Sulfonamide Resistance Genes Sul1 Research Articles

How can the microbial community in watershed sediment maintain its resistance in the presence of shifting antibiotic residuals?

The widespread presence of antibiotics in global watershed environments poses a serious threat to public health and ecosystems. It is essential to examine the resistance of microbial communities in watershed environments in response to shifting antibiotic residues. Sediment samples were collectd from seven sites across a watershed, encompassing surface sediment (0-10 cm) and bottom sediment (30-40 cm) depths. The aim was to replicate exposure scenarios to different antibiotics (oxytetracycline (OTC) and sulfadiazine (SD)) at varying concentrations (0, 10, and 100 μg/L) in sediment overlying water, within controlled laboratory settings. The study findings revealed significant variations in the microbial community structure of sediments between different treatments, with distinct differences observed in the upper stream and top sediment layers compared to the sediments located downstream and in the bottom layers. After the introduction of antibiotics, a significant decrease in microbial nodes was observed in the genus-level co-occurrence network analysis of the bottom sediment layer, particularly in the OTC treatment groups. In contrast, the downstream region displayed more robust correlations among the top 20 genera than the upstream area. There was no significant variance observed in the expression of Antibiotic resistance genes (ARGs), consisting of tetracycline resistance genes (tetC, tetG, tetM, tetW, and tetX) and sulfonamide resistance genes (sul1, sul2, and sul3), between sediments in the top and bottom layers. Nevertheless, downstream samples exhibited significantly higher levels of ARGs when compared to upstream samples. Network correlation analysis indicated notably lower correlations between ARGs and bacterial genera in sediments from upstream or surface layers compared to those in downstream or deeper layers. Moreover, correlations in the sediments from surface layers and upstream regions showed a decreasing trend with increasing SD exposure concentrations, while those in deeper layers and downstream areas remained relatively stable. The presence of antibiotics notably enhanced the correlation between sediment properties and ARGs, particularly emphasizing associations with total carbon, nitrogen, and sulfur content. However, the introduction of SD and OTC resulted in a decrease in the influence of these sediment factors on microbial community functions related to sulfur and nitrogen metabolism, as indicated by KEGG (Kyoto Encyclopedia of Genes and Genomes) annotation. The research provided empirical evidence on how microbial resistance responds to changes in antibiotics in sediment samples taken from various depths and locations within a watershed. It emphasized the urgent need for heightened awareness of the movement and alteration of antibiotic resistance patterns in watershed ecosystems.

Sulfonamide resistance evaluation in five animal species and first report of sul4 in companion animals

Sulfonamides are one of the oldest groups of antibacterial agents with a broad-spectrum, used as first line treatment in bacterial infections. Their widespread use produced a selective pressure on bacteria, as observed by the high incidence of sulfonamides resistance mainly in Gram negative bacteria isolated from animals. In this research, the presence of sulfonamide resistance genes (sul1, sul2, sul3, and sul4) in phenotypically resistant Escherichia coli isolates has been studied. These genes were amplified in isolates recovered from five animal species, with different interactions to humans: cattle, swine, poultry as livestock, and dogs and cats as companion animals. Isolates were collected according to their phenotypic resistance, and the magnetic bead-based Luminex technology was applied to simultaneously detect sul target genes. The frequency of sul genes was highest in swine, among livestock isolates. The sul1 and sul2 were the most frequently sulfonamide resistance genes detected in all phenotypically resistant isolates. Notably, in companion animals, with a closest interaction with human, sul4 gene was detected. To our knowledge, this is the first report of the presence of sul4 gene in E. coli collected from animals, whereas previously the presence of this gene was reported in environmental, municipal wastewater and human clinical isolates. These results highlighted the importance of continuous antimicrobial resistant genes monitoring in animal species, with a special care to companion animals.

Urban stormwater green infrastructure: Evaluating the public health service role of bioretention using microbial source tracking and bacterial community analyses

Bioretention cells (BRCs) control stormwater flow on-site during precipitation, reducing runoff and improving water quality through chemical, physical, and biological processes. While BRCs are effective in these aspects, they provide habitats for wildlife and may face microbial hazards from fecal shedding, posing a potential threat to human health and the nearby environment. However, limited knowledge exists regarding the ability to control microbial hazards (e.g., beyond using typical indicator bacteria) through stormwater biofiltration. Therefore, the purpose of this study is to characterize changes in the bacterial community of urban stormwater undergoing bioretention treatment, with the goal of assessing the public health implications of these green infrastructure solutions. Samples from BRC inflow and outflow in Columbus, Ohio, were collected post-heavy storms from October 2021 to March 2022. Conventional culture-based E. coli monitoring and microbial source tracking (MST) were conducted to identify major fecal contamination extent and its sources (i.e., human, canine, avian, and ruminant). Droplet digital polymerase chain reaction (ddPCR) was utilized to quantify the level of host-associated fecal contamination in addition to three antibiotic resistant genes (ARGs): tetracycline resistance gene (tetQ), sulfonamide resistance gene (sul1), and Klebsiella pneumoniae carbapenemase resistance gene (blaKPC). Subsequently, 16S rRNA gene sequencing was conducted to characterize bacterial community differences between stormwater BRC inflow and outflow. Untreated urban stormwater reflects anthropogenic contamination, suggesting it as a potential source of contamination to waterbodies and urban environments. When comparing inlet and outlet BRC samples, urban stormwater treated via biofiltration did not increase microbial hazards, and changes in bacterial taxa and alpha diversity were negligible. Beta diversity results reveal a significant shift in bacterial community structure, while simultaneously enhancing the water quality (i.e., reduction of metals, total suspended solids, total nitrogen) of urban stormwater. Significant correlations were found between the bacterial community diversity of urban stormwater with fecal contamination (e.g. dog) and ARG (sul1), rainfall intensity, and water quality (hardness, total phosphorous). The study concludes that bioretention technology can sustainably maintain urban microbial water quality without posing additional public health risks, making it a viable green infrastructure solution for heavy rainfall events exacerbated by climate change.

Distribution of bacterial community structures and spread of antibiotic resistome at industrially polluted sites of Mini River, Vadodara, Gujarat, India.

The influence of anthropogenic pollution on the distribution of bacterial diversity, antibiotic-resistant bacteria (ARBs), and antibiotic resistance genes (ARGs) was mapped at various geo-tagged sites of Mini River, Vadodara, Gujarat, India. The high-throughput 16S rRNA gene amplicon sequencing analysis revealed a higher relative abundance of Planctomycetota at the polluted sites, compared to the pristine site. Moreover, the relative abundance of Actinobacteriota increased, whereas Chloroflexi decreased in the water samples of polluted sites than the pristine site. The annotation of functional genes in the metagenome samples of Mini River sites indicated the presence of genes involved in the defence mechanisms against bacitracin, aminoglycosides, cephalosporins, chloramphenicol, streptogramin, streptomycin, methicillin, and colicin. The analysis of antibiotic resistome at the polluted sites of Mini River revealed the abundance of sulfonamide, beta-lactam, and aminoglycoside resistance. The presence of pathogens and ARB was significantly higher in water and sediment samples of polluted sites compared to the pristine site. The highest resistance of bacterial populations in the Mini River was recorded against sulfonamide (≥ 7.943 × 103CFU/mL) and ampicillin (≥ 8.128 × 103CFU/mL). The real-time PCR-based quantification of ARGs revealed the highest abundance of sulfonamide resistance genes sul1 and sul2 at the polluted sites of the Mini River. Additionally, the antimicrobial resistance genes aac(6')-Ib-Cr and blaTEM were also found abundantly at polluted sites of the Mini River. The findings provide insights into how anthropogenic pollution drives the ARG and ARB distribution in the riverine ecosystem, which may help with the development of antimicrobial resistance mitigation strategies.

Exogenous mobile genetic elements and their associated integrons drive the enrichment of antibiotic-resistant genes in the river of a valley basin city (Lanzhou, China).

River is a unique source of drinking water in valley-type cities, affecting local urban development and human lifestyles. However, the key driving factors for dissemination of antibiotic-resistant genes (ARGs) in valley-type urban environments remain unclear. This study aimed to investigate the distribution of ARGs in the Yellow River and to clarify the driving factors of ARGs in a typical valley basin city (Lanzhou, China). The seven selected ARGs with higher abundances including tetracycline resistance genes (tetM, tetX), macrolide resistance genes (ermB, ermF, ereA), and sulfonamide resistance genes (sul1, sul2) were detected. The results showed that the total absolute abundance of all the selected ARGs varied from 9.97 × 1012 to 1.04 × 1015 copies/L in the water body, with higher abundances in the wet season, relative to the dry season. Among these, sulfonamide resistance genes (sul1, sul2) displayed the highest absolute abundance in the river and soil. The ARGs and mobile genetic elements (MGEs) were significantly correlated with bacterial abundance, dissolved organic carbon (DOC), ammonia nitrogen (NH4+), and total nitrogen (TN) levels in the water environment (Mantel test, P < 0.01). Structural equation modeling revealed the direct input of point-source and nonpoint-source ARGs in this area contributed less to the overall level of the ARGs in the water. Among the multiple drivers, the MGEs derived from wastewater treatment plant and anthropogenic nonpoint area positively and directly affected the ARG profiles in water (P < 0.01), rather than the factors of bacterial abundance and physicochemical properties. According to this study, the exogenous MGEs from anthropogenic activities are the main driver for the enrichment of ARGs in the valley-type urban river environment.

Removal of selected sulfonamides and sulfonamide resistance genes from wastewater in full-scale constructed wetlands

Sulfonamides are high-consumption antibiotics that reach the aquatic environment. The threat related to their presence in wastewater and the environment is not only associated with their antibacterial properties, but also with risk of the spread of drug resistance in bacteria. Therefore, the aim of this work was to evaluate the occurrence of eight commonly used sulfonamides, sulfonamide resistance genes (sul1–3) and integrase genes intI1–3 in five full-scale constructed wetlands (CWs) differing in design (including hybrid systems) and in the source of wastewater (agricultural drainage, domestic sewage/surface runoff, and animal runs runoff in a zoo). The CWs were located in low-urbanized areas in Poland and in Czechia. No sulfonamides were detected in the CW treating agricultural tile drainage water. In the other four systems, four sulfonamide compounds were detected. Sulfamethoxazole exhibited the highest concentration in those four CWs and its highest was 12,603.23 ± 1000.66 ng/L in a CW treating a mixture of domestic sewage and surface runoff. Despite the high removal efficiencies of sulfamethoxazole in the tested CWs (86 %–99 %), it was still detected in the treated wastewater. The sul1 genes occurred in all samples of raw and treated wastewater and their abundance did not change significantly after the treatment process and it was, predominantly, at the level 105 gene copies numbers/mL. Noteworthy, sul2 genes were only found in the influents, and sul3 were not detected. The sulfonamides can be removed in CWs, but their elimination is not complete. However, hybrid CWs treating sewage were superior in decreasing the relative abundance of genes and the concentration of SMX. CWs may play a role in the dissemination of sulfonamide resistance genes of the sul1 type and other determinants of drug resistance, such as the intI1 gene, in the environment, however, the magnitude of this phenomenon is a matter of further research.

Prediction and interpretation of pathogenic bacteria occurrence at a recreational beach using data-driven algorithms

Recreational beaches face a threat from pathogenic bacteria that harbor antibiotic resistance genes (ARGs). To predict bacterial occurrence and comprehend their non-linear relationship with hydrometeorological features, advanced machine- and deep-learning algorithms were employed. These algorithms include regression trees (RT), as well as interpretable deep-learning algorithms such as the ‘Input Attention-Long Short-Term Memory (IA-LSTM)’ and ‘Temporal Fusion Transformer (TFT)’. Our focus was on predicting the occurrence of Prevotella, a prevalent pathogenic bacterium found at the beaches. Utilizing model-dependent and model-agnostic interpretation methods, which encompass sensitivity analysis, permutation, and the SHapley Additive exPlanations (SHAP) importance, we evaluated model behavior. RT-based algorithms exhibited predictive capabilities comparable to those of IA-LSTM and TFT, achieving validation Nash–Sutcliffe efficiencies of 0.93, 0.94, and 0.96, respectively. However, the deep-learning algorithms (IA-LSTM and TFT) are surpassed in terms of interpretability. The model-dependent interpretation method identified heavy precipitation as a pivotal hydrometeorological feature linked to increased Prevotella occurrence. Notably, the IA-LSTM identified Prevotella as a potential host for the sulfonamide resistance gene (sul1), suggesting the potential of Prevotella as an indicator for sul1. This research, leveraging interpretable data-driven models, advances our understanding of the hydrometeorological features influencing the occurrence of pathogenic bacteria and the prevalence of ARGs at the beach, and enhances predictive capabilities for bacterial occurrence.

Antibiotic resistance indicator genes in biofilm and planktonic microbial communities after wastewater discharge.

The spread of bacteria with antibiotic resistance genes (ARGs) in aquatic ecosystems is of growing concern as this can pose a risk of transmission to humans and animals. While the impact of wastewater treatment plant (WWTP) effluent on ARG abundance in surface waters has been studied extensively, less is known about the fate of ARGs in biofilms. The proximity and dense growth of microorganisms in combination with the accumulation of higher antibiotic concentrations in biofilms might render biofilms a reservoir for ARGs. Seasonal parameters such as water temperature, precipitation, and antibiotic concentrations should be considered as well, as they may further influence the fate of ARGs in aquatic ecosystems. Here we investigated the effect of WWTP effluent on the abundance of the sulfonamide resistance genes sul1 and sul2, and the integrase gene intI1 in biofilm and surface water compartments of a river in Germany with a gradient of anthropogenic impact using quantitative PCR. Furthermore, we analyzed the bacterial community structure in both compartments via 16S rRNA gene amplicon sequencing, following the river downstream. Additionally, conventional water parameters and sulfonamide concentrations were measured, and seasonal aspects were considered by comparing the fate of ARGs and bacterial community diversity in the surface water compartment between the summer and winter season. Our results show that biofilm compartments near the WWTP had a higher relative abundance of ARGs (up to 4.7%) than surface waters (<2.8%). Sulfonamide resistance genes were more persistent further downstream (>10 km) of the WWTP in the hot and dry summer season than in winter. This finding is likely a consequence of the higher proportion of wastewater and thus wastewater-derived microorganisms in the river during summer periods. We observed distinct bacterial communities and ARG abundance between the biofilm and surface water compartment, but even greater variations when considering seasonal and spatiotemporal parameters. This underscores the need to consider seasonal aspects when studying the fate of ARGs in aquatic ecosystems.

The response of microbial compositions and functions to chronic single and multiple antibiotic exposure by batch experiment

Understanding the response of the microbial community to external disturbances such as micropollutants is vital for ecological risk evaluation. In this study, the effect of chronic antibiotic exposure on community compositions and functions was investigated by two batch experiments. The first experiment investigated the effect of chronic sulfamethoxazole (SMX) exposure, while the second investigated the combined effect of dissolved organic matter (DOM) sources and multi-antibiotic exposure. The results showed that the community responses to chronic antibiotic exposure depended on the dynamic balance among community resistance, adaptation, recovery, and selection, leading to nonlinear composition diversity variations. The disturbance strength of chronic SMX exposure increased with concentration (0.5–50 μg/L). However, complex sources and structures of coexisting organic matter might delay the disturbance by elevating metabolic activity and generating functional redundancy. Especially, when nutrient was a limiting factor, the disturbance strength by DOM source was greater than that by chronic antibiotic exposure. The resistance of abundant taxa to external distributions resulted in a low explanation of community diversity, while rare taxa played key roles in response to community variation and thereby affected community assembly. Long-term SMX exposure reduced the number of key species and favored the deterministic assembly process by 21%. However, elevated community adaptability might weaken the influence of antibiotic selection. Chronic SMX exposure elevated the relative abundance of sulfonamide resistance genes (sul1, sul2) by a factor of 1.2–4.3, while that of nitrogen-fixing genes (nifH, nifK) and the metabolic pathways related to the toluene, ethylbenzene, and dioxin degradation decreased. However, the combined influence of DOM sources and multi-antibiotic exposure barely caused the difference in the genes linking to element metabolism and drug resistance of microbial communities between blank and exposed groups. This study suggested that more concern should be given to the chronic environmental effect of organic micropollutants.

Spatiotemporal distributions of sulfonamide and tetracycline resistance genes and microbial communities in the coastal areas of the Yangtze River Estuary

In this paper, water and sediments were sampled at eight monitoring stations in the coastal areas of the Yangtze River Estuary in summer and autumn 2021. Two sulfonamide resistance genes (sul1 and sul2), six tetracycline resistance genes (tetM, tetC, tetX, tetA, tetO, and tetQ), one integrase gene (intI1), 16 S rRNA genes, and microbial communities were examined and analyzed. Most resistance genes showed relatively higher abundance in summer and lower abundance in autumn. One-way analysis of variance (ANOVA) showed significant seasonal variation of some ARGs (7 ARGs in water and 6 ARGs in sediment). River runoff and WWTPs are proven to be the major sources of resistance genes along the Yangtze River Estuary. Significant and positive correlations between intI1 and other ARGs were found in water samples (P < 0.05), implying that intI1 may influence the spread and propagation of resistance genes in aquatic environments. Proteobacteria was the dominant phylum along the Yangtze River Estuary, with an average proportion of 41.7%. Redundancy analysis indicated that the ARGs were greatly affected by temperature, dissolved oxygen, and pH in estuarine environments. Network analysis showed that Proteobacteria and Cyanobacteria were the potential host phyla for ARGs in the coastal areas of the Yangtze River Estuary.

Dissemination of sulfonamide resistance genes in digester microbiome during anaerobic digestion of food waste leachate

The preeminence of sulfonamide drug resistance genes in food waste (FW) and the increased utilization of high-strength organic FW in anaerobic digestion (AD) to enhance methane production have raised severe public health concerns in wastewater treatment plants worldwide. In this regard, the dissemination patterns of different sulfonamide resistance genes (sul1 and sul2) and their impact on the digester core microbiota during AD of FW leachate (FWL) were evaluated. The presence of various sulfonamide antibiotics (SAs) in FWL digesters improved the final methane yield by 37 % during AD compared with FWL digesters without SAs. Microbial population shifts towards hydrolytic, acidogenic, and acetogenic bacteria in the phyla Actinobacteriota, Bacteroidota, Chloroflexi, Firmicutes, Proteobacteria, and Synergistota occurred due to SA induced substrate digestion and absorption through active transport; butanoate, propanoate, and pyruvate metabolism; glycolysis; gluconeogenesis; the citrate cycle; and pentose phosphate pathway. The initial dominance of Methanosaeta (89–96 %) declined to 47–53 % as AD progressed and shifted towards Methanosarcina (40 %) in digesters with the highest SA concentrations at the end of AD. Dissemination of sul1 depended on class 1 integron gene (intl1)-based horizontal gene transfer to pathogenic members of Chloroflexi, Firmicutes, and Patescibacteria, whereas sul2 was transmitted to Synergistota independent of intl1. Low susceptibility and ability to utilize SAs during methanogenesis shielded methanogenic archaea against selection pressure, thus preventing them from interacting with sul or intl1 genes, thereby minimizing the risk of antibiotic resistance development. The observed emergence of cationic antimicrobial peptide, vancomycin, and β-lactam resistance in the core microbiota during AD of FWL in the presence of SAs suggests that multidrug resistance caused by bacterial transformation could lead to an increase in the environmental resistome through wastewater sludge treatment.

The fate of sulfonamide resistance genes and anthropogenic pollution marker intI1 after discharge of wastewater into a pristine river stream.

Currently there are sparse regulations regarding the discharge of antibiotics from wastewater treatment plants (WWTP) into river systems, making surface waters a latent reservoir for antibiotics and antibiotic resistance genes (ARGs). To better understand factors that influence the fate of ARGs in the environment and to foster surveillance of antibiotic resistance spreading in such habitats, several indicator genes have been proposed, including the integrase gene intI1 and the sulfonamide resistance genes sul1 and sul2. Here we used quantitative PCR and long-read nanopore sequencing to monitor the abundance of these indicator genes and ARGs present as class 1 integron gene cassettes in a river system from pristine source to WWTP-impacted water. ARG abundance was compared with the dynamics of the microbial communities determined via 16S rRNA gene amplicon sequencing, conventional water parameters and the concentration of sulfamethoxazole (SMX), sulfamethazine (SMZ) and sulfadiazine (SDZ). Our results show that WWTP effluent was the principal source of all three sulfonamides with highest concentrations for SMX (median 8.6 ng/l), and of the indicator genes sul1, sul2 and intI1 with median relative abundance to 16S rRNA gene of 0.55, 0.77 and 0.65%, respectively. Downstream from the WWTP, water quality improved constantly, including lower sulfonamide concentrations, decreasing abundances of sul1 and sul2 and lower numbers and diversity of ARGs in the class 1 integron. The riverine microbial community partially recovered after receiving WWTP effluent, which was consolidated by a microbiome recovery model. Surprisingly, the relative abundance of intI1 increased 3-fold over 13 km of the river stretch, suggesting an internal gene multiplication. We found no evidence that low amounts of sulfonamides in the aquatic environment stimulate the maintenance or even spread of corresponding ARGs. Nevertheless, class 1 integrons carrying various ARGs were still present 13 km downstream from the WWTP. Therefore, limiting the release of ARG-harboring microorganisms may be more crucial for restricting the environmental spread of antimicrobial resistance than attenuating ng/L concentrations of antibiotics.

High occurrence of antibiotic resistance genes in intensive aquaculture of hybrid snakehead fish

The increasing abundance of antibiotic resistance genes (ARGs), which are regarded as new pollutants, has raised public health concern. The use of antibiotics in aquaculture has promoted the evolution and spread of ARGs. The occurrence and abundance of ARGs in aquaculture has attracted extensive attention. However, the distribution and transmission of ARGs in aquaculture require further study. This study analyzed water and sediment from intensive culture of hybrid snakehead fish farm in Zhongshan, South China. Twenty-two types of ARGs were detected in all environmental samples. The relative abundance of sulfonamide resistance genes (sul1 and sul2) was the highest, ranging from 3.37×10-2 to 8.53×100 copies/16S rRNA gene. High occurrence of quinolones, phenicols, tetracycline resistance genes, and class 1 integrase gene (intI1) was also observed in pond water samples. This implies that pond water is one of the main reservoirs and origins of ARGs in the aquatic environment. Proteobacteria was the most abundant phylum in all the environmental samples, and its relative abundance ranged from 24.05% to 41.84%. Network and canonical correspondence analyses showed that a high abundance of ARGs (int1, sul1, sul2, qacEΔ1, aac6, and oqxA) was positively correlated with Proteobacteria, Cyanobacteria, and Bacteroidetes, and the abundance of Proteobacteria, Actinobacteria, and Patescibacteria was positively correlated with environmental factors (sulfide, nitrite nitrogen, pH, free chlorine, and ammonia nitrogen). These findings demonstrate the prevalence and persistence of ARGs in intensive fish farming in southern China. This suggests that ARG levels and microbiological community composition in aquaculture should be conventionally determined to assess potential risks to public health.

Distribution and drivers of antibiotic resistance genes in brackish water aquaculture sediment

Brackish water aquaculture has brought numerous economic benefits, whereas anthropogenic activities in aquaculture may cause the dissemination of antibiotic resistance genes (ARGs) in brackish water sediments. The intricate relationships between environmental factors and microbial communities as well as their role in ARGs dissemination in brackish water aquaculture remain unclear. This study applied PCR and 16S sequencing to identify the variations in ARGs, class 1 integron gene (intI1) and microbial communities in brackish water aquaculture sediment. The distribution of ARGs in brackish water aquaculture sediment was similar to that in freshwater aquaculture, and the sulfonamide resistance gene sul1 was the indicator of ARGs. Proteobacteria and Firmicutes were the dominant phyla, and Paenisporosarcina (p_ Firmicutes) was the dominant genus. The results of correlation, network and redundancy analysis indicated that the microbial community in the brackish water aquaculture sediment was function-driven. The neutral model and variation partitioning analysis were used to verify the ecological processes of the bacterial community. The normalized stochasticity ratio showed that pond bacteria community was dominated by determinacy, which was affected by aquaculture activities. The total nitrogen and organic matter influenced the abundance of ARGs, while Proteobacteria and Thiobacillus (p_Proteobacteria) were the key antibiotic-resistant hosts. Our study provides insight into the prevalence of ARGs in brackish water aquaculture sediments, and indicates that brackish water aquaculture is a reservoir of ARGs.

Distribution of antibiotic resistance genes in the sediments of Erhai Lake, Yunnan-Kweichow Plateau, China: Their linear relations with nonpoint source pollution discharges from 26 tributaries

Erhai Lake, a typical plateau deep water lake, experienced long-term nonpoint source (NPS) pollution discharge from 26 tributaries, which significantly affected the abundance and spread of resistance genes. In this study, 25 antibiotic resistance genes (ARGs), classified into six types, and NPS pollution discharges were investigated throughout around the Erhai basin. FCA (mexF) and sulfonamide resistance genes (sul1, sul2 and sul3) were the most common. Although the absolute overall abundance of ARGs there was low so far, the individual gene like sulfonamide resistance gene was high. Regression analysis using an ordinary least squares model (OLS) showed that the discharge of NPS pollution into Erhai Lake would have an obvious effect on the distribution of ARGs. And the relations between them were linear. Concretely speaking, the total nitrogen (TN) pollution input from tributaries could significantly correlated with the increasing of ARG abundance, while the total phosphorus (TP) pollution input showed the opposite correlation, and ultimately affect the distribution of ARGs. Moreover, the effect of TP on ARG distribution was more significant than TN. This study provides a geographical profile of ARG distribution in a subtropical deep lake on Yunnan-Kweichow Plateau. The results are beneficial for predicting the distribution characteristics of ARGs and controlling their pollution in plateau lakes.

Antibiotic resistance genes and their links with bacteria and environmental factors in three predominant freshwater aquaculture modes

Rapid development of aquaculture industry and increasing demand of various inputs (especially antibiotics), are suspected to promote the occurrence and spread of ARGs in aquaculture related environments. However, the occurrences of ARGs under different freshwater aquaculture practices are rarely known. Here, we investigated the seasonal profiles of the main ARGs, intI1 and bacteria in waters from three kinds of predominant freshwater aquaculture practices around the Honghu Lake (China), as well as their co-occurrences and interrelationships with antibiotics, heavy metals and general water quality. The results indicate that quinolone resistance genes (qnrB), tetracycline resistance genes (tetB and tetX) and sulfonamide resistance genes (sul1 and sul2) were the top five predominant ARGs with seasonal variations of abundance. Fish ponds were of the highest absolute abundances of tested ARGs than the other two modes. Crayfish ponds and their adjacent ditches shared similar ARGs profile. Different subtypes of ARGs belonging to the same class of resistance were varied in abundances. Some bacteria were predicted to carry different ARGs, which indicating multi-antibiotic resistances. Moreover, the combined environmental factors (antibiotics, heavy metals and water quality) partially shaped the profiles of ARGs and bacteria composition. Overall, this study provides new comprehensive understanding on the characterization of ARGs contamination in different freshwater aquaculture practices from the perspectives of environmental chemistry, microbiology and ecology. The results would benefit the optimization of aquaculture practices toward environmental integrity and sustainability.

Degradation mechanism of montmorillonite-enhanced antibiotic wastewater: performance, antibiotic resistance genes, microbial communities, and functional metabolism

The effective degradation of Sulfamethoxazole (SMX) is of great importance to alleviate environmental pollution. In this study, the degradation capacity of an ordinary sequencing batch activated sludge system (SBR) and montmorillonite (MMT) system was compared for their ability to degrade different concentrations of SMX. Compared with SBR system, the MMT system exhibited higher stability and degradation capacity. The changes in the composition of tightly bound extracellular polymeric substances (TB-EPS) were likely key to the observed stability of the system. High concentrations of SMX inhibited the degradation performance of SBR. MMT-supplemented reduced the generation of antibiotic resistance genes (ARGs). Thauera is a gene that is able to degrade SMX, and its abundance in MMT system reached 7.84%. As potential hosts of ARGs, the proportions of Paenarthrobacter and Caldilineacea were significantly correlated with sulfonamide resistance genes (sul1 and sul2). Overall, MMT-supplemented system was found to be a favorable method of treating antibiotic.

Bacterial Hosts and Genetic Characteristics of Antibiotic Resistance Genes in Wastewater Treatment Plants of Xinjiang (China) Revealed by Metagenomics

Antibiotic resistance genes (ARGs) pose a widespread concern for human health and wastewater treatment plants (WWTPs) are considered to be a major source of ARG transmission. In this paper, the potential hosts and genetic characteristics of ARGs in the influent, activated sludge and effluent of WWTPs in Xinjiang were studied by metagenomics. Bacitracin resistance gene (bacA), beta-lactamase gene (class A beta-lactamase), multidrug resistance genes (mexD, qacEdelta1), and sulfonamide resistance genes (sul1, and sul2) are persistent antibiotic resistance genes (PARGs). The potential hosts of ARGs were mainly pathogens, with Escherichia coli (12.9%), Acinetobacter johnsonii (8.94%), and Klebsiella pneumoniae (5.30%) accounting for the highest proportions. Chromosomal sequences and plasmid sequences accounted for 42.0% and 22.6% of ARG-carrying contigs (ACCs) in the influent, respectively. Meanwhile, the effluent contained 58.3% of ACCs in plasmids and 8.30% in chromosomes. Bacitracin resistance genes and multidrug resistance genes were mainly carried by chromosomes, while resistance genes for macrolide–lincosamide–streptogramin (MLS), vancomycin, sulfonamide, beta-lactam, tetracycline, chloramphenicol, and aminoglycoside were mainly carried by plasmids. ICEPae690-sul1-qacEdelta1 and ICEPmiChn3-sul2 were stable coexistence structures and heighten the transfer potential of ARGs in the environment. This study provided a clearer picture of host bacterial sources and genetic context of ARGs in the environment.

Occurrence and distribution of antibiotics and antibiotic resistance genes in the guts of shrimp from different coastal areas of China

With the continuous increase in shrimp (Litopenaeus vannamei) aquaculture production, the widespread use of antibiotics as a means of preventing and treating diseases has adversely affected the environment, animal health and symbiotic microorganisms in gut environments. At the same time, antibiotic resistance genes (ARGs) are widespread in aquaculture and pose a great threat to aquatic organisms and humans. Therefore, in the present study, the occurrence and distribution of 17 antibiotics, ARGs and mobile genetic elements (MGEs) were detected in the guts of shrimp collected from 12 coastal regions of China. The results showed that sulfadiazine, ciprofloxacin and norfloxacin were detectable in the guts of L. vannamei at all sampling sites. Sul1, sul2, floR and intI-1 were also detected in the guts of L. vannamei at all sampling sites. The total relative abundances of ARGs and MGEs were significantly positively correlated according to Pearson correlation analysis. Sulfonamide resistance genes (sul1 and sul2) were significantly positively correlated with intI-1. These results indicated that MGEs could increase the risk of horizontal gene transfer of ARGs in a gut environment. MGEs are the most important factors promoting the spread of ARGs. Correlation analysis showed that sulfadiazine was significantly positively correlated with sul1 and sul2 and that fluoroquinolone antibiotics were significantly positively correlated with floR, indicating that antibiotics could induce the production of ARGs. Network analysis indicated that Iamia and Alkaliphilus species may harbor the most antibiotic resistance genes, and these bacteria were closely related to the proliferation and spread of ARGs in a gut environment. Antibiotic use and the spread of ARGs in mariculture systems may have negative effects on shrimp and human health. The use of antibiotics should be strictly regulated to control contaminants in mariculture systems, including pathogens and ARGs, thereby reducing potential risks to human health.

Occurrence of antibiotic resistance genes and multidrug-resistant bacteria during wastewater treatment processes

Wastewater treatment plants (WWTPs) constantly receive a wide variety of contaminants, including pharmaceuticals, and are potential reservoirs of antibiotic resistance genes (ARGs). This favors the development of multidrug-resistant bacteria (MRB) through horizontal gene transfer. Samples from five different WWTP processes were collected in September 2020 and January 2021 to monitor ARG resistomes and culturable MRB in the presence of eight different antibiotics. Nanopore-based ARG abundance and bacterial community analyses suggested that ARG accumulation favors the generation of MRB. Activated and mixed sludges tended to have lower bacterial diversity and ARG abundance because of selective forces that favored the growth of specific microorganisms during aeration processes. Escherichia strains enriched in WWTPs (up to 71%) were dominant in all the samples, whereas Cloacamonas species were highly abundant only in anaerobically digested sludge samples (60%–79%). Two ARG types [sulfonamide resistance genes (sul1) and aminoglycoside resistance genes (aadA1, aadA13, and aadA2)] were prevalent in all the processes. The total counts of culturable MRB, such as Niabella, Enterococcus, Bacillus, and Chryseobacterium species, gradually increased during aerobic WWTP processes. Genomic analyses of all MRB isolated from the samples revealed that the resistome of Enterococcus species harbored the highest number of ARGs (7–18 ARGs), commonly encoding ant(6)-la, lnu(B), erm(B), and tet(S/M). On the other hand, Niablella strains possibly had intrinsic resistant phenotypes without ARGs. All MRB possessed ARGs originating from the same mobile genetic elements, suggesting that WWTPs are hotspots for the migration of ARGs and emergence of MRB.