Antibiotic Resistance Genes In Effluent Research Articles

Biochar and zero-valent iron alleviated sulfamethoxazole and tetracycline co-stress on the long-term system performance of bioretention cells: Insights into microbial community, antibiotic resistance genes and functional genes

Antibiotics and antibiotic resistance genes (ARGs), known as emerging contaminants, have raised widespread concern due to their potential environmental and human health risks. In this study, a conventional bioretention cell (C-BRC) and three modified bioretention cells with biochar (BC-BRC), microbial fuel cell coupled/biochar (EBC-BRC) and zero-valent iron/biochar (Fe/BC-BRC) were established and two antibiotics, namely sulfamethoxazole (SMX) and tetracycline (TC), were introduced into the systems in order to thoroughly investigate the co-stress associated with the long-term removal of pollutants, dynamics of microbial community, ARGs and functional genes in wastewater treatment. The results demonstrated that the SMX and TC co-stress significantly inhibited the removal of total nitrogen (TN) (C-BRC: 37.46%; BC-BRC: 41.64%; EBC-BRC: 55.60%) and total phosphorous (TP) (C-BRC: 53.11%; BC-BRC: 55.36%; EBC-BRC: 62.87%) in C-BRC, BC-BRC and EBC-BRC, respectively, while Fe/BC-BRC exhibited profoundly stable and high removal efficiencies (TN: 89.33%; TP: 98.36%). Remarkably, greater than 99% removals of SMX and TC were achieved in three modified BRCs compared with C-BRC (SMX: 30.86 %; TC: 59.29%). The decreasing absolute abundances of denitrifying bacteria and the low denitrification functional genes (nirK: 2.80 × 105–5.97 × 105 copies/g; nirS: 7.22 × 105–1.69 × 106 copies/g) were responsible for the lower TN removals in C-BRC, BC-BRC and EBC-BRC. The amendment of Fe/BC successfully detoxified SMX and TC to functional bacteria. Furthermore, the co-stress of antibiotics stimulated the propagation of ARGs (sulI, sulII, tetA and tetC) in substrates of all BRCs and only Fe/BC-BRC effectively reduced all the ARGs in effluent by an order of magnitude. The findings contribute to developing robust ecological wastewater treatment technologies to simultaneously remove nutrients and multiple antibiotics.

Iron-sulfur mediated antibiotic resistance genes attenuation and autotrophic denitrification mechanisms in bioelectrochemical systems

Aiming at the problems of antibiotic resistance genes (ARGs) transfer, mobile gene elements (MGEs) and nitrogen removal in livestock wastewater, pyrite was introduced into the bioelectrochemical constructed wetland, mainly focusing on the mechanism of ARGs transfer and autotrophic denitrification in bioelectrochemical system. The results indicated that pyrite promoted the degradation of antibiotics while inhibiting the efflux of ARGs and MGEs in effluent. The removal rate of antibiotics in pyrite-mediated constructed wetland coupled with microbial fuel cell (PCW-MFC) was 26.84 % and 21.20 % higher than constructed wetland-microbial fuel cell (CW-MFC) and pyrite-mediated constructed wetland (PCW). Metagenomic analysis revealed that the abundance of ARGs in effluent and anodic microorganism in PCW-MFC was effectively controlled by inhibiting the expression of genes encoding antibiotic efflux (macB, tetA, smeS). The expression levels of periplasmic nitrate reduction genes (napA, napB) and encoding cytochrome c nitrite reductase small subunit genes (nrfH) in PCW-MFC were much higher than CW-MFC. The total expression of ARGs in CW-MFC anode biofilms was 35.77 % higher than PCW-MFC, indicating that the system can effectively reduce the spread of ARGs and abate environmental risks. The findings can provide theoretical reference for the control of ARGs and efficient nitrogen removal in livestock wastewater.

Biofilm electrode reactor coupled manganese ore substrate up-flow microbial fuel cell-constructed wetland system: High removal efficiencies of antibiotic, zinc (II), and the corresponding antibiotic resistance genes

A coupled system comprised of a biofilm electrode reactor (BER) and a manganese ore substrate microbial fuel cell-constructed wetland (MFC-CW) system was used to remove co-exposed antibiotic and Zn (II), as well as simultaneously reduce copies of antibiotic resistance genes (ARGs) in the current study. In this system, BER primarily reduced the concentrations of antibiotics and Zn (II), and the effluent was used as the input to the MFC-CW, thereby providing electricity to BER. Co-exposure to a high concentration of Zn (II) decreased the relative abundances (RAs) of ARGs in the BER effluent, whereas the remaining sub-lethal concentration of Zn (II) increased the RAs of ARGs in the MFC-CW effluent. Even though the absolute copies of ARGs in the effluents increased during co-exposure, the total number of target ARG copies in the effluent of MFC-CW was significantly lower than that of BER. Moreover, BER pre-treatment eliminated most of Zn (II), which improved the electrical power generation characteristic of the MFC-CW unit. Correspondingly, the bacterial community and the ARGs hosts were analyzed to demonstrate the mechanism. In conclusion, the coupled system demonstrates significant potential to reduce antibiotics, Zn (II) and environmental risks posed by ARGs.

Treatment of hospital wastewater: emphasis on ecotoxicity and antibiotic resistance genes

AbstractBACKGROUNDHospital wastewater (HWW) charges wastewater treatment plants (WWTPs) with a mixture of contaminants such as pharmaceutically active compounds (PhACs) and pathogenic bacteria. This matrix is considered highly toxic to the ecosystem and organisms, and it may induce the development of antibiotic resistant bacteria (ARB) and the transfer of antibiotic resistance genes (ARGs) within microbial communities. Conventional WWTPs cannot treat HWW effectively, because they have not been designed to confront this challenge. Therefore, this study investigated the applicability of photocatalysis to purify HWW, regarding its ecotoxicity and the removal rates of targeted substances, selected pathogenic bacteria and specific ARGs.RESULTSThe HWW samples showed high toxicity towards the bioindicator Daphnia magna population, while they also contained significant levels of ARB and ARGs. Upon application of the photocatalytic treatment, the pharmaceutical concentrations decreased at a rate of >80% and the removal rates of the examined bacteria (Escherichia coli, Enterococci, Klebsiella sp. and Staphylococcus sp.) were >80%. Importantly, the bacteria remaining after photocatalysis were sensitive to the tested antibiotics. Conversely, the examined ARGs were present in high concentrations before and after photocatalytic treatment. For example, the concentrations of the selected genes, namely ampC, sul2, tetA and qnrA, in the effluents were from 104 to 106 gene copies L−1.CONCLUSIONSPhotocatalysis may be a promising treatment technique for the elimination of PhACs and pathogenic bacteria from HWW. Moreover, it proved capable of altering the antibiotic resistance profile of the bacteria surviving after treatment, making them sensitive to certain antibiotic compounds. However, the main concern regarding public health protection remains, as the presence of ARGs in effluents in considerable concentrations may induce antibiotic resistance in bacterial communities of aquatic environments. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

New and traditional methods for antibiotic resistance genes removal: Constructed wetland technology and photocatalysis technology.

Antibiotic resistance genes (ARGs) are a new environmental contaminant that poses a major hazard to humans and the environment. This research discusses the methods and drawbacks of two ARG removal approaches, constructed wetlands (CWs) and photocatalysis. CWs primarily rely on the synergistic effects of substrate adsorption, plant uptake, and microbial processes to remove ARGs. The removal of ARGs can be influenced by wetland plants, substrate type, wetland type, and hydraulic conditions. The absolute abundance of ARGs in effluent decreased, but their relative abundance increased. Photocatalysis deactivates ARGs predominantly through reactive oxygen species, with removal effectiveness determined by catalyst type, radiation type, and radiation intensity. The drawback is that it exposes intracellular resistance genes, perhaps increasing the risk of ARG spread. To address the current shortcomings, this paper proposes the feasibility of combining a constructed wetland with photocatalysis technology, which provides a novel strategy for ARG removal.

Influencing factors of antibiotic resistance genes removal in constructed wetlands: A meta-analysis assisted by multivariate statistical methods

In order to control antibiotic resistance genes (ARGs) diffusion in constructed wetlands, it is critical to explore the main factors influencing ARGs removal and understand its mechanism. Despite the fact that numerous studies have been conducted to determine the factors influencing ARGs removal by constructed wetlands in recent years, attempts to use published data and incorporate them into a comprehensive comparison and analysis are still limited. A framework for literature collection, data extraction and statistical analysis (LDS) was constructed in this study. The main factors influencing antibiotics and ARGs removal by constructed wetlands were identified using this framework. The results showed that nutrients, types of constructed wetlands and hydraulic loading were the principal factors influencing the removal of most antibiotics. The principal factors influencing the most ARGs removal were mobile genetic elements, plants, volume of constructed wetlands and running time. After purification by constructed wetlands, the risk coefficient of antibiotics decreased significantly, while the relative abundance of most ARGs did not change significantly. The analysis results of linear mixed model showed that the relationship between antibiotics and ARGs in effluent was closer than that in influent. LDS framework provides a new platform for the study of influencing factors of pollutant removal based on data mining.

Distribution and removal of antibiotic resistance genes in a landfill leachate treatment process

ABSTRACT Domestic waste landfills have been regarded as the main source of antibiotic resistance genes (ARGs) which are considered to be emerging environmental contaminants. Fluorescent quantitative PCR detection was used to determine the occurrence and abundance of ARGs in a landfill leachate treatment system. Fourteen ARGs were detected initially in the leachate influents. The most abundant ARGs were IntI1, followed by sulI, sulII, sulIII, tetC and tetW. The abundance of ARGs increased in the biological treatment unit and then decreased in the effluent of ultrafiltration membrane treatment. The absolute abundance of ARGs in effluent was 1.05–1.94 orders of magnitude lower than that in influent. There was a very significant strong correlation between various ARGs and heavy metals, especially Zn, Pb, Cu, Cd and As, indicating that there may be obvious co-selection between heavy metals and ARGs. Although the leachate treatment process could effectively reduce the abundance of ARGs, its effect on reducing the number of species of ARGs was relatively limited, which may have potential environmental health risks to the urban sewage plant receiving leachate effluent and the final receiving water body.

Antibiotic resistance genes and bacterial diversity: A comparative molecular study of treated sewage from different origins and their impact on irrigated soils

Present study aims to investigate how is soil affected following irrigation with treated effluents of different origins by analysing the bacterial diversity, metabolic diversity and antibiotic resistance genes (ARGs). Comparative analysis with previously reported ARGs in effluents was performed to understand the mobility of ARGs from treated wastewater to the irrigated soil with respect to the control soil regimen. Acinetobacter, Burkholderia and Pseudomonas were observed as the most abundant genera in all the samples. The metabolic gene abundance of all the samples suggests a prominent contribution to natural mineral recycling. Most abundant ARGs observed encode resistance for clindamycin, kanamycin A, macrolides, paromomycin, spectinomycin and tetracycline. Treated effluent reuse did not appear to enhance the ARG levels in soils in most cases except for institutional treatment site (M), where the ARGs for aminoglycosides, β-lactams and sulfonamides were found to be abundantly present in both treated effluent and the irrigated soil. This study finds the importance of wastewater treatment from different origins and the impact of treated wastewater reuse in irrigation. This study also emphasises on the better understanding of ARGs mobility from water to soil.

Changes of antibiotic resistance genes and bacterial communities in the advanced biological wastewater treatment system under low selective pressure of tetracycline

Effluents of conventional wastewater treatment systems contain antibiotic residues at concentrations below the minimal inhibitory concentrations (MIC), which nevertheless could still select for antibiotic-resistant bacteria. This work focuses on evaluating the changes of antibiotic resistance genes (ARGs) and bacterial communities in a planted advanced biological wastewater treatment system (ABWWTS) under long-term exposure to sub-MIC tetracycline. In the ABWWTS, the removal rates of tetracycline ranged from 97.9% to 99.9%, and a 17.2% decrease in the average removal rates of NH4+-N was observed after the addition of tetracycline. Although the background of ABWWTS contributed to the ARGs in effluents, the concentration of 283 targeted ARGs (ΣARGs) was 83.5% lower in effluents than in influents after sub-MIC tetracycline exposure, and the concentrations of ΣARGs in the ABWWTS were, on average, 30.0% lower than those in an unplanted biological wastewater treatment system (UBWWTS) after a performance of 130 days. The relative abundance of tetracycline resistance genes increased within ABWWTS and UBWWTS under tetracycline exposure. After tetracycline exposure, bacterial diversity in ABWWTS and UBWWTS increased on average by 36.2% and 42.7%, respectively, and the abundances of Nitrosomonas and Nitrospira in the aerobic zone were more than 10-times higher in the ABWWTS than in the UBWWTS. Sub-MIC tetracycline concentrations were linearly correlated with the relative abundance of tetracycline resistance genes in Escherichia coli (E. coli). Long-term exposure to tetracycline at the same concentration increased abundances of the same ARGs (i.e., tetR-02 and tetM-01) in E. coli and the microflora of the ABWWTS, revealing that sub-MIC tetracycline could increase the abundance of ARGs in the ABWWTS by facilitating the vertical transfer of tetracycline resistance genes. These findings demonstrated that planted ABWWTS played a positive role in removing ARGs under low antibiotic selective pressure, which was in accompany with increasing levels of corresponding ARGs within the system.

Climatological and Epidemiological Conditions Are Important Factors Related to the Abundance of blaKPC and Other Antibiotic Resistance Genes (ARGs) in Wastewater Treatment Plants and Their Effluents, in an Endemic Country.

Several physicochemical and season factors have been related to the abundance of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs), considered hotspots of bacterial resistance. However, few studies on the subject have been carried out in tropical countries endemic for resistance mechanisms such as bla KPC. In this study, the occurrence of ARGs, particularly bla KPC, was determined throughout a WWTP, and the factors related to their abundance were explored. In 2017, wastewater samples were taken from a WWTP in Colombia every 15 days for 6 months, and a total of 44 samples were analyzed by quantitative real-time PCR. sul1, sul2, bla KPC, and ermB were found to be the most prevalent ARGs. A low average reduction of the absolute abundance ARGs in effluent with respect to influent was observed, as well as a greater absolute abundance of ARGs in the WWTP effluent in the rainy season. Factors such as temperature, pH, oxygen, total organic carbon (TOC), chemical oxygen demand (COD), and precipitation were significantly correlated with the absolute abundance of several of the ARGs evaluated. A generalized linear mixed-effects model analysis showed that dissolved oxygen and precipitation in the sampling day were important factors related to the absolute concentration of bla KPC over time. In conclusion, the abundance of ARGs in the WWTP could be influenced by endemic conditions and physicochemical and climatological parameters. Therefore, it is necessary to continuously monitor clinical relevant genes in WWTPs from different global regions, even more so in low-income countries where sewage treatment is limited.

Bacterial community change and antibiotic resistance promotion after exposure to sulfadiazine and the role of UV/H2O2-GAC treatment

Effects of sulfadiazine on bacterial community and antibiotic resistance genes (ARGs) in drinking water distribution systems (DWDSs) were investigated in this study. Three DWDSs, including sand filtered (SF) DWDSs, granular active carbon (GAC) filtration DWDSs, and UV/H2O2-GAC DWDSs, were used to deliver sand filtered water, GAC filtered water, and UV/H2O2-GAC treated water, respectively. UV/H2O2-GAC filtration can remove the dissolved organic matter effectively, which resulted in the lowest bacterial diversity, biomass and ARGs in effluents and biofilm of DWDSs. When sulfadiazine was added to the sand filtered water, the dehydrogenase concentration and bacterial activity of bacterial community increased in effluents and biofilm of different DWDSs, inducing more extracellular polymeric substances (EPS) production. The proteins increasement percentage was 26.9%, 11.7% and 19.1% in biofilm of three DWDSs, respectively. And the proteins increased to 830.30 ± 20.56 μg cm−2, 687.04 ± 18.65 μg cm−2 and 586.07 ± 16.24 μg cm−2, respectively. The increase of EPS promoted biofilm formation and increased the chlorine-resistance capability of bacteria. Therefore, the relative abundance of Clostridium_sensu_stricto_1 increased to 12.22%, 10.41% and 0.33% in biofilm of the three DWDSs, respectively. Candidatus_Odyssella also increased in the effluents and biofilm of the three DWDSs. These antibiotic resistance bacteria increase in DWDSs also induced the ARGs promotion, including sul1, sul2, sul3, mexA and class 1 integrons (int1). However, UV/H2O2-GAC filtration induced the lowest increase of dehydrogenase and EPS production through sulfadiazine removal efficiently, resulting in the least bacterial community change and ARGs promotion in UV/H2O2-GAC DWDSs.

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

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

Removal of Antibiotic Resistance Genes at Two Conventional Wastewater Treatment Plants of Louisiana, USA

Wastewater treatment plants (WWTPs) represent all known types of antibiotic resistance mechanisms and are considered as the critical points for the spread of antibiotic resistance genes (ARGs). The purpose of this study is to investigate the removal of a Class 1 integrase gene (intI1) and a selected set of ARGs (blaTEM, ermF, mecA, and tetA) at two conventional WWTPs by using chlorination in Louisiana, USA. We collected 69 wastewater samples (23 each from influent, secondary effluent, and final effluent) and determined the concentrations of ARGs by using quantitative polymerase chain reaction. All tested ARGs, except for mecA, were detected in 83–96% and 30–65% of influent and final effluent samples, respectively. Although the ARGs underwent approximately 3-log10 reduction, two WWTPs on an average still released 3.3 ± 1.7 log10 copies/mL of total ARGs studied in the effluents. Chlorination was found to be critical in the significant reduction of total ARGs (p &lt; 0.05). Correlation analysis and the ability of intI1 to persist through the treatment processes recommend the use of intI1 as a marker of ARGs in effluents to monitor the spread of antibiotic resistance in effluents. Our study suggests that conventional WWTPs using chlorination do not favor the proliferation of antibiotic resistance bacteria and ARGs during wastewater treatment.

Viability-based quantification of antibiotic resistance genes and human fecal markers in wastewater effluent and receiving waters

Antibiotic resistance is a public health issue with links to environmental sources of antibiotic resistance genes (ARGs). ARGs from nonviable sources may pose a hazard given the potential for transformation whereas ARGs in viable sources may proliferate during host growth or conjugation. In this study, ARGs in the effluent from three municipal wastewater treatment plants (WWTPs) and the receiving surface waters were investigated using a viability-based qPCR technique (vPCR) with propidium monoazide (PMA). ARGs sul1, tet(G), and blaTEM, fecal indicator marker BacHum, and 16S rRNA gene copies/mL were found to be significantly lower in viable-cells than in total concentrations for WWTP effluent. Viable-cell and total gene copy concentrations were similar in downstream samples except for tet(G). Differences with respect to season in the prevalence of nonviable ARGs in surface water or WWTP effluent were not observed. The results of this study indicate that qPCR may overestimate viable-cell ARGs and fecal indicator genes in WWTP effluent but not necessarily in the surface water >1.8 km downstream.

Removal of antibiotic resistance genes in four full-scale membrane bioreactors

Antibiotic resistance genes (ARGs) discharged through wastewater treatment plants (WWTPs) has aroused growing public concern for its risk to human health and ecological safety. Membrane bioreactor (MBR) has been recognized as an effective approach to remove ARGs in full-scale WWTPs, but its advantage over traditional processes was not clearly quantified. To address this, we investigated four full-scale WWTPs containing parallel MBR and traditional processes (oxidation ditch or sequencing batch reactor) to compare the reduction of eight types of ARGs (blaTEM, ermB, tetW, tetO, sul1, sul2, addD, and qnrS) and int1. In general, MBRs reduced the ARGs (1.1–7.3 log removal) better than parallel processes (0.4–4.2 log removal). Notably, the dominant ARGs in the influent, such as ermB, sul1 and int1 (106.39–107.79 copies/mL), were more effectively reduced by MBRs (1.5–7.3 log removal) than traditional processes (0.8–3.4 log removal). Meanwhile, the distribution of those ARGs in activated sludge was not significantly different between aforementioned processes (p > 0.05). The separation coefficient (Ksw) was proposed to represent the contribution of solid separation on ARG removal, subsequent analysis revealed surprisingly strong correlation between Ksw values of dominant ARGs (ermB, sul1 and int1) and their log removal by MBR (R = 0.79–0.96, p < 0.05), while such correlation was much weaker in traditional process (R = 0.33–0.37), indicating solid separation was the major pathway for removal of dominant ARGs and int1. According to the canonical correlation analysis between process operation and ARG removal in MBR, sludge retention time (SRT) seemed to be the major factor affecting removal of dominant ARGs and int1. This comparative study can be helpful for further understanding and operating MBR process to reduce the ARGs in effluent.

The changes of bacterial communities and antibiotic resistance genes in microbial fuel cells during long-term oxytetracycline processing

Microbial fuel cell (MFC) is regarded as a promising alternative for enhancing the removal of antibiotic pollutants. In this study, oxytetracycline served as an electron donor in the anode chamber of MFCs, and after continuous operation for 330 days, the efficiency of removal of 10 mg/L oxytetracycline in MFCs increased to 99.00% in 78 h, whereas removal efficiency of only 58.26% was achieved in microbial controls. Compared to microbial controls, higher ATP concentration and persistent electrical stimulation mainly contributed to bioelectrochemical reactions more rapidly to enhance oxytetracycline removal in MFCs. In addition, the analysis of bacterial communities revealed that Eubacterium spp.—as the main functional bacterial genus responsible for oxytetracycline biodegradation—flourished starting from merely 0.00%–91.69% ± 0.27% (mean ± SD) in MFCs. High-throughput quantitative PCR showed that the normalized copy numbers of total antibiotic resistance genes (ARGs) and mobile genetic elements in MFCs were 1.7364 and 0.0065 copies/cell respectively, which were markedly lower than those in the microbial controls. Furthermore, there was no significant correlation between oxytetracycline concentration in the influent and abundance of ARGs in effluent from MFCs. Nevertheless, Tp614, a transposase gene, was found to be enriched in both MFCs and microbial reactors, suggesting that it may be a common challenge for different biological processes for wastewater treatment. This study therefore showed a lower probability of upregulation and transmission of ARGs in MFCs when compared to a traditional anaerobic microbial treatment.

Vertical up-flow constructed wetlands exhibited efficient antibiotic removal but induced antibiotic resistance genes in effluent

The intensive use of antibiotics results in their continuous release into the environment and the subsequent widespread dissemination of antibiotic resistance genes (ARGs), thus posing potential risks for public health. Although vertical up-flow constructed wetlands (VUF-CWs) have been widely used to treat wastewater in remote or rural regions, few studies have assessed the potential risks of ARG dissemination when VUF-CWs are applied to treat wastewaters containing antibiotics. In this study, the removal performance of two typical antibiotics (sulfamethoxazole (SMX) and tetracycline (TC)) and the fate of ARGs were evaluated in three lab-scale VUF-CWs. The results indicated that high removal efficiencies (>98%) could be achieved for both SMX and TC. However, the exposure of antibiotics resulted in harboring abundant ARGs (mainly sul- and tet-related genes), even with increasing abundances with operation time. The abundances of ARGs had a positive correlation with the accumulation of SMX and TC in different layers of VUF-CWs, where the tet and sul genes have the highest abundance in the bottom layer due to the highest antibiotic exposure concentration. Positive correlations were observed between the abundance of tet gene and antibiotic concentration in effluent. Although the effluent had lower abundances of the ARGs than that in the wetland media, the occurrence of ARGs in effluent might still pose risk for public health. Further studies are required to explore effective control strategies to eliminate ARGs from VUF-CWs.

Behavior of antibiotic resistance genes under extremely high-level antibiotic selection pressures in pharmaceutical wastewater treatment plants

Pharmaceutical wastewater treatment plants (PWWTPs), which receive wastewater containing extremely high levels of antibiotics, are regarded as potential hot spots for antibiotic-resistance development in the environment. Six sampling campaigns in six PWWTPs in Southeastern China were carried out to assess the prevalence and fate of antibiotic resistance genes (ARGs). Different genes were monitored in different PWWTPs (PWWTP A: lincosamides; PWWTP B: aminoglycosides and macrolides; PWWTP C: quinolones; PWWTP D: macrolides and quinolones; PWWTP E: cephalosporins; and PWWTP F: quinolones and macrolides) using real-time quantitative polymerase chain reactions (PCRs), according to the antibiotic type produced. The levels of typical ARG subtypes in the final effluents ranged from (1.03±0.91)×101 to (6.78±0.21)×107copies/mL. The absolute abundance of ARGs in effluents accounted for 0%–577% of influents to the six PWWTPs with a median value of 6%. Most of the ARGs are transported to the dewatered sludge, with concentrations from (1.38±0.21)×105 to (6.84±0.43)×1010copies/g dry weight (dw). In different treatment units (before/after biological units), a clear trend of proliferation or attenuation was not observed for the ARGs, aside from a strong attenuation in moving bed bio-film reactor (MBBR) in PWWTP C. Through correlation analyses, this study demonstrated that the bacterial abundance and antibiotic concentrations within the PWWTPs influenced the fate of the associated ARGs, and this was possibly related primarily to the intrinsic resistance mechanisms of corresponding ARGs. Macrolide ARGs, which tend to locate in plasmids and transposons, positively correlate weakly with total macrolide antibiotic concentrations but positively correlate strongly with 16S rRNA concentrations. Furthermore, ARG concentrations in the wastewater from fermentation were significantly higher than in the wastewater from chemical synthesis and preparation. This is the first comprehensive study on the behavior of antibiotic resistance genes under extremely high-level antibiotic selection pressures in pharmaceutical wastewater treatment plants (PWWTPs) in Southeastern China.

Fate and removal of various antibiotic resistance genes in typical pharmaceutical wastewater treatment systems.

The high levels of antibiotic residues in pharmaceutical wastewater treatment plants (PWWTPs) make these plants the hotspots for the proliferation of antibiotic resistance genes (ARGs). This study investigated the fate and removal of 11 ARG subtypes for sulfonamide, tetracycline, β-lactam, and macrolide resistance in each processing stage of two full-scale PWWTPs in northern China. The levels of typical ARG subtypes in the final effluents ranged from (2.56 ± 0.13) × 10(1) to (2.36 ± 0.11) × 10(7) copies/ml. The absolute abundance of ARGs in effluents accounted for only 0.03-78.1% of influents of the two PWWTPs, while the majority of the ARGs were transported to the dewatered sludge with concentrations from (2.65 ± 0.43) × 10(5) to (4.27 ± 0.03) × 10(10) copies/g dry weight (dw). The total loads of ARGs discharged through dewatered sludge plus effluent was 1.01-14.09-fold higher than that in the raw influents, suggesting the proliferation of ARGs occurred in the wastewater treatment. The proliferation of ARGs mainly occurs in biological treatment process, such as aeration tank, anoxic tank, sequencing batch reactor (SBR), and bio-contact oxidation, facilitates the proliferation of various ARGs, implying significant replication of certain ARG subtypes may be attributable to microbial growth. Chemical oxidation seems promising to remove ARGs, with removal efficiency ranged from 29.3 to 85.7%, while the partial correlation analysis showed significant correlations between antibiotic concentration and ARG removal. Thus, the high antibiotic residues within the PWWTPs may have an influence on the proliferation, fate, and removal of the associated ARG subtypes.

Class 1 integrase, sulfonamide and tetracycline resistance genes in wastewater treatment plant and surface water.

Wastewater treatment plants are considered hot spots for multiplication and dissemination of antibiotic-resistant bacteria and resistance genes. In this study, we determined the presence of class 1 integron integrase and genes conferring resistance to tetracyclines and sulfonamides in the genomes of culturable bacteria isolated from a wastewater treatment plant and the river that receives the treated wastewater. Moreover, using PCR-based metagenomic approach, we quantified intI1, tet and sul genes. Wastewater treatment caused the decrease in the total number of culturable heterotrophs and bacteria resistant to tetracycline and sulfonamides, along with the decrease in the number of intI1, sul and tet gene copies per ml, with significant reduction of tet(B). On the other hand, the treatment process increased both the frequency of tetracycline- and sulfonamide-resistant bacteria and intI1-positive strains, and the relative abundance of all quantified antibiotic resistance genes (ARGs) and intI1 gene; in the case of tet(A) and sul2 significantly. The discharge of treated wastewater increased the number of intI1, tet and sul genes in the receiving river water both in terms of copy number per ml and relative abundance. Hence, despite the reduction of the number of ARGs and ARBs, wastewater treatment selects for bacteria with ARGs in effluent.