting at piercing leachate organic at molecular level, nitrogen-containing dissolved organic matter (DOMN) was identified to be the bottleneck that govern the biotreatment potential. The conclusion was made based on two series of experiments that compared the same anoxic-aerobic membrane bioreactor process (A process) operated stably at different regions, and compared with C process that coupling A process with a circulation aeration membrane bioreactor to improve aeration efficiency. The results confirmed that the relative abundance of DOMN was absolutely dominant among the three categories of DOM in all biologically treated samples, contributing to 60.36 %-65.81 % in removed-DOM, 60.33 %-70.95 % in refractory-DOM and 63.14 %-71.36 % in derived-DOM. Specifically, the high latitude A process had much lower DOMN removal rate than the low latitude A process (p < 0.05) and much higher refractory and derivatization rates than the low latitude A process (p < 0.05). DOM had similar results. No statistically significant differences were observed in the proportion of the three categories of DOM (DOMN), the elements composition, and the subcategory composition of the C process compared to the A process, in which the DOM (DOMN) derivation rate of NEC1-C (31.92 % and 33.41 %) was much higher than that of NEC1-A (20.88 % and 22.19 %). However, the AIwa and AImodwa of the derived-DOM (DOMN) were significantly higher in the C process than in the A process, which implied that excessive aeration did not enhance the biological treatment potential of the A process, but instead led to the proliferation of microorganisms and the secretion of extracellular polymer substances, which resulted in the derivation of more complex compounds. The results of the correlation analysis indicated that there were some regional differences in the molecular information of DOMN driven by climate temperature. In addition, it was worth mentioning that the nominal oxidation state of carbon (NOSCwa) of derived-DOMN in different regions of A process was noticeably higher than the corresponding DOM (p < 0.0001), implying that the derived-DOMN were still highly biodegradable, in other words, there was still great room for improving the biological treatment potential of landfill leachate. The present study provided a deeper insight and analysis of landfill leachate at the molecular level (DOMN) through multiple practical engineering cases, with a view to providing a theoretical basis for efficient optimization of biological treatment.

Gamma-ray irradiation as an effective method for mitigating antibiotic resistant bacteria and antibiotic resistance genes in aquatic environments

The prevalence of antibiotic resistance genes (ARGs) in municipal wastewater treatment plants (MWTPs) has emerged as a significant environmental concern. Despite advanced treatment processes, high levels of ARGs persist in the secondary effluent from MWTPs, posing ongoing environmental risks. This study explores the potential of gamma-ray irradiation as a novel approach for sterilizing antibiotic-resistant bacteria (ARB) and reducing ARGs in MWTP secondary effluent. Our findings reveal that gamma-ray irradiation at an absorbed dose of 1.6 kGy effectively deactivates all culturable bacteria, with no subsequent revival observed after exposure to 6.4 kGy and a 96-h incubation in darkness at room temperature. The removal efficiencies for a range of ARGs, including tetO, tetA, blaTEM-1, sulI, sulII, and tetW, were up to 90.5% with a 25.6 kGy absorbed dose. No resurgence of ARGs was detected after irradiation. Additionally, this study demonstrates a considerable reduction in the abundances of extracellular ARGs, with the transformation efficiencies of extracellular tetracycline and sulfadiazine resistance genes decreasing by 56.3-81.8% after 25.6 kGy irradiation. These results highlight the effectiveness of gamma-ray irradiation as an advanced and promising method for ARB sterilization and ARG reduction in the secondary effluent of MWTPs, offering a potential pathway to mitigate environmental risks associated with antibiotic resistance.

Impact of uranium on antibiotic resistance in activated sludge

The emergence of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in the environment is well established as a human health crisis. The impact of radioactive heavy metals on ecosystems and ultimately on human health has become a global issue, especially for the regions suffering various nuclear activities or accidents. However, whether the radionuclides can affect the fate of antibiotic resistance in bacteria remains poorly understood. Here, the dynamics of ARB, three forms of ARGs-intracellular ARGs (iARGs), adsorbed extracellular ARGs (aeARGs), and free extracellular ARGs (feARGs)-and microbial communities were investigated following exposure to uranium (U), a representative radioactive heavy metal. The results showed that 90-d of U exposure at environmentally relevant concentrations of 0.05 mg/L or 5 mg/L significantly increased the ARB concentration in activated sludge (p < 0.05). Furthermore, 90-d of U exposure slightly elevated the absolute abundance of aeARGs (except tetO) and sulfonamide iARGs, but decreased tetracycline iARGs. Regarding feARGs, the abundance of tetC, tetO, and sul1 decreased after 90-d of U stress, whereas sul2 showed the opposite trend. Partial least-squares path model analysis revealed that the abundance of aeARGs and iARGs under U stress was predominantly driven by increased cell membrane permeability/intI1 abundance and cell membrane permeability/reactive oxygen species concentration, respectively. Conversely, the changes in feARGs abundance depended on the composition of the microbial community and the expression of efflux pumps. Our findings shed light on the variations of ARGs and ARB in activated sludge under U exposure, providing a more comprehensive understanding of antibiotic resistance risks aggravated by radioactive heavy metal-containing wastewater.

Antibiotic resistance genes associated with size-segregated bioaerosols from wastewater treatment plants: A review

The antibiotic-resistant pollution in size-segregated bioaerosols from wastewater treatment plants (WWTPs) is of increasing concern due to its public health risks, but an elaborate review is still lacking. This work overviewed the profile, mobility, pathogenic hosts, source, and risks of antibiotic resistance genes (ARGs) in size-segregated bioaerosols from WWTPs. The dominant ARG type in size-segregated bioaerosols from WWTPs was multidrug resistance genes. Treatment units that equipped with mechanical facilities and aeration devices, such as grilles, grit chambers, biochemical reaction tanks, and sludge treatment units, were the primary sources of bioaerosol antibiotic resistome in WWTPs. Higher enrichment of antibiotic resistome in particulate matter with an aerodynamic diameter of <2.5 μm, was found along the upwind-downwind-WWTPs gradient. Only a small portion of ARGs in inhalable bioaerosols from WWTPs were flanked by mobile genetic elements. The pathogens with multiple drug resistance had been found in size-segregated bioaerosols from WWTPs. Different ARGs or antibiotic resistant bacteria have different aerosolization potential associated with bioaerosols from various treatment processes. The validation of pathogenic antibiotic resistance bacteria, deeper investigation of ARG mobility, emission mechanism of antibiotic resistome, and development of treatment technologies, should be systematically considered in future.

Metagenomic insights into the nitrogen metabolism, antioxidant pathway, and antibiotic resistance genes of activated sludge from a sequencing batch reactor under tetracycline stress

Tetracycline is prevalent in wastewater treatment plants and poses a potential threat to biological nitrogen removal under long-term exposure. In the present study, the influence of different tetracycline concentrations on the nitrogen removal, bioactivity response, and the spread of antibiotic resistance genes (ARGs) was assessed in sequencing batch reactor (SBR). The nitrogen removal efficiency, nitrification rate, and denitrification rate and their corresponding enzymatic activities gradually decreased with an increase in tetracycline concentration from 0.5 to 15 mg/L. The remarkable toxicity induced by tetracycline led to a significant increase in the peroxidation and the response of antioxidant system, as evidenced by strengthened antioxidant enzymatic activity and abundant genes (SOD12, katG, PXDN, gpx, and apx). Tetracycline addition significantly inhibited the ammonia-oxidizing bacterium Nitrosomonas and functional genes (amoA, amoB, and amoC). The presence of tetracycline decreased the abundance of citrate synthase and genes (CS, IDH3, and acnA) and interfered with carbon source metabolism, leading to impaired bioactivity and treatment performance. In addition, the presence of tetracycline induces diversity and differences in ARGs. The results provide reliable basic data for a deeper understanding of the effects of tetracycline on the nitrogen removal performance of bioreactors and provide a theoretical basis to build a promising strategy for relieving antibiotic-caused process fluctuations.

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.

Land-derived wastewater facilitates antibiotic resistance contamination in marine sediment of semi-closed bay: A case study in Jiaozhou Bay, China

The emergence of antibiotic resistance is a severe threat to public health. There are few studies on the effects of sewage discharge on antibiotics and antibiotic resistance genes (ARGs) contamination in Jiaozhou Bay sediment. Herein, a total of 281 ARG subtypes, 10 mobile genetic elements (MGEs), 10 antibiotics and bacterial communities in marine sediments from Jiaozhou Bay were characterized. Similar bacterial community structures and ARG profiles were identified between the various sampling sites inside the bay, which were both dominated by multidrug and (fluoro)quinolone resistance genes and harbored lower relative abundances of ARGs than those in the sampling sites near the bay exit. Compared with antibiotics and MGEs, bacterial community composition was a more important driver of ARG diversity and geographic distribution. The abundance of pathogens carrying genetic information increased dramatically in southern Jiaozhou Bay is affected by sewage discharge, which indicating that wastewater discharge facilitated ARG contamination of marine sediments. This study highlights the risk of disseminating antibiotic resistance-influencing factors from treated wastewater discharge into marine environment there is an urgent need to optimize or improve wastewater treatment processes to enhance the removal of antibiotics and ARGs. This study has necessary implications for filling the gap in information on antibiotic resistance in Jiaozhou Bay and developing future pollution regulation and control measures.

Ecological Risks of Antibiotics in Urban Wetlands on the Qinghai-Tibet Plateau, China

Although the ecological risks of antibiotics have been extensively researched globally, fewer studies have been conducted in sensitive and fragile plateau wetland ecosystems. To evaluate the ecological risk of antibiotics in plateau urban wetlands, 18 water samples, 10 plant samples, and 8 sediment samples were collected in March 2022 in the Xining urban wetlands on the Qinghai-Tibet Plateau. The liquid chromatography-electrospray ionization tandem mass spectrometry method was utilized to measure the concentrations of 15 antibiotics in three categories in three types of environmental media. Risk quotients were adopted to assess the ecological risk of antibiotics, and the principal component analysis-multiple linear regression model was used to analyze the source of antibiotics. The results showed that (1) the maximum concentrations of antibiotics in water samples, plants, and sediments reached 1220.86 ng/L, 78.30 ng/g, and 5.64 ng/g, respectively; (2) Tylosin (TYL), norfloxacin (NFX), ofloxacin (OFX), and ciprofloxacin (CFX) in water were at medium and high-risk levels, and OFX had the highest risk value, of 108.04; and (3) the results of source apportionment indicate that 58.94% of the antibiotics came from the Huangshui river and wastewater treatment plant (WWTP) near the wetlands. The current study may provide a reference for the risks and management of antibiotics in plateau urban wetlands.