Total Abundance Of Antibiotic Resistance Genes Research Articles

Seasonal distribution of antibiotic resistance genes under the influence of land-ocean interaction in a semi-enclosed bay.

The irrational use of antibiotics has given rise to the proliferation of antibiotic resistance genes (ARGs) in coastal bays. There were few reports on the seasonal distribution of ARGs under the influence of land-ocean interaction in coastal bay. This work studied the seasonal and spatial proliferation of ARGs under the influences of land-ocean interaction in the Sishili Bay. Ten ARGs including tetB, tetG, tetX, sul1, sul2, qnrA, qnrB, qnrS, ermF, ermT and class 1 integron-integrase gene (intI1) were detected and quantified. The relative abundances of intI1 and most of ARGs were in orders of magnitude of 1×10-7-2 copies/16S rRNA copies. The abundances of total ARGs in autumn and summer were much higher than those in the other seasons. Estuary, port and aquaculture farms were important reservoirs of ARGs in the bay. The nutrient levels in coastal water were positively associated with most of the ARGs and intI1, indicating that the water quality was an important driver of ARGs and their transmission. The land-based discharge and seawater stratification were proved to be the dominant driving factors for the seasonal distribution of ARGs in the coastal bay. The land-based discharge and seawater stratification were enhanced from spring to summer, which led to the sharp increase in ARGs in the surface water of the bay.

Unveiling the risks and critical mechanisms of polyhexamethylene guanidine on the antibiotic resistance genes propagation during sludge fermentation process

This study mainly investigated the environmental risks of polyhexamethylene guanidine (PHMG) occurred in waste activated sludge (WAS) on the antibiotic resistance genes (ARGs) spread during anaerobic fermentation, and disclosed the critical mechanisms. The total ARGs abundance was increased by 32.2–46.4% at different stressing levels of PHMG. The main resistance mechanism categories of ARGs shifted to the target alternation and efflux pump. PHMG disintegrated WAS structure and increased the cell permeability, which benefitted the mobile genetic elements (MGEs) release and horizontal transfer of ARGs. Besides, PHMG induced the enrichment of potential ARGs hosts (i.e., Burkholderia, Bradyrhizobium and Aeromonas). Moreover, PHMG upregulated the metabolic pathways (i.e., two-component system, quorum sensing, and ATP-binding cassette transporters) and critical genes expression (i.e., metN, metQ, rpfF, rstA and rstB) related with ARGs generation and dissemination. Structural equation model analysis revealed that microbial community structure was the predominant contributor to the ARGs propagation.

Globally distributed mining-impacted environments are underexplored hotspots of multidrug resistance genes

Mining is among the human activities with widest environmental impacts, and mining-impacted environments are characterized by high levels of metals that can co-select for antibiotic resistance genes (ARGs) in microorganisms. However, ARGs in mining-impacted environments are still poorly understood. Here, we conducted a comprehensive study of ARGs in such environments worldwide, taking advantage of 272 metagenomes generated from a global-scale data collection and two national sampling efforts in China. The average total abundance of the ARGs in globally distributed studied mine sites was 1572 times per gigabase, being rivaling that of urban sewage but much higher than that of freshwater sediments. Multidrug resistance genes accounted for 40% of the total ARG abundance, tended to co-occur with multimetal resistance genes, and were highly mobile (e.g. on average 16% occurring on plasmids). Among the 1848 high-quality metagenome-assembled genomes (MAGs), 85% carried at least one multidrug resistance gene plus one multimetal resistance gene. These high-quality ARG-carrying MAGs considerably expanded the phylogenetic diversity of ARG hosts, providing the first representatives of ARG-carrying MAGs for the Archaea domain and three bacterial phyla. Moreover, 54 high-quality ARG-carrying MAGs were identified as potential pathogens. Our findings suggest that mining-impacted environments worldwide are underexplored hotspots of multidrug resistance genes.

Natural selenium stress influences the changes of antibiotic resistome in seleniferous forest soils

BackgroundMetal(loid)s can promote the spread and enrichment of antibiotic resistance genes (ARGs) in the environment through a co-selection effect. However, it remains unclear whether exposure of microorganisms to varying concentrations of selenium (Se), an essential but potentially deleterious metal(loid) to living organisms, can influence the migration and distribution of ARGs in forest soils.ResultsPrecisely 235 ARGs conferring resistance to seven classes of antibiotics were detected along a Se gradient (0.06–20.65 mg kg−1) across 24 forest soils. (flor)/(chlor)/(am)phenicol resistance genes were the most abundant in all samples. The total abundance of ARGs first increased and then decreased with an elevated available Se content threshold of 0.034 mg kg−1 (P = 2E−05). A structural equation model revealed that the dominant mechanism through which Se indirectly influences the vertical migration of ARGs is by regulating the abundance of the bacterial community. In addition, the methylation of Se (mediated by tehB) and the repairing of DNA damages (mediated by ruvB and recG) were the dominant mechanisms involved in Se resistance in the forest soils. The co-occurrence network analysis revealed a significant correlated cluster between Se-resistance genes, MGEs and ARGs, suggesting the co-transfer potential. Lelliottia amnigena YTB01 isolated from the soil was able to tolerate 50 μg mL−1 ampicillin and 1000 mg kg−1 sodium selenite, and harbored both Se resistant genes and ARGs in the genome.ConclusionsOur study demonstrated that the spread and enrichment of ARGs are enhanced under moderate Se pressure but inhibited under severe Se pressure in the forest soil (threshold at 0.034 mg kg−1 available Se content). The data generated in this pilot study points to the potential health risk associated with Se contamination and its associated influence on ARGs distribution in soil.

Effects of Trophic Level and Land Use on the Variation of Animal Antibiotic Resistome in the Soil Food Web.

In recent years, it has been increasingly recognized that soil animals are hidden reservoirs of antibiotic resistance genes (ARGs) and play a vital role in spreading ARGs in soil ecosystems. However, little is known about the variation of ARGs among different animals in the soil food web and effects of trophic levels and land uses on them. We characterized the antibiotic resistomes of 495 soil animal samples collected from six regions across China, including two different land uses. A total of 265 ARGs were detected in all animal samples, and relative abundances of ARGs in animals were significantly higher than in soils. In addition, significant differences in ARGs were observed among different animal groups. Twelve common ARGs were identified among all animal groups, accounting for 17.4% of total ARGs abundance. A positive and significant correlation was found between δ15N values (trophic level) and total ARGs abundance in animals. The relative abundance of ARGs in the soil food web from arable land was higher than forest land. Changes in soil antibiotics may indirectly affect animal resistome by altering soil ARGs. This study suggests that the risk of ARGs spreading through the food web is greater in arable than in forest ecosystems.

Fate of Antibiotic Resistance Genes and Changes in Bacterial Community With Increasing Breeding Scale of Layer Manure.

The use of antimicrobials in intensive poultry production is becoming increasingly common because of its high throughput of meat and egg products. However, the profile of antibiotic resistance genes (ARGs) and the underlying mechanisms in different breeding scale farms were not fully explored. The study examined the profiles of ARGs in layer manure from three free-range and 12 intensive layer farms with different scales (N500, N5000, N10000, and N20000). A quantitative PCR (qPCR) array was used to quantify ARGs, and microbial community structure was analyzed by 16S rRNA gene sequencing. A total of 48 ARGs, belonging to seven major types, were identified in the layer manure samples, with sul2, tetM-01, and ermB being the predominant ones. The abundance, diversity, and mobility potential of ARGs in layer manure changed significantly with the increasing of the breeding scale. The abundances of total ARGs had significantly positive correlations with mobile genetic elements (MGEs), suggesting the mobility potential of ARGs in layer manure samples. Bacterial abundance did not show significant differences among the five group manure samples. However, bacterial diversity showed an increasing trend along the breeding scale. Pathogenic Bacteroidetes increased in the largest-scale layer manure samples and showed significant positive correlations with most ARGs. Network analysis revealed significant co-occurrence patterns between ARGs and microbial taxa, indicating ARGs had a wide range of bacterial hosts. Proteobacteria and Firmicutes were potential hosts for tetracycline and macrolide-lincosamide-streptogramin B (MLSB) resistant genes. Our results indicated that the expansion of the breeding scale of a farm promotes the abundance, diversity, and mobility potential of ARGs in layer manure.

Long-Term, Simultaneous Impact of Antimicrobials on the Efficiency of Anaerobic Digestion of Sewage Sludge and Changes in the Microbial Community

The aim of this study was to evaluate the influence of simultaneous, long-term exposure to increasing concentrations of three classes of antimicrobials (β-lactams, fluoroquinolones and nitroimidazoles) on: (1) the efficiency of anaerobic digestion of sewage sludge, (2) qualitative and quantitative changes in microbial consortia that participate in methane fermentation, and (3) fate of antibiotic resistance genes (ARGs). Long-term supplementation of sewage sludge with a combination of metronidazole, amoxicillin and ciprofloxacin applied at different doses did not induce significant changes in process parameters, including the concentrations of volatile fatty acids (VFAs), or the total abundance of ARGs. Exposure to antibiotics significantly decreased methane production and modified microbial composition. The sequencing analysis revealed that the abundance of OTUs characteristic of Archaea was not correlated with the biogas production efficiency. The study also demonstrated that the hydrogen-dependent pathway of methylotrophic methanogenesis could significantly contribute to the stability of anaerobic digestion in the presence of antimicrobials. The greatest changes in microbial biodiversity were noted in substrate samples exposed to the highest dose of the tested antibiotics, relative to control. The widespread use of antimicrobials increases antibiotic concentrations in sewage sludge, which may decrease the efficiency of anaerobic digestion, and contribute to the spread of antibiotic resistance (AR).

Monitoring and evaluation of antibiotic resistance genes in three rivers in northeast China.

Antibiotic resistance genes (ARGs) have become an important public health problem. In this study, we used metagenomic sequencing to analyze the composition of ARGs in selected original habitats of northeast China, comprising three different rivers and riverbank soils of the Heilongjiang River, Tumen River, and Yalu River.Twenty types of ARG were detected in the water samples. The major ARGs were multidrug resistance genes, at approximately 0.5 copies/16S rRNA, accounting for 57.5% of the total ARG abundance. The abundance of multidrug, bacitracin, beta-lactam, macrolide-lincosamide-streptogramin, sulfonamide, fosmidomycin, and polymyxin resistance genes covered 96.9% of the total ARG abundance. No significant ecological boundary of ARG diversity was observed. The compositions of the resistance genes in the three rivers were very similar to each other, and 92.1% of ARG subtypes were shared by all water samples. Except for vancomycin resistance genes, almost all ARGs in riverbank soils were detected in the river water. About 31.05% ARGs were carried by Pseudomonas. Opportunistic pathogenic bacteria carrying resistance genes were mainly related to diarrhea and respiratory infections. Multidrug and beta-lactam resistance genes correlated positively with mobile genetic elements (MGEs), indicating a potential risk of diffusion.The composition of ARGs in three different rivers was similar, indicating that climate plays an important role in ARG occurrence. ARG subtypes in river water were almost completely the same as those in riverbank soil. ARGs had no significant geographical distribution characteristics. Many ARGs were carried by human pathogenic bacteria related to diarrhea and respiratory infections, such as Pseudomonas aeruginosa and Aeromonas caviae. In general, our results provide a valuable dataset of river water ARG distribution in northeast China. The related ecological and geographical distribution characteristics should be further explored.

Migration of antibiotic resistance genes and evolution of flora structure in the Xenopus tropicalis intestinal tract with combined exposure to roxithromycin and oxytetracycline

The intestinal flora is one of the most important environments for antibiotic resistance development, owing to its diverse mix of bacteria. An excellent medicine model organism, Xenopus tropicalis, was selected to investigate the spread of antibiotic resistance genes (ARGs) in the intestinal bacterial community with single or combined exposure to roxithromycin (ROX) and oxytetracycline (OTC). Seventeen resistance genes (tetA, tetB, tetE, tetM, tetO, tetS, tetX, ermF, msrA, mefA, ereA, ereB, mphA, mphB, intI1, intI2, intI3) were detected in the intestines of Xenopus tropicalis living in three testing tanks (ROX tanks, OTC tanks, ROX + OTC tanks) and a blank tank for 20 days. The results showed that the relative abundance of total ARGs increased obviously in the tank with single stress but decreased in the tank with combined stress, and the genes encoding the macrolide antibiotic efflux pump (msrA), phosphatase (mphB) and integron (intI2, intI3) were the most sensitive. With the aid of AFM scanning, DNA was found to be scattered short chain in the blank, became extended or curled and then compacted with the stress from a single antibiotic, and was compacted and then fragmented with combined stress, which might be the reason for the variation of the abundance of ARGs with stress. The ratio of Firmicutes/Bacteroides related to diseases was increased by ROX and OTC. The very significant correlation between intI2 and intI3 with tetS (p ≤ 0.001) hinted at a high risk of ARG transmission in the intestines. Collectively, our results suggested that the relative abundance of intestinal ARGs could be changed depending on the intestinal microbiome and DNA structures upon exposure to antibiotics at environmental concentrations.

Resistome and mobilome in surface runoff from manured soil as affected by setback distance

Land application of livestock manure introduces antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) into the soil environment. The objectives of this study were to examine the changes of resistome and mobilome in runoff and soil as a function of setback distance, i.e., the distance between manured soil and surface water, and to quantify the contributions of manure and background soil to the ARGs and MGEs in surface runoff. The resistome and mobilome in runoff and soil from a field-scale plot study were characterized using a high throughput quantitative polymerase chain reaction (HT-qPCR) array. It was estimated that a setback distance of ~40 m is required to reduce the total abundance of ARGs and MGEs in runoff from amended plots to that in control runoff. The resistome and mobilome of the soil in the setback region was not affected by manure-borne ARGs and MGEs. SourceTracker analyses revealed that background soil gradually became the predominant source of the ARGs and MGEs in runoff as setback distance increased. The results demonstrate how manure-borne ARGs and MGEs dissipated in agricultural runoff with increasing setback distance and had limited impacts on the resistome and mobilome of soil within the setback region.

Response behavior of antibiotic resistance genes to zinc oxide nanoparticles in cattle manure thermophilic anaerobic digestion process: A metagenomic analysis

This work investigated the metagenomics-based behavior of antibiotic resistance genes (ARGs) during cattle manure anaerobic digestion with zinc oxide nanoparticles (ZnO NPs) that are commonly used as animal feed additives. The 6.6% decrease in total ARGs abundance while remained unchanged ARGs diversity with ZnO NPs (5 mg/g total solid), suggested ZnO NPs may mitigate ARGs risk by abundance. Also, ZnO NPs affected ARGs with mechanisms specifically of antibiotic inactivation and antibiotic target change, and declined potential hosts’ abundance (bacterial genus Ruminiclostridium, Riminococcus, and Paenibacillus) which mainly contributed to the decreased ARGs’ abundance. Besides, microbial chemotaxis decreased by 17% with ZnO NPs compared to that without nanoparticles indicated a depression on potential hosts, who could develop the mechanism to adapt to altered digestion conditions, which probably inhibited the ARGs’ propagation. These findings are important to promote understanding of the potential ARGs risks in treatments of livestock wastes containing animal feed additives.

Reduction effect of individual N, P, K fertilization on antibiotic resistance genes in reclaimed water irrigated soil

The transfer of antibiotic resistance genes (ARGs) in soil under reclaimed water irrigation poses a potential environmental risk. Regulation of NPK fertilizer could influence the behavior of bacterial communities, mobile genetic elements (MGEs), and soil properties, which determine the fate of ARGs. To identify the key element in NPK fertilizer and realize efficient regulation, we explored the effect of individual N, P, K fertilization on ARG variation in tomato rhizosphere and bulk soils. Compared with an unfertilized treatment, N fertilization resulted in greater decreases in the abundance of ARGs (decreases of 24.06%–73.09%) than did either P fertilization (increases of up to 35.84%, decreases of up to 58.80%) or K fertilization (decreases of 13.47%–72.47%). The influence of different forms of N (CO(NH2)2, NaNO3, and NH4HCO3), P (Ca(H2PO4)2 and CaMgO4P+), and K (KCl and K2(SO4)) fertilizers was also investigated in this study, and showed the influence of NaNO3, CaMgO4P+, and K2(SO4) on reducing ARGs abundance was greater in different types of N, P, K fertilizers. Bacterial communities showed the strongest response to N fertilization. The reduced bacterial diversity and abundance of ARG-host and non-host organisms explained the decline of total ARG abundance in soil. In soils fertilized with either P or K, the effect of soil properties, especially total nitrogen and pH, on ARG variation was greater than that of bacterial community and MGEs. These results suggest that N regulation of in NPK fertilizer may be an effective way to reduce the risks of ARGs in soil associated with reclaimed water irrigation.

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

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

Effects of mineral additives on antibiotic resistance genes and related mechanisms during chicken manure composting

In this study, two typical minerals (diatomite and bentonite) were applied during composting, and their influences on antibiotics, antibiotic resistance genes (ARGs), intI1 and the bacterial communities were investigated. The relative abundance of total ARGs decreased by 53.72% and 59.54% in diatomite and bentonite addition compared with control on day 42. The minerals addition also reduced the relative abundance of intI1, as much as 41.41% and 59.81% in diatomite and bentonite treatments. Proteobacteria and Firmicutes were the dominant candidate hosts of the major ARGs. There was a significant correlation between total ARGs and intI1 during the composting. Structural equation models further demonstrated that intI1 and antibiotics were the predominant direct factors responsible for ARG variations, and composting properties and bacterial community composition also shifted the variation of ARG profiles by influencing intI1. Overall, these findings suggest that diatomite and bentonite could decrease the potential proliferation of ARGs in chicken manure.

Intervention of antimicrobial peptide usage on antimicrobial resistance in aquaculture

Antibiotic resistance genes (ARGs) widely exist in diverse matrices to pose potential risks and attract global attention. This study performed tilapia-cultivation experiment to discuss the intervention of antimicrobial peptide usage on antimicrobial resistance in aquaculture by analyzing 29 target ARGs in water, residue, and fish muscle samples. The sul1 gene was the dominant ARG in most of samples while absolute abundances of total ARGs were in the range of 1.5 × 102-2.3 × 107 copies/mL in water samples and 2.1 × 108-3.9 × 109 copies/g in the residue and fish muscle samples. Compared with antibiotic treatment, the cecropin treatment could significantly reduce the absolute abundance of ARGs and intI1 in all samples. Proteobacteria were the dominant phylum for most of samples while Aeromonas/Cetobacterium served as the dominant genus for samples with antibiotic/cecropin treatment. Network analysis showed that cecropin treatment could significantly reduce occurrence of multi-drug resistant bacteria and the correlation between genera and ARGs. Results of partial least squares structural equation modeling which was used to discuss the influential factors of ARGs exhibited that antibiotics could increase ARGs, further proving that cecropin peptide could effectively reduce ARGs in aquaculture. This study will provide important information on controlling ARGs in aquaculture in terms of antimicrobial peptide application.

Behaviors of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) during the pilot-scale biophysical drying treatment of sewage sludge: Reduction of ARGs and enrichment of MRGs

Biophysical drying (BPD) is one of the best alternatives for reducing the moisture content from sewage sludge by utilizing biological heat from aerobic reactions. However, the fate of emerging pollutants during BPD process is largely unknown. In this study, the fates of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) were investigated during a pilot-scale BPD treatment of sewage sludge. A total of 20 types (388 subtypes) of ARGs and 16 types (364 subtypes) of MRGs were detected by metagenomic sequencing and annotation. The total abundance of ARGs decreased from 1.78 ± 0.13 copies/16S rRNA to 0.55 ± 0.01 copies/16S rRNA while the total abundance of MRGs increased from 3.81 ± 0.01 copies/16S rRNA to 6.30 ± 0.02 copies/16S rRNA, showing the distinct behaviors of ARGs and MRGs during BPD process. The ARGs were effectively reduced during the mesophilic and thermophilic stages of BPD process and the reduction of ARGs fitted the first-order kinetic model (p < 0.01). Microbial community analysis showed that the abundance of potential pathogens also decreased during BPD process. On the contrary, the abundances of most MRG subtypes (78.3%) were enriched during BPD process with up to 122-fold change, implying the potential threats for the end product of BPD process. These results together indicate that although the ARGs and potential pathogens can be effectively reduced during BPD process, the safety for the end product still needs to be considered due to the enrichment of MRGs.

Can radicals-orientated chemical oxidation improve the reduction of antibiotic resistance genes (ARGs) by mesophilic anaerobic digestion of sludge?

The dissemination of antibiotic resistance genes (ARGs) increases risks towards human health and environmental safety. This work investigates the control of ARGs abundance and bacterial community evolution involved in waste activated sludge (WAS) treatment by chemical conditioning and subsequent mesophilic anaerobic digestion (MAD). The different chemical oxidation processes of ferrous iron-activated oxone and hydrogen peroxide (PMS-Fe2+ and H2O2-Fe2+) and thermal-activated oxone (PMS@80 ℃) were investigated, and the ferric chloride (FeCl3) and inactivated oxone (PMS) were compared. PMS@80 ℃ decreased the absolute abundance of most ARGs by 10.6–99.3% and that of total ARGs by 66.3%. Interestingly, oxidation pretreatment increased rather than decreased the relative abundance of most ARGs. MAD with PMS@80 ℃ pretreatment increased the absolute abundance of total ARGs by 51.6%, and other MAD processes decreased it by 8.6–47.4%. PMS-Fe2+ and PMS@80 ℃ negatively inhibited methane production from 98.3 to 81.7 and 94.4 mL/g VSS in MAD. MAD effluent showed high abundance of Arcobacter genus in the range of 8.1–17.4% upon PMS-based pretreatment, possibly related to sulfur oxidation, nitrate reduction, and blaVEB enrichment. The radicals-orientated chemical oxidation can hardly improve the ARGs elimination by MAD due to the extremely high competitive organics in sludge.

An assessment of resistome and mobilome in wastewater treatment plants through temporal and spatial metagenomic analysis

Wastewater treatment plants (WWTPs) are regarded as critical points in disseminating antibiotic resistance genes (ARGs). In particular, the discharging effluents from WWTPs generally bring downstream catchment areas exogenous ARGs and resistant bacteria. However, there lacks a sufficient assessment of the resistome and mobilome in effluents. In this study, a consecutive monthly sampling was conducted over 13 months in three Hong Kong (HK) WWTPs for metagenomic sequencing. Prevalence information of ARGs and mobile genetic elements (MGEs) was compared with counterparts in effluents from cities of North America, South America, Europe, and Asia. Moreover, a publicly accessible platform integrating the exposure ranking scheme, which was based on the global archive of ARG abundance, and a readily implementable online pipeline was developed to benefit communication in academia and government consultancy. Results demonstrated HK WWTPs were featured high ARG removal efficiency of 2.34–2.43 log reduction rate, and effluents were ranked in moderate levels of Level 2 and Level 3 in the exposure prioritizing scheme based on total ARG abundance. Moreover, absolute quantification of temporal variations of effluent resistome disclosed distinct changes over time among varied ARG types which were associated with prevalently used antibiotics, including quinolone and sulfonamide. This reinforces the need for real-time management of WWTP systems. Notably, ARGs of anthropogenic prevalence, high mobility, and potential pathogenicity were found to be present in HK effluents, drawing attention to the necessity for improved risk management. In addition, source tracking of effluent resistome and structural equation model analysis was conducted to explore the disparity in ARG abundance and diversity in different samples. The discovery of this study and the recommendation of a comprehensive exposure assessment will facilitate decision-making in resistome management in WWTPs to reduce the ARG and antibiotic resistant bacteria (ARB) contamination in the receiving environments.

Implications for mitigation of antibiotic resistance: Differential response of intracellular and extracellular antibiotic resistance genes to sludge fermentation coupled with thermal hydrolysis

Thermal hydrolysis pretreatment (THP) can effectively remove the antibiotic resistance genes (ARGs) from sewage sludge, but the rebounding effects in the subsequent anaerobic fermentation are often observed. The purpose of this study was to elucidate the distribution and fate of intracellular and extracellular ARGs (iARGs and eARGs) in the sludge acidogenic fermentation process coupled with THP. Our results revealed that THP significantly reduced the absolute abundance of total ARGs in raw sludge but increased eARGs by 0.3–1.4 log units under practical conditions (140 °C for 30 min). There is no significant difference in the removal of total ARGs between the two acidogenic fermenters receiving raw and hydrolyzed sludge, with iARGs prevailing in the produced biosolids. The succession of bacterial community and the co-occurrence relationships among ARG type, mobile genetic elements and bacterial taxa were observed, suggesting a phylogenetic basis for the iARGs patterns in fermented sludge. However, eARGs were susceptible to biodegradation with a half-life of 2.34 h and they contributed limitedly to the ARGs propagation through transformation. These findings suggest an emphasis on the mitigation of iARGs during the acidogenic fermentation of sludge, which would be achieved by lowering the richness and physicochemical destruction of potential hosts.

Fate of land-based antibiotic resistance genes in marginal-sea sediment: Territorial differentiation and corresponding drivers

No large-scale investigations on fate of land-based antibiotic resistance genes (ARGs) in marginal sea have been reported. The Yellow Sea which is an important marginal sea was selected to investigate the fate, territorial differentiation, and drivers of target ARGs in marginal-sea sediments. ARGs might spread from land to sea with the average absolute abundance of total ARGs in marine/coastal sediments reaching 1.23 × 104/9.79 × 104 copies/g. The Yellow Sea Cold Water Mass was firstly observed to possibly have potential inhibition effect on occurrence of ARGs in marine sediments. Marine sediments showed significant difference from coastal sediments by considering ARGs, microbial community, and sediment features. Network analysis showed that interaction between ARGs and microbial community in coastal sediments was more frequent than that in marine sediment. The anthropogenic factors posed high positive effect on ARGs in marine/coastal sediments with contribution coefficient of 0.524/1.094 while bacterial community mainly posed positive effect on ARGs in marine sediments with contribution coefficient of 0.475, illustrating that spread and proliferation of land-based ARGs in marine sediments might be mainly affected by anthropogenic and microbial factors. These findings provided new information on fate and drivers of ARGs in marginal sea.