Persistence of antibiotic resistance genes and bacterial community changes in drinking water treatment system: From drinking water source to tap water

Removal behavior and key drivers of antibiotic resistance genes in two full-scale leachate treatment plants

Leachate is a critical reservoir of antibiotic resistance genes (ARGs) and its proper treatment is closely related to human health and ecosystem safety. Here, we used high-throughput qPCR to explore the removal behavior of ARGs in two full-scale leachate treatment plants (LTPs) where biological treatment and membrane filtration processes were integrated. A total of 286 ARGs and 55 mobile genetic elements (MGEs) were detected, with aminoglycoside, multidrug and MLSB resistance genes being the most prevalent and abundant. Anaerobic digestion was found to be an important pretreatment process for leachate, while anoxic/aerobic tanks in membrane bioreactor (MBR) acted as incubators for ARGs due to their significant proliferation effect on ARGs. Integrated membrane filtration (UF-NF-RO) excelled in ARGs removal with absolute abundances reduced by 3 to 6 orders of magnitude, from about 10⁹ copies/mL in raw leachate to 10³-10⁵ copies/mL in effluents. Our results also showed that leachate treatment processes significantly altered the composition of ARGs and bacterial communities. Procrustes analysis and network analysis revealed strong associations between microbes and ARGs, with several hub genes and bacterial genera identified. Structural equation models (SEMs) indicated that bacterial composition, MGEs and basic water properties were the key drivers shaping ARGs dynamics in the raw leachate, biological system and filtration system, respectively. Notably, several pathogens (e.g., Klebsiella, Vibrio, Aeromonas) were closely correlated with ARGs in raw leachate and may amplify the dissemination risks of ARGs. Moreover, insertion sequences in biological systems would accelerate the horizontal gene transfer of ARGs. In short, this study provides new insights into the mechanisms of ARGs removal and dissemination behavior in industrial-scale LTPs.

Spatial and temporal effects of fish feed on antibiotic resistance in coastal aquaculture farms

For the first time, both spatial and temporal effects of fish feed on changes in abundance of antibiotic resistance genes (ARGs) were investigated in South Korea via quantifying ARGs and analyzing physicochemical parameters in the influent (IN) and effluent before (BF) and 30 min after (AF) the fish feeding time of sixteen flow-through fish farms. The absolute abundance of ARGs in AF samples was 5 times higher than in BF and 12 times higher than in IN samples. Values of physicochemical parameters such as ammonia, total nitrogen, suspended solids and turbidity in the effluent significantly increased by 21.6, 4.2, 2.6 and 1.65 times, respectively, after fish feeding. Spatially, the fish farms on Jeju Island exhibited higher relative abundance (3.02 × 10^-4 - 6.1 × 10^-2) of ARGs compared to the farms in nearby Jeollanam-do (3.4 × 10^-5 - 8.3 × 10^-3). Seasonally, samples in summer and autumn showed a higher abundance of ARGs than in winter and spring. To assess risk to the food chain as well as public health, further studies are warranted to explore the pathogenic potential of these ARGs.

Metagenomic binning and assembled genome analysis revealed the distinct composition of resistome and mobilome in the Ili River

Rivers play an important role in receiving and transporting the resistome among different environmental compartments. However, the difference in resistome and mobilome between the water and sediment and their underlying mechanisms were still poorly understood. In this study, the Ili River, an important water source in the arid area of Central Asia, was selected as the studied target. The comprehensive profile of resistome and mobilome and their host in water and sediment were studied based on metagenomic binning and assembled genome (MAG) analysis. The relative abundance of resistome and mobilome in sediment were 28.0 - 67.8 × /Gb and 46.5 - 121.1 × /Gb, respectively, which were significantly higher than those in water (23.1 - 52.8 ×/Gb and 25.3 - 67.7 ×/Gb). Multidrug and macrolides-lincosamides-streptogramin (MLS) resistance genes were the main ARG types in both water and sediment from relative abundance. Transposases dominated the relative abundance of mobilome, followed by insert elements and integrases. Strong correlations were found between the relative abundance of resistome and mobilome (r > 0.6 and p < 0.01) in both water and sediment, indicating the mobilome played an important role in the propagation of resistome in the Ili River. The main hosts for multidrug resistance genes via MAG analysis differed in water (Alphaproteobacteria and Gammaproteobacteria) and sediment (Gammaproteobacteria). Distinct compositions of resistome and mobilome existed between water and sediment in the Ili River. Specificity-occupancy analysis of the differential resistome and mobilome showed that occurrence frequencies and habitat selections of the differential ARGs shaped the resistome of water and sediment. In contrast, habitat was the main driver that shaped the mobilome in the Ili River.

The formation of specific bacterial communities contributes to the enrichment of antibiotic resistance genes in the soil plastisphere

Soil serves as a major reservoir of both antibiotic resistance genes (ARGs) and microplastics. However, the characteristics of the antibiotic resistome in the soil plastisphere remain largely unknown. In this study, we used metagenomic approaches to reveal the changing patterns of ARGs and the bacterial community and their associations in response to three types of microplastics (light density polyethylene, LDPE; polypropylene, PP; polystyrene, PS) using particles 550 µm or 75 µm in diameter. The total ARG abundances significantly increased in the plastisphere and varied across plastic types. The LDPE plastisphere had the highest ARG total abundance and lowest Shannon diversity index, indicating that this plastic had the most severe negative impact on soil bacterial diversity. The PP plastisphere contained higher relative abundances of the pathogenic bacteria Acinetobacter johnsonii and Escherichia coli, demonstrating the higher pathogenic risk of the microbial communities enriched in the plastisphere. Specifically, multidrug resistance genes (ceoB and MuxB) co-existed with more than four microbial taxa, increasing the potential risk of ARG spread in pathogenic bacteria. These findings implied that the plastisphere acts as a hotspot for acquiring and spreading antibiotic resistance and may have long-term negative effects on the soil ecosystem and human health.

The elimination of cell-associated and non-cell-associated antibiotic resistance genes during membrane filtration processes: A review

With increasing water reuse as a sustainable water management strategy, antibiotic resistance genes (ARGs) which have been identified as emerging contaminants in wastewater are attracting global attentions. Given that wastewater treatment plants are now well-established as a sink and source of ARGs in both cell-associated and non-cell-associated forms, a need is acknowledged to reduce their proliferation and protect public health. Due to their different characteristics, cell-associated and non-cell-associated ARGs may have distinct responses to membrane filtration processes which are widely used as advanced treatment to the secondary effluent. This review improves the understanding of the abundance of cell-associated and non-cell-associated ARGs in wastewaters and the secondary effluents and compares the elimination of ARGs in cell-associated and non-cell-associated forms by low-pressure and high-pressure membrane filtration processes. The former process reduces the concentration of cell-associated ARGs by more than 2-logs on average. An increase of the retention efficiency of non-cell-associated ARGs is observed with decreasing molecular weight cut-offs in ultrafiltration. The high-pressure membrane filtration (i.e., nanofiltration and reverse osmosis) can effectively eliminate both cell-associated and non-cell-associated ARGs, with averagely more than 4.6-log reduction. In general, the two forms of ARGs can be removed from water by the membrane filtration processes via the effects of size exclusion, adsorption, and electrostatic repulsion. The size and conformation of cell-associated and non-cell-associated ARGs, characteristics of membranes, coexisting substances, and biofilm formation influence ARG retention. Accumulation and potential proliferation of cell-associated and non-cell-associated ARGs in foulants and concentrate and corresponding control strategies warrant future research.

Metagenomic shifts in mucus, tissue and skeleton of the coral Balanophyllia europaea living along a natural CO2 gradient

Using the Mediterranean coral Balanophyllia europaea naturally growing along a pH gradient close to Panarea island (Italy) as a model, we explored the role of host-associated microbiomes in coral acclimatization to ocean acidification (OA). Coral samples were collected at three sites along the gradient, mimicking seawater conditions projected for 2100 under different IPCC (The Intergovernmental Panel on Climate Change) scenarios, and mucus, soft tissue and skeleton associated microbiomes were characterized by shotgun metagenomics. According to our findings, OA induced functional changes in the microbiomes genetic potential that could mitigate the sub-optimal environmental conditions at three levels: i. selection of bacteria genetically equipped with functions related to stress resistance; ii. shifts in microbial carbohydrate metabolism from energy production to maintenance of cell membranes and walls integrity; iii. gain of functions able to respond to variations in nitrogen needs at the holobiont level, such as genes devoted to organic nitrogen mobilization. We hence provided hypotheses about the functional role of the coral associated microbiome in favoring host acclimatation to OA, remarking on the importance of considering the crosstalk among all the components of the holobiont to unveil how and to what extent corals will maintain their functionality under forthcoming ocean conditions.

Dispersal of antibiotic resistance genes in an agricultural influenced multi-branch river network

Rivers in agricultural regions serve as an important sink for livestock and poultry farm runoff, fertilizer runoff, and country living sewage, which could bring antibiotic resistance genes (ARGs) contaminations. However, the diversity and distribution of ARGs has not been well documented in the agricultural influenced river. Here, the diversity of ARGs, and their relationship with biochemical factors were determined in the surface water in an agricultural region of the Jialing River and its five rural branches. The 218 unique ARGs encoding resistance to eight major antibiotic classes have been detected using high-throughput quantitative PCR. The branches of the river had a remarkably higher abundance of ARGs than the mainstream. The aminoglycoside, beta_Lactamase, MLSB, and Multidrug resistance genes were significantly enriched in the branches compared to the mainstream. Compared with the mainstream, the ARGs profiles in the branches showed obvious higher spatial variability. Significant correlation between ARGs profiles and bacterial community structures were observed, and network analysis further showed that the ARGs were associated with their potential hosts, such as Ottowia and Novosphingobium. Redundancy discrimination analysis revealed that Cu content has a significant contribution to the increase of ARGs in the river. The microbial diversity index was negatively correlated with the abundance of the ARGs. These results provide evidence for the enrichment of ARGs in the agricultural influenced river and branches due to the joint influence of chemical and microbial variables.

Associations of Boiled Water and Lifespan Water Sources With Mortality: A Cohort Study of 33,467 Older Adults

Background:

There were few studies to report whether drinking water sources and habits affected health outcomes. Therefore, this study aimed to examine how boiled water and lifespan water sources affected the risks of cardiovascular disease (CVD) and all-cause mortality in the elderly.

Methods

This study was a 20-year cohort study. All participants aged ≥60 years were eligible. Exposures of interest included lifespan drinking water sources and habits, which were collected using a validated questionnaire. Drinking water sources included wells, surface water, spring, and tap water in childhood, around the age of 60 years, and at present. Drinking habits included boiled and un-boiled water. The main end events included CVD and all-cause mortality.

Results

There were 33,467 participants in this study. Compared to tap water, drinking well and surface water around the age of 60 years were associated with a higher risk of all-cause mortality (HR: 1.092, 95% CI: 1.051–1.134, P < 0.001; and HR: 1.136, 95% CI: 1.081–1.194, P < 0.001, respectively). However, only drinking spring around aged 60 years and drinking well at present were associated with a lower CVD mortality (HR: 0.651, 95% CI: 0.452–0.939, P = 0.022; and HR: 0.757, 95% CI: 0.665–0.863, P < 0.001, respectively). Boiled water was not associated with mortality.

Conclusions

Drinking water from well and surface water around the age of 60 years were associated with increased all-cause mortality. Drinking water from spring around the age of 60 years and well at present was associated with a decreased CVD mortality. However, boiled water was not associated with mortality.

Electrochemical degradation of antibiotics using flow-through graphene sponge electrodes

Graphene sponge electrodes doped with atomic boron and nitrogen were employed for electrochemical degradation of antibiotics sulfamethoxazole, trimethoprim, ofloxacin, and erythromycin. The removal of antibiotics that displayed strong π-π interactions (i.e., ofloxacin) with reduced graphene oxide (RGO) coating was less limited by the mass transfer and removal efficiencies > 80% were observed for the investigated range of electrolyte flowrates. At the highest applied flowrate (700 LMH), increase in the anodic current significantly worsened the removal of trimethoprim and erythromycin due to the detrimental impact of the evolving gas bubbles. Increase in current at 700 LMH led to a stepwise increase in the removal efficiency of sulfamethoxazole due to its enhanced electrosorption. Electrochemical degradation was achieved via ozone, hydrogen peroxide and hydroxyl radical (^•OH). Extraction of the employed graphene sponges confirmed the degradation of the strongly adsorbing antibiotics. Identified electrochemical transformation products of erythromycin confirmed the participation of ^•OH, through N-demethylation of the dimethylamine group. In real tap water, removal efficiencies were lower for all target antibiotics. Lower electric conductivity of tap water and thus increased thickness of the electric double layer likely limited their interaction with the graphene sponge surface, in addition to the presence of low amounts of organic matter.

A review of the global climate change impacts, adaptation, and sustainable mitigation measures

Climate change is a long-lasting change in the weather arrays across tropics to polls. It is a global threat that has embarked on to put stress on various sectors. This study is aimed to conceptually engineer how climate variability is deteriorating the sustainability of diverse sectors worldwide. Specifically, the agricultural sector's vulnerability is a globally concerning scenario, as sufficient production and food supplies are threatened due to irreversible weather fluctuations. In turn, it is challenging the global feeding patterns, particularly in countries with agriculture as an integral part of their economy and total productivity. Climate change has also put the integrity and survival of many species at stake due to shifts in optimum temperature ranges, thereby accelerating biodiversity loss by progressively changing the ecosystem structures. Climate variations increase the likelihood of particular food and waterborne and vector-borne diseases, and a recent example is a coronavirus pandemic. Climate change also accelerates the enigma of antimicrobial resistance, another threat to human health due to the increasing incidence of resistant pathogenic infections. Besides, the global tourism industry is devastated as climate change impacts unfavorable tourism spots. The methodology investigates hypothetical scenarios of climate variability and attempts to describe the quality of evidence to facilitate readers' careful, critical engagement. Secondary data is used to identify sustainability issues such as environmental, social, and economic viability. To better understand the problem, gathered the information in this report from various media outlets, research agencies, policy papers, newspapers, and other sources. This review is a sectorial assessment of climate change mitigation and adaptation approaches worldwide in the aforementioned sectors and the associated economic costs. According to the findings, government involvement is necessary for the country's long-term development through strict accountability of resources and regulations implemented in the past to generate cutting-edge climate policy. Therefore, mitigating the impacts of climate change must be of the utmost importance, and hence, this global threat requires global commitment to address its dreadful implications to ensure global sustenance.

A Critical Review of the Antimicrobial and Antibiofilm Activities of Green-Synthesized Plant-Based Metallic Nanoparticles

Metallic nanoparticles (MNPs) produced by green synthesis using plant extracts have attracted huge interest in the scientific community due to their excellent antibacterial, antifungal and antibiofilm activities. To evaluate these pharmacological properties, several methods or protocols have been successfully developed and implemented. Although these protocols were mostly inspired by the guidelines from national and international regulatory bodies, they suffer from a glaring absence of standardization of the experimental conditions. This situation leads to a lack of reproducibility and comparability of data from different study settings. To minimize these problems, guidelines for the antimicrobial and antibiofilm evaluation of MNPs should be developed by specialists in the field. Being aware of the immensity of the workload and the efforts required to achieve this, we set out to undertake a meticulous literature review of different experimental protocols and laboratory conditions used for the antimicrobial and antibiofilm evaluation of MNPs that could be used as a basis for future guidelines. This review also brings together all the discrepancies resulting from the different experimental designs and emphasizes their impact on the biological activities as well as their interpretation. Finally, the paper proposes a general overview that requires extensive experimental investigations to set the stage for the future development of effective antimicrobial MNPs using green synthesis.

Recent Progress of Cellulose-Based Hydrogel Photocatalysts and Their Applications

With the development of science and technology, photocatalytic technology is of great interest. Nanosized photocatalysts are easy to agglomerate in an aqueous solution, which is unfavorable for recycling. Therefore, hydrogel-based photocatalytic composites were born. Compared with other photocatalytic carriers, hydrogels have a three-dimensional network structure, high water absorption, and a controllable shape. Meanwhile, the high permeability of these composites is an effective way to promote photocatalysis technology by inhibiting nanoparticle photo corrosion, while significantly ensuring the catalytic activity of the photocatalysts. With the growing energy crisis and limited reserves of traditional energy sources such as oil, the attention of researchers was drawn to natural polymers. Like almost all abundant natural polymer compounds in the world, cellulose has the advantages of non-toxicity, degradability, and biocompatibility. It is used as a class of reproducible crude material for the preparation of hydrogel photocatalytic composites. The network structure and high hydroxyl active sites of cellulose-based hydrogels improve the adsorption performance of catalysts and avoid nanoparticle collisions, indirectly enhancing their photocatalytic performance. In this paper, we sum up the current research progress of cellulose-based hydrogels. After briefly discussing the properties and preparation methods of cellulose and its descendant hydrogels, we explore the effects of hydrogels on photocatalytic properties. Next, the cellulose-based hydrogel photocatalytic composites are classified according to the type of catalyst, and the research progress in different fields is reviewed. Finally, the challenges they will face are summarized, and the development trends are prospected.

Organic fertilizer potentiates the transfer of typical antibiotic resistance gene among special bacterial species

The propagation of antibiotic resistance genes (ARGs) in environments has evoked many attentions, however, how to identify their host pathogenic bacteria in situ remains a great challenge. Here we explored the bacterial host distribution and dissemination of a typical ARG, sul1 gene, in agricultural soils through the simultaneous detection of sul1 and its host 16S rRNA gene by emulsion paired isolation and concatenation PCR (epicPCR). Compared to chemical fertilizer, organic fertilizer (chicken manure) led to a higher prevalence of sul1 gene in the soil, and dominant bacterial hosts of sul1 gene were classified into Proteobacteria and Bacteroidetes phyla. Additionally, significant higher diversity of antibiotic resistance bacteria (ARB), higher rate of horizontal gene transfer (HGT), higher rate of mobile genetic elements (MGE) and higher proportion of pathogens were all observed in the treatment of organic fertilizer. This study alerts potential health risks of manure applications in agricultural soils.

Molecular Diagnostic Tools Applied for Assessing Microbial Water Quality

Microbial water quality is of vital importance for human, animal, and environmental health. Notably, pathogenically contaminated water can result in serious health problems, such as waterborne outbreaks, which have caused huge economic and social losses. In this context, the prompt detection of microbial contamination becomes essential to enable early warning and timely reaction with proper interventions. Recently, molecular diagnostics have been increasingly employed for the rapid and robust assessment of microbial water quality implicated by various microbial pollutants, e.g., waterborne pathogens and antibiotic-resistance genes (ARGs), imposing the most critical health threats to humans and the environment. Continuous technological advances have led to constant improvements and expansions of molecular methods, such as conventional end-point PCR, DNA microarray, real-time quantitative PCR (qPCR), multiplex qPCR (mqPCR), loop-mediated isothermal amplification (LAMP), digital droplet PCR (ddPCR), and high-throughput next-generation DNA sequencing (HT-NGS). These state-of-the-art molecular approaches largely facilitate the surveillance of microbial water quality in diverse aquatic systems and wastewater. This review provides an up-to-date overview of the advancement of the key molecular tools frequently employed for microbial water quality assessment, with future perspectives on their applications.

Antibiotic Resistance in the Drinking Water: Old and New Strategies to Remove Antibiotics, Resistant Bacteria, and Resistance Genes

Bacterial resistance is a naturally occurring process. However, bacterial antibiotic resistance has emerged as a major public health problem in recent years. The accumulation of antibiotics in the environment, including in wastewaters and drinking water, has contributed to the development of antibiotic resistant bacteria and the dissemination of antibiotic resistance genes (ARGs). Such can be justified by the growing consumption of antibiotics and their inadequate elimination. The conventional water treatments are ineffective in promoting the complete elimination of antibiotics and bacteria, mainly in removing ARGs. Therefore, ARGs can be horizontally transferred to other microorganisms within the aquatic environment, thus promoting the dissemination of antibiotic resistance. In this review, we discuss the efficiency of conventional water treatment processes in removing agents that can spread/stimulate the development of antibiotic resistance and the promising strategies for water remediation, mainly those based on nanotechnology and microalgae. Despite the potential of some of these approaches, the elimination of ARGs remains a challenge that requires further research. Moreover, the development of new processes must avoid the release of new contaminants for the environment, such as the chemicals resulting from nanomaterials synthesis, and consider the utilization of green and eco-friendly alternatives such as biogenic nanomaterials and microalgae-based technologies.

Characteristics and removal of antibiotics and antibiotic resistance genes in a constructed wetland from a drinking water source in the Yangtze River Delta

Safe drinking water is crucial to public health. However, approximately one-third of the world's population lacks access to clean drinking water. The presence of antibiotics and antibiotic resistance genes (ARGs) in drinking water sources has become a severe problem worldwide due to its potential threat to human health. We monitored the occurrence and variations of 23 antibiotics and 9 ARGs in different treatment processes in a constructed wetland serving as drinking water source in the Yangtze River Delta, China. The studied wetland is consisted of four treatment processes: pretreatment area, pump station lifting, root-channel ecological purification area and deep purification area. Except for sulfapyridine and roxithromycin, 21 antibiotics were detected at concentrations ranging from 0.15 to 59.52 ng/L. The concentration of macrolides was the highest in this wetland, especially tylosin (42.86-59.52 ng/L). TetG, tetX and sul2 were the dominant ARGs in both water (2.41 × 10^-4-1.87 × 10^-2) and sediment (6.65 × 10^-5-4.92 × 10^-3). In addition, a strong correlation between ARGs in water and ARGs in sediment (Pearson, R² > 0.9, p < 0.05) indicated an exchange between the two phases. Moreover, the significantly positive correlation of ARGs between the inlet and outlet of each subsystem illustrated that upstream pollution was the primary source for downstream processes. In general, the wetland system could efficiently eliminate antibiotics (9.0-53.8%) and ARGs (14.5-94.1%), with the deep purification area having the highest removal efficiency. Overall, our results provide important insights into the occurrence, abundance and removal of antibiotics and ARGs in the constructed wetland serving as drinking water sources.

Characteristics of Antibiotic Resistance Genes and Antibiotic-Resistant Bacteria in Full-Scale Drinking Water Treatment System Using Metagenomics and Culturing

The contamination of antibiotic resistance genes (ARGs) may directly threaten human health. This study used a metagenomic approach to investigate the ARG profile in a drinking water treatment system (DWTS) in south China. In total, 317 ARG subtypes were detected; specifically, genes encoding bacitracin, multidrug, and sulfonamide were widely detected in the DWTS. Putative ARG hosts included Acidovorax (6.0%), Polynucleobacter (4.3%), Pseudomonas (3.4%), Escherichia (1.7%), and Klebsiella (1.5%) as the enriched biomarkers in the DWTS, which mainly carried bacitracin, beta-lactam, and aminoglycoside ARGs. From a further analysis of ARG-carrying contigs (ACCs), Stenotrophomonas maltophilia and Pseudomonas aeruginosa were the most common pathogens among the 49 ACC pathogens in the DWTS. The metagenomic binning results demonstrated that 33 high-quality metagenome-assembled genomes (MAGs) were discovered in the DWTS; particularly, the MAG identified as S. maltophilia-like (bin.195) harbored the greatest number of ARG subtypes (n = 8), namely, multidrug (n = 6; smeD, semE, multidrug_transporter, mexE, semB, and smeC), beta-lactam (n = 1; metallo-beta-lactamase), and aminoglycoside [n = 1; aph(3’)-IIb]. The strong positive correlation between MGEs and ARG subtypes revealed a high ARG dissemination risk in the DWTS. Based on the pure-culture method, 93 isolates that belong to 30 genera were recovered from the DWTS. Specifically, multidrug-resistant pathogens and opportunistic pathogens such as P. aeruginosa, Bacillus cereus, and S. maltophilia were detected in the DWTS. These insights into the DWTS’s antibiotic resistome indicated the need for more comprehensive ARG monitoring and management in the DWTS. Furthermore, more effective disinfection methods need to be developed to remove ARGs in DWTSs, and these findings could assist governing bodies in the surveillance of antibiotic resistance in DWTSs.

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

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

Functionalization and Antibacterial Applications of Cellulose-Based Composite Hydrogels

Pathogens, especially drug-resistant pathogens caused by the abuse of antibiotics, have become a major threat to human health and public health safety. The exploitation and application of new antibacterial agents is extremely urgent. As a natural biopolymer, cellulose has recently attracted much attention due to its excellent hydrophilicity, economy, biocompatibility, and biodegradability. In particular, the preparation of cellulose-based hydrogels with excellent structure and properties from cellulose and its derivatives has received increasing attention thanks to the existence of abundant hydrophilic functional groups (such as hydroxyl, carboxy, and aldehyde groups) within cellulose and its derivatives. The cellulose-based hydrogels have broad application prospects in antibacterial-related biomedical fields. The latest advances of preparation and antibacterial application of cellulose-based hydrogels has been reviewed, with a focus on the antibacterial applications of composite hydrogels formed from cellulose and metal nanoparticles; metal oxide nanoparticles; antibiotics; polymers; and plant extracts. In addition, the antibacterial mechanism and antibacterial characteristics of different cellulose-based antibacterial hydrogels were also summarized. Furthermore, the prospects and challenges of cellulose-based antibacterial hydrogels in biomedical applications were also discussed.

Aeromonas spp. Prevalence, Virulence, and Antimicrobial Resistance in an Ex Situ Program for Threatened Freshwater Fish—A Pilot Study with Protective Measures

Simple Summary

Knowledge regarding best practices to prevent bacterial disease and antimicrobial resistance acquisition in aquatic ex situ programs is limited. This pilot study aimed to investigate the role of protective measures in the prevalence, antimicrobial resistance profiles, and virulence signatures of Aeromonas spp. in Portuguese nase (Iberochondrostoma lusitanicum) kept in an ex situ program. Fish were randomly divided into two tanks (i.e., with and without protective measures). Bacterial sampling was performed weekly for 5 weeks, and Aeromonas spp. prevalence, antimicrobial resistance, and virulence signatures were compared. We observed an increase in antimicrobial resistance among collected isolates over the experiment duration, with a trend of Aeromonas spp. prevalence and virulence decreasing when using protective measures. This pilot study sheds light on Aeromonas spp. prevalence, antimicrobial resistance, and virulence dynamics in aquatic ex situ programs, while constituting a first approach in the determination of the potential use of protective measures in such settings.

Abstract

Ex situ breeding programs are important conservation tools for endangered freshwater fish. However, developing husbandry techniques that decrease the likelihood of disease, antimicrobial resistance, and virulence determinants acquisition during this process is challenging. In this pilot study, we conducted a captivity experiment with Portuguese nase (Iberochondrostoma lusitanicum), a critically endangered leuciscid species, to investigate the influence of simple protective measures (i.e., material disinfection protocols and animal handling with gloves) on the dynamics of a potential pathogenic genus, Aeromonas, as well as its virulence profiles and antimicrobial resistance signatures. Our findings show that antimicrobial resistance in Aeromonas spp. collected from I. lusitanicum significantly increased during the extent of the assay (5 weeks), with all isolates collected at the end of the study classified as multidrug-resistant. Additionally, humans handling fishes without protective measures were colonized by Aeromonas spp. The use of protective measures suggested a decreasing trend in Aeromonas spp. prevalence in I. lusitanicum, while bacterial isolates displayed significantly lower virulence index values when virulence phenotypical expression was tested at 22 °C. Despite this study representing an initial trial, which needs support from further research, protective measures tested are considered a simple tool to be applied in ex situ breeding programs for aquatic animals worldwide. Furthermore, current results raise concern regarding antimicrobial resistance amplification and zoonotic transmission of Aeromonas spp. in aquatic ex situ programs.

A TbPO4-based capturer for environmental extracellular antibiotic genes by interrogating lanthanide phosphates nanoneedles

Accurate determination of antibiotic resistance genes (ARGs) in environmental DNA molecules (eDNA) is challenging owing to its low abundance in the aquatic environment. Here we report a facile and cost-efficient approach to extract trace amount of eDNAs in the aquatic environment using LnPO₄ nanomaterials. Among the nanomaterials, less crystalline TbPO₄ nanoneedles was identified as the most prominent candidate for long stranded DNA and short stranded DNA with adsorption efficiency above 97%. The adsorbed DNA was washed off from TbPO₄ nanoneedles by optimized eluant (85% PBS, 15% EtOH, 4 g/L glycine, pH 10.0) with an optimal DNA recovery of 78.83%. Our approach showed a comparable or better eDNA extraction efficiency than a commercial extraction method for different environmental samples, but 89% less cost. The high purity of the extracted eDNA was demonstrated by a high A_260/280 ratio. Using qPCR experiment, the occurrence of six common ARGs in the eDNA were detected with abundance ranging from 4.06 × 10³ to 3.51 × 10⁹ copies/L in river samples. This specific DNA capturer is valuable for the evaluation of spatial and temporal dynamic of ARGs pollution to provide insight into the potential risk with regard to the human health.

Ancient Oriental Wisdom still Works: Removing ARGs in Drinking Water by Boiling as compared to Chlorination

Antibiotic resistance genes (ARGs) in municipal drinking water may not be effectively removed during centralized treatment. To reduce potential health risks, water disinfection at the point-of-use scale is warranted. This study investigated the performance of boiling, a prevalent household water disinfection means, in response to ARGs contamination. We found that boiling was more efficient in inactivating both Escherichia coli and environmental bacteria compared to chlorination and pasteurization. Boiling of environmental bacteria suspension removed a much broader spectrum of ARGs and mobile genetic elements (up to 141 genes) than chlorination (up to 13 genes), such better performance was largely attributed to a stronger inactivation of chlorine-tolerant bacteria including Acinetobacter and Bacillus. Accumulation of extracellular ARGs was found during low-temperature heating (≤ 80°C) and in the initial stage of chlorination (first 3 min when initial chlorine was 5 mg/L and first 12 min when initial chlorine was 1 mg/L). These extracellular ARGs as well as the intracellular ARGs got removed as the heating temperature increased or the chlorination time prolonged. Under the same treatment time (30 min), high-temperature heating (≥ 90.1°C) damaged the DNA structure more thoroughly than chlorination (5 mg/L). Taking into account the low transferability of ARGs after DNA melting, boiling may provide an effective point-of-use approach to attenuating bacterial ARGs in drinking water and is still worth promoting in the future.

Fate, mobility, and pathogenicity of drinking water treatment plant resistomes deciphered by metagenomic assembly and network analyses

Antibiotic resistance genes (ARGs) have been regarded as emerging environmental contaminants. The profile of resistome (collection of all ARGs) in drinking water and its fate during drinking water treatment remain unclear. This study applied metagenomic assembly combined with network analysis to decipher the profile, mobility, host, and pathogenicity of resistomes in two full-scale drinking water treatment plants (DWTPs), each applying conventional treatment and advanced treatment of ozonation followed by biological activated carbon filtration. In source waters and effluents of each treatment process collected from both DWTPs, 215 ARGs belonging to 20 types were detected with total concentration ranging from 6.30 ± 1.83 to 5.20 ± 0.26 × 10⁴ copies/mL. Both the conventional and advanced DWTPs were revealed to effectively reduce the concentration of total ARGs, with the average removal efficiency of 3.61-log₁₀ and 2.21-log₁₀, respectively. Multiple statistical analyses (including network analysis) indicated drinking water resistome correlated tightly with mobile gene elements (MGEs) and bacterial community, with the latter acting as the premier driver of resistome alteration in DWTPs. Further analysis of ARG-carrying contigs (ACCs) assembled from drinking water metagenomes (i) tracked down potential bacterial hosts of ARGs (e.g., Proteobacteria phylum as the major pool of resistome), (ii) provided co-localization information of ARGs and MGEs (e.g., MacB-E7196 plasmid1), and (iii) identified ARG-carrying human pathogens (e.g., Enterococcus faecium and Ralstonia pickettii). This work firstly determined the concentration, mobility incidence, and pathogenicity incidence of DWTP resistomes, based on which the actual health risk regarding antibiotic resistance could be quantitatively assessed in further study, providing a useful direction for decision-making concerning the risk control of ARGs in DWTPs.

Higher abundance of core antimicrobial resistant genes in effluent from wastewater treatment plants

Wastewater treatment plants (WWTPs) receive sewage water from a variety of sources, including livestock farms, hospitals, industries, and households, that contain antimicrobial resistant bacteria (ARB) and antimicrobial resistant genes (ARGs). Current treatment technologies are unable to completely remove ARB and ARGs, which are eventually released into the aquatic environment. This study focused on the core resistome of urban WWTPs that are persistent through wastewater treatment processes. We adopted the Hiseq-based metagenomic sequencing approach to identify the core resistome, their genetic context, and pathogenic potential of core ARGs in the influent (IN) and effluent (EF) samples of 12 urban WWTPs in South Korea. In this study, the abundance of ARGs ranged from 0.32 to 3.5 copies of ARGs per copy of the 16S rRNA gene, where the IN samples were relatively higher than the EF samples, especially for the macrolide-lincosamide-streptogramin (MLS)- and tetracycline- resistant genes. On the other hand, there were 43 core ARGs sharing up to 90% of the total, among which the relative abundance of sul1, APH(3'')-lb, and RbpA was higher in EF than in IN (p < 0.05). Moreover, tetracycline and sulfonamide-related core ARGs in both EF and IN were significantly more abundant on plasmids than on chromosomes (p < 0.05). We also found that the majority of core ARGs were carried by opportunistic pathogens such as Acinetobacter baumannii, Enterobacter cloacae, and Pseudomonas aeruginosa in both IN and EF. In addition, phages were the only mobile elements whose abundance correlated with that of core ARGs in EF, suggesting that transduction may play a major role in disseminating ARGs in the receiving water environment of the urban WWTP. The persistent release of core ARGs with pathogenic potential into environmental water is of immediate concern. The mobility of ARGs and ARBs in the environment is a major public health concern. These results should be taken into consideration when developing policy to mitigate environmental dissemination of ARG by WWTPs.

Seasonal distribution of antibiotic resistance genes in the Yellow River water and tap water, and their potential transmission from water to human

The prevalence and transmission of antibiotic resistance genes (ARGs) and opportunistic pathogens in water environments can pose great threat to public health. However, the dissemination of ARGs and opportunistic pathogens from water environments to humans has been poorly explored. Here, we employed 16S rRNA gene sequencing and high-throughput quantitative PCR techniques to explore the seasonal distribution of ARGs and opportunistic pathogens in the Yellow River water (source water) and tap water, as well as their relationships with healthy humans at Lanzhou, China. Physiochemical analysis was applied to detect water quality parameters and heavy metal contents. The absolute abundance and diversity of ARGs in the Yellow River and tap water demonstrated distinct seasonal patterns. In winter, the Yellow river water had the highest ARG abundance and diversity, while tap water owned the lowest. Mobile genetic elements (MGEs) were the predominant driver of ARG profiles in both the Yellow river and tap water. Null model analysis showed that ARG assembly in the Yellow River was more influenced by stochastic processes than tap water and this was independent of seasons. Total organic carbon and arsenic contents exhibited positive correlations with many ARGs. Opportunistic pathogens Aeromonas and Pseudomonas may be potential hosts for ARGs. Approximately 80% of detected ARGs were shared between water samples and the human gut. These persistent ARGs could not be entirely eliminated through drinking water treatment processes. Thus, it is crucial to protect sources of tap water from anthropogenic pollution and improve water treatment technologies to reduce the dissemination of ARGs and ensure drinking-water biosafety for human health.

Rainfall facilitates the transmission and proliferation of antibiotic resistance genes from ambient air to soil

Antibiotic resistance is common in bacterial communities and appears to be correlated with human activities. However, the source of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in remote regions remains unclear. In this study, we examined the abundance of ARGs in fine particulate matter (PM_2.5) as a carrier throughout the rainfall process (4 mm rain/h) to observe the effects of rainfall on the transmission of ARGs. The results suggested that rainwater served as a reservoir that facilitated the spread of ARGs and that wind and particulate matter (PM) concentrations might be meteorological parameters that influence the distribution of ARGs in rainwater. In addition, soil microcosm experiments were performed to investigate the influence of rainfall on antibiotic resistance in soils with different environmental backgrounds. Rainwater facilitated the proliferation of ARGs and mobile genetic elements (MGEs) from ambient air to soil, and this influence was more obvious in heavy metal-contaminated soil. This is the first study to investigate the routes by which rainfall acts as a mobile reservoir to facilitate the transmission and proliferation of ARGs, and the results indicate the potential source of ARGs in remote regions where humans rarely interfere.

Legacy and Emerging Pollutants in an Urban River Stretch and Effects on the Bacterioplankton Community

River contamination is due to a chemical mixture of point and diffuse pollution, which can compromise water quality. Polycyclic Aromatic Hydrocarbons (PAHs) and emerging compounds such as pharmaceuticals and antibiotics are frequently found in rivers flowing through big cities. This work evaluated the presence of fifteen priority PAHs, eight pharmaceuticals including the antibiotics ciprofloxacin (CIP) and sulfamethoxazole (SMX), together with their main antibiotic resistant genes (ARGs) and the structure of the natural bacterioplankton community, in an urbanized stretch of the river Danube. SMX and diclofenac were the most abundant chemicals found (up to 20 ng/L). ARGs were also found to be detected as ubiquitous contaminants. A principal component analysis of the overall microbiological and chemical data revealed which contaminants were correlated with the presence of certain bacterial groups. The highest concentrations of naphthalene were associated with Deltaproteobacteria and intI1 gene. Overall, the most contaminated site was inside the city and located immediately downstream of a wastewater treatment plant. However, both the sampling points before the river reached the city and in its southern suburban area were still affected by emerging and legacy contamination. The diffuse presence of antibiotics and ARGs causes particular concern because the river water is used for drinking purposes.

Response of microbial nitrogen transformation processes to antibiotic stress in a drinking water reservoir

Effects of antibiotics on microbial nitrogen transformation processes in natural aquatic ecosystems are largely unknown. In this study, we utilized the ¹⁵N stable isotope tracers and metagenomic sequencing to identify how antibiotics drive nitrogen transformation processes in Danjiangkou Reservoir, which is the largest artificial drinking water reservoir in China. We retrieved 51 nitrogen functional genes, and found that the highest abundances of nitrate reduction and denitrification-related genes occurred in dissimilatory nitrogen transformation pathways. ¹⁵N-labelling analysis substantiated that denitrification was the main pathway for nitrogen removal, accounting for 57.1% of nitrogen loss. Nitrogen functional genes and antibiotic resistance genes co-occurred in Danjiangkou Reservoir, and they were mainly carried by the denitrifying bacteria such as Rhodoferax, Polaromonas, Limnohabitans, Pararheinheimera, Desulfobulbus, and Pseudopelobacter. Genome annotation revealed that antibiotic deactivation, Resistance-Nodulation-Division and facilitator superfamily efflux pumps were responsible for the multiple-resistance to antibiotics in these bacteria. Moreover, antibiotics showed non-significant effects on nitrogen transformation processes. It is speculated that denitrifying bacteria harboring ARGs played crucial roles in protecting nitrogen transformation from low-level antibiotics stress in the reservoir. Our results highlight that denitrifying bacteria are important hosts of ARGs, which provides a novel perspective for evaluating the effects of antibiotics on nitrogen cycle in natural aquatic ecosystems.

Vertical and horizontal distributions of clinical antibiotic resistance genes and bacterial communities in Danjiangkou Reservoir, China

The Danjiangkou Reservoir is an important water source for the middle route of the South-to-North Water Diversion Project in China. The current anthropogenic pollution of this reservoir is a great public health concern. Therefore, the horizontal and vertical distributions of seven clinical antibiotic resistance genes (ARGs) and bacterial communities in the Danjiangkou Reservoir were investigated using qPCR and next-generation sequencing, respectively. The average relative abundance of ARGs was 3.01 × 10^-4 to 1.90 × 10^-3 and 4.66 × 10^-4 to 1.85 × 10^-3 in horizontal and vertical profiles, respectively. There was a significant difference in the vertical composition of ARGs, which was caused by different media (i.e. water column vs. sediment). No significant differences in the composition of ARGs were found in the horizontal profile. Proteobacteria was the most abundant phylum, followed by Actinobacteria in the Danjiangkou Reservoir. The beta diversity pattern of the microbial communities in the vertical profile was consistent with that of the ARGs. Moreover, a significant difference in the horizontal composition of the bacterial communities among these water columns was found. All of these factors have resulted in noticeably different co-occurrence patterns of ARGs and bacterial communities between water columns and surface sediment samples. ARGs were closely associated with Proteobacteria and Chloroflexi in the sediment samples, indicating potential anthropogenic pollution in the Danjiangkou Reservoir. Although there was no significant correlation between the occurrence of ARGs and 11 opportunistic pathogens, our results point to potential risks for the development of multi-resistant pathogens due to the simultaneous presence of ARGs and pathogens in the study area. These results provide a good basis for thorough ecological evaluation and remediation of the Danjiangkou Reservoir.

The role of antibiotics and heavy metals on the development, promotion, and dissemination of antimicrobial resistance in drinking water biofilms

Antimicrobial resistance (AMR), as well as the development of biofilms in drinking water distribution systems (DWDSs), have become an increasing concern for public health and management. As bulk water travels from source to tap, it may accumulate contaminants of emerging concern (CECs) such as antibiotics and heavy metals. When these CECs and other selective pressures, such as disinfection, pipe material, temperature, pH, and nutrient availability interact with planktonic cells and, consequently, DWDS biofilms, AMR is promoted. The purpose of this review is to highlight the mechanisms by which AMR develops and is disseminated within DWDS biofilms. First, this review will lay a foundation by describing how DWDS biofilms form, as well as their basic intrinsic and acquired resistance mechanisms. Next, the selective pressures that further induce AMR in DWDS biofilms will be elaborated. Then, the pressures by which antibiotic and heavy metal CECs accumulate in DWDS biofilms, their individual resistance mechanisms, and co-selection are described and discussed. Finally, the known human health risks and current management strategies to mitigate AMR in DWDSs will be presented. Overall, this review provides critical connections between several biotic and abiotic factors that influence and induce AMR in DWDS biofilms. Implications are made regarding the importance of monitoring and managing the development, promotion, and dissemination of AMR in DWDS biofilms.

Evaluating aquatic macrophytes for removing erythromycin from contaminated water: floating or submerged?

Water contamination by antibiotics is an emerging global problem, with impacts on both public health and the environment. Erythromycin has been encountered in bodies of water throughout the world, which demands the development of efficient remediation technologies. We investigated the physiological responses and phytoremediation capacity of four species of aquatic macrophytes, two floating (Salvinia molesta and Lemna minor) and two submerged (Myriophyllum aquaticum and Rotala rotundifolia). The plants were exposed to relevant environmental concentrations of erythromycin (0 and 1.7 µg l^-1) in artificially contaminated water for seven days. Physiological evaluations evidenced the ability of that antibiotic to promote oxidative events in those plants, such as the activation of antioxidant enzymes (ascorbate peroxidase and/or catalase). S. molesta exposed to erythromycin demonstrated accumulations of hydrogen peroxide and oxidative damage (lipid peroxidation) that was reflected in growth reductions. The erythromycin removal efficiency of floating plants varied from 9 to 12%, while submerged species varied from 31 to 44%. As such, submerged macrophyte species demonstrated the most efficient removal of erythromycin from contaminated waters, and are therefore more indicated for antibiotic phytoremediation projects.

Structure and Functional Attributes of Bacterial Communities in Premise Plumbing Across the United States

Microbes that thrive in premise plumbing can have potentially important effects on human health. Yet, how and why plumbing-associated microbial communities vary across broad spatial scales remain undetermined. We characterized the bacterial communities in 496 showerheads collected from across the continental United States. The overall community structure, determined by 16S rRNA gene amplicon sequencing, revealed high levels of bacterial diversity. Although a large fraction of the observed variation in community composition could not be explained, differences in bacterial community composition were associated with water supply (private well water vs public municipal water), water source (groundwater vs surface water), and associated differences in water chemistry (pH and chlorine). Most notably, showerheads in homes supplied with public water had higher abundances of Blastomonas, Mycobacterium, and Porphyrobacter, while Pseudorhodoplanes, Novosphingobium, and Nitrospira were more abundant in those receiving private well water. We conducted shotgun metagenomic analyses on 92 of these samples to assess differences in genomic attributes. Public water-sourced showerheads had communities enriched in genes related to lipid and xenobiotic metabolisms, virulence factors, and antibiotic resistance. In contrast, genes associated with oxidative stress and membrane transporters were over-represented in communities from private well water-sourced showerheads compared to those supplied by public water systems. These results highlight the broad diversity of bacteria found in premise plumbing across the United States and the role of the water source and treatment in shaping the microbial community structure and functional potential.

Annual trends and health risks of antibiotics and antibiotic resistance genes in a drinking water source in East China

The extensive pollution of antibiotics and antibiotic resistance genes (ARGs) in drinking water has aroused worldwide concern. Successive monitoring of these pollutants has noteworthy significance for drinking water safety. Accordingly, this study conducted successive monitoring of antibiotics and ARGs from 2015 to 2017 in a drinking water source in East China. The total antibiotic concentration ranged from 19.68 ng/L to 497.00 ng/L, and decreased slightly from 2015 to 2017. Eighteen out of forty-one ARG subtypes showing resistance to six antibiotic classes and one class I integrase gene intI1, were detected in the drinking water source at concentrations ranging from 6.5 × 10⁴ copies/mL to 1.6 × 10⁶ copies/mL. Importantly, the total ARG concentration increased on an annual basis from 2015 to 2017 with an average annual increment of 0.25 orders of magnitude, which was mainly attributed to the increase in specific ARG subtypes, such as sul1, sul2, sul3, tetA, qnrB, and ermB. Most ARGs was positively correlated with the intI1 genes (r = 0.47-0.55, P < 0.01). Furthermore, the variation of antibiotics and ARGs appeared to be related to the water indices, particularly of the values of COD, BOD_5, NO₂-N (P < 0.05). This study provides basic data on antibiotic and ARG pollution in the studied drinking water source. Importantly, the findings expound that although the residual antibiotics in this drinking water source decreased slightly from 2015 to 2017, while its biological effect, the antibiotic resistance, increased annually, which give a warning of the antibiotic resistance pollution in the drinking water source.

Antibiotics: An overview on the environmental occurrence, toxicity, degradation, and removal methods

Antibiotics, as antimicrobial drugs, have been widely applied as human and veterinary medicines. Recently, many antibiotics have been detected in the environments due to their mass production, widespread use, but a lack of adequate treatment processes. The environmental occurrence of antibiotics has received worldwide attention due to their potential harm to the ecosystem and human health. Research status of antibiotics in the environment field is presented by bibliometrics. Herein, we provided a comprehensive overview on the following important issues: (1) occurrence of antibiotics in different environmental compartments, such as wastewater, surface water, and soil; (2) toxicity of antibiotics toward non-target organisms, including aquatic and terrestrial organisms; (3) current treatment technologies for the degradation and removal of antibiotics, including adsorption, hydrolysis, photodegradation and oxidation, and biodegradation. It was found that macrolides, fluoroquinolones, tetracyclines, and sulfonamides were most frequently detected in the environment. Compared to surface and groundwaters, wastewater contained a high concentration of antibiotic residues. Both antibiotics and their metabolites exhibited toxicity to non-target organisms, especially aquatic organisms (e.g., algae and fish). Fluoroquinolones, tetracyclines, and sulfonamides can be removed through abiotic process, such as adsorption, photodegradation, and oxidation. Fluoroquinolones and sulfonamides can directly undergo biodegradation. Further studies on the chronic effects of antibiotics at environmentally relevant concentrations on the ecosystem were urgently needed to fully understand the hazards of antibiotics and help the government to establish the permissible limits. Biodegradation is a promising technology; it has numerous advantages such as cost-effectiveness and environmental friendliness.

Microalgae-based technology for antibiotics removal: From mechanisms to application of innovational hybrid systems

Antibiotics contamination is an emerging environmental concern, owing to its potential risks to ecosystems and human health. Microalgae-based technology has been widely reported as a promising alternative to conventional wastewater treatment, since it is a solar-power driven, ecologically friendly, cost-effective, and sustainable reclamation strategy. This review provides fundamental insights into the major mechanisms underpinning microalgae-based antibiotics removal, including bioadsorption, bioaccumulation, and biodegradation. The critical role of extracellular polymeric substances on bioadsorption and extracellular biodegradation of antibiotics are also covered. Moreover, this review sheds light on the important factors affecting the removal of antibiotics by microalgae, and summarizes several novel approaches to improve the removal efficiency, including acclimation, co-metabolism and microbial consortium. Besides, hybrid systems (such as, microalgae-based technologies combined with the conventional activated sludge, advanced oxidation processes, constructed wetlands, and microbial fuel cells), and genetic engineering are also recommended, which will be feasible for enhanced removal of antibiotics. Finally, this review also highlights the need for further studies aimed at optimizing microalgae-based technology, with emphasis on improving performance and expanding its application in large-scale settings, especially in terms of technical, environmental-friendly and economically competitiveness. Overall, this review summarizes current understanding on microalgae-based technologies for removal of antibiotics and outlines future research directions.

Hormetic dose-responses for silver antibacterial compounds, quorum sensing inhibitors, and their binary mixtures on bacterial resistance of Escherichia coli

Silver antibacterial compounds (SACs) and quorum sensing inhibitors (QSIs), as the potential antibiotic substitutes, have been recommended to prevent and treat microbial infections for the purpose of controlling the increasingly serious bacterial resistance induced by the abuse of antibiotics. However, there is little information regarding the resistance risk of these compounds, especially their mixtures. In this study, bacterial mutation and RP4 plasmid conjugative transfer among bacteria were used to characterize the bacterial endogenous and exogenous resistance, respectively. The effects of SACs (including silver nitrate (AgNO₃) and silver nanoparticle (AgNP)), QSIs, and their binary mixtures on the bacterial resistance were investigated via setting the frequency of mutation and conjugative transfer in Escherichia coli (E. coli) as the test endpoints. The results indicated that these two endpoints exhibited hormetic dose-responses to each treatment. Furthermore, the joint resistance actions between SACs and QSIs were all judged to be antagonism. Correlation analysis suggested that the promotion of the bacterial resistance in each treatment was closely related to its toxicity. It was speculated that AgNO₃ and AgNP might both release Ag⁺ ions to facilitate the E. coli resistance, while QSIs probably acted on LsrR and SdiA proteins to stimulate the bacterial mutation and accelerate the RP4 plasmid conjugative transfer, respectively. These findings imply that the bacteria may generate targeted stress response to the survival pressure from environmental compounds, displaying hormetic phenomenon in resistance-related test endpoints. This study provides a new insight into the resistance risk induced by SACs and QSIs, benefiting the environmental risk assessment of these compounds from the perspective of bacterial resistance.

High-Throughput Single-Cell Technology Reveals the Contribution of Horizontal Gene Transfer to Typical Antibiotic Resistance Gene Dissemination in Wastewater Treatment Plants

The spread of antibiotic resistance genes (ARGs) has gained much attention worldwide, while the contribution of vertical gene transfer (VGT) and horizontal gene transfer (HGT) is still elusive. Here, we improved an emerging high-throughput single-cell-based technology, emulsion, paired isolation, and concatenation polymerase chain reaction (epicPCR), by lengthening the sequence of ARG in the fused ARG-16S rRNA fragments to cover the variance of both ARG and its hosts. The improved epicPCR was applied to track the hosts of a widely detected ARG, sul1 gene, in five urban wastewater treatment plants (UWTPs) during two seasons. The sul1 host bacteria were highly diverse and mostly classified as Proteobacteria and Bacteroidetes. Clear seasonal divergence of α-diversity and interaction networks were present in the host community. The consensus phylogenetic trees of the sul1 gene and their host demonstrated incorrespondence on the whole and regularity on abundant groups, suggesting the important role of both HGT and VGT, respectively. The relative importance of these two ways was further measured; HGT (54%) generally played an equal or even more important role as VGT (46%) in UWTPs. The application of the improved epicPCR technology provides a feasible approach to quantify the relative contributions of VGT and HGT in environmental dissemination of ARGs.

Identification and characterization of chlorine-resistant bacteria from water distribution sites of Mumbai

Chlorination is the oldest and widely practiced method for disinfection of potable water across the globe but some microorganisms survive the chlorine treatment and become resistant. In this study, chlorine-resistant bacteria were isolated from 36 reservoirs of the Municipal Corporation of Greater Mumbai. Water was collected in winter, summer and rainy season. The 8 isolates (out of 89) found to be resistant to 20 ppm of chlorine were identified and belong to the Acinetobacter and Serratia sp. The antibiotic resistance profile showed that the isolates were resistant to a broad spectrum of antibiotics which is of concern. Biofilm production was also observed in most of the isolates. Presence of chlorine-resistant bacteria in drinking water is an alarming situation which needs further analysis especially to understand the further characteristics of these isolates for their antibiotic resistance.

Advances in antimicrobial activity analysis of fluoroquinolone, macrolide, sulfonamide, and tetracycline antibiotics for environmental applications through improved bacteria selection

The widespread use of antibiotics has led to their ubiquitous presence in water and wastewater and raised concerns about antimicrobial resistance. Clinical antibiotic susceptibility assays have been repurposed to measure removal of antimicrobial activity during water and wastewater treatment processes. The corresponding protocols have mainly employed growth inhibition of Escherichia coli. The present work focused on optimizing bacteria selection to improve the sensitivity of residual antimicrobial activity measurements by broth microdilution assays. Thirteen antibiotics from four classes (i.e., fluoroquinolones, macrolides, sulfonamides, tetracyclines) were investigated against three gram-negative organisms, namely E. coli, Mycoplasma microti, and Pseudomonas fluorescens. The minimum inhibitory concentration (MIC) and half-maximal inhibitory concentration (IC₅₀) were calculated for each antibiotic-bacteria pair. P. fluorescens produces a fluorescent siderophore, pyoverdine, that was used to assess sublethal effects and further enhance the sensitivity of antimicrobial activity measurements. The optimal antibiotic-bacteria pairs were as follows: fluoroquinolone-E. coli (growth inhibition); macrolide- and sulfonamide-M. microti (growth inhibition); and, tetracycline-P. fluorescens (pyoverdine inhibition). Compared to E. coli growth inhibition, the sensitivity of antimicrobial activity analysis was improved by up to 728, 19, and 2.7 times for macrolides (tylosin), sulfonamides (sulfamethoxazole), and tetracyclines (chlortetracycline), facilitating application of these bioassays at environmentally-relevant conditions.

Comparative study on the bacterial diversity and antibiotic resistance genes of urban landscape waters replenished by reclaimed water and surface water in Xi'an, China

Pathogenic bacteria and antibiotic resistance genes (ARGs) in urban landscape waters may pose a potential threat to human health. However, the investigation of their occurrence in the urban landscape waters replenished by reclaimed water (RW) and surface water (SW) is still insufficient. The water samples collected from six urban landscape waters replenished by RW or SW were used to analyze bacterial diversity using high-throughput sequencing of 16S rRNA gene and to detect 18 ARGs and 2 integron-integrase genes by means of quantitative PCR array. Results indicated that Proteobacteria was the dominant phylum in all six urban landscape waters. The bacterial species richness was lower in urban landscape waters replenished by RW than that by SW. Sulfonamide resistance genes (sulI and sulIII) were the major ARGs in these urban landscape waters. No significant difference in the relative abundance of sulfonamide resistance genes, tetracycline resistance genes, and most of beta-lactam resistance genes was observed between RW-replenished and SW-replenished urban landscape waters. By contrast, the relative abundance of bla_ampC gene and qnrA gene in RW-replenished urban landscape waters was significantly higher than that in SW-replenished urban landscape waters (p < 0.05), which suggested that use of RW may increase the amount of specific ARGs to urban landscape waters. Interestingly, among six urban landscape waters, RW-replenished urban landscape waters had a relatively rich variety of ARGs (12-15 of 18 ARGs) but a low relative abundance of ARGs (458.90-1944.67 copies/16S × 10⁶). The RW replenishment was found to have a certain impact on the bacterial diversity and prevalence of ARGs in urban landscape waters, which provide new insight into the effect of RW replenishment on urban landscape waters.

Effect of preferential UV photolysis on the source control of antibiotic resistome during subsequent biological treatment systems

The environmental spread of antibiotic resistance genes (ARGs) from the direct application of traditional biological treatment systems for antibiotics in water is a potential public health threat. UV photolysis has been proved to be an efficient pretreatment method for antibacterial activity elimination, but the fate of antibiotic resistome in subsequent bioreactors fed with pretreated florfenicol (FLO) in synthetic wastewater is still unknown. Antibacterial activity in synthetic wastewater was effectively eliminated by UV irradiation pretreatment, and the diversity and abundance of detected ARGs in both aerobic and anaerobic bioreactors were significantly lower than those without pretreatment. Meanwhile, UV irradiation pretreatment shaped the structure and composition of sludge microbial communities in the subsequent bioreactors closer to those of the FLO-free groups. The relative abundances of Pseudomonas and Escherichia-Shigella working as the potential hosts of ARGs were significantly reduced in aerobic and anaerobic bioreactors, respectively. The significantly positive correlation between floR and intI1 and the decrease of intI1 abundance in UV photolytic pretreatment groups indicated that the horizontal transfer of floR was decreased. The study provides new insights into the effect of preferential UV photolysis as a pretreatment method on the source control of antibiotic resistome in subsequent biological treatment process.

Microbial communities of biofilms developed in a chlorinated drinking water distribution system: A field study of antibiotic resistance and biodiversity

Antibiotic resistance and biodiversity were investigated in microbial communities attached to inner surfaces of water supply fittings in a chlorinated drinking water distribution system (DWDS) supplied by two independent water treatment plants (WTPs) drawing the same source water. The investigation of the effect of the season, the applied water treatment technology, and type, material, and age of water supply fittings on both antibiotic resistance and biodiversity in biofilms involved collection of tubercles during summer and winter seasons throughout the DWDS. A total of 16 samples were collected (8 per season) from areas supplied by two independent WTPs. Culturable aerobic antibiotic resistant bacteria (ARB) proved more prevalent in summer. Various antibiotic resistance genes (ARGs) were detected, confirming the role of biofilms as ARGs reservoirs, but the abundances of quantified genes (sulI, ermB, qacEΔ1, intI1) were low (a range of <LOQ to 2313 gene copies/mg dry mass of tubercles) throughout the DWDS. In terms of microbial community composition, Proteobacteria were dominant in each sample (51.51-97.13%), and the most abundant genus was Desulfovibrio (0.01-66.69%) belonging to sulphate-reducing bacteria. Biodiversity of microbial communities was shaped by many coexisting factors, including season, water supply fitting material, and sampling site location. Spatial distribution analysis revealed that although only samples collected at the same sampling sites were similar to each other in terms of antibiotic resistance, some samples collected in the close proximity were similar in terms of biodiversity. This suggests that antibiotic resistance spreads only locally over small distances in drinking water biofilms. Although actual drinking water biofilms have been previously investigated in terms of microbial biodiversity, this is the first study that characterised both antibiotic resistance and biodiversity of microbial communities attached to inner surfaces of a real DWDS functioning for decades.

Oxytetracycline Adsorption from Aqueous Solutions on Commercial and High-Temperature Modified Activated Carbons

The aim of the work was to evaluate the possibility of using commercial and modified activated carbons for the removal of oxytetracycline from aqueous solutions. The kinetics and statics of adsorption as well as the effect of the activated carbon dose and solution pH on the efficiency of the oxytetracycline adsorption were analyzed. Based on the study of oxytetracycline adsorption isotherms, the activated carbons were ranked in the following order: F-300 > WG-12 > Picabiol > ROW08 > WACC 8 × 30 > F-100 > WAZ 0.6–2.4. The most effective activated carbons were characterized by large specific surfaces. The best matching results were obtained for: Redlich–Peterson, Thot and Jovanovic models, and lower for the most frequently used Freundlich and Langmuir models. The adsorption proceeded better from solutions with pH = 6 than with pH = 3 and 10. Two ways of modifying activated carbon were also assessed. A proprietary method of activated carbon modification was proposed. It uses the heating of activated carbon as a result of current flow through its bed. Both carbons modified at 400 °C in the rotary kiln and on the proprietary SEOW (Joule-heat) modification stand enabled to obtain adsorbents with higher and comparable monolayer capacities. The advantage of the proposed modification method is low electricity consumption.

Preparation and bacteriostatic research of porous polyvinyl alcohol / biochar / nanosilver polymer gel for drinking water treatment

Microbial contamination in drinking water has become an important threat to human health. There is thus an urgent need to develop antibacterial materials to treat drinking water. Here, porous silver-loaded biochar (C–Ag) was prepared using corn straw as the substrate and silver as the antibacterial agent. C–Ag was then uniformly distributed in polyvinyl alcohol gel beads of eluted calcium carbonate to prepare p-PVA/C–Ag antibacterial composite. The polymer composites were tested by FT-IR, XRD, SEM and TG-DSC. The results showed that C–Ag was more evenly distributed in the PVA gel spheres. Antibacterial experiments showed that p-PVA/C–Ag greatly inhibited Escherichia coli. Practical application tests revealed that p-PVA/C–Ag showed high and sustained bactericidal inhibition and reusability. Generally, p-PVA/C–Ag composite shows high potential to be applied to drinking water treatment.

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.