Comparison of Antibiotic Resistance Removal Efficiencies Using Ozone Disinfection under Different pH and Suspended Solids and Humic Substance Concentrations

Enhanced removal of antibiotic-resistant bacteria and resistance genes by three-dimensional electrochemical process using MgFe2O4-loaded biochar as both particle electrode and catalyst for peroxymonosulfate activation

In this study, MgFe2O4-loaded biochar (MFBC) was used as a three-dimensional particle electrode to active peroxymonosulfate (EC/MFBC/PMS) for the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). The results demonstrated that, under the conditions of 1.0 mM PMS concentration, 0.4 g/L material dosage, 5 V voltage intensity, and MFBC preparation temperature of 600 °C, the EC/MFBC600/PMS system achieved complete inactivation of E. coli DH5α within 5 min and the intracellular sul1 was reduced by 81.5 % after 30 min of the treatment. Compared to EC and PMS alone treatments, the conjugation transfer frequency of sul1 rapidly declined by 92.9 % within 2 min. The cell membrane, proteins, lipids, as well as intracellular and extracellular ARGs in E. coli DH5α were severely damaged by free radicals in solution and intracellular reactive oxygen species (ROS). Furthermore, up-regulation was observed in genes associated with oxidative stress, SOS response and cell membrane permeability in E. coli DH5α, however, no significant changes were observed in functional genes related to gene conjugation and transfer mechanisms. This study would contribute to the underlying of PMS activation by three-dimensional particle electrode, and provide novel insights into the mechanism of ARB inactivation and ARGs degradation under PMS advanced oxidation treatment.

Combined ozonation-biological activated carbon process for antibiotic resistance control in treated effluent from wastewater treatment plant

Biological activated carbon (BAC) treatment plays a crucial role in wastewater treatment plants due to its economic and effective promotion of organic matter degradation or mineralization. However, whether the changes in antibiotic resistance (AR) resulting from BAC or O3-BAC treatment are related to environmental factors remains unclear, as previous studies have primarily focused on isolated aspects, or have combined these aspects without systematically comparing the BAC and O3-BAC treatment processes or analyzing their interrelationships. In this study, to gain a clearer understanding of the factors related to AR during the BAC treatment, the treatment process of BAC and O3-BAC were comprehensively compared, including antibiotics removal, wastewater matrix changes, antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and bacterial community characteristics. The roles of O3 pretreatment and the bed depth of BAC were also clarified. ARGs were found to be not as sensitive to ozone as ARB. In addition, further strengthening of control measures should be needed for trimethoprim and tetracycline, due to their low removal efficiencies by ozone pretreatment, and their close relationship with the increased AR. Besides, 2 mg/L ozonation pretreatment could significantly influence the microbial community composition of wastewater and biofilm samples, while 1 mg/L ozonation could not. Finally, the correlation of environmental factors, bacterial communities, and ARGs revealed that to reduce the AR risks of O3-BAC treatment, antibiotics in wastewater should be strictly controlled, since they were positively correlated with the accumulation of ARGs and Pseudomonadota, Actinomycetota, and Bacteroidota, which were responsible for carrying and disseminating ARGs. The results showed that higher dose ozonation pre-treatment and longer bed depth of BAC process could help control the AR of BAC.

Copper single-atom catalysts for broad-spectrum antibiotic-resistant bacteria (ARBs) antimicrobial: Activation of peroxides and mechanism of ARBs inactivation

Antibiotic-resistant bacteria (ARBs) have been widely detected in wastewater and become a potential threat to human health. This work found that low-load single-atom copper (0.1 wt%) anchored on g-C3N4 (SA-Cu/g-C3N4) exhibited excellent ability to activate H2O2 and inactivate ARBs during the photo-Fenton process. The presence of SA-Cu/g-C3N4 (0.4 mg/mL) and H2O2 (0.1 mM) effectively inactivated ARBs. More than 99.9999 % (6-log) of methicillin-resistant Staphylococcus aureus (MRSA), and carbapenem-resistant Acinetobacter baumannii (CRAB) could be inactivated within 5 min. Extended-spectrum β-lactamase-producing pathogenic Escherichia coli (ESBL-E) and vancomycin-resistant Enterococcus faecium (VRE) were killed within 10 and 30 min, respectively. In addition, more than 5-log of these ARBs were killed within 60 min in real wastewater. Furthermore, D2O-labeling with Raman spectroscopy revealed that SA-Cu/g-C3N4 completely suppressed the viable but nonculturable (VBNC) state and reactivation of bacteria. Electron paramagnetic resonance spectroscopy results demonstrated that g-C3N4 mainly produced 1O2, while SA-Cu/g-C3N4 simultaneously produced both 1O2 and •OH. The •OH and 1O2 cause lipid peroxidation damage to the cell membrane, resulting in the death of the bacteria. These findings highlight that the SA-Cu/g-C3N4 catalyst is a promising photo-Fenton catalyst for the inactivation of ARBs in wastewater.

Molecular interaction mechanism for humic acids fouling resistance on charged, zwitterion-like and zwitterionic surfaces

Humic acids (HA) are ubiquitous in surface waters, leading to significant fouling challenges. While zwitterion-like and zwitterionic surfaces have emerged as promising candidates for antifouling, a quantitative understanding of molecular interaction mechanism, particularly at the nanoscale, still remains elusive. In this work, the intermolecular forces between HA and charged, zwitterion-like or zwitterionic monolayers in aqueous environments were quantified using atomic force microscope. Compared to cationic MTAC ([2-(methacryloyloxy)ethyl]trimethylammonium chloride), which exhibited an adhesion energy of ∼1.342 mJ/m2 with HA due to the synergistic effect of electrostatic attraction and possible cation-π interaction, anionic SPMA (3-sulfopropyl methacrylate) showed a weaker adhesion energy (∼0.258 mJ/m2) attributed to the electrostatic repulsion. Zwitterion-like MTAC/SPMA mixture, driven by electrostatic attraction between opposite charges, formed a hydration layer that prevented the interaction with HA, thereby considerably reducing adhesion energy to ∼0.123 mJ/m2. In contrast, zwitterionic MPC (2-methacryloyloxyethyl phosphorylcholine) and DMAPS ([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide) displayed ultralow adhesion energy (0.06-0.07 mJ/m2) with HA, arising from their strong dipole moments which could induce a tight hydration layer that effectively inhibited HA fouling. The pH-mediated electrostatic interaction resulted in the increased adhesion energy for MTAC but decreased adhesion energy for SPMA with elevated pH, while the adhesion energy for zwitterion-like and zwitterionic surfaces was independent of environmental pH. Density functional theory (DFT) simulation confirmed the strong binding capability of MPC and DMAPS with water molecules (∼-12 kcal mol-1). This work provides valuable insights into the molecular interaction mechanisms underlying humic-substance-fouling resistance of charged, zwitterion-like and zwitterionic materials at the nanoscale, shedding light on developing more effective strategy for HA antifouling in water treatment.

Dielectric barrier discharge plasma promotes disinfection-residual-bacteria inactivation via electric field and reactive species

Traditional disinfection processes face significant challenges such as health and ecological risks associated with disinfection-residual-bacteria due to their single mechanism of action. Development of new disinfection processes with composite mechanisms is therefore urgently needed. In this study, we employed liquid ground-electrode dielectric barrier discharge (lgDBD) to achieve synergistic sterilization through electric field electroporation and reactive species oxidation. At a voltage of 12 kV, Pseudomonas fluorescens (ultraviolet and ozone-resistant) and Bacillus subtilis (chlorine-resistant) were completely inactivated within 8 and 6 min, respectively, surpassing a 7.0-log reduction. The lgDBD process showed good disinfection performance across a wide range of pH values and different practical water samples. Staining experiments suggest that cellular membrane damage contributes to this inactivation. In addition, we used a two-dimensional parallel streamer solver with kinetics code to fashion a representative model of the basic discharge unit, and discovered the presence of a persistent electric field during the discharge process with a peak value of 2.86 × 106 V/m. Plasma discharge generates excited state species such as O(1D) and N2(C3Πu), and further forms reactive oxygen and nitrogen species at the gas-liquid interface. The physical process, which is driven by electric field-induced cell membrane electroporation, synergizes with the bactericidal effects of reactive oxygen and nitrogen species to provide effective disinfection. Adopting the lgDBD process enhances sterilization efficiency and adaptability, underscoring its potential to revolutionize physicochemical synergistic disinfection practices.

Molecular level removal of antibiotic resistant bacteria and genes: A review of interfacial chemical in advanced oxidation processes

As a kind of novel and persistent environmental pollutants, antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been frequently detected in different aquatic environment, posing potential risks to public health and ecosystems, resulting in a biosecurity issue that cannot be ignored. Therefore, in order to control the spread of antibiotic resistance in the environment, advanced oxidation technology (such as Fenton-like, photocatalysis, electrocatalysis) has become an effective weapon for inactivating and eliminating ARB and ARGs. However, in the process of advanced oxidation technology, studying and regulating catalytic active sites at the molecular level and studying the adsorption and surface oxidation reactions between catalysts and ARGs can achieve in-depth exploration of the mechanism of ARGs removal. This review systematically reveals the catalytic sites and related mechanisms of catalytic antagonistic genes in different advanced oxidation processes (AOPs) systems. We also summarize the removal mechanism of ARGs and how to reduce the spread of ARGs in the environment through combining a variety of characterization methods. Importantly, the potential of various catalysts for removing ARGs in practical applications has also been recognized, providing a promising approach for the deep purification of wastewater treatment plants.

Chloramine Disinfection of Levofloxacin and Sulfaphenazole: Unraveling Novel Disinfection Byproducts and Elucidating Formation Mechanisms for an Enhanced Understanding of Water Treatment

The unrestricted utilization of antibiotics poses a critical challenge to global public health and safety. Levofloxacin (LEV) and sulfaphenazole (SPN), widely employed broad-spectrum antimicrobials, are frequently detected at the terminal stage of water treatment, raising concerns regarding their potential conversion into detrimental disinfection byproducts (DBPs). However, current knowledge is deficient in identifying the potential DBPs and elucidating the precise transformation pathways and influencing factors during the chloramine disinfection process of these two antibiotics. This study conducts a comprehensive analysis of reaction pathways, encompassing piperazine ring opening/oxidation, Cl-substitution, OH-substitution, desulfurization, and S-N bond cleavage, during chloramine disinfection. Twelve new DBPs were identified in this study, exhibiting stability and persistence even after 24 h of disinfection. Additionally, an examination of DBP generation under varying disinfectant concentrations and pH values revealed peak levels at a molar ratio of 25 for LEV and SPN to chloramine, with LEV contributing 11.5% and SPN 23.8% to the relative abundance of DBPs. Remarkably, this research underscores a substantial increase in DBP formation within the molar ratio range of 1:1 to 1:10 compared to 1:10 to 1:25. Furthermore, a pronounced elevation in DBP generation was observed in the pH range of 7 to 8. These findings present critical insights into the impact of the disinfection process on these antibiotics, emphasizing the innovation and significance of this research in assessing associated health risks.

Tertiary/quaternary treatment of urban wastewater by UV/H2O2 or ozonation: Microplastics may affect removal of E. coli and contaminants of emerging concern

The aim of this study was to investigate the interference of polyethylene microplastics (MPs) on ultraviolet irradiation/hydrogen peroxide (UV/H2O2) and ozonation processes in the inactivation of E. coli bacteria (tertiary treatment) and removal of contaminants of emerging concern (CECs) (quaternary treatment) from simulated and real secondary treated urban wastewater. Three pharmaceuticals were investigated as model CECs, namely carbamazepine, sulfamethoxazole and trimethoprim. Experimental results showed that disinfection efficiency of UV/H2O2 treatment decreased (2.4, 1.8 and 1.3 log reductions of E. coli, initial H2O2 dose of 30 mg/L, 2.5 min treatment) as the initial concentration of MPs was increased (0.25, 0.5 and 1.0 g/L, respectively). Similarly, an increase in MPs concentration (0.25, 0.5 and 1.0 g/L) reduced the inactivation (4.7, 4.1 and 3.7 log reductions) of the target bacteria after 60 min of ozonation treatment. Although the disinfection efficiency of both treatment processes was negatively affected by the presence of MPs, UV/H2O2 was more effective than the ozonation, despite ozonation being investigated at high doses to better discriminate the effect of MPs. Noteworthy, CECs degradation by UV/H2O2 under realistic operating conditions was affected to some extent by MPs, while a lower effect was observed for ozonation, at not realistic ozone dose.

Efficient inactivation of amoeba spores and their intraspore bacteria by solar/chlorine: Kinetics and mechanisms

Amoebae are widespread in water and serve as environment vectors for pathogens, which may threaten public health. This study evaluated the inactivation of amoeba spores and their intraspore bacteria by solar/chlorine. Dictyostelium discoideum and Burkholderia agricolaris B1qs70 were selected as model amoebae and intraspore bacteria, respectively. Compared to solar irradiation and chlorine, solar/chlorine enhanced the inactivation of amoeba spores and intraspore bacteria, with 5.1 and 5.2-log reduction at 20 min, respectively. The enhancement was similar in real drinking water by solar/chlorine under natural sunlight. However, the spore inactivation decreased to 2.97-log by 20 min solar/chlorine under oxygen-free condition, indicating that ozone played a crucial role in the spore inactivation, as also confirmed by the scavenging test using tert‑butanol to scavenge the ground-state atomic oxygen (O(3P)) as a ozone precursor. Moreover, solar/chlorine induced the shape destruction and structural collapse of amoeba spores by scanning electron microscopy. As for intraspore bacteria, their inactivation was likely ascribed to endogenous reactive oxygen species. As pH increased from 5.0 to 9.0, the inactivation of amoeba spores decreased, whereas that of intraspore bacteria was similar at pH 5.0 and 6.5 during solar/chlorine treatment. This study first reports the efficient inactivation of amoeba spores and their intraspore pathogenic bacteria by solar/chlorine in drinking water.

Efficient Degradation of Intracellular Antibiotic Resistance Genes by Photosensitized Erythrosine-Produced 1O2

Intracellular antibiotic resistance genes (iARGs) constitute the important part of wastewater ARGs and need to be efficiently removed. However, due to the dual protection of intracellular DNA by bacterial membranes and the cytoplasm, present disinfection technologies are largely inefficient in iARG degradation. Herein, we for the first time found that erythrosine (ERY, an edible dye) could efficiently degrade iARGs by producing abundant 1O2 under visible light. Seven log antibiotic-resistant bacteria were inactivated within only 1.5 min, and 6 log iARGs were completely degraded within 40 min by photosensitized ERY (5.0 mg/L). A linear relationship was established between ARG degradation rate constants and 1O2 concentrations in the ERY photosensitizing system. Surprisingly, a 3.2-fold faster degradation of iARGs than extracellular ARGs was observed, which was attributed to the unique indirect oxidation of iARGs induced by 1O2. Furthermore, ERY photosensitizing was effective for iARG degradation in real wastewater and other photosensitizers (including Rose Bengal and Phloxine B) of high 1O2 yields could also achieve efficient iARG degradation. The findings increase our knowledge of the iARG degradation preference by 1O2 and provide a new strategy of developing technologies with high 1O2 yield, like ERY photosensitizing, for efficient iARG removal.

Multidrug-resistant plasmid RP4 increases NO and N2O yields via the electron transport system in Nitrosomonas europaea ammonia oxidation

Antibiotic resistance genes (ARGs) have recently become an important public health problem and therefore several studies have characterized ARG composition and distribution. However, few studies have assessed their impact on important functional microorganisms in the environment. Therefore, our study sought to investigate the mechanisms through which multidrug-resistant plasmid RP4 affected the ammonia oxidation capacity of ammonia-oxidizing bacteria, which play a key role in the nitrogen cycle. The ammonia oxidation capacity of N. europaea ATCC25978 (RP4) was significantly inhibited, and NO and N2O were produced instead of nitrite. Our findings demonstrated that the decrease in electrons from NH2OH decreased the ammonia monooxygenase (AMO) activity, leading to a decrease in ammonia consumption. In the ammonia oxidation process, N. europaea ATCC25978 (RP4) exhibited ATP and NADH accumulation. The corresponding mechanism was the overactivation of Complex Ⅰ, ATPase, and the TCA cycle by the RP4 plasmid. The genes encoding TCA cycle enzymes related to energy generation, including gltA, icd, sucD, and NE0773, were upregulated in N. europaea ATCC25978 (RP4). These results demonstrate the ecological risks of ARGs, including the inhibition of the ammonia oxidation process and an increased production of greenhouse gases such as NO and N2O.

Optimizing ozone dose and contact time for removal of antibiotic-resistant P. aeruginosa, A. baumannii, E. coli, and associated resistant genes in effluent of an activated sludge process in a municipal WWTP

This study aimed to investigate the impact of ozonation on inactivation of antibiotic-resistant bacteria (ARB) including E. coli, P. aeruginosa, and A. baumannii, as well as on removal of 16S-rRNA gene and their associated antibiotic-resistant genes (ARGs) indigenously present in effluent of municipal wastewater treatment plant. The Chick-Watson model was used to describe bacterial inactivation rates at specific ozone doses. Maximum reduction of total cultivable A. baumannii, E. coli, and P. aeruginosa were found to be 7.6, 7.1, and 4.7 log, respectively, with the highest ozone dose of 0.48 gO₃/gCOD at 12 min contact time. According to the study results, complete inactivation of ARB and bacterial regrowth was not observed after 72 h incubation. The culture methods overestimated the performance of disinfection processes and propidium monoazide combined with qPCR, and showed the presence of viable but non-culturable bacteria after ozonation. ARGs were more persistent to ozone than ARB. The results of this study highlighted the significance of specific ozone dose and contact time in ozonation process considering the bacterial species and associated ARGs as well as the wastewater physicochemical characteristics, in order to help diminish the entrance of the biological microcontaminants into the environment.

Organic amendment treatments for antimicrobial resistance and mobile element genes risk reduction in soil-crop systems

Agricultural fertilization with organic amendments of animal origin often leads to antibiotic resistance dissemination. In this study, we evaluated the effect of different treatments (anaerobic digestion, biochar application, ozonation, zerovalent iron nanoparticle application, and spent mushroom substrate addition) on the resistome in dairy cow manure-derived amendments (slurry, manure, and compost). Anaerobic digestion and biochar application resulted in the highest reduction in antibiotic resistance gene (ARG) and mobile genetic element (MGE) gene abundance. These two treatments were applied to cow manure compost, which was then used to fertilize the soil for lettuce growth. After crop harvest, ARG and MGE gene absolute and relative abundances in the soil and lettuce samples were determined by droplet digital PCR and high-throughput qPCR, respectively. Prokaryotic diversity in cow manure-amended soils was determined using 16S rRNA metabarcoding. Compared to untreated compost, anaerobic digestion led to a 38% and 83% reduction in sul2 and intl1 absolute abundances in the soil, respectively, while biochar led to a 60% reduction in intl1 absolute abundance. No differences in lettuce gene abundances were observed among treatments. We conclude that amendment treatments can minimize the risk of antibiotic resistance in agroecosystems.

Investigating changes in the characteristics of antibiotic resistance genes at different reaction stages of high solid anaerobic digestion with pig manure

Contamination of antibiotic resistance genes (ARGs) from animals is a serious issue as they may spread to human pathogenic bacteria. The reduction of ARG contamination from livestock waste is thus essential. High solid anaerobic digestion (HSAD) is a new and effective technology although some aspects, such as change characteristics of ARGs at different reaction stages, have not been fully investigated. This study focused firstly on the variations in ARGs at different reaction stages in HSAD systems with five different starting methods: 1 natural start (the control) and 4 rapid starts by changing leachate reflux forms. The results showed that the rapid starting methods could accelerate start-up and increase biogas production by 312.5%. The starting and acidification stages showed higher microbial richness and diversity compared with the other stages. ARGs found to be reduced at acidification stage. Variation in ARGs at the starting and acidification stages was mainly driven by a combination of microbial community, mobile genetic elements (MGEs), and environmental factors; while the main contributory factors at the gas production stage were biomass and several unexplained factors. At the ending stage, the main driving factors were biomass and microbial communities. Most of the potential hosts (16/20) of the ARGs belonged to the Firmicutes phylum, which showed the lowest connections with the ARGs at the gas production stage.

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

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

Potent Activity of a High Concentration of Chemical Ozone against Antibiotic-Resistant Bacteria

BACKGROUND

Health care-associated infections (HAIs) are a significant public health problem worldwide, favoring multidrug-resistant (MDR) microorganisms. The SARS-CoV-2 infection was negatively associated with the increase in antimicrobial resistance, and the ESKAPE group had the most significant impact on HAIs. The study evaluated the bactericidal effect of a high concentration of O3 gas on some reference and ESKAPE bacteria.

MATERIAL AND METHODS

Four standard strains and four clinical or environmental MDR strains were exposed to elevated ozone doses at different concentrations and times. Bacterial inactivation (growth and cultivability) was investigated using colony counts and resazurin as metabolic indicators. Scanning electron microscopy (SEM) was performed.

RESULTS

The culture exposure to a high level of O3 inhibited the growth of all bacterial strains tested with a statistically significant reduction in colony count compared to the control group. The cell viability of S. aureus (MRSA) (99.6%) and P. aeruginosa (XDR) (29.2%) was reduced considerably, and SEM showed damage to bacteria after O3 treatment Conclusion: The impact of HAIs can be easily dampened by the widespread use of ozone in ICUs. This product usually degrades into molecular oxygen and has a low toxicity compared to other sanitization products. However, high doses of ozone were able to interfere with the growth of all strains studied, evidencing that ozone-based decontamination approaches may represent the future of hospital cleaning methods.

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.

Distinctive signatures of pathogenic and antibiotic resistant potentials in the hadal microbiome

BACKGROUND

Hadal zone of the deep-sea trenches accommodates microbial life under extreme energy limitations and environmental conditions, such as low temperature, high pressure, and low organic matter down to 11,000 m below sea level. However, microbial pathogenicity, resistance, and adaptation therein remain unknown. Here we used culture-independent metagenomic approaches to explore the virulence and antibiotic resistance in the hadal microbiota of the Mariana Trench.

RESULTS

The results indicate that the 10,898 m Challenger Deep bottom sediment harbored prosperous microbiota with contrasting signatures of virulence factors and antibiotic resistance, compared with the neighboring but shallower 6038 m steep wall site and the more nearshore 5856 m Pacific basin site. Virulence genes including several famous large translocating virulence genes (e.g., botulinum neurotoxins, tetanus neurotoxin, and Clostridium difficile toxins) were uniquely detected in the trench bottom. However, the shallower and more nearshore site sediment had a higher abundance and richer diversity of known antibiotic resistance genes (ARGs), especially for those clinically relevant ones (e.g., fosX, sul1, and TEM-family extended-spectrum beta-lactamases), revealing resistance selection under anthropogenic stresses. Further analysis of mobilome (i.e., the collection of mobile genetic elements, MGEs) suggests horizontal gene transfer mediated by phage and integrase as the major mechanism for the evolution of Mariana Trench sediment bacteria. Notably, contig-level co-occurring and taxonomic analysis shows emerging evidence for substantial co-selection of virulence genes and ARGs in taxonomically diverse bacteria in the hadal sediment, especially for the Challenger Deep bottom where mobilized ARGs and virulence genes are favorably enriched in largely unexplored bacteria.

CONCLUSIONS

This study reports the landscape of virulence factors, antibiotic resistome, and mobilome in the sediment and seawater microbiota residing hadal environment of the deepest ocean bottom on earth. Our work unravels the contrasting and unique features of virulence genes, ARGs, and MGEs in the Mariana Trench bottom, providing new insights into the eco-environmental and biological processes underlying microbial pathogenicity, resistance, and adaptative evolution in the hadal environment.

Ozonation of organic compounds in water and wastewater: A critical review

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, β-diketones) and antibiotic resistance genes.

Insights into capture-inactivation/oxidation of antibiotic resistance bacteria and cell-free antibiotic resistance genes from waters using flexibly-functionalized microbubbles

The spread of antibiotic resistance in the aquatic environment severely threatens the public health and ecological security. This study investigated simultaneously capturing and inactivating/oxidizing the antibiotic resistant bacteria (ARB) and cell-free antibiotic resistance genes (ARGs) in waters by flexibly-functionalized microbubbles. The microbubbles were obtained by surface-modifying the bubbles with coagulant (named as coagulative colloidal gas aphrons, CCGAs) and further encapsulating ozone in the gas core (named as coagulative colloidal ozone aphrons, CCOAs). CCGAs removed 92.4-97.5% of the sulfamethoxazole-resistant bacteria in the presence of dissolved organic matter (DOM), and the log reduction of cell-free ARGs (particularly, those encoded in plasmid) reached 1.86-3.30. The ozone release from CCOAs led to efficient in-situ oxidation: 91.2% of ARB were membrane-damaged and inactivated. In the municipal wastewater matrix, the removal of ARB increased whilst that of cell-free ARGs decreased by CCGAs with the DOM content increasing. The ozone encapsulation into CCGAs reinforced the bubble performance. The predominant capture mechanism should be electrostatic attraction between bubbles and ARB (or cell-free ARGs), and DOM enhanced the sweeping and bridging effect. The functionalized microbubble technology can be a promising and effective barrier for ARB and cell-free ARGs with shortened retention time, lessened chemical doses and simplified treatment unit.

Effect of ozonation-based disinfection methods on the removal of antibiotic resistant bacteria and resistance genes (ARB/ARGs) in water and wastewater treatment: a systematic review

Antibiotic resistance is considered a universal health threat of the 21st century which its distribution and even development are mainly mediated by water-based media. Disinfection processes with the conventional methods are still the most promising options to combat such crises in aqueous matrices especially wastewater. Knowing that the extent of effectiveness and quality of disinfection is of great importance, this paper aimed to systematically review and discuss ozonation (as one of the main disinfectants with large scale application) effect on removing antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from aqueous solutions, for which no study has been reported. For this, a comprehensive literature survey was performed within the international databases using appropriate keywords which yielded several studies involving different aspects and the effectiveness extent of ozonation on ARB & ARGs. The results showed that no definite conclusion could be drawn about the superiority of ozone alone or in a hybrid form. Mechanism of action was carefully evaluated and discussed although it is still poorly understood. Evaluation of the studies from denaturation and repairment perspectives showed that regrowth cannot be avoided after ozonation, especially for some ARB & ARGs variants. In addition, the comparison of the effectiveness on ARB & ARGs showed that ozonation is more effective for resistant bacteria than their respective genes. The degradation efficiency was found to be mainly influenced by operational parameters of CT (i.e. ozone dose & contact time), solids, alkalinity, pH, and type of pathogens and genes. Moreover, the correlation between ARB & ARGs removal and stressors (such as antibiotic residuals, heavy metals, aromatic matters, microcystins, opportunistic pathogens, etc.) has been reviewed to give the optimal references for further in-depth studies. The future perspectives have also been reported.

Inactivation of antibiotic resistant bacteria and their resistance genes in sewage by applying pulsed electric fields

We evaluated the suitability of pulsed electric field (PEF) technology as a new disinfection option in the sewage treatment plants (STPs) that can inactivate antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). It was shown that PEF applied disinfection could inactivate not only vancomycin-resistant enterococci (VRE), but also vanA resistance gene. Cultivable VRE could be effectively inactivated by PEF applied disinfection, and were reduced to below the detection limit (log reduction value of VRE > 5 log). Although the vanA also showed a reduction of more than 4 log, it remained in the order of 10⁵ copies/mL, suggesting that ARGs are more difficult to be inactivated than ARB in PEF applied disinfection. Among parameters in each applying condition verified in this study, the initial voltage was found to be the most important for inactivation of ARB and ARGs. Furthermore, frequency was a parameter that affects the increase or decrease of the duration time, and it was suggested that the treatment time could be shortened by increasing the frequency. Our results strongly suggested that PEF applied disinfection may be a new disinfection technology option for STPs that contributes to the control of ARB and ARGs contamination in the aquatic environments.

Toxicity impact of hydrogen peroxide on the fate of zebrafish and antibiotic resistant bacteria

Hydrogen peroxide (H₂O₂) is applied in various environments. It could be present at concentrations ranging from nanomolar to micromolar in a water system. It is produced through pollutants and natural activities. Since few studies have been conducted about the impact of naturally produced H₂O₂ on aquatic organisms, the objective of the present study was to monitor changes in responses of aquatic model organisms such as zebrafish and antibiotic-resistant bacteria to different exogenous H₂O₂ exposure. Increases in exposure concentration and time induced decreases in the perception of zebrafish larvae (up to 69%) and movement of adult zebrafish (average speed, average acceleration, movement distance, and activity time) compared to the control (non-exposed group). In addition, as a function of H₂O₂ exposure concentration (0-100,000 nM) and time, up to 20-fold increase (p = 5.00*10^-6) of lipid peroxidation compared to control was observed. For microorganisms, biofilm, an indirect indicator of resistance to external stressors, was increased up to 68% and gene transfer was increased (p = 2.00*10^-6) by more than 30% after H₂O₂ exposure. These results imply that naturally generated H₂O₂ could adversely affect aquatic environment organisms and public health. Thus, more careful attention is needed for H₂O₂ production in an aquatic system.

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

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

Detrimental Effect of Ozone on Pathogenic Bacteria

(1) Background: Disinfection of medical devices designed for clinical use associated or not with the growing area of tissue engineering is an urgent need. However, traditional disinfection methods are not always suitable for some biomaterials, especially those sensitive to chemical, thermal, or radiation. Therefore, the objective of this study was to evaluate the minimal concentration of ozone gas (O₃) necessary to control and kill a set of sensitive or multi-resistant Gram-positive and Gram-negative bacteria. The cell viability, membrane permeability, and the levels of reactive intracellular oxygen (ROS) species were also investigated; (2) Material and Methods: Four standard strains and a clinical MDR strain were exposed to low doses of ozone at different concentrations and times. Bacterial inactivation (cultivability, membrane damage) was investigated using colony counts, resazurin as a metabolic indicator, and propidium iodide (PI). A fluorescent probe (H₂DCFDA) was used for the ROS analyses; (3) Results: No reduction in the count colony was detected after O₃ exposure compared to the control group. However, the cell viability of E. coli (30%), P. aeruginosa (25%), and A. baumannii (15%) was reduced considerably. The bacterial membrane of all strains was not affected by O₃ but presented a significant increase of ROS in E. coli (90 ± 14%), P. aeruginosa (62.5 ± 19%), and A. baumanni (52.6 ± 5%); (4) Conclusion: Low doses of ozone were able to interfere in the cell viability of most strains studied, and although it does not cause damage to the bacterial membrane, increased levels of reactive ROS are responsible for causing a detrimental effect in the lipids, proteins, and DNA metabolism.

Reduction of antibiotic resistance determinants in urban wastewater by ozone: Emphasis on the impact of wastewater matrix towards the inactivation kinetics, toxicity and bacterial regrowth

This study investigated the impact of bench-scale ozonation on the inactivation of total cultivable and antibiotic-resistant bacteria (faecal coliforms, Escherichia coli, Pseudomonas aeruginosa, Enterococcus spp., and total heterotrophs), and the reduction of gene markers (16S rRNA and intl1) and antibiotic resistance genes (qacEΔ1, sul1, aadA1 and dfrA1) indigenously present in wastewater effluents treated by membrane bioreactor (MBR) or conventional activated sludge (CAS). The Chick-Watson model-predicted ozone exposure (CT) requirements, showed that higher CT values were needed for CAS- than MBR-treated effluents to achieve a 3-log reduction of each microbial group, i.e., ~30 and 10 gO₃ min gDOC^-1 respectively. Ozonation was efficient in inactivating the examined antibiotic-resistant bacteria, and no bacterial regrowth was observed after 72 h. The genes abundance decreased significantly by ozone, but an increase in their abundance was detected 72 h after storage of the treated samples. A very low removal of DOC was achieved and at the same time phyto- and eco-toxicity increased after the ozonation treatment in both wastewater matrices. The gene abundance, regrowth and toxicity results of this study may be of high environmental significance for comprehensive evaluation of ozone and may guide future studies in assessing these parameters for other oxidants/disinfectants.

Combat of antimicrobial resistance in municipal wastewater treatment plant effluent via solar advanced oxidation processes: Achievements and perspectives

This review aims to gather main achievements and limitations associated to the application of solar photocatalytic processes with regard to the removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from municipal wastewater treatment plant effluent (MWWTPE). Solar photocatalytic processes were chosen considering the context of developing tropical countries. Among these processes, solar photo-Fenton has been proved effective for the elimination of ARB from MWWTPE at neutral pH in bench and pilot scale and also under continuous flow. Yet, ARG removal varies as according to the gene. Irradiation intensity and matrix composition play a key role on treatment efficiency for this purpose. The use of sulfate radical in modified solar photo-Fenton is still incipient for ARB and ARG removal. Also, investigations related to ARB resistance profile and horizontal gene transfer rates after solar photo-Fenton treatment must be further analyzed. Regarding solar heterogeneous photocatalysis, TiO₂ and TiO₂-composites applied in suspension are the most commonly investigated for the removal of ARB and ARGs. Irradiation intensity, temperature and catalyst dosage affect treatment efficiency. However, most studies were performed in synthetic solutions using reduced sample volumes. Extended exposition times and addition of H₂O₂ to the system (solar/TiO₂/H₂O₂) are required to prevent bacteria regrowth and ensure ARG abatement. In addition, enhancement of TiO₂ with graphene or (semi)metals improved ARB elimination. Differences concerning irradiation intensity, matrix composition, catalyst dosage, and model ARB and ARGs used in studies analyzed in this review hinder the comparison of photocatalysts synthesized by various research groups. Finally, future research should aim at evaluating the efficiency of solar photocatalytic processes in real matrices originated from sewage treatment systems applied in developing countries; determining indicators of antimicrobial resistance in MWWTPE; and investigating ARB mutation rate as well as the removal of cell-free ARGs present in suspension in MWWTPE.

Degradation and deactivation of plasmid-encoded antibiotic resistance genes during exposure to ozone and chlorine

Degradation and deactivation kinetics of an antibiotic resistance gene (ARG) by ozone (O₃) and free available chlorine (FAC) were investigated in phosphate-buffered solutions at pH 7 for O₃ (in the presence of tert‑butanol), and pH 6.8 or 8.1 for FAC. We used a plasmid (pUC19)-encoded ampicillin resistance gene (amp^R) in both extracellular (e-) and intracellular (i-) forms. The second-order rate constant (k_O3) for degradation of 2686 base pair (bp) long e-pUC19 toward O₃, which was determined by quantitative polymerase chain reaction assay, was calculated to be ~2 × 10⁵ M^-1s^-1. The deactivation rate constants of e-pUC19 by O₃ measured with various recipient E. coli strains were within a factor of 2 compared with the degradation rate constant for e-pUC19. The degradation/deactivation kinetics of i-pUC19 were similar to those of e-pUC19, indicating only a minor influence of cellular components on O₃ reactivity toward i-pUC19. For FAC, the degradation and deactivation rates of e-pUC19 were decreased in the presence of tert‑butanol, implying involvement of direct FAC as well as some radical (e.g., ^•OH) reactions. The degradation rates of e-amp^R segments by direct FAC reaction could be explained by a previously-reported two-step sequential reaction model, in which the rate constants increased linearly with e-amp^R segment length. The deactivation rate constants of e-pUC19 during exposure to FAC were variable by a factor of up to 4.3 for the different recipient strains, revealing the role of DNA repair in the observed deactivation efficiencies. The degradation/deactivation of e-pUC19 were significantly faster at pH 6.8 than at pH 8.1 owing to pH-dependent FAC speciation variation, whereas i-pUC19 kinetics exhibited much smaller dependence on pH, demonstrating intracellular plasmid DNA reactions with FAC occurred at cytoplasmic pH (~7.5). Our results are useful for predicting and/or measuring the degradation/deactivation efficiency of plasmid-encoded ARGs by water treatment with ozonation and chlorination.

Monitoring antibiotic resistance genes in wastewater treatment: Current strategies and future challenges

Antimicrobial resistance (AMR) is a growing threat to human and animal health. Progress in molecular biology has revealed new and significant challenges for AMR mitigation given the immense diversity of antibiotic resistance genes (ARGs), the complexity of ARG transfer, and the broad range of omnipresent factors contributing to AMR. Municipal, hospital and abattoir wastewater are collected and treated in wastewater treatment plants (WWTPs), where the presence of diverse selection pressures together with a highly concentrated consortium of pathogenic/commensal microbes create favourable conditions for the transfer of ARGs and proliferation of antibiotic resistant bacteria (ARB). The rapid emergence of antibiotic resistant pathogens of clinical and veterinary significance over the past 80 years has re-defined the role of WWTPs as a focal point in the fight against AMR. By reviewing the occurrence of ARGs in wastewater and sludge and the current technologies used to quantify ARGs and identify ARB, this paper provides a research roadmap to address existing challenges in AMR control via wastewater treatment. Wastewater treatment is a double-edged sword that can act as either a pathway for AMR spread or as a barrier to reduce the environmental release of anthropogenic AMR. State of the art ARB identification technologies, such as metagenomic sequencing and fluorescence-activated cell sorting, have enriched ARG/ARB databases, unveiled keystone species in AMR networks, and improved the resolution of AMR dissemination models. Data and information provided in this review highlight significant knowledge gaps. These include inconsistencies in ARG reporting units, lack of ARG/ARB monitoring surrogates, lack of a standardised protocol for determining ARG removal via wastewater treatments, and the inability to support appropriate risk assessment. This is due to a lack of standard monitoring targets and agreed threshold values, and paucity of information on the ARG-pathogen host relationship and risk management. These research gaps need to be addressed and research findings need to be transformed into practical guidance for WWTP operators to enable effective progress towards mitigating the evolution and spread of AMR.

Degradation Kinetics of Antibiotic Resistance Gene mecA of Methicillin-Resistant Staphylococcus aureus (MRSA) during Water Disinfection with Chlorine, Ozone, and Ultraviolet Light

Degradation kinetics of antibiotic resistance genes (ARGs) by free available chlorine (FAC), ozone (O₃), and UV₂₅₄ light (UV) were investigated in phosphate buffered solutions at pH 7 using a chromosomal ARG (mecA) of methicillin-resistant Staphylococcus aureus (MRSA). For FAC, the degradation rates of extracellular mecA (extra-mecA) were accelerated with increasing FAC exposure, which could be explained by a two-step FAC reaction model. The degradation of extra-mecA by O₃ followed second-order reaction kinetics. The degradation of extra-mecA by UV exhibited tailing kinetics, which could be described by a newly proposed kinetic model considering cyclobutane pyrimidine dimer (CPD) formation, its photoreversal, and irreversible (6-4) photoproduct formation. Measured rate constants for extra-mecA increased linearly with amplicon length for FAC and O₃, or with number of intrastrand pyrimidine doublets for UV, which enabled prediction of degradation rate constants of extra-mecA amplicons based on sequence length and/or composition. In comparison to those of extra-mecA, the observed degradation rates of intracellular mecA (intra-mecA) were faster for FAC and O₃ at low oxidant exposures but significantly slower at high exposures for FAC and UV. Differences in observed extra- and intracellular kinetics could be due to decreased DNA recovery efficiency and/or the presence of MRSA aggregates protected from disinfectants.

Mechanism concerning the occurrence and removal of antibiotic resistance genes in composting product with ozone post-treatment

The soil application of composting product will probably cause the spread of antibiotic resistance genes (ARGs) to environment, thereby it is crucial to remove ARGs in composting product. Ozone was adopted for the first time as a post-treatment method to remove the ARGs in composting product in this study. Ozone treatment significantly removed the total ARGs and mobile genetic elements (MGEs) once ozonation process finished. After 10-day storage stage, although the amount of total intracellular ARGs and MGEs increased, the total extracellular ARGs and MGEs decreased in the ozone-treated compost product. Correlation analysis revealed that the reduction in intracellular 16S rRNA contributed to intracellular tetQ and tetW removal, while the variations of other ARGs after ozonation related to MGEs abundance. Network analysis suggested that the reduction of potential host bacteria, as well as the decline in NH₄⁺-N and TOC after the ozonation, contributed to the intracellular ARGs removal.

Treatment Processes for Microbial Resistance Mitigation: The Technological Contribution to Tackle the Problem of Antibiotic Resistance

Advances generated in medicine, science, and technology have contributed to a better quality of life in recent years; however, antimicrobial resistance has also benefited from these advances, creating various environmental and health problems. Several determinants may explain the problem of antimicrobial resistance, such as wastewater treatment plants that represent a powerful agent for the promotion of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG), and are an important factor in mitigating the problem. This article focuses on reviewing current technologies for ARB and ARG removal treatments, which include disinfection, constructed wetlands, advanced oxidation processes (AOP), anaerobic, aerobic, or combined treatments, and nanomaterial-based treatments. Some of these technologies are highly intensive, such as AOP; however, other technologies require long treatment times or high doses of oxidizing agents. From this review, it can be concluded that treatment technologies must be significantly enhanced before the environmental and heath problems associated with antimicrobial resistance can be effectively solved. In either case, it is necessary to achieve total removal of bacteria and genes to avoid the possibility of regrowth given by the favorable environmental conditions at treatment plant facilities.

A critical review on the occurrence of resistomes in the environment and their removal from wastewater using apposite treatment technologies: Limitations, successes and future improvement

Recent reports are pointing towards the potential increasing risks of resistomes in human host. With no permissible limit in sight, resistomes are continually multiplying at an alarming rate in the ecosystem, with a disturbing level in drinking water source. The morphology and chemical constituent of resistomes afford them to resist degradation, elude membrane and counter ionic charge, thereby, rendering both conventional and advanced water and wastewater treatment inefficient. Water and wastewater matrix may govern the propagation of individual resistomes sub-type, co-selection and specific interaction towards precise condition may have enhanced the current challenge. This review covers recent reports (2011-2019) on the occurrence of ARB/ARGs and ease of spread of resistance genes in the aquatic ecosystem. The contributions of water matrix to the spread and mitigation, treatment options, via bulk removal or capture, and intracellular and extracellular DNA lysis were discussed. A complete summary of recent occurrences of ARB/ARGs, fate after disinfection and optimum conditions of individual treatment technology or in tandem, including process limitations, with a brief assessment of removal or degradation mechanism were highlighted.

Acidic conditions enhance the removal of sulfonamide antibiotics and antibiotic resistance determinants in swine manure

Manure pH may vary depending on its inherent composition or additive contents. However, the effect of pH on the fate of antibiotics and antibiotic resistance determinants in manure remains unclear. This work demonstrated that pH adjustment promoted the removal of different sulfonamide antibiotics (SAs) within swine manure under incubation conditions, which increased from 26-60.8% to 75.0-86.0% by adjusting the initial pH from neutral (7.4) to acidic (5.4-4.8). Acidification was also demonstrated to inhibit the accumulation of antibiotic resistance genes in manure during incubation. Acidified manure contained both lower absolute and relative abundances of sul1 and sul2 than those at a neutral pH like 7.4. Further investigation indicated that acidification promoted the reduction of sul genes in manure by restricting sulfonamide-resistant bacteria (SRB) proliferation and inhibiting IntI1 accumulation. Furthermore, pH adjustment significantly influenced the composition of the manure bacterial community after incubation, which increased Firmicutes and decreased Proteobacteria. Close relationships were observed between pH-induced enrichment of the Firmicutes bacterial phylum, enhanced SAs degradation, and the fates of antibiotic resistance determinants. Overall, lowering the pH of manure promotes the degradation of SAs, decreases sul genes and SRB, and inhibits horizontal sul gene transfer, which could be a simple yet highly-effective manure management option to reduce antibiotic resistance.

Selective Adsorption and Photocatalytic Degradation of Extracellular Antibiotic Resistance Genes by Molecularly-Imprinted Graphitic Carbon Nitride

There is a growing need to mitigate the discharge of extracellular antibiotic resistance genes (ARGs) from municipal wastewater treatment systems. Here, molecularly-imprinted graphitic carbon nitride (MIP-C₃N₄) nanosheets were synthesized for selective photocatalytic degradation of a plasmid-encoded ARG (bla_NDM-1, coding for multidrug resistance New Delhi metallo-β-lactamase-1) in secondary effluent. Molecular imprinting with guanine enhanced ARG adsorption, which improved the utilization of photogenerated oxidizing species to degrade bla_NDM-1 rather than being scavenged by background nontarget constituents. Consequently, photocatalytic removal of bla_NDM-1 in secondary effluent with MIP-C₃N₄ (k = 0.111 ± 0.028 min^-1) was 37 times faster than with bare graphitic carbon nitride (k = 0.003 ± 0.001 min^-1) under UVA irradiation (365 nm, 3.64 × 10^-6 Einstein/L·s). MIP-C₃N₄ can efficiently catalyze the fragmentation of bla_NDM-1, which decreased the potential for ARG repair by transformed bacteria. Molecular imprinting also changed the primary degradation pathway; electron holes (h⁺) were the predominant oxidizing species responsible for bla_NDM-1 removal with MIP-C₃N₄ versus free radicals (i.e., ·OH and O₂^-) for coated but nonimprinted C₃N₄. Overall, MIP-C₃N₄ efficiently removed bla_NDM-1 from secondary effluent, demonstrating the potential for molecular imprinting to enhance the selectivity and efficacy of photocatalytic processes to mitigate dissemination of antibiotic resistance from sewage treatment systems.

Inactivation and change of tetracycline-resistant Escherichia coli in secondary effluent by visible light-driven photocatalytic process using Ag/AgBr/g-C3N4

Control of antibiotic-resistant bacteria (ARB) and their related genes in secondary effluents has become a serious issue because of increased awareness of their health risks. A considerable number of techniques have been developed in recent years, particularly in relation to advanced oxidation. However, limited information is known about cellular behavior and resistance characteristic change during photocatalytic treatment. In this study, the inactivation of tetracycline (TC)-resistant Escherichia coli (TC-E. coli), removal of TC-resistant genes (TC-RGs), and antibiotic susceptibility were evaluated by employing photocatalytic treatment using Ag/AgBr/g-C₃N₄ with visible light irradiation. The effects of light intensity, photocatalyst dosage, and reaction ambient temperature on photocatalysis were modelled and investigated. The rate of TC-E. coli removal was also optimized. Results demonstrated that the optimal conditions for TC-E. coli removal included light intensity of 96.0 mW/cm², photocatalyst dosage of 211.0 mg/L, and reaction ambient temperature of 23.7 °C. Under such conditions, the ARB removal rate was 6.1 log after 90 min and the related TC-RG removal rates were 49%, 86%, 69%, and 86% for tetA, tetM, tetQ, and intl1, respectively. The minimum inhibitory concentration test after photocatalysis shows that the antibiotic resistance of TC-E. coli was enhanced, which may be mainly due to the changes in the membrane potential and resulted in difficulty in destroying the bacteria through antibiotic contact. Hence, photocatalytic treatment could be an ideal method for ARB and antibiotic-resistant gene (ARG) control in wastewater, but the health risks of the remaining ARB and ARG should be investigated further.

Synergistic Effect of Permanganate and in Situ Synthesized Hydrated Manganese Oxide for Removing Antibiotic Resistance Genes from Wastewater Treatment Plant Effluent

An increasing amount of attention has been given to antimicrobial resistance in the environment because of its substantial threat to human health. The effluent from municipal wastewater treatment plants has been regarded as one of the important sources for the spread of antibiotic resistance genes (ARGs). However, conventional disinfection techniques fail to effectively remove ARGs from effluents. In this work, in situ synthesized hydrated manganese oxide (HMO) coupled with permanganate was applied for the first time in ARG removal from the effluent of wastewater treatment plants. The results show that five ARGs (sulI, sulII, tetQ, tetO, and tetW) as well as the intI1 and 16S rRNA genes had removal efficiencies of 2.46-4.23 logs, which were significantly higher than those obtained by using these reagents individually. This implied that there was a synergistic effect between permanganate and HMO toward the removal of ARGs. Moreover, the contributions of HMO coagulation and permanganate oxidation to ARG removal were semiquantitatively studied, which demonstrated that destruction of the microbial cells by oxidation and removal of the extracellular ARGs released by coagulation were the two main processes in this system. The results of this study provide an alternative method for ARG removal from the effluent of wastewater treatment plants with high efficiencies to control the spreading of ARGs.

Freshwater environments as reservoirs of antibiotic resistant bacteria and their role in the dissemination of antibiotic resistance genes

Freshwater environments are susceptible to possible contamination by residual antibiotics that are released through different sources, such as agricultural runoffs, sewage discharges and leaching from nearby farms. Freshwater environment can thus become reservoirs where an antibiotic impact microorganisms, and is an important public health concern. Degradation and dilution processes are fundamental for predicting the actual risk of antibiotic resistance dissemination from freshwater reservoirs. This study reviews major approaches for detecting and quantifying antibiotic resistance bacteria (ARBs) and genes (ARGs) in freshwater and their prevalence in these environments. Finally, the role of dilution, degradation, transmission and the persistence and fate of ARB/ARG in these environments are also reviewed. Culture-based single strain approaches and molecular techniques that include polymerase chain reaction (PCR), quantitative polymerase chain reaction (qPCR) and metagenomics are techniques for quantifying ARB and ARGs in freshwater environments. The level of ARBs is extremely high in most of the river systems (up to 98% of the total detected bacteria), followed by lakes (up to 77% of the total detected bacteria), compared to dam, pond, and spring (<1%). Of most concern is the occurrence of extended-spectrum β-lactamase producing Enterobacteriaceae, methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococcus (VRE), which cause highly epidemic infections. Dilution and natural degradation do not completely eradicate ARBs and ARGs in the freshwater environment. Even if the ARBs in freshwater are effectively inactivated by sunlight, their ARG-containing DNA can still be intact and capable of transferring resistance to non-resistant strains. Antibiotic resistance persists and is preserved in freshwater bodies polluted with high concentrations of antibiotics. Direct transmission of indigenous freshwater ARBs to humans as well as their transitory insertion in the microbiota can occur. These findings are disturbing especially for people that rely on freshwater resources for drinking, crop irrigation, and food in form of fish.

State of the art of tertiary treatment technologies for controlling antibiotic resistance in wastewater treatment plants

Antibiotic resistance genes (ARGs) have been considered as emerging contaminants of concern nowadays. There are no special technologies designed to directly remove ARGs in wastewater treatment plants (WWTPs). In order to reduce the risk of ARGs, it is vital to understand the efficiency of advanced treatment technologies in removing antibiotic resistance genes in WWTPs. This review highlights the application and efficiency of tertiary treatment technologies on the elimination of ARGs, s, based on an understanding of their occurrence and fate in WWTPs. These technologies include chemical-based processes such as chlorination, ozonation, ultraviolet, and advanced oxidation technology, as well as physical separation processes, biological processes such as constructed wetland and membrane bioreactor, and soil aquifer treatment. The merits, limitations and ameliorative measures of these processes are discussed, with the view to optimizing future treatment strategies and identifying new research directions.

Antibiotic microbial resistance (AMR) removal efficiencies by conventional and advanced wastewater treatment processes: A review

The World Health Organization (WHO) has identified the spread of antibiotic resistance as one of the major risks to global public health. An important transfer route into the aquatic environment is the urban water cycle. In this paper the occurrence and transport of antibiotic microbial resistance in the urban water cycle are critically reviewed. The presence of antibiotic resistance in low impacted surface water is being discussed to determine background antibiotic resistance levels, which might serve as a reference for treatment targets in the absence of health-based threshold levels. Different biological, physical and disinfection/oxidation processes employed in wastewater treatment and their efficacy regarding their removal of antibiotic resistant bacteria and antibiotic resistance geness (ARGs) were evaluated. A more efficient removal of antibiotic microbial resistance abundances from wastewater effluents can be achieved by advanced treatment processes, including membrane filtration, ozonation, UV-irradiation or chlorination, to levels typically observed in urban surface water or low impacted surface water.

Continuous ozonation of urban wastewater: Removal of antibiotics, antibiotic-resistant Escherichia coli and antibiotic resistance genes and phytotoxicity

This work evaluated the removal of a mixture of eight antibiotics (i.e. ampicillin (AMP), azithromycin (AZM), erythromycin (ERY), clarithromycin (CLA), ofloxacin (OFL), sulfamethoxazole (SMX), trimethoprim (TMP) and tetracycline (TC)) from urban wastewater, by ozonation operated in continuous mode at different hydraulic retention times (HRTs) (i.e. 10, 20, 40 and 60 min) and specific ozone doses (i.e. 0.125, 0.25, 0.50 and 0.75 gO₃ gDOC^{- 1}). As expected, the efficiency of ozonation was highly ozone dose- and contact time-dependent. The removal of the parent compounds of the selected antibiotics to levels below their detection limits was achieved with HRT of 40 min and specific ozone dose of 0.125 gO₃ gDOC^{- 1}. The effect of ozonation was also investigated at a microbiological and genomic level, by studying the efficiency of the process with respect to the inactivation of Escherichia coli and antibiotic-resistant E. coli, as well as to the reduction of the abundance of selected antibiotic resistance genes (ARGs). The inactivation of total cultivable E. coli was achieved under the experimental conditions of HRT 40 min and 0.25 gO₃ gDOC^-1, at which all antibiotic compounds were already degraded. The regrowth examinations revealed that higher ozone concentrations were required for the permanent inactivation of E. coli below the Limit of Quantification (<LOQ = 0.01 CFU mL^{- 1}). Also, the abundance of the examined ARGs (intl1, aadA1, dfrA1, qacEΔ1 and sul1) was found to decrease with increasing HRT and ozone dose. Despite the fact that the mildest operating parameters were able to eliminate the parent compounds of the tested antibiotics in wastewater effluents, it was clearly demonstrated in this study that higher ozone doses were required in order to confer permanent damage and/or death and prevent potential post-treatment re-growth of both total bacteria and ARB, and to reduce the abundance of ARGs below the LOQ. Interestingly, the mineralization of wastewater, in terms of Dissolved Organic Carbon (DOC) removal, was found to be significantly low even when the higher ozone doses were applied, leading to an increased phytotoxicity towards various plant species. The findings of this study clearly underline the importance of properly optimising the ozonation process (e.g. specific ozone dose and contact time) taking into consideration both the bacterial species and associated ARGs, as well as the wastewater physicochemical properties (e.g. DOC), in order to mitigate the spread of ARB&ARGs, as well as to reduce the potential phytotoxicity.

Occurrence and reduction of antibiotic resistance genes in conventional and advanced drinking water treatment processes

Antibiotic resistance is extensively detected in drinking water sources, threatening its safety and human health, which deserves further attention to the removal of antibiotic resistance genes (ARGs) in the drinking water system. In this study, the occurrence and reduction of integrase gene intI1 and forty-one ARG subtypes, which confers resistance to six antibiotic classes (β-lactam, aminoglycoside, macrolide, tetracycline, sulfonamide, and quinolone), were investigated in a drinking water treatment plant (DWTP). Seventeen ARG subtypes with absolute concentrations ranging from 1.4 × 10⁰ to 7.3 × 10⁵ and 3.9 × 10⁴ genes/mL (intI1) were detected in the raw water; and sul1 and sul2 were the two dominant ARG subtypes. Overall, the whole DWTPs achieved 0.03-2.4 log reduction of ARGs compared with those presented in raw water. The reduction efficiencies of sul1, strA, and intI1 were the highest (1.0-2.4 log) in both conventional and advanced processes. However, the levels of sul1, sul2, and ermC still remained high (1.3 × 10⁰-1.9 × 10⁴ genes/mL) in finished water. The treatment units, including pre-flocculation/sedimentation/sand filtration, and ozonation units, were beneficial for the reduction of ARGs, which was mostly ascribed to the decline in biomass and the strong oxidizing properties of ozone. However, the reduction effect was subsequently counteracted by the granular activated carbon and chlorination units. This study provides basic data for ARG pollution in the drinking water system, and suggests that ARGs persist in drinking water, even after conventional chlorination or advanced treatment processes, highlighting the need for new and efficient water purification technologies.

Applying UV absorbance and fluorescence indices to estimate inactivation of bacteria and formation of bromate during ozonation of water and wastewater effluent

Ozone is an effective oxidant and disinfectant commonly used for elimination of micropollutants and inactivation of resistant microbes. However, undesirable oxidation/disinfection byproducts such as bromate might form during ozonation. In this study, the UV absorbance and fluorescence indices were applied as surrogate indicators for predicting the inactivation of bacteria and formation of bromate during ozonation of water and wastewater effluents. The inactivation efficiencies of lab-cultured Escherichia coli (E. coli) and autochthonous bacteria were measured by plating (for E. coli only) and flow cytometry with fluorescence staining. During ozonation of E. coli spiked into wastewater effluents (∼10⁶ cell/mL), the priority of inactivation efficiency determined by different cell viability methods were in the order of CFU > membrane damage > DNA damage. Approximately, 99% membrane damage and/or 90% DNA damage are conservatively supposed as an indicator for sufficient bacterial inactivation as well as degradation of antibiotic resistance genes. The related required O₃ dosing thresholds for sufficient inactivation of E. coli and autochthonous bacteria refer to ∼0.6 O₃/DOC (g/g), ∼50% decrease of UVA254, ∼60% decrease of UVA280, or ∼80% decrease of humic-like fluorescence. Within the range of 10⁶-10⁸ cell/mL, the bacterial concentration did not have significant effects on the required thresholds of the specific O₃ doses or spectroscopic indicators required for bacterial inactivation. The addition of 50 mM tert-BuOH as ·OH scavenger increased the required specific ozone doses but decreased the losses of spectroscopic indicators necessary for sufficient bacterial inactivation, and also suggested that the membrane/DNA damages for bacterial inactivation were mainly attributed to the direct O₃ attacks. The bromate concentration was determined using ion chromatography with MS/MS detection. The results showed that when O₃ was dosed at the required thresholds for sufficient bacterial inactivation, bromate formation could usually be suppressed below 10 μg/L. The present work supports that it is possible to reach a balance between bacterial inactivation and bromate formation.

Reduction of Antibiotic Resistant Bacteria During Conventional and Advanced Wastewater Treatment, and the Disseminated Loads Released to the Environment

The occurrence of new chemical and microbiological contaminants in the aquatic environment has become an issue of increasing environmental concern. Thus, wastewater treatment plants (WWTPs) play an important part in the distribution of so-called new emerging pathogens and antibiotic resistances. Therefore, the daily loads released by the WWTP were calculated including a model system for the distribution of these loads within the receiving water body. UV-, as well as ozone-treatment in separate or in combination for wastewater treatment were under investigation aiming at the reduction of these loads. Here, the impact of these treatments on the DNA integrity via antibody staining and PCR efficiencies experiments were included. All three facultative pathogenic bacteria [enterococci (23S rRNA), Pseudomonas aeruginosa (ecfX), and Escherichia coli (yccT)] and seven clinically relevant antibiotic resistance genes (ARGs) (mecA (methicillin resistance gene), ctx-M32 (β- lactame resistance gene), ermB (erythromycine resistance gene), bla_TEM (β- lactame resistance gene), sul1 (sulfonamide resistance gene), vanA (vancomycin resistance gene), and intI1 (Integrase1 gene) associated with mobile genetic elements were detected in wastewaters. Different reduction efficiencies were analyzed during advanced wastewater treatments. ARGs were still found to be present in the effluents under the parameters of 1.0 g ozone per g dissolved organic carbon (DOC) and 400 J/m², like ctx-M32, ermB, bla_TEM, sul1, and intI1. Especially UV radiation induced thymidine dimerization which was analyzed via antibody mediated detection in the metagenome of the natural wastewater population. These specific DNA alterations were not observed during ozone treatment and combinations of UV/ozone treatment. The dimerization or potential other DNA alterations during UV treatment might be responsible for a decreased PCR efficiency of the 16S rRNA amplicons (176, 490, and 880 bp fragments) from natural metagenomes compared to the untreated sample. This impact on PCR efficiencies was also observed for the combination of ozone and UV treatment.

Multi-barrier approach for removing organic micropollutants using mobile water treatment systems

The diversity of organic micropollutants (OMPs) in aquatic environments has been increasing rapidly during the last decade. Therefore, it is important to monitor and attenuate emerging contaminants before they can negatively affect the aquatic environment. However, due to the diversity and complexity of OMPs, there are limitations to using a single method for treating a combination of these pollutants. To address this issue, a mobile water treatment system (MWTS) equipped with different treatment units was designed to remove OMPs under field conditions. The MWTS was configured with various modular units including coagulation, flocculation, dissolved air flotation, membrane filtration, ozone oxidation, granular activated carbon, and UV disinfection. Each treatment unit could be operated either individually or in different combinations to identify the optimal configuration of treatment units for the removal of OMPs. To investigate the effectiveness of the MWTS, twelve OMPs were selected and introduced simultaneously into the feed water samples collected from different rivers throughout Korea. The current study proved that the MTWS is an effective solution to treat OMPs and is a time saving treatment system. The combined effects of the different treatment units removed over 99% of the selected OMPs, regardless of their physicochemical properties. Moreover, since the system is mobile, on-site analyses can be conducted to identify the most effective treatment method and configuration for each OMP.

Behaviour of aqueous sulfamethizole solution and temperature effects in cold plasma oxidation treatment

The increase in volume and variety of pharmaceuticals found in natural water bodies has become an increasingly serious environmental problem. The implementation of cold plasma technology, specifically gas-phase pulsed corona discharge (PCD), for sulfamethizole abatement was studied in the present work. It was observed that sulfamethizole is easily oxidized by PCD. The flow rate and pH of the solution have no significant effect on the oxidation. Treatment at low pulse repetition frequency is preferable from the energy efficiency point of view but is more time-consuming. The maximum energy efficiency was around 120 g/kWh at half-life and around 50 g/kWh at the end of the treatment. Increasing the solution temperature from room temperature to 50 °C led to a significant reaction retardation of the process and decrease in energy efficiency. The pseudo-first order reaction rate constant (k₁) grows with increase in pulse repetition frequency and does not depend on pH. By contrast, decreasing frequency leads to a reduction of the second order reaction rate constant (k₂). At elevated temperature of 50 °C, the k₁, k₂ values decrease 2 and 2.9 times at 50 pps and 500 pps respectively. Lower temperature of 10 °C had no effect on oxidation efficiency compared with room temperature.

Industrial wastewater advanced treatment via catalytic ozonation with an Fe-based catalyst

An Fe-based catalyst was used as a heterogeneous catalyst for the ozonation of industrial wastewater, and key operational parameters (pH and catalyst dosage) were studied. The results indicated that the Fe-based catalyst significantly improved the mineralization of organic pollutants in wastewater. TOC (total organic carbon) removal was high, at 78.7%, with a catalyst concentration of 200 g/L, but only 31.6% with ozonation alone. The Fe-based catalyst significantly promoted ozone decomposition by 70% in aqueous solution. Hydroxyl radicals (·OH) were confirmed to be existed directly via EPR (electron paramagnetic resonance) experiments, and ·OH were verified to account for about 34.4% of TOC removal with NaHCO₃ as a radical scavenger. Through characterization by SEM-EDS (field emission scanning electron microscope with energy-dispersive spectrometer), XRD (X-ray powder diffraction) and XPS (X-ray photoelectron spectroscopy), it was deduced that FeOOH on the surface of the catalyst was the dominant contributor to the catalytic efficiency. The catalyst was certified as having good stability and excellent reusability based on 50 successive operations and could be used as a filler simultaneously. Thereby, it is a promising catalyst for practical industrial wastewater advanced treatment.

Toward a Comprehensive Strategy to Mitigate Dissemination of Environmental Sources of Antibiotic Resistance

Antibiotic resistance is a pervasive global health threat. To combat the spread of resistance, it is necessary to consider all possible sources and understand the pathways and mechanisms by which resistance disseminates. Best management practices are urgently needed to provide barriers to the spread of resistance and maximize the lifespan of antibiotics as a precious resource. Herein we advise upon the need for coordinated national and international strategies, highlighting three essential components: (1) Monitoring, (2) Risk Assessment, and (3) Mitigation of antibiotic resistance. Central to all three components is What exactly to monitor, assess, and mitigate? We address this question within an environmental framework, drawing from fundamental microbial ecological processes driving the spread of resistance.

Inactivation efficiency of plasmid-encoded antibiotic resistance genes during water treatment with chlorine, UV, and UV/H2O2

This study assessed the inactivation efficiency of plasmid-encoded antibiotic resistance genes (ARGs) both in extracellular form (e-ARG) and present within Escherichia coli (intracellular form, i-ARG) during water treatment with chlorine, UV (254 nm), and UV/H₂O₂. A quantitative real-time PCR (qPCR) method was used to quantify the ARG damage to amp^R (850 bp) and kan^R (806 bp) amplicons, both of which are located in the pUC4K plasmid. The plate count and flow cytometry methods were also used to determine the bacterial inactivation parameters, such as culturability and membrane damage, respectively. In the first part of the study, the kinetics of E. coli inactivation and ARG damage were determined in phosphate buffered solutions. The ARG damage occurred much more slowly than E. coli inactivation in all cases. To achieve 4-log reduction of ARG concentration at pH 7, the required chlorine exposure and UV fluence were 33-72 (mg × min)/L for chlorine and 50-130 mJ/cm² for UV and UV/H₂O₂. After increasing pH from 7 to 8, the rates of ARG damage decreased for chlorine, while they did not vary for UV and UV/H₂O₂. The i-ARGs mostly showed lower rates of damage compared to the e-ARGs due to the protective roles of cellular components against oxidants and UV. The contribution of OH radicals to i-ARG damage was negligible in UV/H₂O₂ due to significant OH radical scavenging by cellular components. In all cases, the ARG damage rates were similar for amp^R versus kan^R, except for the chlorination of e-ARGs, in which the damage to amp^R occurred faster than that to kan^R. Chlorine and UV dose-dependent ARG inactivation levels determined in a wastewater effluent matrix could be reasonably explained by the kinetic data obtained from the phosphate buffered solutions and the expected oxidant (chlorine and OH radicals) demands by water matrix components. These results can be useful in optimizing chlorine and UV-based disinfection systems to achieve ARG inactivation.

Distribution of antibiotic resistance in the effluents of ten municipal wastewater treatment plants in China and the effect of treatment processes

Municipal wastewater treatment plant (WWTP) effluents represent an important contamination source of antibiotic resistance, threatening the ecological safety of receiving environments. In this study, the release of antibiotic resistance to sulfonamides and tetracyclines in the effluents of ten WWTPs in China was investigated. Results indicate that the concentrations of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) ranged from 1.1 × 10¹ to 8.9 × 10³ CFU mL^-1 and 3.6 × 10¹ (tetW) to 5.4 × 10⁶ (tetX) copies mL^-1, respectively. There were insignificant correlations of the concentrations of ARB and ARGs with those of corresponding antibiotics. Strong correlations were observed between the total concentrations of tetracycline resistance genes and sulfonamide resistance genes, and both of which were significantly correlated with intI1 concentrations. Statistical analysis of the effluent ARG concentrations in different WWTPs revealed an important role of disinfection in eliminating antibiotic resistance. The release rates of ARB and ARGs through the effluents of ten WWTPs ranged from 5.9 × 10¹² to 4.8 × 10¹⁵ CFU d^-1 and 6.4 × 10¹² (tetW) to 1.7 × 10¹⁸ (sul1) copies d^-1, respectively. This study helps the effective assessment and scientific management of ecological risks induced by antibiotic resistance discharged from WWTPs.