Water Disinfection Byproducts Induce Antibiotic Resistance-Role of Environmental Pollutants in Resistance Phenomena

Effects of emerging pollutants on the occurrence and transfer of antibiotic resistance genes: A review

The emergence and spread of antibiotic resistance genes (ARGs) have become major concerns for both public health and environmental ecosystems. Emerging pollutants (EPs) that accumulate in environmental compartments also pose a potential risk for the enrichment of ARGs in indigenous microorganisms. This paper presents a comprehensive review of the effects and intrinsic mechanisms of EPs, including microplastics, engineered nanomaterials, disinfection byproducts, pharmaceuticals, and personal care products, on the occurrence and dissemination of ARGs. State-of-the-art methods for identifying culture-independent ARG-host interactions and monitoring horizontal gene transfer (HGT) processes in real-time are first reviewed. The contributions of EPs to the abundance and diversity of ARGs are then summarized. Finally, we discussed the underlying mechanisms related to the regulation of HGT, increased mutagenesis, and the evolution of microbial communities. Further details of three HGT (i.e., conjugation, transformation, and transduction) frequency patterns in response to various EPs are also examined. This review contemplates and reassesses the risks of ARG evolution posed by the manufacture and application of EPs.

Plasma induced efficient removal of antibiotic-resistant Escherichia coli and antibiotic resistance genes, and inhibition of gene transfer by conjugation

Antibiotic-resistant bacteria (ARB) and their resistance genes (ARGs) are emerging environmental pollutants that pose great threats to human health. In this study, a novel strategy using plasma was developed to simultaneously remove antibiotic-resistant Escherichia coli (AR bio-56954 E. coli) and its ARGs, aiming to inhibit gene transfer by conjugation. Approximately 6.6 log AR bio-56954 E. coli was inactivated within 10 min plasma treatment, and the antibiotic resistance to tested antibiotics (tetracycline, gentamicin, and amoxicillin) significantly decreased. Reactive oxygen and nitrogen species (RONS) including •OH, ¹O₂, O₂•^-, NO₂^-, and NO₃^- contributed to ARB and ARGs elimination; their attacks led to destruction of cell membrane, accumulation of excessive intracellular reactive oxygen substances, deterioration of conformational structures of proteins, and destroy of nucleotide bases of DNA. As a result, the ARGs (tet(C), tet(W), blaTEM-1, aac(3)-II), and integron gene intI1), and conjugative transfer frequency of ARGs significantly decreased after plasma treatment. The results demonstrated that plasma has great prospective application in removing ARB and ARGs in water, inhibiting gene transfer by conjugation.

Ecotoxicological effects, environmental fate and risks of pharmaceutical and personal care products in the water environment: A review

Due to the extensive use and incomplete removal, pharmaceutical and personal care products (PPCPs) are introduced into the water continuously. It has been proved that the unique properties of PPCPs are influential to organisms and the environment, and gradually affect human health. In this paper, the toxicological effects of typical PPCPs, and the environmental behavior of PPCPs in aquatic are reviewed. The risk assessments of PPCPs in the water are summarized. The research directions of environmental toxicology research of PPCPs in the future are proposed. Many PPCPs were found to be toxic or even highly toxic toward aquatic organisms, and have the potential for bioaccumulation. It is essential to study the acute and long-term toxicity of PPCPs and their metabolites, evaluate the environmental behaviors and make a reasonable assessment of ecotoxicology and human health risks of PPCPs.

Biocide-tolerance and antibiotic-resistance in community environments and risk of direct transfers to humans: Unintended consequences of community-wide surface disinfecting during COVID-19?

During the current pandemic, chemical disinfectants are ubiquitously and routinely used in community environments, especially on common touch surfaces in public settings, as a means of controlling the virus spread. An underappreciated risk in current regulatory guidelines and scholarly discussions, however, is that the persisting input of chemical disinfectants can exacerbate the growth of biocide-tolerant and antibiotic-resistant bacteria on those surfaces and allow their direct transfers to humans. For COVID-19, the most commonly used disinfecting agents are quaternary ammonium compounds, hydrogen peroxide, sodium hypochlorite, and ethanol, which account for two-thirds of the active ingredients in current EPA-approved disinfectant products for the novel coronavirus. Tolerance to each of these compounds, which can be either intrinsic or acquired, has been observed on various bacterial pathogens. Of those, mutations and horizontal gene transfer, upregulation of efflux pumps, membrane alteration, and biofilm formation are the common mechanisms conferring biocide tolerance in bacteria. Further, the linkage between disinfectant use and antibiotic resistance was suggested in laboratory and real-life settings. Evidence showed that substantial bacterial transfers to hands could effectuate from short contacts with surrounding surfaces and further from fingers to lips. While current literature on disinfectant-induced antimicrobial resistance predominantly focuses on municipal wastes and the natural environments, in reality the community and public settings are most severely impacted by intensive and regular chemical disinfecting during COVID-19 and, due to their proximity to humans, biocide-tolerant and antibiotic-resistant bacteria emerged in these environments may pose risks of direct transfers to humans, particularly in densely populated urban communities. Here we highlight these risk factors by reviewing the most pertinent and up-to-date evidence, and provide several feasible strategies to mitigate these risks in the scenario of a prolonging pandemic.

Chlorine disinfectants promote microbial resistance in Pseudomonas sp

The substantial use of disinfectants has increased antibiotic resistance, thereby mediating serious ecological safety issues worldwide. Accumulating studies have reported the role of chlorine disinfectants in promoting disinfectant resistance. The present study sought to investigate the role of chlorine disinfectants in developing multiple resistance in Pseudomonas sp. isolated from the river through antioxidant enzyme measurement, global transcriptional analyses, Gene Ontology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The results demonstrated that 100 mg/L sodium hypochlorite could increase disinfectant resistance and antibiotic resistance. The SOS response (a conserved response to DNA damage) triggered by oxidative stress makes bacteria resistant to chlorine. An increase in antibiotic resistance could be attributed to a decreased membrane permeability, increased expression of MuxABC-OpmB efflux pump, beta-lactamase, and antioxidant enzymes. Additionally, KEGG enrichment analysis suggested that the differentially expressed genes were highly enriched in the metabolic pathways. In summary, the study results revealed the impact of chlorine disinfectants in promoting microbial disinfectant resistance and antibiotic resistance. This study will provide insight into disinfectant resistance mechanisms.

Synergistic effect of sulfidated nano zerovalent iron and persulfate on inactivating antibiotic resistant bacteria and antibiotic resistance genes

Antimicrobial resistance continues to be a rising global threat to public health. It is well recognized that wastewater treatment plants are reservoirs of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). However, traditional disinfection techniques are not effective to simultaneously remove ARB and ARGs, and the dynamic analysis of ARB inactivation have also been deficient. In this study, sulfidated nano zerovalent iron (S-nZVI) coupled with persulfate (PS) was applied to simultaneously remove both ARB (E. coli K-12 with RP4 plasmid) and ARGs (extra- and intracellular ARGs). S-nZVI/PS completely inactivated ARB (~7.8-log reduction) within 10 min and degraded all extracellular ARGs (~8.0-log reduction) within 5 min. These efficiencies were significantly higher (decay rate constant, k = 0.138 min^-1) than those achieved individually (S-nZVI: k = 0.076 min^-1; PS: k = 0.008 min^-1), implying a synergistic effect between S-nZVI and PS against ARB and ARGs. The efficient removal rate of ARB was also supported by confocal microscopy and microfluidics at a single-cell level. The complete inactivation of ARB by S-nZVI/PS was also demonstrated in real drinking water and real wastewater effluent that contained natural organic matter and suspended solids. Regrowth assays showed that the treated ARB was not observed after 72 h or longer incubation, suggesting that ARB was permanently inactivated by radicals such as SO₄^•- and •OH. The destruction of bacterial cells compromised the removal efficiency of the intracellular ARGs, with only ~4.0-log reduction after 60 min treatment by S-nZVI/PS. Collectively, our results suggest the feasibility of S-nZVI coupled with PS for simultaneous ARB and ARGs removal in real water matrices.

Molecular detection of virulence markers to identify diarrhoeagenic Escherichia coli isolated from Mula-Mutha river, Pune District, India

In this study presence of virulence genes in multidrug resistant Escherichia coli isolated from Mula-Mutha river, Pune, India was undertaken. The objective was to understand whether the isolates were of diarrhoeagenic or of environmental origin. This was essential since the river flows through urban and rural parts of Pune and its water is used not only for industrial and agricultural purposes but also for domestic usage. One hundred and two multidrug E. coli isolates were selected from our previous study which detected genes coding for antibiotic resistance as well as identified integrons associated with multidrug resistance. Isolates were subjected to multiplex PCR to detect presence of virulence genes, set1A, set1B, sen astA, aggA, aafA, pet, stx1 and stx. Sequencing was performed to confirm the amplified PCR product. Seven of the 102 E. coli isolates showed gene set1A alone identifying them as Enteroaggregative E. coli. Thus, the findings revealed that majority of drug resistant E. coli were environmental in origin. The presence of antibiotic resistant genes, integrons in the environment as well as diarrhoeagenic E. coli isolates is a warning and calls for efficient public health measures to ensure that untreated sewage and industrial waste does not enter the Mula-Mutha river.

Removal of antibiotic-resistant genes during drinking water treatment: A review

Once contaminate the drinking water source, antibiotic resistance genes (ARGs) will propagate in drinking water systems and pose a serious risk to human health. Therefore, the drinking water treatment processes (DWTPs) are critical to manage the risks posed by ARGs. This study summarizes the prevalence of ARGs in raw water sources and treated drinking water worldwide. In addition, the removal efficiency of ARGs and related mechanisms by different DWTPs are reviewed. Abiotic and biotic factors that affect ARGs elimination are also discussed. The data on presence of ARGs in drinking water help come to the conclusion that ARGs pollution is prevalent and deserves a high priority. Generally, DWTPs indeed achieve ARGs removal, but some biological treatment processes such as biological activated carbon filtration may promote antibiotic resistance due to the enrichment of ARGs in the biofilm. The finding that disinfection and membrane filtration are superior to other DWTPs adds weight to the advice that DWTPs should adopt multiple disinfection barriers, as well as keep sufficient chlorine residuals to inhibit re-growth of ARGs during subsequent distribution. Mechanistically, DWTPs obtain direct and inderect ARGs reduction through DNA damage and interception of host bacterias of ARGs. Thus, escaping of intracellular ARGs to extracellular environment, induced by DWTPs, should be advoided. This review provides the theoretical support for developping efficient reduction technologies of ARGs. Future study should focus on ARGs controlling in terms of transmissibility or persistence through DWTPs due to their biological related nature and ubiquitous presence of biofilm in the treatment unit.

Metagenomic insights into dissemination of antibiotic resistance across bacterial genera in wastewater treatment

The aim of this study was to evaluate the impacts of conventional wastewater treatment processes including secondary treatment and chlorination on the removal of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB), and to assess the association of ARGs with their potential hosts in each treatment process. The results showed chlorination with subinhibitory concentration (<8 mg/L) resulted in an increased ARB number in the disinfection effluent. qPCR analysis indicated secondary treatment increased relative abundance of ARGs in remaining bacteria whereas disinfection reduced the relative abundance of those genes effectively. Metagenomic analysis revealed a significant shift of dominating bacterial genera harboring ARGs. Along the treatment train, 48, 95 and 80 genera were identified to be the ARG carriers in primary effluent, secondary effluent, and disinfection effluent, respectively. It was also found that secondary treatment increased the diversity of potential ARG hosts while both secondary treatment and chlorination broadened the host range of some ARGs at the genus level, which may be attributed to the spread of antibiotic resistance across bacterial genera through horizontal transfer. This study highlights the growing concerns that wastewater treatment plants (WWTPs) may disseminate ARGs by associating this effect to specific treatment stages and by correlating ARGs with their bacterial hosts.

Stable dechlorination of Trichloroacetic Acid (TCAA) to acetic acid catalyzed by palladium nanoparticles deposited on H2-transfer membranes

Trichloroacetic acid (TCAA) is a common disinfection byproduct (DBP) produced during chlorine disinfection. With the outbreak of the Coronavirus Disease 2019 (COVID-19) pandemic, the use of chlorine disinfection has increased, raising the already substantial risks of DBP exposure. While a number of methods are able to remove TCAA, their application for continuous treatment is limited due to their complexity and expensive or hazardous inputs. We investigated a novel system that employs palladium (Pd⁰) nanoparticles (PdNPs) for catalytic reductive dechlorination of TCAA. H₂ was delivered directly to PdNPs in situ coated on the surface of bubble-free hollow-fiber gas-transfer membranes. The H₂-based membrane Pd film reactor (H₂-MPfR) achieved a high catalyst-specific TCAA reduction rate, 32 L/g-Pd/min, a value similar to the rate of using homogeneously suspended PdNP, but orders of magnitude higher than with other immobilized PdNP systems. In batch tests, over 99% removal of 1 mM TCAA was achieved in 180 min with strong product selectivity (≥ 93%) to acetic acid. During 50 days of continuous operation, over 99% of 1 mg/L influent TCAA was removed, again with acetic acid as the major product (≥ 94%). We identified the reaction pathways and their kinetics for TCAA reductive dechlorination with PdNPs using direct delivery of H₂. Sustained continuous TCAA removal, high selectivity to acetic acid, and minimal loss of PdNPs support that the H₂-MPfR is a promising catalytic reactor to remove chlorinated DBPs in practice.

Prevalence of antibiotic resistance genes in wastewater collected from ornamental fish market in northern China

Large amounts of antibiotics/disinfectants are used in the farming of ornamental fish so as to prevent and treat bacterial infection. This may exert considerable selection pressures on the prevalence and propagation of antibiotic resistance genes (ARGs). However, the levels of ARGs and their potential prevalence mechanism in the wastewater of the ornamental fish industry remains unclear. In this work, wastewater is collected from a representative ornamental fish market (OFM) that is located at the northern China to study the occurrence and abundance of 21 ARGs and 2 integrase genes. Results indicated that 15 different ARGs and 2 integrase genes are existent and prevalent in the wastewater of OFM, whereby concentrations range from 2.01 to 10.34 copies/L. Proteobacteria, Bacteroidetes, Verrucomicrobia, and Firmicutes are the predominant phyla in the wastewater samples. 17 species of human opportunistic pathogens are present with relative abundance of up to 0.01%, which suggests a considerable risk of pathogens acquiring and disseminating ARGs. Moreover, oxytetracycline, ciprofloxacin, norfloxacin, sulfadiazine, and chloramphenicol are most frequently detected in wastewater, with concentrations of up to 1150, 877, 514, 1970, and 1700 ng/L, respectively. Notably, good correlations have been determined among ARGs and antibiotics, non-antibiotic environmental factors in wastewater of OFM. This current study reveals, for the first time, that OFM is a previously unperceived reservoir for ARG prevalence in aquatic environment and water environmental factors (particularly antibiotics), and their induced shifts in the microbial communities are the key factors for distribution of ARGs in OFM.

Novel class 1 integron harboring antibiotic resistance genes in wastewater-derived bacteria as revealed by functional metagenomics

Combatting antibiotic resistance is critical to our ability to treat infectious diseases. Here, we identified and characterized diverse antimicrobial resistance genes, including potentially mobile elements, from synthetic wastewater treatment microcosms exposed to the antibacterial agent triclosan. After seven weeks of exposure, the microcosms were subjected to functional metagenomic selection across 13 antimicrobials. This was achieved by cloning the combined genetic material from the microcosms, introducing this genetic library into E. coli, and selecting for clones that grew on media supplemented with one of the 13 antimicrobials. We recovered resistant clones capable of growth on media supplemented with a single antimicrobial, yielding 13 clones conferring resistance to at least one antimicrobial agent. Antibiotic susceptibility analysis revealed resistance ranging from 4 to >50 fold more resistant, while one clone showed resistance to multiple antibiotics. Using both Sanger and SMRT sequencing, we identified the predicted active gene(s) on each clone. One clone that conferred resistance to tetracycline contained a gene encoding a novel tetA-type efflux pump that was named TetA(62). Three clones contained predicted active genes on class 1 integrons. One integron had a previously unreported genetic arrangement and was named In1875. This study demonstrated the diversity and potential for spread of resistance genes present in human-impacted environments.

Acceleration of emergence of E. coli antibiotic resistance in a simulated sublethal concentration of copper and tetracycline co-contaminated environment

An environment co-contaminated with metals and antibiotics ultimately exposes bacteria to these metals and antibiotics simultaneously. This study aims to explore the efficacy of sublethal concentrations of copper ions contaminated with tetracycline regarding antibiotic resistance in a sensitive strain of E. coli K12. The study proved that a copper ions and tetracycline co-contaminated environment could considerably enhance the mutation frequencies of chloramphenicol and polymyxin B resistance in antibiotic susceptible E. coli; however, the equivalent copper ions and tetracycline alone showed weaker effects. Results also demonstrated that an environment co-contaminated with relatively high sublethal concentrations of copper ion and tetracycline co-contaminated environment could induce much higher antibiotic resistance than the low sublethal and control groups. Whole-genome characterization results indicated that variability existed within the genotype and phenotype involved in antibiotic resistance. Additionally, the evolved resistant strains displayed hereditary resistance after 5 round culture cycles in LB broth over 5 days. Results implied that co-contamination with metals and antibiotics environment could strengthen resistance and contribute to the induction and dissemination of antibiotic resistance in metal and antibiotic co-contaminated environment.

Virus removal by membrane bioreactors: A review of mechanism investigation and modeling efforts

The increasing pressure on the global water supply calls for more advanced solutions with higher efficiency and better sustainability, leading to the promptly developing water reclamation and reuse schemes including treatment technologies and risk management strategies where microbial safety is becoming a crucial aspect in the interest of public health. Backed up by the development of membrane technology, membrane bioreactors (MBR) have received substantial attention for their superiority over conventional treatment methods in many ways and are considered promising in the water reclamation realm. This review paper provides an overview of the efforts made to manage and control the potential waterborne viral disease risks raised by the use of effluent from MBR treatment processes, including the mechanisms involved in the virus removal process and the attempts to model the dynamics of the removal process. In principle, generalized and integrated virus removal models that provide insight into real-time monitoring are urgently needed for advanced real-time control purpose. Future studies of approaches that can well handle the inherent uncertainty and nonlinearity of the complex removal process are crucial to the development and promotion of related technologies.

Hierarchical Bi2O2CO3 wrapped with modified graphene oxide for adsorption-enhanced photocatalytic inactivation of antibiotic resistant bacteria and resistance genes

There is growing pressure for wastewater treatment plants to mitigate the discharge of antibiotic resistant bacteria (ARB) and extracellular resistance genes (eARGs), which requires technological innovation. Here, hierarchical Bi₂O₂CO₃ microspheres were wrapped with nitrogen-doped, reduced graphene oxide (NRGO) for enhanced inactivation of multidrug-resistant E. coli NDM-1 and degradation of the plasmid-encoded ARG (bla_NDM-1) in secondary effluent. The NRGO shell enhanced reactive oxygen species (ROS) generation (•OH and H₂O₂) by about three-fold, which was ascribed to broadened light absorption region (red-shifted up to 459 nm) and decreased electron-transfer time (from 55.3 to 19.8 ns). Wrapping enhanced E. coli adsorption near photocatalytic sites to minimize ROS scavenging by background constituents, which contributed to the NRGO-wrapped microspheres significantly outperforming commercial TiO₂ photocatalyst. ROS scavenger tests indicated that wrapping also changed the primary inactivation pathway, with photogenerated electron holes and surface-attached hydroxyl radicals becoming the predominant oxidizing species with wrapped microspheres, versus free ROS (e.g., •OH, H₂O₂ and •O₂^-) for bare microspheres. Formation of resistance plasmid-composited microsphere complexes, primary due to the π-π stacking and hydrogen bonding between the shell and nucleotides, also minimized ROS scavenging and kept free plasmid concentrations below 10² copies/mL. As proof-of-concept, this work offers promising insight into the utilization of NRGO-wrapped microspheres for mitigating antibiotic resistance propagation in the environment.

Effective blockage of chloride ion quenching and chlorinated by-product generation in photocatalytic wastewater treatment

Photocatalytic degradation of pollutants in high salinity wastewater usually shows extremely low activities and produces highly toxic by-products, often related to the presence of excess chloride ion (Cl^-). Herein, we report for the first time that involvement of Cl^- (quenching active species and generating chlorinated by-products) could be effectively blocked during photocatalytic processes. Based on a comprehensive investigation of its mechanism, we found that Cl^- could quench superoxide radicals (O₂^-) through a cyclic indirect quenching model with holes (h⁺) and hydroxyl radicals (OH) quenching as "initiators". Thus, scavenging h⁺ and OH could successfully block the chain reactions between Cl^- and O₂^-, and photocatalytic degradation of methyl orange (a refractory dye, with O₂^- as dominant attacking species) could be enhanced by nearly 50 times, even when Cl^- content was up to 10 wt%. More importantly, both HPLC-MS analyses and DFT calculation validated that, by blocking its quenching effect, Cl^- could be successfully excluded from the pollutant degradation processes, thus preventing the generation of toxic chlorinated by-products. This work provides new insights into control of chlorinated by-products and proposes feasible strategies to extend photocatalytic technology in high salinity wastewater.

Drinking water biofiltration: Behaviour of antibiotic resistance genes and the association with bacterial community

Antibiotic resistance genes (ARGs) are being detected in drinking water frequently, constituting a major public health issue. As a typical drinking water treatment process, the biofilter may harbour various ARGs due to the filter biofilms established during the filtration process. The objective of this study was to investigate the behaviour of ARGs (bla_CTX-M, bla_OXA-1, bla_TEM, ermB, tetA, tetG, tetQ, tetW, tetX, sul 1, sul 2, dfrA1 and dfrA12) and their possible association with bacteria in a bench-scale biofiltration system. The impact of filter media on horizontal gene transfer (HGT) was also explored using a model conjugative plasmid, RP1. The biofiltration system comprised four types of biofilters, including sand, granular activated carbon (GAC), GAC sandwich, and anthracite-sand biofilters. Results showed that although the absolute abundance of ARGs decreased (0.97-log reduction on average), the ARGs' abundance normalised to bacterial numbers showed an increasing trend in the filtered water. Biofilms collected from the surface layer revealed the lowest relative abundance of ARGs (p < 0.01) compared to the deeper layer biofilms, indicating that the proportion of ARG-carrying bacteria was greater in the lower position. Most chosen ARG numbers correlated to Proteobacteria, Acidobacteria and Nitrospirae phyla, which accounted for 51.9%, 5.2% and 2.0% of the biofilm communities, respectively. GAC media revealed the highest transfer frequency (2.60 × 10^-5), followed by anthracite (5.31 × 10^-6) and sand (2.47 × 10^-6). Backwashing can reduce the transferability of RP1 plasmid significantly in biofilms but introduces more transconjugants into the planktonic phase. Overall, the results of this study could enhance our understanding of the prevalence of ARGs in drinking water biofiltration treatment.

Exposure to Environmental Levels of Pesticides Stimulates and Diversifies Evolution in Escherichia coli toward Higher Antibiotic Resistance

Antibiotic resistance is one of the most challenging issues in public health. Antibiotics have been increasingly used not only for humans and animals but also for crop protection as pesticides. Thus, antibiotics often coexist with pesticides in some environments. To investigate the effects of the co-occurring, nonantibiotic pesticides on the development of antibiotic resistance, we conducted long-term exposure experiments using an Escherichia coli K-12 model strain. The results reveal that (1) the exposure to pesticides (in mg/L) alone led to the emergence of mutants with significantly higher resistance to streptomycin; (2) the exposure to pesticides (in μg/L) together with a subinhibitory level (in high μg/L) of ampicillin synergistically stimulated the selection of ampicillin resistance and the cross-resistance to other antibiotics (i.e., ciprofloxacin, chloramphenicol, and tetracycline). Distinct and diversified genetic mutations emerged in the resistant mutants selected from the coexposure to both pesticides and ampicillin. The genetic mutations likely caused a holistic transcriptional regulation (e.g., biofilm formation, oxidative stress defense) when grown under antibiotic stress and led to increased antibiotic resistance. Together, these findings provide important fundamental insights into the development of antibiotic resistance and the resistance mechanisms under environmentally relevant conditions where antibiotics and nonantibiotic micropollutants coexist.

Resistance of anammox granular sludge to copper nanoparticles and oxytetracycline and restoration of performance

Nanoparticles and antibiotics, the two most frequently detected emerging pollutants from different wastewater sources, are eventually discharged into wastewater treatment plants. In this study, the widely used materials CuNPs and oxytetracycline (OTC) were selected as target pollutants to investigate their joint effects on anaerobic ammonium oxidation (anammox). The results indicated that the environmental concentration slightly inhibited the performance of the reactors, while the performance rapidly deteriorated within a week under high-level combined shocks (5.0 mg L^-1 CuNPs and 2.0 mg L^-1 OTC). After the second shock (2.5 mg L^-1 CuNPs and 2.0 mg L^-1 OTC), the resistance of anammox bacteria was enhanced, with an elevated relative abundance of Candidatus Kuenenia and absolute abundance of hzsA, nirS, and hdh. Moreover, the extracellular polymeric substance (EPS) content and specific anammox activity (SAA) showed corresponding changes. Improved sludge resistance was observed with increasing CuNP and OTC doses, which accelerated the recovery of performance.

Occurrence of antibiotics and risk of antibiotic resistance evolution in selected Kenyan wastewaters, surface waters and sediments

Active pharmaceutical ingredients, especially antibiotics, are micropollutants whose continuous flow into hydrological cycles has the potential to mediate antibiotic resistance in the environment and cause toxicity to sensitive organisms. Here, we investigated the levels of selected antibiotics in four wastewater treatment plants and the receiving water bodies. The measured environmental concentrations were compared with the proposed compound-specific predicted no-effect concentration for resistance selection values. The concentration of doxycycline, amoxicillin, sulfamethoxazole, trimethoprim, ciprofloxacin and norfloxacin within the influents, effluents, surface waters and river sediments ranged between 0.2 and 49.3 μgL^-1, 0.1 to 21.4 μgL^-1; ˂ 0.1 and 56.6 μgL^-1; and 1.8 and 47.4 μgkg^-1, respectively. Compared to the effluent concentrations, the surface waters upstream and downstream one of the four studied treatment plants showed two to five times higher concentrations of ciprofloxacin, norfloxacin and sulfamethoxazole. The risk quotient for bacterial resistance selection in effluent and surface water ranged between ˂0.1 and 53, indicating a medium to high risk of antibiotic resistance developing within the study areas. Therefore, risk mitigation and prevention strategies are a matter of priority in the affected areas.

MoS4 2- intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.

Response of the Bacterial Community and Antibiotic Resistance in Overnight Stagnant Water from a Municipal Pipeline

Although drinking water safety has raised considerable concern, to date, the hidden health risks in newly released overnight water from a municipal pipeline have seldom received attention. In this study, bacterial community composition and the response of antibiotic-resistant bacteria (ARB) to ciprofloxacin, azithromycin, tetracycline, penicillin, and cephalosporin in overnight stagnant water were analyzed. With increases in heterotrophic bacteria plate count (HPC) during water stagnation, the numbers of ARB and the ARB/HPC ratios for the five antibiotics in resident water were observed to increase, which illustrated that the prevalence of ARB rose in the pipe network water during stagnation time (ST). Furthermore, during water stagnation for 12 h, an increase in bacteria related to fermentation was also observed. When the ST rose to 48 h, the fermentation bacteria become non-significant, and this was related to the exchange of pipe network water during daytime stagnation within the 48-h period. The antibiotic resistance index (ARI) showed that tetracycline had the highest resistance level in fresh water, and then decreased during water stagnation. When ST increased to 12 h, all ARI values of the five antibiotics were low, which was associated with changes in parameters during water retention and reduced resistance during short-term stagnation. When the ST increased to 24 and 48 h, the resistance to most antibiotics (except for tetracycline) increased, which showed that increasing antibiotic resistance is caused by the formation of biofilms in the pipeline during water stagnation.

Prevalence of antibiotic resistance genes in cell culture liquid waste and the virulence assess for isolated resistant strains

Cell culture liquid waste containing antibiotic resistance genes (ARGs) and microbial community were still not received enough recognition, which pose potential risks to human health. Sixty-eight resistance genes and intl1 were detected in eight samples by Quantitative real-time PCR, while intl1 was only detected in hospital group. Meanwhile, the bacterial community was complex and diverse in each sample by 16S rRNA gene high-throughput sequencing, in addition, Morganella and Enterococcus presented a significant difference between two groups. Whole genome shotgun sequencing revealed that Morganella morganii had more resistance genes and virulence factors in hospital group, and three extended-spectrum beta-lactamase (ESBL) genotypes were found to be blaDHA-5, blaOXA-1, and blaTEM-1. This study provided a preliminary report on ARGs and resistant strains, which reminded people attention to the health risks of potential pathogens in this waste.

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.

The impact and mechanism of quaternary ammonium compounds on the transmission of antibiotic resistance genes

The emergence of antibiotic resistance genes (ARGs) in microbes can be largely attributed to the abuse and misuse of antibiotics and biocides. Quaternary ammonium compounds (QACs) have been used worldwide as common disinfectants and detergents; however, their potential impact on the spread and diffusion of ARGs is still unknown. In this study, we detected the QAC resistance gene (qacEΔ1), the 1 integron gene (intI1), and 12 ARGs (sul1, sul2, cfr, cml, fexA, tetA, tetG, tetQ, tetX, ermB, bla_TEM, and dfrA1) in 48 water samples from three watersheds by quantitative PCR (qPCR). We investigated the evolution of bacterial antibiotic resistance under QAC and antibiotic environmental pressures by long-term continuous culture. In addition, five QACs were selected to investigate the effect of QAC on the efficiency of conjugation transfer. The changes in bacterial cell membrane and production of reactive oxygen species (ROS) were detected by flow cytometry, revealing the mechanism by which QAC affects the spread of antibiotic resistance. Our results showed that the QAC resistance gene was ubiquitous in watersheds and it had significant correlation with intI1 and seven ARGs (r = 0.999, p < 0.01). QACs could increase the resistance of bacteria to multiple antibiotics. Furthermore, all five QACs promoted the conjugation transfer of the RP4 plasmid; the optimal concentration of QACs was about 10^-1-10^-2 mg/L and their transfer efficiencies were between 1.33 × 10^-6 and 8.87 × 10^-5. QACs enhanced membrane permeability of bacterial cells and stimulated bacteria to produce ROS, which potentially promoted the transfer of plasmids between bacteria. In conclusion, this study demonstrated that QACs may facilitate the evolution and gene transfer of antibiotic resistance gene among microbiome.

Expression of the nirS, hzsA, and hdh genes and antibiotic resistance genes in response to recovery of anammox process inhibited by oxytetracycline

The inhibitory effects of oxytetracycline (OTC) on the anaerobic ammonium oxidation (anammox) performance were relieved by employing bio-augmentation (BA) tactics. However, the recovery mechanism was vague. The response of specific anammox activity (SAA), heme c, functional genes, extracellular polymeric substance (EPS) and antibiotics resistance genes (ARGs) to OTC inhibition and BA aid were traced in the present study. The results indicated that response of SAA, heme c content and functional genes, such as nirS, hzsA and hdh to OTC inhibition were not synchronous. The presence of the tetC, tetG, tetX, and intI1 genes enhanced the resistance of anammox sludge to OTC, thus accelerating the performance recovery when aided by BA. A significant correlation existed between number of anammox 16S rRNA gene copies and protein level in the soluble microbial products (SMP), between tetG gene relative abundance and polysaccharose in SMP and between tetG gene relative abundance and protein in bound EPS (EPSs). In nutshell, the current findings provide the first description of a recovery mechanism regarding OTC-inhibited anammox performance aided by BA based on functional genes and highlights the contribution of ARGs and the self-resistance ability of EPS.

CO2 promotes the conjugative transfer of multiresistance genes by facilitating cellular contact and plasmid transfer

The dissemination of antibiotic resistance genes (ARGs), especially via the plasmid-mediated conjugation, is becoming a pervasive global health threat. This study reported that this issue can be worse by CO₂, as increased CO₂ was found to facilitate the conjugative transfer of ARGs carried on plasmid RP4 by 2.4-9.0 and 1.3-3.8 fold within and across genera, respectively. Mechanistic studies revealed that CO₂ benefitted the cell-to-cell contact by increasing cell surface hydrophobicity and decreasing cell surface charge, both of which resulted in the reduced intercellular repulsion. Besides, the transcriptional expression of genes responsible for global regulator (korA, korB and trbA), plasmid transfer and replication system (trfAp), and mating pair formation system (traF and traG) were all influenced by CO₂, facilitating the mobilization and channel transfer of plasmid. Furthermore, the presence of CO₂ induced the release of intracellular Ca²⁺ and increased the transmembrane potential of recipients, which contributed to the increased proton motive force (PMF), providing more power for DNA uptake. This is the first study addressing the potential risks of increased CO₂ on the propagation of ARGs, which provides a new insight into the concerns of anthropogenic CO₂ emissions and CO₂ storage.

Adaptive Evolution of Escherichia coli to Ciprofloxacin in Controlled Stress Environments: Contrasting Patterns of Resistance in Spatially Varying versus Uniformly Mixed Concentration Conditions

A microfluidic gradient chamber (MGC) and a homogeneous batch culturing system were used to evaluate whether spatial concentration gradients of the antibiotic ciprofloxacin allow development of greater antibiotic resistance in Escherichia coli strain 307 (E. coli 307) compared to exclusively temporal concentration gradients, as indicated in an earlier study. A linear spatial gradient of ciprofloxacin and Luria-Bertani broth (LB) medium was established and maintained by diffusion over 5 days across a well array in the MGC, with relative concentrations along the gradient of 1.7-7.7× the original minimum inhibitory concentration (MIC_original). The E. coli biomass increased in wells with lower ciprofloxacin concentrations, and only a low level of resistance to ciprofloxacin was detected in the recovered cells (∼2× MIC_original). Homogeneous batch culture experiments were performed with the same temporal exposure history to ciprofloxacin concentration, the same and higher initial cell densities, and the same and higher nutrient (i.e., LB) concentrations as in the MGC. In all batch experiments, E. coli 307 developed higher ciprofloxacin resistance after exposure, ranging from 4 to 24× MIC_original in all replicates. Hence, these results suggest that the presence of spatial gradients appears to reduce the driving force for E. coli 307 adaptation to ciprofloxacin, which suggests that results from batch experiments may over predict the development of antibiotic resistance in natural environments.

Antibiotic resistance genes attenuated with salt accumulation in saline soil

Salt accumulation on the surface of the soil layer driven by the strong evaporation is a natural phenomenon that usually happens in the dry season, particularly on the coastal lands reclaimed from tidal flats. However, the influence of salt accumulation on the distribution profile of antibiotic resistance genes (ARGs) and mobile gene elements (MGEs) remains unclear. In this study, we sampled a wild saline soil where the salt accumulation was frequently observed to investigate the vertical distribution profiles of ARGs and MGEs. The results showed that an increasing gradient of ARGs and MGEs was observed from the top to deep layer with the decreasing of electrical conductivity (EC1:5 values) indicating the salt-influenced attenuation of ARGs in the saline soil. The competing test suggested that the attenuation of ARGs in response to salinity gradient was attributable to the elimination of the ARG-harboring plasmids, due to the reduction of the relative fitness of plasmid-harboring strains. Additionally, the network analyses showed that the attenuation of ARGs might be associated with decreased abundance of Actinobacteria. Overall, this study identifies that salinity as an abiotic stress could re-shape the distribution of ARGs, which may influence the dissemination of ARGs in the environment.

Graphene oxide as a tool for antibiotic-resistant gene removal: a review

Environmental pollutants, including antibiotics (ATBs), have become an increasingly common health hazard in the last several decades. Overdose and abuse of ATBs led to the emergence of antibiotic-resistant genes (ARGs), which represent a serious health threat. Moreover, water bodies and reservoirs are places where a wide range of bacterial species with ARGs originate, owing to the strong selective pressure from presence of ATB residues. In this regard, graphene oxide (GO) has been utilised in several fields including remediation of the environment. In this review, we present a brief overview of resistant genes of frequently used ATBs, their occurrence in the environment and their behaviour. Further, we discussed the factors influencing the binding of nucleic acids and the response of ARGs to GO, including the presence of salts in the water environment or water pH, because of intrinsic properties of GO of not only binding to nucleic acids but also catalysing their decomposition. This would be helpful in designing new types of water treatment facilities.

Water Disinfection Byproducts Increase Natural Transformation Rates of Environmental DNA in Acinetobacter baylyi ADP1

The process of natural transformation allows for the stable uptake, integration, and functional expression of extracellular DNA. This mechanism of horizontal gene transfer has been widely linked to the acquisition of antibiotic resistance and virulence factors. Here, we demonstrate that bromoacetic acid (BAA)-a regulated drinking water disinfection byproduct (DBP)-can stimulate natural transformation rates in the model organism Acinetobacter baylyi ADP1. We demonstrate that transformation stimulation in response to BAA is concentration-dependent and is linked to the ability of this compound to generate DNA damage via oxidative stress. In presence of BAA, transcription of recA was upregulated 20-40% compared to the nontreated controls, indicating that this component of the DNA damage response could be associated with the increase in transformation. Other genes associated with DNA translocation across the cytoplasmic membrane (i.e., pilX, comA) did not exhibit increased transcription in the presence of BAA, indicating that the enhancement of transformation is not associated with increased translocation rates of environmental DNA. Overall, these results lead us to speculate that elevated recA transcription levels could lead to increased integration rates of foreign DNA within the recipient cell during DNA repair. Lastly, we show that an artificial DBP cocktail simulating the environmental concentrations of five water DBP classes stimulates natural transformation by almost 2-fold. The results of this study suggest that mutagens like DBPs may play an important role in enhancing the fixation rates of extracellular DNA in the environmental metagenome.

Elimination of antibiotic resistance genes and control of horizontal transfer risk by UV-based treatment of drinking water: A mini review

Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been recognized as one of the biggest public health issues of the 21st century. Both ARB and ARGs have been determined in water after treatment with conventional disinfectants. Ultraviolet (UV) technology has been seen growth in application to disinfect the water. However, UV method alone is not adequate to degrade ARGs in water. Researchers are investigating the combination of UV with other oxidants (chlorine, hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and photocatalysts) to harness the high reactivity of produced reactive species (Cl·, ClO·, Cl2·-, ·OH, and SO4·-) in such processes with constituents of cell (e.g., deoxyribonucleic acid (DNA) and its components) in order to increase the degradation efficiency of ARGs. This paper briefly reviews the current status of different UV-based treatments (UV/chlorination, UV/H2O2, UV/PMS, and UV-photocatalysis) to degrade ARGs and to control horizontal gene transfer (HGT) in water. The review also provides discussion on the mechanism of degradation of ARGs and application of q-PCR and gel electrophoresis to obtain insights of the fate of ARGs during UV-based treatment processes.

Methods for field measurement of antibiotic concentrations: limitations and outlook

The growing prevalence of antibiotic resistance poses an increasingly serious threat to human health. Although an important driver of antibiotic resistance is the continuous exposure of bacteria to sublethal concentrations of antibiotics in natural environments, antibiotic pollutants are not currently tracked globally or systematically. This limits the international capacity to address the rise of antibiotic resistance at its source. To address this lack of data, the development of methods to measure antibiotic concentrations on-site is essential. These methods, ideally, must be sensitive to sublethal concentrations of antibiotics and require minimal technical expertise. Furthermore, factors such as cost, selectivity, biosafety and the ability to multiplex must be evaluated in the context of field use. Based on these criteria, we provide a critical review of current methods in antibiotic detection and evaluate their adaptability for use on-site. We categorize these methods into microbiological assays, physical and chemical assays, immunoassays, aptasensors and whole-cell biosensors. We recommend continued development of a dipstick or microfluidics approach with a bacterial promoter-based mechanism and colorimetric output. This technique would incorporate the advantageous aspects of existing methods, maximize shelf-life and ease-of-use, and require minimal resources to implement in the field.

Sub-lethal concentrations of heavy metals induce antibiotic resistance via mutagenesis

The emergence of antibiotic resistance is a growing problem worldwide. Numerous studies have demonstrated that heavy metals facilitate the spread of bacterial drug-resistance in the environment. However, the actions and mechanisms of metals at relatively low sub-lethal levels (far below the minimal inhibitory concentration [MIC]) on antibiotic resistance remain unclear. In this study, we investigated the effect of sub-lethal levels of heavy metals [Ag(I), Zn(II), and Cu(II)] on antibiotic resistance and explored the underlying mechanisms. The results demonstrated that sub-lethal levels of metal ions increased the mutation rates and enriched de novo mutants that exhibited significant resistance to multiple antibiotics. The resistant mutants exhibited hereditary resistance after 5-day of sub-culture. Whole-genome analysis revealed distinct mutations in genes involved in multiple drug and drug-specific resistance, as well as genes that are not associated with antibiotic resistance to data. The number and identities of genetic changes were distinct for mutants induced by different metals. This study provides evidence and mechanistic insights into the induction of antibiotic resistance by sub-lethal concentrations of heavy metals, which may enhance the emergence of antibiotic resistance in various environments. More consideration and regulations should be given to this potential health risk for long-standing and harmful heavy metals.

Development and evaluation of diffusive gradients in thin films based on nano-sized zinc oxide particles for the in situ sampling of tetracyclines in pig breeding wastewater

The pollution of antibiotics, including tetracyclines (TCs), in aquatic environments has become an issue of concern in recent years. Herein, an in situ sampling of TCs in pig breeding wastewater that utilizes the technique of diffusive gradients in thin films (DGT), based on commercial nanosized ZnO (nanoZnO) particles as the potential effective binding agent and a polyethersulfone (PES) membrane as the diffusion layer, was developed. The diffusion coefficients of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in a PES membrane at 25 °C were (1.37 ± 0.06) × 10^-6 cm² s^-1, (1.29 ± 0.05) × 10^-6 cm² s^-1 and (1.94 ± 0.07) × 10^-6 cm² s^-1, respectively. The results showed that the adsorption capacities of a gel disc containing 2.5 g L^-1 of nanoZnO particles were as high as 3.93 ± 0.20 mg disc^-1 for TC, 3.21 ± 0.20 mg disc^-1 for OTC and 4.62 ± 0.22 mg disc^-1 for CTC. Both a solution pH in the range of 5-9 and an ionic strength (as pNaCl) in the range of 1-3 had an insignificant influence on the TCs uptake by nanoZnO-DGT samplers. There was no significant influence of fulvic acid or tannic acid on the TC uptake by nanoZnO-DGT samplers at the tested mass ratios. For all spiked freshwater samples, there was no notable interference of matrices on the performance of the nanoZnO-DGT samplers, suggesting that the nanoZnO-DGT samplers yielded satisfactory results for the uptake of TCs at concentrations existing in the spiked freshwater samples. Field deployment of the nanoZnO-DGT samplers in pig breeding wastewater also exhibited excellent precision and accuracy, indicating that the nanoZnO-DGT samplers could be used as a promising method for the in situ sampling of TC antibiotics in aquatic environments.

Antiepileptic drug carbamazepine promotes horizontal transfer of plasmid-borne multi-antibiotic resistance genes within and across bacterial genera

Antibiotic resistance is a severe global threat for public health, causing around 700,000 deaths per year. Horizontal gene transfer (HGT) is one of the most significant pathways to disseminate antibiotic resistance. It is commonly acknowledged that sub-minimum inhibition concentrations of antibiotics are major contributors in promoting antibiotic resistance through HGT. Pharmaceuticals are occurring in our environments at increased levels, yet little is known whether non-antibiotic pharmaceuticals cause or accelerate the dissemination of antibiotic resistance. Here, we report for the first time that the antiepileptic drug, carbamazepine, promotes conjugative transfer of antibiotic resistance genes. It was seen that environmentally relevant concentrations of carbamazepine (e.g., 0.05 mg/L) significantly enhanced the conjugative transfer of multiresistance genes carried by plasmid within and across bacterial genera. The underlying mechanisms of the enhanced HGT were revealed by detecting oxidative stress and cell membrane permeability, in combination with MinION DNA sequencing, genome-wide RNA sequencing, and proteomic analysis. Carbamazepine induced a series of acute responses, including increased levels of reactive oxygen species, the SOS response; increased cell membrane permeability, and pilus generation. Expressional levels of genes related to these processes were significantly upregulated during carbamazepine exposure. Given that HGT occurs widely among different species in various environments, these findings are an early warning for a wide assessment of the roles of non-antibiotic pharmaceuticals in the spread of antibiotic resistance.

Selective antibiotic resistance genes in multiphase samples during biofilm growth in a simulated drinking water distribution system: Occurrence, correlation and low-pressure ultraviolet removal

The aim of this study was to gain comprehensive insights into the characteristics of antibiotic resistance genes (ARGs) in multiphase samples from drinking water distribution pipelines using a simulated biofilm reactor. During 120 d of continuous operation, common parameters and six ARGs (ermA, ermB, aphA2, ampC, sulII, and tetO) in samples of three phases (water, particle, and biofilm) from the reactor were investigated, which demonstrated secondary contamination by ARGs. Abundances of the six ARGs in the reactor effluent increased gradually, and in the 120 d effluent, the relative abundances of aphA2 and sulII were the highest, at 9.9 × 10^-4 and 1.3 × 10^-3, respectively, with a 1.5-fold and 2.8-fold increase, compared with those in the influent. The relative abundances of the six ARGs in the biofilm phase increased significantly (P < 0.05) at 120 d, which was caused by robust bacteria in biofilm that was newly exposed following the detachment of a large piece of aging biofilm. In the particle phase, four of the ARGs did not change significantly during the 120 d period. The six ARGs in the samples of three phases showed a negative correlation with residual chlorine in the pipe water, which demonstrated that low abundance of ARGs in the samples of three phases was related to the improvement of residual chlorine. The proportion of cultivable bacteria illustrated that the robust and active bacteria were negatively correlated with the six ARGs in the biofilm. Total organic carbon (TOC) in the pipeline showed a positive correlation with the proportion of cultivable bacteria in both the water and biofilm phases, which indicated that a TOC reduction in the pipeline contributed to low abundance of ARGs. With low-pressure ultraviolet (LP-UV) irradiation of 20 mJ/cm², ARGs in the samples of three phases were efficiently controlled, which showed that LP-UV can be used for ARG removal in terminal water for supplemental bactericidal treatment of pipeline effluent.

Nano-metal oxides induce antimicrobial resistance via radical-mediated mutagenesis

The widespread use of nanoparticles has triggered increasing concern and interest due to the adverse effects on global public health and environmental safety. Whether the presence of nano-metal oxides (NMOs) could facilitate the formation of new antimicrobial resistance genes (ARGs) via de novo mutation is largely unknown. Here, we proved that two widely used NMOs could significantly improve the mutation frequencies of CIP- and CHL-resistant E. coli isolates; however, the corresponding metal ions have weaker effects. Distinct concentration-dependent increases of 1.0-14.2 and 1.1-456.3 folds were observed in the resistance mutations after treatment with 0.16-100 mg/L nano-Al₂O₃ and 0.16-500 mg/L nano-ZnO, respectively, compared with those in the control. The resistant mutants showed resistance to multiple antibiotics and hereditary stability after sub-culturing for 5 days. We also explored the mechanism underlying the induction of antimicrobial resistance by NMOs. Whole-genome sequencing analysis showed that the mutated genes correlated with mono- and multidrug resistance, as well as undetected resistance to antibiotics. Furthermore, NMOs significantly promoted intracellular reactive oxygen species (ROS), which would lead to oxidative DNA damage and an error-prone SOS response, and consequently, mutation rates were enhanced. Our findings indicate that NMOs could accelerate the mutagenesis of multiple-antibiotic resistance and expanded the understanding of the mechanisms in nanoparticle-induced resistance, which may be significant for guiding the production and application of nanoparticles.

Antidepressant fluoxetine induces multiple antibiotics resistance in Escherichia coli via ROS-mediated mutagenesis

BACKGROUND

Antibiotic resistance poses a great threat to global public health. Overuse of antibiotics is generally considered as the major factor contributing to it. However, little is known about whether non-antibiotic drugs could play potential roles in the emergence of antibiotic resistance.

OBJECTIVE

We aimed to investigate whether antidepressant fluoxetine induces multiple antibiotic resistances and reveal underlying mechanisms.

METHODOLOGY

Escherichia coli K12 was exposed to different concentrations of fluoxetine (0, 0.5, 5, 50 and 100 mg/L) and the resistant strains were isolated by plating on antibiotic containing plates. Resistant strains were randomly selected to determine the increase of minimum inhibition concentration (MIC) of multiple antibiotics. Genome-wide DNA sequencing was performed on cells cultured in lysogeny broth (LB) without any fluoxetine or antibiotics exposure. RNA sequencing and proteomic profiling of isolated mutants grown in LB with 100 mg/L fluoxetine were analyzed to reveal the underlying mechanisms.

RESULTS

Exposure of Escherichia coli to fluoxetine at 5-100 mg/L after repeated subculture in LB for 30 days promoted its mutation frequency resulting in increased resistance against the antibiotics chloramphenicol, amoxicillin and tetracycline. This increase was up to 5.0 × 10⁷ fold in a dose-time pattern. Isolated mutants with resistance to one of these antibiotics also exhibited multiple resistances against fluoroquinolone, aminoglycoside, β-lactams, tetracycline and chloramphenicol. According to global transcriptional and proteomic analyses, the AcrAB-TolC pump together with the YadG/YadH transporter, a Tsx channel and the MdtEF-TolC pump have been triggered to export the antibiotics to the exterior of the cell. Whole-genome DNA analysis of the mutants further revealed that ROS-mediated mutagenesis (e.g., deletion, insertion, and substitution) of DNA-binding transcriptional regulators (e.g., marR, rob, sdiA, cytR and crp) to up-regulate the expression of efflux pumps, may further enhance the antibiotic efflux.

CONCLUSIONS

Our findings for the first time demonstrated that the exposure to antidepressant fluoxetine induces multiple antibiotic resistance in E. coli via the ROS-mediated mutagenesis.

Non-antibiotic antimicrobial triclosan induces multiple antibiotic resistance through genetic mutation

Antibiotic resistance poses a major threat to public health. Overuse and misuse of antibiotics are generally recognized as the key factors contributing to antibiotic resistance. However, whether non-antibiotic, anti-microbial (NAAM) chemicals can directly induce antibiotic resistance is unclear. We aim to investigate whether the exposure to a NAAM chemical triclosan (TCS) has an impact on inducing antibiotic resistance on Escherichia coli. Here, we report that at a concentration of 0.2 mg/L TCS induces multi-drug resistance in wild-type Escherichia coli after 30-day TCS exposure. The oxidative stress induced by TCS caused genetic mutations in genes such as fabI, frdD, marR, acrR and soxR, and subsequent up-regulation of the transcription of genes encoding beta-lactamases and multi-drug efflux pumps, together with down-regulation of genes related to membrane permeability. The findings advance our understanding of the potential role of NAAM chemicals in the dissemination of antibiotic resistance in microbes, and highlight the need for controlling biocide applications.

Photocatalytic Reactive Ultrafiltration Membrane for Removal of Antibiotic Resistant Bacteria and Antibiotic Resistance Genes from Wastewater Effluent

Biological wastewater treatment is not effective in removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In this study, we fabricated a photocatalytic reactive membrane by functionalizing polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane with titanium oxide (TiO₂) nanoparticles for the removal of ARB and ARGs from a secondary wastewater effluent. The TiO₂-modified PVDF membrane provided complete retention of ARB and effective photocatalytic degradation of ARGs and integrons. Specifically, the total removal efficiency of ARGs (i.e., plasmid-mediated floR, sul1, and sul2) with TiO₂-modified PVDF membrane reached ∼98% after exposure to UV irradiation. Photocatalytic degradation of ARGs located in the genome was found to be more efficient than those located in plasmid. Excellent removal of integrons (i.e., intI1, intI2, and intI3) after UV treatment indicated that the horizontal transfer potential of ARGs was effectively controlled by the TiO₂ photocatalytic reaction. We also evaluated the antifouling properties of the TiO₂-UF membrane to demonstrate its potential application in wastewater treatment.

The occurrence, maintenance, and proliferation of antibiotic resistance genes (ARGs) in the environment: influencing factors, mechanisms, and elimination strategies

Here, we review the possible reasons responsible for the occurrence, maintenance and proliferation of antibiotic resistance genes (ARGs) in the environment, as well as the corresponding mechanisms of their development, diffusion and transfer. Additionally, elimination strategies are also discussed. The factors that influence the development of ARGs are selection pressure, including that from antibiotics, metal and multiple other factors, co-resistance and cross-resistance, microbial consortium structure, nutrients in the environment and oxidative stress responses. Process parameters, transport pathways, and elimination strategies to reduce the health risk caused by ARGs are also reviewed in detail. Moreover, knowledge gaps and future opportunities of ARGs are addressed.

Flux, Impact, and Fate of Halogenated Xenobiotic Compounds in the Gut

Humans and their associated microbiomes are exposed to numerous xenobiotics through drugs, dietary components, personal care products as well as environmental chemicals. Most of the reciprocal interactions between the microbiota and xenobiotics, such as halogenated compounds, occur within the human gut harboring diverse and dense microbial communities. Here, we provide an overview of the flux of halogenated compounds in the environment, and diverse exposure routes of human microbiota to these compounds. Subsequently, we review the impact of halogenated compounds in perturbing the structure and function of gut microbiota and host cells. In turn, cultivation-dependent and metagenomic surveys of dehalogenating genes revealed the potential of the gut microbiota to chemically alter halogenated xenobiotics and impact their fate. Finally, we provide an outlook for future research to draw attention and attract interest to study the bidirectional impact of halogenated and other xenobiotic compounds and the gut microbiota.

Sub-inhibitory concentrations of heavy metals facilitate the horizontal transfer of plasmid-mediated antibiotic resistance genes in water environment

Although widespread antibiotic resistance has been mostly attributed to the selective pressure generated by overuse and misuse of antibiotics, recent growing evidence suggests that chemicals other than antibiotics, such as certain metals, can also select and stimulate antibiotic resistance via both co-resistance and cross-resistance mechanisms. For instance, tetL, merE, and oprD genes are resistant to both antibiotics and metals. However, the potential de novo resistance induced by heavy metals at environmentally-relevant low concentrations (much below theminimum inhibitory concentrations [MICs], also referred as sub-inhibitory) has hardly been explored. This study investigated and revealed that heavy metals, namely Cu(II), Ag(I), Cr(VI), and Zn(II), at environmentally-relevant and sub-inhibitory concentrations, promoted conjugative transfer of antibiotic resistance genes (ARGs) between E. coli strains. The mechanisms of this phenomenon were further explored, which involved intracellular reactive oxygen species (ROS) formation, SOS response, increased cell membrane permeability, and altered expression of conjugation-relevant genes. These findings suggest that sub-inhibitory levels of heavy metals that widely present in various environments contribute to the resistance phenomena via facilitating horizontal transfer of ARGs. This study provides evidence from multiple aspects implicating the ecological effect of low levels of heavy metals on antibiotic resistance dissemination and highlights the urgency of strengthening efficacious policy and technology to control metal pollutants in the environments.

Research progress on distribution, migration, transformation of antibiotics and antibiotic resistance genes (ARGs) in aquatic environment

Antimicrobial and antibiotics resistance caused by misuse or overuse of antibiotics exposure is a growing and significant threat to global public health. The spread and horizontal transfer of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) by the selective pressure of antibiotics in an aquatic environment is a major public health issue. To develop a better understanding of potential ecological risks die to antibiotics and ARGs, this study mainly summarizes research progress about: (i) the occurrence, concentration, fate, and potential ecological effects of antibiotics and ARGs in various aquatic environments, (ii) the threat, spread, and horizontal gene transfer (HGT) of ARGs, and (iii) the relationship between antibiotics, ARGs, and ARB. Finally, this review also proposes future research direction on antibiotics and ARGs.