Antimicrobial resistance in Enterococcus spp. isolated in inflow, effluent and sludge from municipal sewage water treatment plants

The risk of viable but non-culturable (VBNC) enterococci and antibiotic resistance transmission during simulated municipal sludge composting

Sludge composting is a sludge resource utilization method that can reduce pollutants, such as pathogens. Enterococci are regarded as more reliable and conservative indicators of pathogen inactivation than fecal coliforms, which are typically used as indicators of fecal pollution. Non-spore pathogenic bacteria may enter a viable but non-culturable (VBNC) state during composting, leading to residual risk. The VBNC status of bacteria is related to their survival during composting. However, the survival mechanisms of enterococci during sludge composting remain unclear. Therefore, this study aimed to investigate the VBNC state of enterococci in different phases of simulated sludge composting and the fate of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) during the composting process. This study is expected to provide a basis for subsequent exploration of possible methods to completely inactivate enterococci and reduce ARGs during sludge composting. Culturable enterococci were reduced in the thermophilic phase of sludge composting, but the proportion of VBNC subpopulation increased. It was reported for the first time that most VBNC enterococci were killed by extending the cooling phase of sludge compost, and by prolonging the cooling phase the types of ARG were reduced. However, there was a certain quantity (approximately 104/g dry weight) of culturable and VBNC enterococci in the compost products. In addition, MGEs and ARGs exist in both bacteria and compost products, leading to the risk of spreading antibiotic-resistant bacteria and antibiotic resistance when sludge compost products are used.

Proteomic profiling of antibiotic-resistant Escherichia coli GW-AmxH19 isolated from hospital wastewater treated with physical plasma

Microorganisms which are resistant to antibiotics are a global threat to the health of humans and animals. Wastewater treatment plants are known hotspots for the dissemination of antibiotic resistances. Therefore, novel methods for the inactivation of pathogens, and in particular antibiotic-resistant microorganisms (ARM), are of increasing interest. An especially promising method could be a water treatment by physical plasma which provides charged particles, electric fields, UV-radiation, and reactive species. The latter are foremost responsible for the antimicrobial properties of plasma. Thus, with plasma it might be possible to reduce the amount of ARM and to establish this technology as additional treatment stage for wastewater remediation. However, the impact of plasma on microorganisms beyond a mere inactivation was analyzed in more detail by a proteomic approach. Therefore, Escherichia coli GW-AmxH19, isolated from hospital wastewater in Germany, was used. The bacterial solution was treated by a plasma discharge ignited between each of four pins and the liquid surface. The growth of E. coli and the pH-value decreased during plasma treatment in comparison with the untreated control. Proteome and antibiotic resistance profile were analyzed. Concentrations of nitrite and nitrate were determined as long-lived indicative products of a transient chemistry associated with reactive nitrogen species (RNS). Conversely, hydrogen peroxide served as indicator for reactive oxygen species (ROS). Proteome analyses revealed an oxidative stress response as a result of plasma-generated RNS and ROS as well as a pH-balancing reaction as key responses to plasma treatment. Both, the generation of reactive species and a decreased pH-value is characteristic for plasma-treated solutions. The plasma-mediated changes of the proteome are discussed also in comparison with the Gram-positive bacterium Bacillus subtilis. Furthermore, no effect of the plasma treatment, on the antibiotic resistance of E. coli, was determined under the chosen conditions. The knowledge about the physiological changes of ARM in response to plasma is of fundamental interest to understand the molecular basis for the inactivation. This will be important for the further development and implementation of plasma in wastewater remediation.

Effectiveness of wastewater treatment plant at the removal of nutrients, pathogenic bacteria, and antibiotic-resistant bacteria in wastewater from hospital source

This study is aimed at assessing the effectiveness of hospital's wastewater treatment plant (WWTP) in removing nutrients, pathogenic bacteria, and addressing antibiotic resistance using a case study of a tertiary hospital in Ibadan, Nigeria. During the dry and wet seasons in the month of July and December, respectively, samples were collected, and analyzed using standard guidelines to examine significant physicochemical parameters of the WTTP; to evaluate the removal efficiency of biological oxygen demand (BOD) and chemical oxygen demand (COD), and to examine the prevalence of pathogenic and antibiotic-resistant bacteria. The results of this study showed that during the dry season, certain parameters exceeded acceptable limits, including temperature, total suspended solids (TSS), total dissolved solids (TDS), phosphate, and nitrate. Although there were reductions in BOD (1555 mg/L to 482 mg/L) and COD levels (3160 mg/L to 972 mg/L), they remained above acceptable limits by World Health Organization. In the wet season, the level of COD (20 mg/L) in the effluent was within acceptable limit, while the BOD (160 mg/L) was above the acceptable limit. The WWTP effectively removed nutrients and reduced the microbial load, as evident from the absence of fecal coliforms in the effluent in both seasons. In respect to BOD removal efficiency, the level of purification of wastewater by the WWTP was 69% during the dry season, while the removal efficiency of COD was 83.54% which showed the efficiency of the WWTP at the removal of COD. However, antibiotic resistance was still present. The study concludes that while the WWTP effectively addressed nutrients and microbial load, additional measures such as tertiary treatment methods like chlorination and UV radiation are necessary to tackle antibiotic resistance. This is crucial to prevent the release of antibiotic-resistant bacteria into the environment, safeguarding human health, animals, plants, and overall environmental well-being.

Risk control of antibiotics, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) during sewage sludge treatment and disposal: A review

Sewage sludge is an important reservoir of antibiotics, antibiotic resistance genes (ARGs), and antibiotic resistant bacteria (ARB) in wastewater treatment plants (WWTPs), and the reclamation of sewage sludge potentially threats human health and environmental safety. Sludge treatment and disposal are expected to control these risks, and this review summarizes the fate and controlling efficiency of antibiotics, ARGs, and ARB in sludge involved in different processes, i.e., disintegration, anaerobic digestion, aerobic composting, drying, pyrolysis, constructed wetland, and land application. Additionally, the analysis and characterization methods of antibiotics, ARGs, and ARB in complicate sludge are reviewed, and the quantitative risk assessment approaches involved in land application are comprehensively discussed. This review benefits process optimization of sludge treatment and disposal, with regard to environmental risks control of antibiotics, ARGs, and ARB in sludge. Furthermore, current research limitations and gaps, e.g., the antibiotic resistance risk assessment in sludge-amended soil, are proposed to advance the future studies.

Effect of Indole-Containing Pyrazino[2,1-b]quinazoline-3,6-diones in the Virulence of Resistant Bacteria

Drug resistance is rising to alarming levels, constituting one of the major threats to global health. The overexpression of efflux pumps and the formation of biofilms constitute two of the most common resistance mechanisms, favoring the virulence of bacteria. Therefore, the research and development of effective antimicrobial agents that can also counteract resistance mechanisms are extremely important. Pyrazino[2,1-b]quinazoline-3,6-diones, from marine and terrestrial organisms and simpler synthetic analogues, were recently disclosed by us as having relevant antimicrobial properties. In this study, using a multi-step approach, it was possible to synthesize new pyrazino[2,1-b]quinazoline-3,6-diones focusing on compounds with fluorine substituents since, to the best of our knowledge, the synthesis of fluorinated fumiquinazoline derivatives had not been attempted before. The new synthesized derivatives were screened for antibacterial activity and, along with previously synthetized pyrazino[2,1-b]quinazoline-3,6-diones, were characterized for their antibiofilm and efflux-pump-inhibiting effects against representative bacterial species and relevant resistant clinical strains. Several compounds showed relevant antibacterial activity against the tested Gram-positive bacterial species with MIC values in the range of 12.5-77 μM. Furthermore, some derivatives showed promising results as antibiofilm agents in a crystal violet assay. The results of the ethidium bromide accumulation assay suggested that some compounds could potentially inhibit bacterial efflux pumps.

Strategic insight into enhanced photocatalytic remediation of pharmaceutical contaminants using spherical CdO nanoparticles in visible light region

The sustainable control of pharmaceutical micropollutants in water and wastewater environments is a great challenge in the 21st century. To address these issues, unique CdO nanoparticles (NPs) were synthesized using a facile hydrothermal approach and investigated for photocatalytic control of the antibiotic tetracycline, multidrug-resistant bacteria (MDRB), and total coliform in the wastewater effluent. The NPs were characterized using a range of techniques and it exhibited a spherical-like crystal structure with a mean size of 40 nm. The vibrational stretching mode of 1419 cm^-1 confirmed the formation of Cd-O (M - O). The synthesis protocol formed smoother surfaces and 1.88 eV band gap energy of CdO NPs, inducing excellent photocatalytic activity under visible LED light (blue and white) irradiation. The optimal catalyst dose and pH were 100 mg/L and 8-9, respectively. Blue light proved more effective than white light, resulting in 28% higher efficiency (93 ± 0.47%) in tetracycline degradation than white light under an identical intensity (20 mW/cm²). White light required a four-fold higher light intensity (80 mW/cm²) than blue light to induce comparable photocatalytic MDRB inactivation. Bacterial cell lysis by the photocatalytic treatment was confirmed by transmission electron microscopy (TEM). The used catalyst was easily recovered by 5 min of centrifugation and re-used without any noticeable change in the photocatalytic decomposition. The trapping experiment revealed that the CdO-based NPs contributed primarily to the generation of •O₂^- and •OH radicals (Type I), but the •O₂^- radicals were the dominant reactive oxygen species (ROS) in the photocatalytic process.

Antibiotic-resistant bacteria in hospital wastewater treatment plant effluent and the possible consequences of its reuse in agricultural irrigation

Wastewater from hospitals should be monitored precisely and treated properly before discharge and reuse to avoid epidemic and pandemic complications, as it contains hazardous pollutants for the ecosystem. Antibiotic residues in treated hospital wastewater effluents constitute a major environmental concern since they resist various wastewater treatment processes. The emergence and spread of multi-drug-resistant bacteria, that cause public health problems, are therefore always a major concern. The aims and objectives of this study were mainly to characterize the chemical and microbial properties of the hospital effluent of wastewater treatment plant (WWTP) before discharge to the environment. Special attention was paid to the presence of multiple resistant bacteria and the effects of hospital effluent reuse in irrigation on zucchini as an economically important plant. The risk of cell-free DNA carrying antibiotic resistance genes contained in the hospital effluent as a long-lasting hazard had been discussed. In this study, 21 bacterial strains were isolated from the effluent of a hospital WWTP. Isolated bacteria were evaluated for multi-drug resistance ability against 5 antibiotics (Tetracycline, Ampicillin, Amoxicillin, Chloramphenicol, and Erythromycin) at a concentration of 25 ppm. Out of them, three isolates (AH-03, AH-07, and AH-13) were selected because they recorded the highest growth in presence of tested antibiotics. Selected isolates were identified using 16S rRNA gene sequence homology as Staphylococcus haemolyticus (AH-03), Enterococcus faecalis (AH-07), and Escherichia coli (AH-13). Their susceptibility to ascending concentrations of tested antibiotics indicated that they were all susceptible at a concentration above 50 ppm. Results of the greenhouse experiment regarding the effect of hospital WWTP effluent reuse on zucchini plant fresh weights compared to that irrigated with fresh water indicated that the former recorded a limited increase in total fresh weights (6.2 g and 5.3 g/plant, respectively). Our results demonstrated the low impact of the reuse of Hospital WWTP effluent in agriculture irrigation compared to its greater risk in transferring multiple antibiotic bacteria and antibiotic resistance genes to soil bacteria through natural transformation.

Evolution and Emergence of Antibiotic Resistance in Given Ecosystems: Possible Strategies for Addressing the Challenge of Antibiotic Resistance

Antibiotics were once considered the magic bullet for all human infections. However, their success was short-lived, and today, microorganisms have become resistant to almost all known antimicrobials. The most recent decade of the 20th and the beginning of the 21st century have witnessed the emergence and spread of antibiotic resistance (ABR) in different pathogenic microorganisms worldwide. Therefore, this narrative review examined the history of antibiotics and the ecological roles of antibiotics, and their resistance. The evolution of bacterial antibiotic resistance in different environments, including aquatic and terrestrial ecosystems, and modern tools used for the identification were addressed. Finally, the review addressed the ecotoxicological impact of antibiotic-resistant bacteria and public health concerns and concluded with possible strategies for addressing the ABR challenge. The information provided in this review will enhance our understanding of ABR and its implications for human, animal, and environmental health. Understanding the environmental dimension will also strengthen the need to prevent pollution as the factors influencing ABR in this setting are more than just antibiotics but involve others like heavy metals and biocides, usually not considered when studying ABR.

An emerging unrated mobile reservoir for antibiotic resistant genes: Does transportation matter to the spread

The regional distribution of antibiotic resistance genes has been caused by the use and preference of antibiotics. Not only environmental factors, but also the population movement associated with transportation development might have had a great impact, but yet less is known regarding this issue. This research study has investigated and reported that the high-speed railway train was a possible mobile reservoir of bacteria with antibiotic resistance, based on the occurrence, diversity, and abundance of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and mobile gene elements (MGEs) in untreated train wastewater. High-throughput 16S rRNA sequencing analyses have indicated that opportunistic pathogens like Pseudomonas and Enterococcuss were the predominant bacteria in all samples, especially in cultivable multi-antibiotic resistant bacteria. The further isolated Enterococcus faecalis and Enterococcus faecium exhibited multi-antibiotic resistance ability, potentially being an indicator for disinfection proficiency. Positive correlations amongst ARGs and MGEs were observed, such as between intI1 and tetW, tetA, blaTEM, among Tn916/154 and mefA/F, qnrS, implying a broad dissemination of multi-ARGs during transportation. The study findings suggested that the high-speed railway train wastewater encompassed highly abundant antibiotic-resistant pathogens, and the wastewater discharge without effective treatment may pose severe hazards to human health and ecosystem safety.

Persistence of wastewater-associated antibiotic resistant bacteria in river microcosms

The spread of antibiotic-resistant bacteria (ARB) associated with wastewater is a significant environmental concern, but little is known about the persistence and proliferation of these organisms in receiving water bodies after discharge. To address this knowledge gap, we performed a series of microcosm experiments in which river water was amended with either untreated or treated wastewater, and the abundance of viable ciprofloxacin-, Bactrim-, and erythromycin-resistant bacteria was monitored for 72 h. Both types of wastewater amendments significantly increased the initial abundance of ARB compared to microcosms containing only river water (all p < 0.03). The increase was greatest with untreated wastewater, but that effect decreased steadily over time. In contrast, microcosms amended with treated wastewater saw a smaller initial increase and more complex temporal dynamics. Following a brief lag, ARB abundance bloomed for all three of the antibiotics that we considered. This suggests that ARB that survive wastewater treatment are particularly hardy and may proliferate in riverine conditions after a short recovery period. To determine how interactions with the native river microbial community impacted the persistence of wastewater-associated ARB, an additional set of microcosms was prepared using filter-sterilized river water. Peak abundance in these microcosms was significantly higher by 1-2 orders of magnitude compared to microcosms containing an intact river microbial community (all p < 0.05), which suggests that biotic interactions play a significant role in regulating the persistence and proliferation of ARB. The data presented in this paper are among the first available that specifically consider persistence of viable ARB and represent an important step toward understanding AR-related human health risks downstream from wastewater discharge points and following sewer overflow events. Additional studies that consider longer time scales and the interplay of biotic and abiotic variables are essential for modeling public health risks associated with wastewater inputs of ARB to rivers and other aquatic environments.

Effect of Wastewater Treatment on Bacterial Community, Antibiotic-Resistant Bacteria and Endoparasites

Wastewater and wastewater treatment plants serve as urban reservoirs of pathogenic microorganisms. Wastewaters frequently contain bacteria, antibiotic-resistant bacteria, and developmental stages of parasites with significant zoonotic potential. Five wastewater treatment plants in the central part of Slovakia were investigated to determine the effect of treatment on bacterial community, antibiotic-resistant bacteria, and the occurrence of helminth eggs. Although all monitored chemical factors (chemical oxygen demand, biochemical oxygen demand, N-NH4, total nitrogen, and total phosphorus) in the effluent were in line with the legislative standards for discharge into public waterways, the results of minimal inhibitory concentrations show that reclaimed water harbors E. coli resistant to several commonly used antibiotics (ampicillin, piperacillin, and tazobactam, combine ampicillin and sulbactam, cefotaxime, tetracycline). The presence of endoparasite developmental stages in wastewater and sludge (Ascaris spp., Hymenolepis nana, eggs from the Ancylostomatidae family, Giardia duodenalis) indicates potential health risks for humans and workers at these sites. Treatment such as composting before applying sludge to land is necessary to reduce human pathogens.

Efficient bio-refractory industrial wastewater treatment with mitigated membrane fouling in a membrane bioreactor strengthened by the micro-scale ZVI@GAC galvanic-cells-initiated radical generation and coagulation processes

Micro-scale ZVI@GAC-based iron-carbon galvanic-cells (ZVI@GACs) were prepared with the Ca-Si-H/Ca-H formation process and first applied to initiate radical generation and coagulation processes in MBR for treating bio-refractory industrial wastewater (IWW). Batch tests revealed the H2O2 production (0.19-0.28 mg/L) and •OH generation (p-CBA decay, k1 = 0.040 min-1) in ZVI@GACs-dosed system (packing volume of 5%) under aeration. Adoption of ZVI@GACs into aerobic activated sludge process (ZVI@GACs/AS) enhanced TOC degradation (k2) and phenolic compounds (PHENs) destruction (k3). ZVI@GACs/AS at ZVI@GACs packing volume of 5%, 10% and 20% improved k2 from 0.11 h-1 (bare AS) to 0.17, 0.21 and 23 h-1 and k3 from 0.24 h-1 to 0.36, 0.49 and 0.57 h-1, respectively. The oxygen uptake rate (OUR) and 15-min acute bio-toxicity demonstrated that the bio-toxicity of IWW was reduced and the activity of biomass was enhanced in the ZVI@GACs/AS system. In MBR, ZVI@GACs at packing volume of 10% enhanced COD and PHENs removal by 14% and 22%, respectively. Membrane fouling cycle was prolonged by 71%. The accumulations of EPS-proteins, EPS-polysaccharides, SMP-proteins and SMP-polysaccharides were reduced by 6%, 67%, 27% and 60%, respectively. Fourier transform infrared spectroscopy (FTIR) confirmed the oxidation of SMP-polysaccharides in ZVI@GACs-MBR. The iron ions released from ZVI@GACs showed inhibition on the secretion of SMP-/EPS-proteins. Floc particle size distribution (PSD) and X-ray diffraction (XRD) spectrum confirmed that the coagulation effects of Fe(OH)3 and FeOOH triggered by Fe3+ increased the sludge floc size and contributed to membrane fouling mitigation. Genus Enterococcus was enriched in MBR with the destruction of PHENs by the ZVI@GACs-initiated radical generation process. The findings of this study confirmed successful development and adoption of ZVI@GACs into MBR for bio-refractory IWW treatment. It also provided an in-depth understanding on the mechanisms of ZVI@GACs-MBR system.

Analysis of migration of pathogenic drug-resistant bacteria to soils and groundwater after fertilization with sewage sludge

The paper discusses the analysis of the effect of using sewage sludge for fertilization on the level of soil and groundwater contamination with drug-resistant bacteria. Other sanitary contaminants in these environments were also analysed. Composted sewage sludge was introduced into the sandy soil over a period of 6 months. The examinations were conducted under conditions of a lysimetric experiment with the possibility of collecting soil leachates (in natural conditions). The following doses of sewage sludge were used: 0, 10, 20, 30 and 40 t/ha calculated per experimental object containing 10 kg of sandy soil. The research were carried out within the time frame of one year. Dactylis glomerata grass was grown on the fertilized soils. In soils and leachates from soils (which may have polluted groundwater) collected from fertilized experimental objects, the sanitary condition and quantity of drug-resistant bacteria (mainly from the families Enterobacteriaceae and Enterococcus) were analysed one year after fertilization. Their drug resistance to selected antibiotics was also analysed based on current recommendations. The study showed that fertilization with sewage sludge (even after stabilization and hygienization) results in contamination of soil and infiltrating waters with many species of drug-resistant pathogenic bacteria. The lowest level of contamination of soil and water environment was found after the application of sewage sludge at a dose of 10 t/ha. The isolated drug-resistant strains of intestinal bacteria were less sensitive to older generations of antibiotics including cefazolin, ampicillin, and co-amoxiclav.

Control strategies for the vertical gene transfer of quinolone ARGs in Escherichia coli through molecular modification and molecular dynamics

This study investigates the regulation of the vertical gene transfer of quinolones' antibiotic resistance genes (ARGs) through a combination of source modification and process control. In source prevention, 29 Escherichia coli (E. coli) DNA gyrase subunit A mutant proteins were constructed, the B-G mutant protein displayed the greatest reduction in binding effect (-25.98%). Based on this, a 3D-QSAR model was constructed, and LEV-2 and LEV-9 QNs derivatives were designed based on Levofloxacin (LEV), and their binding effect with B-G mutant protein was found be increased by 13.24% and 19.40%. The drug resistance mechanism of E. coli was explored based on molecular docking technology and protein hydrophobic interaction theory. Most of the amino acid resistance mutations changed from hydrophilic to lipophilic, which inhibited the binding of QNs to mutant protein A subunit, and further reduced the bactericidal effect of QNs. In process control, Huoxiang-Zhengqi, stroke-physiological saline solution (SPSS), and Lycium barbarum (L. barbarum) was found to be 164.82% higher than that of the blank control group. The purpose of this study is to provide a theoretical support for the joint regulation of QNs' ARGs in organisms and the research and development on green alternatives to QNs compounds.

Diversity of Multidrug-Resistant Bacteria in an Urbanized River: A Case Study of the Potential Risks from Combined Sewage Overflows

Wastewater contamination and urbanization contribute to the spread of antibiotic resistance in aquatic environments. This is a particular concern in areas receiving chronic pollution of untreated waste via combined sewer overflow (CSO) events. The goal of this study was to expand knowledge of CSO impacts, with a specific focus on multidrug resistance. We sampled a CSO-impacted segment of the James River (Virginia, USA) during both clear weather and an active overflow event and compared it to an unimpacted upstream site. Bacteria resistant to ampicillin, streptomycin, and tetracycline were isolated from all samples. Ampicillin resistance was particularly abundant, especially during the CSO event, so these isolates were studied further using disk susceptibility tests to assess multidrug resistance. During a CSO overflow event, 82% of these isolates were resistant to five or more antibiotics, and 44% were resistant to seven or more. The latter statistic contrasts starkly with the upstream reference site, where only 4% of isolates displayed resistance to more than seven antibiotics. DNA sequencing (16S rRNA gene) revealed that ~35% of our isolates were opportunistic pathogens, comprised primarily of the genera Stenotrophomonas, Pseudomonas, and Chryseobacterium. Together, these results demonstrate that CSOs can be a significant source of viable clinically-relevant bacteria to the natural environment and that multidrug resistance is an important understudied component of the environmental spread of antibiotic resistance.

Urban wastewater as a conduit for pathogenic Gram-positive bacteria and genes encoding resistance to β-lactams and glycopeptides

The emergence and spread of clinical pathogens, antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment pose a direct threat to human and animal health worldwide. In this study, we analyzed qualitatively and quantitatively urban sewage resistome for the occurrence of genes encoding resistance to β-lactams and glycopeptides in the genomes of culturable bacteria, as well as in the wastewater metagenome of the Central Wastewater Treatment Plant in Koziegłowy (Poland). Moreover, we estimated the presence of pathogenic Gram-positive bacteria in wastewater based on analysis of species-specific virulence genes in the wastewater metagenome. The results show that the final effluent contains alarm pathogens with particularly dangerous mechanisms of antibiotic resistance, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). We also noticed that during the wastewater treatment, there is an increase in the frequency of MRSA and VRE. Furthermore, the results prove the effective removal of vanA, but at the same time show that wastewater treatment increases the relative abundance of mecA and virulence genes (groES and sec), indicating the presence of clinical pathogens E. faecalis and S. aureus in the effluent released to surface waters. We also observed an increase in the relative abundance of mecA and vanA genes already in the aeration tank, which suggests accumulation of contaminants affecting enhanced selection and HGT processes in the activated sludge. Moreover, we found a relation between the taxonomic composition and the copy number of ARGs as well as the presence of pathogens at various stages of wastewater treatment. The presence of clinically relevant pathogens, ARB, including multi-resistant bacteria, and ARGs in the effluent indicates that wastewater treatment plant play a key role in the existence of pathogens and antimicrobial resistance spreading pathway in the environment and human communities, which is a direct threat to public health and environmental protection.

Prevalence, antibiotic resistance and virulence of Enterococcus spp. from wastewater treatment plant effluent and receiving waters in South Africa

Poorly operating wastewater treatment plants (WWTPs) result in faecal pollution of receiving waters, posing a health risk to humans and animals. The aim of this study was to determine the antimicrobial resistance patterns and presence of virulent genes in Enterococcus spp. isolated from three WWTPs' final effluent and receiving waters in the North West Province, South Africa. Sixty-three Enterococcus spp. were identified and their antimicrobial susceptibility, as well as the presence of five virulence genes, determined. The antibiotic inhibition zone diameter data were subject to cluster analysis. Sixty-eight percent of the screened Enterococcus spp. were resistant to three or more antibiotics and harboured plasmids. Five virulence genes were detected and six multi-virulence profiles observed. Cluster analysis indicated groupings of isolates from all three effluent points downstream together, and between plants 1 and 2 together. The findings of this study have demonstrated that Enterococcus spp. harbouring virulence factors and plasmids that mediate multiple antibiotic resistance are present in effluent and receiving water systems that support various social needs. This is a cause for concern and it is recommended that Enterococcus be used as an additional faecal indicator when microbiological quality of water is assessed.

Monitoring antibiotic resistomes and bacterial microbiomes in the aerosols from fine, hazy, and dusty weather in Tianjin, China using a developed high-volume tandem liquid impinging sampler

Accurate quantification of the airborne antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is critically important to assess their health risks. However, the currently widely used high-volume filter sampler (HVFS) often causes the desiccation of the sample, interfering with subsequent bacterial culture. To overcome this limitation, a high-volume tandem liquid impinging sampler (HVTLIS) was developed and optimized to investigate the airborne bacterial microbiomes and antibiotic resistomes under different weathers in Tianjin, China. Results revealed that HVTLIS can capture significantly more diverse culturable bacteria, ARB, and ARGs than HVFS. Compared with fine and hazy weathers, dusty weather had significantly more diverse and abundant airborne bacteria, ARGs, and human opportunistic pathogens with the resistance to last-resort antibiotics of carbapenems and polymyxin B, implicating a potential human health threat of dusty bioaerosols. Intriguingly, we represented the first report of Saccharibacteria predominance in the bioaerosol, demonstrating that the potential advantage of HVTLIS in collecting airborne microbes.

Antibiotic resistant and extended-spectrum β-lactamase producing faecal coliforms in wastewater treatment plant effluent

Wastewater treatment plants (WWTPs) provide optimal conditions for the maintenance and spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In this work we describe the occurrence of antibiotic resistant faecal coliforms and their mechanisms of antibiotic resistance in the effluent of two urban WWTPs in Ireland. This information is critical to identifying the role of WWTPs in the dissemination of ARB and ARGs into the environment. Effluent samples were collected from two WWTPs in Spring and Autumn of 2015 and 2016. The bacterial susceptibility patterns to 13 antibiotics were determined. The phenotypic tests were carried out to identify AmpC or extended-spectrum β-lactamase (ESBL) producers. The presence of ESBL genes were detected by PCR. Plasmids carrying ESBL genes were transformed into Escherichia coli DH5α recipient and underwent plasmid replicon typing to identify incompatibility groups. More than 90% of isolated faecal coliforms were resistant to amoxicillin and ampicillin, followed by tetracycline (up to 39.82%), ciprofloxacin (up to 31.42%) and trimethoprim (up to 37.61%). Faecal coliforms resistant to colistin (up to 31.62%) and imipenem (up to 15.93%) were detected in all effluent samples. Up to 53.98% of isolated faecal coliforms expressed a multi-drug resistance (MRD) phenotype. AmpC production was confirmed in 5.22% of isolates. The ESBL genes were confirmed for 11.84% of isolates (9.2% of isolates carried bla_TEM, 1.4% bla_SHV-12, 0.2% bla_CTX-M-1 and 1% bla_CTX-M-15). Plasmids extracted from 52 ESBL isolates were successfully transformed into recipient E. coli. The detected plasmid incompatibility groups included the IncF group, IncI1, IncHI1/2 and IncA/C. These results provide evidence that treated wastewater is polluted with ARB and MDR faecal coliforms and are sources of ESBL-producing, carbapenem and colistin resistant Enterobacteriaceae.

Eutrophication and Related Antibiotic Resistance of Enterococci in the Minjiang River, China

Antimicrobial resistance (AMR) in the aquatic environment has received increasing attention in recent years, and growing eutrophication problems may contribute to AMR in aquatic ecosystems. To evaluate whether and how eutrophication affects AMR, 40 surface water samples were collected from the Minjiang River, Fujian Province, China. Total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD_Mn) were measured as eutrophication factors. Additionally, enterococci species were isolated and their resistance to six common antibiotics was tested. Eutrophication generally showed a trend of increasing with the flow direction of the Minjiang River, with 25 sites (62.5%) having a TN/TP value over the Redfield value (16:1), which indicated that eutrophication in this region was of phosphorus limitation. High nutrition sites were in or near urban areas. Poor quality water was found in the middle and lower reaches of the Minjiang River system. The resistance frequency of 40 enterococci isolates to the six antibiotics tested was as follows: oxytetracycline > erythromycin > ciprofloxacin > chloramphenicol > ampicillin > vancomycin (70, 50, 17.5, 12.5, 2.5, 0%), and the multi-resistant rate reached 50% with eight resistance phenotypes. AMR also increased along the direction of water flow downstream, and most of the sites with the highest AMR were in or near urban areas, as was true for nutrition levels. Positive correlations between AMR and eutrophication factors (TN, TP, and COD_Mn) were identified using the Pearson's correlation coefficient, and TN/TP generally was negatively related to AMR. These results indicated that eutrophication may induce or selective for resistance of water-borne pathogens to antibiotics, with a high resistance level and a wide resistance spectrum.

Cell-Free DNA: An Underestimated Source of Antibiotic Resistance Gene Dissemination at the Interface Between Human Activities and Downstream Environments in the Context of Wastewater Reuse

The dissemination of antimicrobial resistance (AMR) is one of the biggest challenges faced by mankind in the public health domains. It is currently favored by a lack of confinement between waste disposal and food production in the environmental compartment. To date, much effort has been devoted into the elucidation and control of cell-associated propagation of AMR. However, substantial knowledge gaps remain on the contribution of cell-free DNA to promote horizontal transfers of resistance genes in wastewater and downstream environments. Cell free DNA, which covers free extracellular DNA (exDNA) as well as DNA encapsulated in vesicles or bacteriophages, can persist after disinfection and promote gene transfer in the absence of physical and temporal contact between a donor and recipient bacteria. The increasing water scarcity associated to climatic change requires developing innovative wastewater reuse practices and, concomitantly, a robust evaluation of AMR occurrence by implementing treatment technologies able to exert a stringent control on AMR propagation in downstream environments exposed to treated or non-treated wastewater. This necessarily implies understanding the fate of ARGs on various forms of cell-free DNA, especially during treatment processes that are permissive to their formation. We propose that comprehensive approaches, investigating both the occurrence of ARGs and their compartmentalization in different forms of cellular or cell-free associated DNA should be established for each treatment technology. This should then allow selecting and tuning technologies for their capacity to limit the propagation of ARGs in any of their forms.

Mitigation of antibiotic resistance in a pilot-scale system treating wastewater from high-speed railway trains

Wastewater from high-speed railway trains represents a mobile reservoir of microorganisms with antibiotic resistance. It harbors abundant and diverse antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). This study investigated the removal of ARB and ARGs in a pilot-scale reactor, which consisted of an anaerobic/anoxic/oxic process, anaerobic/anoxic/aerobic process, and ozone-based disinfection to treat 1 m³/day wastewater from an electric multiple unit high-speed train. Further, the high prevalence of two mobile genetic elements (intI1 and Tn916/615) and five ARGs (tetA, tetG, qnrA, qnrS, bla_NDM-1, and ermF) was investigated using quantitative PCR. Significant positive correlations between ARGs (tetA, bla_NDM-1, and qnrA) and intI1 were identified (R² of 0.94, 0.85, and 0.70, respectively, P < 0.01). Biological treatment could significantly reduce Tn916/1545 (2.57 logs reduction) and Enterococci (2.56 logs reduction of colony forming unit (CFU)/mL), but the qnrS abundance increased (1.19 logs increase). Ozonation disinfection could further significantly decrease ARGs and Enterococci in wastewater, with a reduction of 1.67-2.49 logs and 3.16 logs CFU/mL, respectively. Moreover, food-related bacteria families which may contain opportunistic or parasitic pathogens (e.g., Moraxellaceae, Carnobacteriaceae, and Ruminococcaceae) were detected frequently. Enterococci filtered in this study shows multi-antibiotic resistance. Our study highlights the significance to mitigate antibiotic resistance from wastewater generated from high-speed railway trains, as a mobile source.

Treatment enhances the prevalence of antibiotic-resistant bacteria and antibiotic resistance genes in the wastewater of Sri Lanka, and India

Wastewater treatment plants (WWTPs) are being debated for being the hot spots for the development of antibiotic resistance in pathogenic microbial communities. We observed the prevalence of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARG), and multidrug resistance (MDR) in two municipal WWTPs and one hospital WWTP in Western and Southern Sri Lanka, and compared the results with particular reference to Indian and the World scenario to trace the imprints of treatment on ARB and ARG. Result suggests that although wastewater treatment resulted in higher than 1.06 log Escherichia coli (E. coli) reduction at all WWTPs, yet the percent of E. coli resistant to most of the antibiotics increased from influent to effluent. Higher prevalence of ARB, ARG, and MDR were noted in hospital WWTP owing to the higher antibiotic concentrations used and excreted by the patients. With reference to India, the WWTPs in Sri Lanka showed more ARB and a consistent increase in its percentages after the treatment but were less resistant to Fluoroquinolone (FQ). E. coli strains isolated from each location of both countries showed multidrug resistance, which has increased after the treatment and was strongly correlated with FQ in every WWTP. Resistant genes for Fluoroquinolone (FQ) (aac-(6')-1b-cr, qnrB, qnrS), β-lactams (ampC), and sulphonamides (sul1) were common in all the wastewaters except additional parC gene in the hospital effluent of Sri Lanka, implying much higher resistance for quinolones, especially for Ciprofloxacin. Multivariate statistical treatments suggest that effluent showed higher loadings and association for MDR/ARB, where pH change and more extensive interaction with metals during the treatment processes seem to have profound effects.

The effects of ultraviolet disinfection on vancomycin-resistant Enterococcus faecalis

The emergence of vancomycin-resistant Enterococcus faecalis (E. faecalis) in water is threatening the health of human beings. The effect of ultraviolet disinfection on vancomycin-resistant E. faecalis, including the effectiveness, photoreactivation and dark repair of E. faecalis, and the deactivation mechanism were investigated in this work. Ultraviolet disinfection could quickly inactivate the target antibiotic resistant bacterium (ARB), E. faecalis, and it caused damage to the cell membrane and induced the decrease of the total adenosine triphosphate (ATP) content and the superoxide dismutase (SOD) activity significantly (p < 0.05). E. faecalis could reactivate after ultraviolet disinfection especially under light conditions. Furthermore, the removal of the selected antibiotic resistance gene (ARG), vanB, by ultraviolet radiation and the effect on the vancomycin resistance of E. faecalis were investigated, which showed that ultraviolet disinfection had no significant effect on the vancomycin resistance of E. faecalis (p > 0.05).

Comparative genomics of multidrug-resistant Enterococcus spp. isolated from wastewater treatment plants

BACKGROUND

Wastewater treatment plants (WWTPs) are considered hotspots for the environmental dissemination of antimicrobial resistance (AMR) determinants. Vancomycin-Resistant Enterococcus (VRE) are candidates for gauging the degree of AMR bacteria in wastewater. Enterococcus faecalis and Enterococcus faecium are recognized indicators of fecal contamination in water. Comparative genomics of enterococci isolated from conventional activated sludge (CAS) and biological aerated filter (BAF) WWTPs was conducted.

RESULTS

VRE isolates, including E. faecalis (n = 24), E. faecium (n = 11), E. casseliflavus (n = 2) and E. gallinarum (n = 2) were selected for sequencing based on WWTP source, species and AMR phenotype. The pangenomes of E. faecium and E. faecalis were both open. The genomic fraction related to the mobilome was positively correlated with genome size in E. faecium (p < 0.001) and E. faecalis (p < 0.001) and with the number of AMR genes in E. faecium (p = 0.005). Genes conferring vancomycin resistance, including vanA and vanM (E. faecium), vanG (E. faecalis), and vanC (E. casseliflavus/E. gallinarum), were detected in 20 genomes. The most prominent functional AMR genes were efflux pumps and transporters. A minimum of 16, 6, 5 and 3 virulence genes were detected in E. faecium, E. faecalis, E. casseliflavus and E. gallinarum, respectively. Virulence genes were more common in E. faecalis and E. faecium, than E. casseliflavus and E. gallinarum. A number of mobile genetic elements were shared among species. Functional CRISPR/Cas arrays were detected in 13 E. faecalis genomes, with all but one also containing a prophage. The lack of a functional CRISPR/Cas arrays was associated with multi-drug resistance in E. faecium. Phylogenetic analysis demonstrated differential clustering of isolates based on original source but not WWTP. Genes related to phage and CRISPR/Cas arrays could potentially serve as environmental biomarkers.

CONCLUSIONS

There was no discernible difference between enterococcal genomes from the CAS and BAF WWTPs. E. faecalis and E. faecium have smaller genomes and harbor more virulence, AMR, and mobile genetic elements than other Enterococcus spp.

Quantification and Multidrug Resistance Profiles of Vancomycin-Resistant Enterococci Isolated from Two Wastewater Treatment Plants in the Same Municipality

Wastewater treatment plants (WWTPs) are points of control for the environmental dissemination of antimicrobial resistant bacteria. Vancomycin-resistant enterococci (VRE) were used as indicators of antimicrobial resistance (AMR) in two WWTPs (biologically aerated filter (BAF) and conventional activated sludge (CAS)) in the same municipality. The removal and abundance of enterococci and VRE as well as the species and antimicrobial resistance profiles of VRE were assessed. Enterococci and VRE from the primary and final effluents were enumerated. Results were assessed from an ecological context. VRE was not selected for by either WWTP but the BAF system outperformed the CAS system for the removal of enterococci/VRE. Enterococcus faecalis (n = 151), E. faecium (n = 94) and E. casseliflavus/E. gallinarum (n = 59) were the dominant VRE species isolated. A decrease in levofloxacin resistance in enterococci was observed in the BAF WWTP. An increase in nitrofurantoin resistant (p < 0.001) and a decrease in quinupristin/dalfopristin (p = 0.003) and streptomycin (p = 0.022) resistant enterococci were observed in the CAS WWTP, corresponding to a shift of VRE from E. faecalis to E. faecium. Wastewater treatment processes can be managed to limit the dissemination of antimicrobial resistance determinants into the surrounding environment.

Enhanced inactivation of antibiotic-resistant bacteria isolated from secondary effluents by g-C3N4 photocatalysis

The extensive use of antibiotics has resulted in the development of antibiotic-resistant bacteria (ARB), which may not be completely removed by traditional wastewater treatment processes. More effective approaches to disinfection are needed to prevent the release of ARB into the surface water. The metal-free photocatalyst graphitic carbon nitride (g-C₃N₄) has aroused great interest as a possible agent for water and wastewater treatment, due to its low cytotoxicity and photoactivity with visible light. In this study, the efficacy of g-C₃N₄ was assessed as a possible means to enhance ARB inactivation by irradiation. ARB were isolated and purified from secondary effluents in 4 municipal wastewater treatment plants. Of these, 4 typical multi-drug ARB isolates, belonging to Enterobacteriaceae, were selected for irradiation experiments. Inactivation was seen to increase with irradiation time. At 60 min, the inactivation of the 4 ARB isolates by light at > 300 nm and > 400 nm was in the range of 0.25-0.39 log and 0.16-0.19 log, respectively. The use of g-C₃N₄-mediated photocatalysis at the same wavelengths significantly enhanced that to 0.64-1.26 log and 0.31-0.41 log, respectively. The antibiotic susceptibility of the ARB isolates remained unchanged either prior to or after irradiation and was independent of photon fluence, reaction time, and the presence of g-C₃N₄. This study establishes a baseline for understanding the effectiveness of g-C₃N₄ photocatalysis on inactivation of ARB in wastewaters and lays the foundation for further improvement in the use of photocatalysis for wastewater treatment.

Metagenomic and Resistome Analysis of a Full-Scale Municipal Wastewater Treatment Plant in Singapore Containing Membrane Bioreactors

Reclaimed water provides a water supply alternative to address problems of scarcity in urbanized cities with high living densities and limited natural water resources. In this study, wastewater metagenomes from 6 stages of a wastewater treatment plant (WWTP) integrating conventional and membrane bioreactor (MBR) treatment were evaluated for diversity of antibiotic resistance genes (ARGs) and bacteria, and relative abundance of class 1 integron integrases (intl1). ARGs confering resistance to 12 classes of antibiotics (ARG types) persisted through the treatment stages, which included genes that confer resistance to aminoglycoside [aadA, aph(6)-I, aph(3')-I, aac(6')-I, aac(6')-II, ant(2″)-I], beta-lactams [class A, class C, class D beta-lactamases (bla OXA)], chloramphenicol (acetyltransferase, exporters, floR, cmIA), fosmidomycin (rosAB), macrolide-lincosamide-streptogramin (macAB, ereA, ermFB), multidrug resistance (subunits of transporters), polymyxin (arnA), quinolone (qnrS), rifamycin (arr), sulfonamide (sul1, sul2), and tetracycline (tetM, tetG, tetE, tet36, tet39, tetR, tet43, tetQ, tetX). Although the ARG subtypes in sludge and MBR effluents reduced in diversity relative to the influent, clinically relevant beta lactamases (i.e., bla KPC, bla OXA) were detected, casting light on other potential point sources of ARG dissemination within the wastewater treatment process. To gain a deeper insight into the types of bacteria that may survive the MBR removal process, genome bins were recovered from metagenomic data of MBR effluents. A total of 101 close to complete draft genomes were assembled and annotated to reveal a variety of bacteria bearing metal resistance genes and ARGs in the MBR effluent. Three bins in particular were affiliated to Mycobacterium smegmatis, Acinetobacter Iwoffii, and Flavobacterium psychrophila, and carried aquired ARGs aac(2')-Ib, bla OXA-278, and tet36 respectively. In terms of indicator organisms, cumulative log removal values (LRV) of Escherichia coli, Enterococci, and P. aeruginosa from influent to conventional treated effluent was lower (0-2.4), compared to MBR effluent (5.3-7.4). We conclude that MBR is an effective treatment method for reducing fecal indicators and ARGs; however, incomplete removal of P. aeruginosa in MBR treated effluents (<8 MPN/100 mL) and the presence of ARGs and intl1 underscores the need to establish if further treatment should be applied prior to reuse.

Antimicrobial-Resistant Escherichia coli from Environmental Waters in Northern Colorado

Waterborne Escherichia coli are a major reservoir of antimicrobial resistance (AMR), including but not limited to extended-spectrum beta-lactamase (ESBL) and Klebsiella pneumoniae carbapenemase (KPC) mechanisms. This study quantified and described ESBL- and KPC-producing E. coli in Northern Colorado from sewer water, surface water, and influent and effluent wastewater treatment sources. Total detected bacteria and E. coli abundances, and the percentages that contain ESBL and/or KPC, were compared between water sources. Seventy E. coli isolates from the various waters had drug resistance validated with a panel of 17 antibiotics using a broth microdilution assay. The diverse drug resistance observed across E. coli isolates was further documented by polymerase chain reaction of common ESBL genes and functional relatedness by PhenePlate assay-generated dendrograms (n=70). The total E. coli abundance decreased through the water treatment process as expected, yet the percentages of E. coli harboring ESBL resistance were increased (1.70%) in surface water. Whole-genome sequencing analysis was completed for 185 AMR genes in wastewater E. coli isolates and confirmed the presence of diverse AMR gene classes (e.g., beta-lactams and efflux pumps) in isolate genomes. This study completed surveillance of AMR patterns in E. coli that reside in environmental water systems and suggests a role for integrating both phenotypic and genotypic profiling beyond ESBL and KPC mechanisms. AMR screening via multiple approaches may assist in the prevention of drug-resistant E. coli spread from waters to animals and humans.

Occurrence of super antibiotic resistance genes in the downstream of the Yangtze River in China: Prevalence and antibiotic resistance profiles

The super antibiotic resistance genes (SARGs) demonstrate more severe threats than other antibiotic resistance genes while have not received enough attention in the environment. The study explored the prevalence and the antibiotic tolerance profiles of two typical SARGs, MCR-1 and NDM-1, and their hosting bacteria in the downstream of the Yangtze River and the nearby wastewater treatment plant (WWTP) and drinking water treatment plant (DWTP). Results indicated that MCR-1 and NDM-1 were prevalent in the influent and biological units of the WWTP. Their hosting bacteria were effectively removed, but 2.49 × 10⁸ copies/L MCR-1 and 7.00 × 10⁶ copies/L NDM-1 were still persistent in the effluent. In the Yangtze River, MCR-1 and NDM-1 were detected with higher abundance and antibiotic tolerance than the WWTP effluent and were significantly affected by nearby water contamination and human activities. In the DWTP, MCR-1 and NDM-1 were detected with average values 5.56 × 10⁷ copies/L and 2.14 × 10⁵ copies/L in the influent. Their hosting bacteria were undetectable in the effluent, but the two SARGs were still persistent with 1.39 × 10⁷ copies/L and 6.29 × 10⁴ copies/L, and were greatly enriched in the sludge. Molecular ecological networks demonstrated wide hosting relationships between MCR-1/NDM-1 and bacteria community in the DWTP. Redundancy analysis found that MCR-1 positively correlated with COD and NH₃-N, while negatively correlated with turbidity. Additionally, MCR-1 hosting bacteria positively correlated with NO₃^--N and negatively correlated with COD and NH₃-N. NDM-1 positively correlated with turbidity and NDM-1 hosting bacteria positively correlated with COD and NO₂^--N. The study demonstrated that the WWTP could not effectively remove SARGs with high amount of them being discharged into the Yangtze River. Then they were transported into the DWTP and the persistent SARGs in the effluent would probably be transferred into human, thus imposing great threats on public health.

Occurrence, diversity, and persistence of antibiotic resistant enterococci in full-scale constructed wetlands treating urban wastewater in Sicily

Enterococci isolated from different sites of an urban wastewater treatment plant (consisting of three horizontal subsurface flow constructed wetlands) were investigated. One-hundred-thirty isolates were identified at species level and tested for resistance to eleven antibiotics, by microdilution method, and their clonal relatedness was established by SmaI-PFGE analysis. Results highlighted the persistence of enterococcal population in all effluents and the dominance of E. faecium species. A high incidence of antibiotic resistance against erythromycin, chloramphenicol, rifampicin and ampicillin was observed, with 120 strains (93%) showing a multi-drug-resistance. Numerous pulso-types with a unique pattern were detected indicating a high diversity within enterococcal population. The recurrence of some pulso-types in different effluents was disclosed and, within the same pulso-types, different resistance patterns were observed. Comparing the MIC values of strains from inlet and outlet, different trends were observed, highlighting a certain variability among constructed wetlands in affecting the antibiotic resistance among enterococcal population.

Evaluation of antibiotic resistant lactose fermentative opportunistic pathogenic Enterobacteriaceae bacteria and blaTEM-2 gene in cephalosporin wastewater and its discharge receiving river

This study investigated the concentration of cephalosporin, the resistant levels of lactose fermentative opportunistic pathogenic Enterobacteriaceae bacteria (LFOPEB) against seven antibiotics and one cephalosporin-resistant gene in cephalosporin wastewater (CPWW) treatment plant and its discharge receiving river. Although large numbers of bacteria have been removed during the CPWW treatment process, the antibiotic resistant rates of the isolates to β-lactam antibiotics significantly increased (p = 0.032) after treatment, while the percentage of resistant LFOPEB to non-β-lactam antibiotics did not change dramatically. Furthermore, the discharge of the effluent of CPWW treatment plant (CPWW_eff) led to an obvious increase in the percentages of β-lactam antibiotic-resistant LFOPEB and relative abundance of the blaTEM-2 gene in the downstream receiving river (RW_down) in comparison with those in the upstream receiving river (RW_up). The antibiotic resistant phenotypes of isolates in the influent of CPWW treatment plant (CPWW_in), CPWW_eff and RW_down appeared to be seriously affected by the cephalosporin residues, which suggested that main antibiotic resistance phenotypes in antibiotic contaminated water were closely associated with its antibiotic composition. Therefore, CPWW treatment process has been proved to result in selective growth of ARB and proliferation of ARG. Besides, CPWW_eff was also proved to be an important supplier of ARB and ARG to the receiving river.

River water analysis using a multiparametric approach: Portuguese river as a case study

The Ave River in northern Portugal has a history of riverbanks and water quality degradation. The river water quality was assessed by physicochemical, biological (macroinvertebrates) and microbiological (Enterococcus spp. and Escherichia coli) parameters in six locations (A-F, point A being the nearest to the source) throughout its course during a year. Epilithic biofilms were studied through polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). Antimicrobial susceptibility testing helped with selecting isolates (n = 149 E. coli and n = 86 enterococci) for further genetic characterization. Pursuant to physicochemical and macroinvertebrates-based parameters, the river water was of reasonable quality according to European legislation (Directive 2000/60/EC). However, the microbiological analysis showed increased fecal contamination downstream from point C. At point D, four carbapenem-resistant E. coli isolates were recovered. Paradoxically, point D was classified as a point of 'Good Water Quality' according to macroinvertebrates results. Point F presented the highest contamination level and incidence of multidrug-resistant (MDR) isolates in the water column (13 MDR enterococci out of 39 and 33 MDR E. coli out of 97). Epilithic biofilms showed higher diversity in pristine points (A and B). Thus, biological and microbiological parameters used to assess the water quality led to divergent results; an outcome that reinforces the need for a holistic evaluation.

Prevalence and transmission of antibiotic resistance and microbiota between humans and water environments

The transmission routes for antibiotic resistance genes (ARGs) and microbiota between humans and water environments is poorly characterized. Here, we used high-throughput qPCR analyses and 16S rRNA gene sequencing to examine the occurrence and abundance of antibiotic resistance genes and microbiota in both healthy humans and associated water environments from a Chinese village. Humans carried the most diverse assemblage of ARGs, with 234 different ARGs being detected. The total abundance of ARGs in feces, on skin, and in the effluent from domestic sewage treatment systems were approximately 23, 2, and 7 times higher than their abundance in river samples. In total, 53 ARGs and 28 bacteria genera that were present in human feces could also be found in the influent and effluent of rural sewage treatment systems, and also downstream of the effluent release point. We identified the bacterial taxa that showed a significant association with ARGs (P < 0.01, r > 0.8) by network analysis, supporting the idea that these bacteria could carry some ARGs and transfer between humans and the environment. Analysis of ARGs and microbiota in humans and in water environments helps to define the transmission routes and dynamics of antibiotic resistance within these environments. This study highlights human contribution to the load of ARGs into the environment and suggests means to prevent such dissemination.

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.

Human and veterinary antibiotics during composting of sludge or manure: Global perspectives on persistence, degradation, and resistance genes

Wastewater treatment plant effluent, sludge and manure are the main sources of contamination by antibiotics in the whole environment compartments (soil, sediment, surface and underground water). One of the major consequences of the antibiotics discharge into the environment could be the prevalence of a bacterial resistance to antibiotic. In this review, four groups of antibiotics (Tetracyclines, Fluoroquinolones, Macrolides and Sulfonamides) were focused for the background on their wide spread occurrence in sludge and manure and for their effects on several target and non-target species. The antibiotics concentrations range between 1 and 136,000 μg kg^-1 of dry matter in sludge and manure, representing a potential risk for the human health and the environment. Composting of sludge or manure is a well-known and used organic matter stabilization technology, which could be effective in reducing the antibiotics levels as well as the antibiotic resistance genes. During sludge or manure composting, the antibiotics removals range between 17-100%. The deduced calculated half-lives range between 1-105 days for most of the studied antibiotics. Nevertheless, these removals are often based on the measurement of concentration without considering the matter removal (lack of matter balance) and very few studies are emphasized on the removal mechanisms (biotic/abiotic, bound residues formation) and the potential presence of more or less hazardous transformation products. The results from the few studies on the fate of the antibiotic resistance genes during sludge or manure composting are still inconsistent showing either decrease or increase of their concentration in the final product. Whether for antibiotic or antibiotic resistance genes, additional researches are needed, gathering chemical, microbiological and toxicological data to better understand the implied removal mechanisms (chemical, physical and biological), the interactions between both components and the environmental matrices (organic, inorganic bearing phases) and how composting process could be optimized to reduce the discharge of antibiotics and antibiotic resistance genes into the environment.

Antimicrobial-resistant CC17 Enterococcus faecium: The past, the present and the future

Enterococcus faecium is a robust opportunistic pathogen that is most commonly found as a commensal of the human and animal gut but can also survive in the environment. Since the introduction and use of antimicrobials, E. faecium has been found to rapidly acquire resistance genes that, when expressed, can effectively circumvent the effects of most antimicrobials. The rapid acquisition of multiple antimicrobial resistances has led to the adaptation of specific E. faecium clones in the hospital environment, collectively known as clonal complex 17 (CC17). CC17 E. faecium are responsible for a significant proportion of hospital-associated infections, which can cause severe morbidity and mortality. Here we review the history of E. faecium from commensal to a significant hospital-associated pathogen, its robust phenotypic characteristics, commonly used laboratory typing schemes, and antimicrobial resistances with a focus on vancomycin and its associated mechanism of resistance. Finally, we review the global epidemiology of vancomycin-resistant E. faecium and potential solutions to problems faced in public health.

Survival of antibiotic resistant bacteria following artificial solar radiation of secondary wastewater effluent

Urban wastewater treatment plant effluents represent one of the major emission sources of antibiotic-resistant bacteria (ARB) in natural aquatic environments. In this study, the effect of artificial solar radiation on total culturable heterotrophic bacteria and ARB (including amoxicillin-resistant, ciprofloxacin-resistant, rifampicin-resistant, sulfamethoxazole-resistant, and tetracycline-resistant bacteria) present in secondary effluent was investigated. Artificial solar radiation was effective in inactivating the majority of environmental bacteria, however, the proportion of strains with ciprofloxacin-resistance and rifampicin-resistance increased in the surviving populations. Isolates of Pseudomonas putida, Serratia marcescens, and Stenotrophomonas maltophilia nosocomial pathogens were identified as resistant to solar radiation and to at least three antibiotics. Draft genome sequencing and typing revealed isolates carrying multiple resistance genes; where S. maltophilia (resistant to all studied antibiotics) sequence type was similar to strains isolated in blood infections. Results from this study confirm that solar radiation reduces total bacterial load in secondary effluent, but may indirectly increase the relative abundance of ARB.

What happens with organic micropollutants during UV disinfection in WWTPs? A global perspective from laboratory to full-scale

The phototransformation of 18 organic micropollutants (OMPs) commonly detected in wastewater treatment plant (WWTP) effluents was examined attempting to explain their fate during UV disinfection in WWTPs. For this purpose, a lab-scale UV reactor (lamp emitting at 254nm) was used to study the influence of the operational conditions (UV dose, temperature and water matrix) on OMPs abatement and disinfection efficiency. Chemical properties of OMPs and the quality of treated effluent were identified as key factors affecting the phototransformation rate of these compounds. Sampling campaigns were carried out at the inlet and outlet of UV systems of three WWTPs, and the results evidenced that only the most photosensitive compounds, such as sulfamethoxazole and diclofenac, are eliminated. Therefore, despite UV treatment is an effective technology to phototransform OMPs, the UV doses typically applied for disinfection (10-50mJ/cm²) are not sufficient to remove them. Consequently, small modifications (increase of UV dose, use of catalysts) should be applied in WWTPs to enhance the abatement of OMPs in UV systems.

Cell-free DNA: A Neglected Source for Antibiotic Resistance Genes Spreading from WWTPs

Cell-associated ARGs in wastewater treatment plants (WWTPs) has been concerned, however, cell-free ARGs in WWTPs was rarely studied. In this study, the abundances of four representative ARGs, sulII, tetC, bla_PSE-1, and ermB, in a large municipal WWTP were investigated in both cell-associated and cell-free fractions. Cell-associated ARGs was the dominant ARGs fraction in the raw wastewater. After biological treatment, sludge settling, membrane filtration, and disinfection, cell-associated ARGs were substantially reduced, though the ratios of ARG/16S rRNA gene were increased with disinfection. Cell-free ARGs persisted in the WWTP with a removal of 0.36 log to 2.68 logs, which was much lower than the removal of cell-associated ARGs (3.21 logs to 4.14 logs). Therefore, the abundance ratio of cell-free ARGs to cell-associated ARGs increased from 0.04-1.59% to 2.00-1895.08% along the treatment processes. After 25-day-storage, cell-free ARGs in both biological effluent and disinfection effluent increased by 0.14 log to 1.99 logs and 0.12 log to 1.77 logs respectively, reflecting the persistence and low decay rate of cell-free ARGs in the discharge water. Therefore, cell-free ARGs might be a kind of important but previously neglected pollutant from WWTPs, which added potential risks to the effluent receiving environments.

The potential implications of reclaimed wastewater reuse for irrigation on the agricultural environment: The knowns and unknowns of the fate of antibiotics and antibiotic resistant bacteria and resistance genes - A review

The use of reclaimed wastewater (RWW) for the irrigation of crops may result in the continuous exposure of the agricultural environment to antibiotics, antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In recent years, certain evidence indicate that antibiotics and resistance genes may become disseminated in agricultural soils as a result of the amendment with manure and biosolids and irrigation with RWW. Antibiotic residues and other contaminants may undergo sorption/desorption and transformation processes (both biotic and abiotic), and have the potential to affect the soil microbiota. Antibiotics found in the soil pore water (bioavailable fraction) as a result of RWW irrigation may be taken up by crop plants, bioaccumulate within plant tissues and subsequently enter the food webs; potentially resulting in detrimental public health implications. It can be also hypothesized that ARGs can spread among soil and plant-associated bacteria, a fact that may have serious human health implications. The majority of studies dealing with these environmental and social challenges related with the use of RWW for irrigation were conducted under laboratory or using, somehow, controlled conditions. This critical review discusses the state of the art on the fate of antibiotics, ARB and ARGs in agricultural environment where RWW is applied for irrigation. The implications associated with the uptake of antibiotics by plants (uptake mechanisms) and the potential risks to public health are highlighted. Additionally, knowledge gaps as well as challenges and opportunities are addressed, with the aim of boosting future research towards an enhanced understanding of the fate and implications of these contaminants of emerging concern in the agricultural environment. These are key issues in a world where the increasing water scarcity and the continuous appeal of circular economy demand answers for a long-term safe use of RWW for irrigation.

Antibiotic-Resistance Genes in Waste Water

Waste water and waste water treatment plants can act as reservoirs and environmental suppliers of antibiotic resistance. They have also been proposed to be hotspots for horizontal gene transfer, enabling the spread of antibiotic resistance genes between different bacterial species. Waste water contains antibiotics, disinfectants, and metals which can form a selection pressure for antibiotic resistance, even in low concentrations. Our knowledge of antibiotic resistance in waste water has increased tremendously in the past few years with advances in the molecular methods available. However, there are still some gaps in our knowledge on the subject, such as how active is horizontal gene transfer in waste water and what is the role of the waste water treatment plant in the environmental resistome? The purpose of this review is to briefly describe some of the main methods for studying antibiotic resistance in waste waters and the latest research and main knowledge gaps on the issue. In addition, some future research directions are proposed.

Occurrence of antibiotic resistance genes and mobile genetic elements in enterococci and genomic DNA during anaerobic digestion of pharmaceutical waste sludge with different pretreatments

Pharmaceutical waste sludge harbors large amounts of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), and it is necessary to study the reduction of ARGs and MGEs during sludge treatment. Therefore, the antibiotic resistance phenotypes and genotypes of enterococci, and the ARGs and MGEs in genomic DNA were investigated during anaerobic digestion (AD) with microwave (MW), thermal hydrolysis (TH) and ozone pretreatment. Results showed that sludge pretreatment increased the occurrence of the resistance phenotypes and genotypes of enterococci. During AD, the resistance of enterococci to macrolides decreased, except for in the MW-pretreated sludge. Horizontal gene transfer and co-occurrence of ermB and tetM in enterococci resulted in increased tetracycline resistance of enterococci throughout the sludge treatment. MGEs such as intI1, ISCR1 and Tn916/1545 had a significant effect on the distribution of ARGs. AD with pretreatment, especially TH pretreatment, resulted in greater ARGs and MGEs reduction and improved methane production.

Influence of Select Antibiotics on Vibrio fischeri and Desmodesmus subspicatus at μg L-1 Concentrations

The presence of pharmaceuticals in the aquatic environment is a contemporary reality and it is necessary to understand more about the effects of this presence on organisms. The purpose of this work was to assess the ecotoxicity of antibiotics metronidazole, nitrofurantoin, trimethoprim, and sulphamethoxazole (single and mixture) in Vibrio fischeri and Desmodesmus subspicatus at μg L^-1 concentrations. The evaluation of the toxic effect of the antibiotics on V. fischeri and D. subspicatus was based on fluorescence and bioluminescence tests, respectively, using nominal concentrations. When tested individually, the four antibiotics gave rise to a toxic effect on the evaluated organisms. Sulphamethoxazole caused a higher toxic effect on V. fischeri and D. subspicatus from 7.81 to 500 μg L^-1. Trimethoprim and sulphamethoxazole showed hormesis for the concentrations, which ranged from 7.81 to 62.5 μg L^-1. The mixture of antibiotics induced a toxic effect on the V. fischeri and D. subspicatus organisms (from 0.03 to 1 μg L^-1 concentrations) than when the antibiotics were evaluated individually. These results were significant since water quality problems are widespread all over the word, and emerging pollutants such as antibiotics have been detected in the aquatic environment in very low concentrations.

Characterization of antibiotic resistance genes in representative organic solid wastes: Food waste-recycling wastewater, manure, and sewage sludge

In this research, the distribution of antibiotic resistance genes (ARGs) was characterized in representative organic solid waste (OSW) in Korea: food waste-recycling wastewater (FRW), manure, and sewage sludge. The amounts of total ARG (gene copies/16S rRNA gene copies) was greatest in manure followed by sewage sludge and FRW. Interestingly, there were significantly different patterns in the diversity and mechanisms of ARGs. For example, a significant proportion of ARGs were tetracycline resistant genes in all the OSW (40.4-78.2%). β-lactam antibiotics resistant genes were higher in the FRW samples than in other types of OSW but sulfonamides resistant genes represented the greatest proportion in sludge. Regarding the characteristics of antibiotic resistance mechanisms, there was a relatively higher proportion of the ribosomal protection mechanism to tetracycline observed in the FRW and manure samples. However, tetracycline resistant genes with direct interaction were relatively higher in the sewage sludge samples. sul1 was the dominant subtype in all the OSW types and detection of ermB was observed although there was no ermC detected in sewage sludge. There were significant correlations between the occurrences of ARG subtypes: tetB and tetG in all OSW (P<0.01); tetE and tetQ only in sludge (P<0.01). The Class 1 integron-integrase gene (intI1) was significantly correlated with total ARGs only in manure and sludge (P<0.05), revealing potential horizontal gene transfer in these OSW.

Metagenomic insights into ultraviolet disinfection effects on antibiotic resistome in biologically treated wastewater

High-throughput sequencing-based metagenomic approaches were used to comprehensively investigate ultraviolet effects on the microbial community structure, and diversity and abundance of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in biologically treated wastewater. After ultraviolet radiation, some dominant genera, like Aeromonas and Halomonas, in the wastewater almost disappeared, while the relative abundance of some minor genera including Pseudomonas and Bacillus increased dozens of times. Metagenomic analysis showed that 159 ARGs within 14 types were detectable in the samples, and the radiation at 500 mJ/cm(2) obviously increased their total relative abundance from 31.68 ppm to 190.78 ppm, which was supported by quantitative real time PCR. As the dominant persistent ARGs, multidrug resistance genes carried by Pseudomonas and bacitracin resistance gene bacA carried by Bacillus mainly contributed to the ARGs abundance increase. Bacterial community shift and MGEs replication induced by the radiation might drive the resistome alteration. The findings may shed new light on the mechanism behind the ultraviolet radiation effects on antibiotic resistance in wastewater.