Evolution of corresponding resistance genes in the water of fish tanks with multiple stresses of antibiotics and heavy metals

Aspirin altered antibiotic resistance genes response to sulfonamide in the gut microbiome of zebrafish

Pharmaceuticals are widespread in aquatic environments and might contribute to the prevalence of antibiotic resistance. However, the co-effect of antibiotics and non-antibiotic pharmaceuticals on the gut microbiome of fish is poorly understood. In this study, we characterized the variation of the zebrafish gut microbiome and resistome after exposure to sulfamethoxazole (SMX) and aspirin under different treatments. SMX contributed to the significant increase in the antibiotic resistance genes (ARGs) richness and abundance with 46 unique ARGs and five mobile genetic elements (MGEs) detected. Combined exposure to SMX and aspirin enriched total ARGs abundance and rearranged microbiota under short-term exposure. Exposure time was more responsible for resistome and the gut microbiome than exposure concentrations. Perturbation of the gut microbiome contributed to the functional variation related to RNA processing and modification, cell motility, signal transduction mechanisms, and defense mechanisms. A strong significant positive correlation (R = 0.8955, p < 0.001) was observed between total ARGs and MGEs regardless of different treatments revealing the key role of MGEs in ARGs transmission. Network analysis indicated most of the potential ARGs host bacteria belonged to Proteobacteria. Our study suggested that co-occurrence of non-antibiotics and antibiotics could accelerate the spread of ARGs in gut microbial communities and MGEs played a key role.

Potential effects of Cu2+ stress on nitrogen removal performance, microbial characteristics, and metabolism pathways of biofilm reactor

Sequencing batch biofilm reactors (SBBR) were utilized to investigate the impact of Cu2+ on nitrogen (N) removal and microbial characteristics. The result indicated that the low concentration of Cu2+ (0.5 mg L-1) facilitated the removal of ammonia nitrogen (NH4+-N), total nitrogen (TN), nitrate nitrogen (NO3--N), and chemical oxygen demand (COD). In comparison to the average effluent concentration of the control group, the average effluent concentrations of NH4+-N, NO3--N, COD, and TN were found to decrease by 40.53%, 17.02%, 10.73%, and 15.86%, respectively. Conversely, the high concentration of Cu2+ (5 mg L-1) resulted in an increase of 94.27%, 55.47%, 22.22%, and 14.23% in the aforementioned parameters, compared to the control group. Low concentrations of Cu2+ increased the abundance of nitrifying bacteria (Rhodanobacter, unclassified-o-Sacharimonadales), denitrifying bacteria (Thermomonas, Comamonas), denitrification-associated genes (hao, nosZ, norC, nffA, nirB, nick, and nifD), and heavy-metal-resistant genes related to Cu2+ (pcoB, cutM, cutC, pcoA, copZ) to promote nitrification and denitrification. Conversely, high concentration Cu2+ hindered the interspecies relationship among denitrifying bacteria genera, nitrifying bacteria genera, and other genera, reducing denitrification and nitrification efficiency. Cu2+ involved in the N and tricarboxylic acid (TCA) cycles, as evidenced by changes in the abundance of key enzymes, such as (EC:1.7.99.1), (EC:1.7.2.4), and (EC:1.1.1.42), which initially increased and then decreased with varying concentrations of Cu2+. Conversely, the abundance of EC1.7.2.1, associated with the accumulation of nitrite nitrogen (NO2--N), gradually declined. These findings provided insights into the impact of Cu2+ on biological N removal.

Opposite Effects of Planting on Antibiotic Resistomes in Rhizosphere Soil with Different Sulfamethoxazole Levels

Achieving consensus about the rhizosphere effect on soil antibiotic resistomes is challenging due to the variability in antibiotic concentrations, sources, and the elusory underlying mechanisms. Here, we characterized the antibiotic resistomes in both the rhizosphere and bulk soils of soybean plants grown in environments with varying levels of antibiotic contamination, using sulfamethoxazole (SMX) as a model compound. We also investigated the factors influencing resistome profiles. Soybean cultivation altered the structure of antibiotic-resistant genes (ARGs) and increased their absolute abundance. However, the rhizosphere effect on the relative abundance of ARGs was dependent on SMX concentrations. At low SMX levels, the rhizosphere effect was characterized by the inhibition of antibiotic-resistant bacteria (ARBs) and the promotion of sensitive bacteria. In contrast, at high SMX levels, the rhizosphere promoted the growth of ARBs and facilitated horizontal gene transfer of ARGs. This novel mechanism provides new insights into accurately assessing the rhizosphere effect on soil antibiotic resistomes.

Horizontal gene transfer plays a crucial role in the development of antibiotic resistance in an antibiotic-free shrimp farming system

Antibiotic selective pressure in aquaculture systems often results in the antibiotic resistance genes (ARGs) proliferation. Nonetheless, a paucity of data exists concerning the mechanisms of ARGs development in aquaculture systems without the influences of antibiotics. This study utilized metagenomic approaches to elucidate the dynamics and transfer mechanisms of ARGs throughout the aquaculture of Pacific white shrimp. A marked change in the resistome was observed throughout the aquaculture without antibiotics. The total ARGs relative abundance increased from 0.05 to 0.33 by day 90 of cultivation, with even higher in mixed wastewater (0.44). Both bacterial communities and mobile genetic elements play pivotal roles in the development of ARGs. Metagenome-assembled genomes showed enrichment of environmentally intrinsic ARGs on chromosomes including macB and mdtK. The plasmid-mediated horizontal transfer was recognized as a principal factor contributing to the rise of ARGs, particularly for tetG and floR, and this led to an escalation of resistance risk, peaking at a risks core of 35.43 on day 90. This study demonstrates that horizontal gene transfer plays a crucial role in ARGs development without antibiotic pressure, which can provide a theoretical foundation for controlling ARGs proliferation in aquaculture systems.

The contribution of swine wastewater on environmental pathogens and antibiotic resistance genes: Antibiotic residues and beyond

Swine wastewater application can introduce antibiotics, antibiotic resistance genes (ARGs) into environments. Herein, the full-scale transmission of antibiotics, ARGs and their potential carriers from an intensive swine feedlot to its surroundings were explored. Results showed that lincomycin and doxycycline hydrochloride were dominant antibiotics in this ecosystem. Lincomycin concentration were strongly associated with soil bacterial communities. According to the risk quotient (RQ), lincomycin was identified as posing higher ecological risk in aquatic environments. ARGs and mobile genetic elements (MGEs) abundance in wastewater were reduced after anaerobic treatment. Notably, ARGs composition of environmental samples were clustered into two groups based on if they were directly affected by the wastewater. However, there were no remarkable difference of ARGs abundance among environmental samples. The total abundance of ARGs was positively related to that of MGEs. Pathogens Escherichia coli and Enterococcus revealed strong connection with qnrS, tet and sul. Overall, this study highlights the importance of responsible antibiotics use in livestock production and appropriate treatment technology before agricultural application and discharge.

A thorough investigation into the adsorption behavior of sophorolipid-modified fly ash towards compound pollution of lead and tetracycline

Heavy metal ions and antibiotics were simultaneously detected in authentic water systems. This research, for the first time, employed synthesized sophorolipid-modified fly ash(SFA) to eliminate tetracycline(TC) and lead(Pb2+) from wastewater. Various characterization techniques, including SEM-EDS, FTIR, XPS, BET, and Zeta, were employed to investigate the properties of the SFA. The results showed that the sophorolipid modification significantly improved the fly ash's adsorption capacities for the target pollutants. The static adsorption experiments elucidated the adsorption behaviors of SFA towards TC and Pb2+ in single and binary systems, highlighting the effects of different Environmental factors on the adsorption behavior in both types of systems. In single systems, SFA exhibited a maximum adsorption capacity of 128.96 mg/g for Pb2+ and 55.57 mg/g for TC. The adsorption of Pb2+ and TC followed pseudo-second-order kinetics and Freundlich isotherm models. The adsorption reactions are endothermic and occur spontaneously. SFA demonstrates varying adsorption mechanisms for two different types of pollutants. In the case of Pb2+, the primary mechanisms include ion exchange, electrostatic interaction, cation-π interaction, and complexation, while TC primarily engages in hydrogen bonding, π-π interaction, and complexation. The interaction between Pb2+ and TC has been shown to improve adsorption efficiency at low concentrations. Additionally, adsorption-desorption experiments confirm the reliable cycling performance of modified fly ash, highlighting its potential as a cost-effective and efficient adsorbent for antibiotics and heavy metals.

Metagenomic approach revealed the mobility and co-occurrence of antibiotic resistomes between non-intensive aquaculture environment and human

BACKGROUND

Aquaculture is an important food source worldwide. The extensive use of antibiotics in intensive large-scale farms has resulted in resistance development. Non-intensive aquaculture is another aquatic feeding model that is conducive to ecological protection and closely related to the natural environment. However, the transmission of resistomes in non-intensive aquaculture has not been well characterized. Moreover, the influence of aquaculture resistomes on human health needs to be further understood. Here, metagenomic approach was employed to identify the mobility of aquaculture resistomes and estimate the potential risks to human health.

RESULTS

The results demonstrated that antibiotic resistance genes (ARGs) were widely present in non-intensive aquaculture systems and the multidrug type was most abundant accounting for 34%. ARGs of non-intensive aquaculture environments were mainly shaped by microbial communities accounting for 51%. Seventy-seven genera and 36 mobile genetic elements (MGEs) were significantly associated with 23 ARG types (p < 0.05) according to network analysis. Six ARGs were defined as core ARGs (top 3% most abundant with occurrence frequency > 80%) which occupied 40% of ARG abundance in fish gut samples. Seventy-one ARG-carrying contigs were identified and 75% of them carried MGEs simultaneously. The qacEdelta1 and sul1 formed a stable combination and were detected simultaneously in aquaculture environments and humans. Additionally, 475 high-quality metagenomic-assembled genomes (MAGs) were recovered and 81 MAGs carried ARGs. The multidrug and bacitracin resistance genes were the most abundant ARG types carried by MAGs. Strikingly, Fusobacterium_A (opportunistic human pathogen) carrying ARGs and MGEs were identified in both the aquaculture system and human guts, which indicated the potential risks of ARG transfer.

CONCLUSIONS

The mobility and pathogenicity of aquaculture resistomes were explored by a metagenomic approach. Given the observed co-occurrence of resistomes between the aquaculture environment and human, more stringent regulation of resistomes in non-intensive aquaculture systems may be required. Video Abstract.

The potential contribution of aquatic wildlife to antibiotic resistance dissemination in freshwater ecosystems: A review

Antibiotic resistance (AR) is one of the major health threats of our time. The presence of antibiotics in the environment and their continuous release from sewage treatment plants, chemical manufacturing plants and animal husbandry, agriculture and aquaculture, result in constant selection pressure on microbial organisms. This presence leads to the emergence, mobilization, horizontal gene transfer and a selection of antibiotic resistance genes, resistant bacteria and mobile genetic elements. Under these circumstances, aquatic wildlife is impacted in all compartments, including freshwater organisms with partially impermeable microbiota. In this narrative review, recent advancements in terms of occurrence of antibiotics and antibiotic resistance genes in sewage treatment plant effluents source compared to freshwater have been examined, occurrence of antibiotic resistance in wildlife, as well as experiments on antibiotic exposure. Based on this current state of knowledge, we propose the hypothesis that freshwater aquatic wildlife may play a crucial role in the dissemination of antibiotic resistance within the environment. Specifically, we suggest that organisms with high bacterial density tissues, which are partially isolated from the external environment, such as fishes and amphibians, could potentially be reservoirs and amplifiers of antibiotic resistance in the environment, potentially favoring the increase of the abundance of antibiotic resistance genes and resistant bacteria. Potential avenues for further research (trophic transfer, innovative exposure experiment) and action (biodiversity eco-engineering) are finally proposed.

Metagenomic and transcriptomic analysis revealing the impact of oxytetracycline and ciprofloxacin on gut microbiota and gene expression in the Chinese giant salamander (Andrias davidianus)

Excessive antibiotic use has led to the spread of antibiotic resistance genes (ARGs), impacting gut microbiota and host health. However, the effects of antibiotics on amphibian populations remain unclear. We investigated the impact of oxytetracycline (OTC) and ciprofloxacin (CIP) on Chinese giant salamanders (Andrias davidianus), focusing on gut microbiota, ARGs, and gene expression by performing metagenome and transcriptome sequencing. A. davidianus were given OTC (20 or 40 mg/kg) or CIP (50 or 100 mg/kg) orally for 7 days. The results revealed that oral administration of OTC and CIP led to distinct changes in microbial composition and functional potential, with CIP treatment having a greater impact than OTC. Antibiotic treatment also influenced the abundance of ARGs, with an increase in fluoroquinolone and multi-drug resistance genes observed post-treatment. The construction of metagenome-assembled genomes (MAGs) accurately validated that CIP intervention enriched fish-associated potential pathogens Aeromonas hydrophila carrying an increased number of ARGs. Additionally, mobile genetic elements (MGEs), such as phages and plasmids, were implicated in the dissemination of ARGs. Transcriptomic analysis of the gut revealed significant alterations in gene expression, particularly in immune-related pathways, with differential effects observed between OTC and CIP treatments. Integration of metagenomic and transcriptomic data highlighted potential correlations between gut gene expression and microbial composition, suggesting complex interactions between the host gut and its gut microbiota in response to antibiotic exposure. These findings underscore the importance of understanding the impact of antibiotic intervention on the gut microbiome and host health in amphibians, particularly in the context of antibiotic resistance and immune function.

Portable luminescent fiber- and glove-based nanosensor for multicolor visual detection of tetracycline in food samples

An intelligent fluorescent nanoprobe (lignite-CDs-Eu) was constructed by an effective and facile method based on lignite-derived carbon dots (CDs) and lanthanide europium ions (Eu3+), which exhibited high sensitivity, low detection limit (13.35 nM) and visual color variation (from blue to red) under ultraviolet light towards tetracycline (TC) detection. Significantly, portable and economical sensors were developed using lignite-CDs-Eu immobilized fiber material of filter paper and wearable glove with the aid of color extracting and image processing application (APP) in the smartphone. Facile, fast and real-time visual detection of TC in food samples was realized. Moreover, logic gate circuit was also designed to achieve intelligent and semi-quantitative inspection of TC. To some extent, this study extended the cross-application of intelligent computer software in food analytical science, and provided a certain reference for the development of small portable detection sensors which were suitable for convenience and non-professional use in daily life.

A combined evaluation of the characteristics and antibiotic resistance induction potential of antibiotic wastewater during the treatment process

Antibiotic wastewater contains a variety of pollutant stressors that can induce and promote antibiotic resistance (AR) when released into the environment. Although these substances are mostly in concentrations lower than those known to induce AR individually, it is possible that antibiotic wastewater discharge might still promote the AR transmission risk via additive or synergistic effects. However, the comprehensive effect of antibiotic wastewater on AR development has rarely been evaluated, and its treatment efficiency remains unknown. Here, samples were collected from different stages of a cephalosporin production wastewater treatment plant, and the potential AR induction effect of their chemical mixtures was explored through the exposure of the antibiotic-sensitive Escherichia coli K12 strain. Incubation with raw cephalosporin production wastewater significantly promoted mutation rates (3.6 × 103-9.3 × 103-fold) and minimum inhibition concentrations (6.0-6.7-fold) of E. coli against ampicillin and chloramphenicol. This may be attributed to the inhibition effect and oxidative stress of cephalosporin wastewater on E. coli. The AR induction effect of cephalosporin wastewater decreased after the coagulation sedimentation treatment and was completely removed after the full treatment process. A Pearson correlation analysis revealed that the reduction in the AR induction effect had a strong positive correlation with the removal of organics and biological toxicity. This indicates that the antibiotic wastewater treatment had a collaborative processing effect of conventional pollutants, toxicity, and the AR induction effect. This study illustrates the potential AR transmission risk of antibiotic wastewater and highlights the need for its adequate treatment.

Cefotaxime Exposure-Caused Oxidative Stress, Intestinal Damage and Gut Microbial Disruption in Artemia sinica

Cefotaxime (CTX) is an easily detectable antibiotic pollutant in the water environment, but little is known about its toxic effects on aquatic invertebrates, especially on the intestine. Here, we determined the oxidative stress conditions of A. sinica under CTX exposure with five concentrations (0, 0.001, 0.01, 0.1 and 1 mg/L) for 14 days. After that, we focused on changes in intestinal tissue morphology and gut microbiota in A. sinica caused by CTX exposure at 0.01 mg/L. We found malondialdehyde (MDA) was elevated in CTX treatment groups, suggesting the obvious antibiotic-induced oxidative stress. We also found CTX exposure at 0.01 mg/L decreased the villus height and muscularis thickness in gut tissue. The 16S rRNA gene analysis indicated that CTX exposure reshaped the gut microbiota diversity and community composition. Proteobacteria, Actinobacteriota and Bacteroidota were the most widely represented phyla in A. sinica gut. The exposure to CTX led to the absence of Verrucomicrobia in dominant phyla and an increase in Bacteroidota abundance. At the genus level, eleven genera with an abundance greater than 0.1% exhibited statistically significant differences among groups. Furthermore, changes in gut microbiota composition were accompanied by modifications in gut microbiota functions, with an up-regulation in amino acid and drug metabolism functions and a down-regulation in xenobiotic biodegradation and lipid metabolism-related functions under CTX exposure. Overall, our study enhances our understanding of the intestinal damage and microbiota disorder caused by the cefotaxime pollutant in aquatic invertebrates, which would provide guidance for healthy aquaculture.

Impact of uranium on antibiotic resistance in activated sludge

The emergence of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in the environment is well established as a human health crisis. The impact of radioactive heavy metals on ecosystems and ultimately on human health has become a global issue, especially for the regions suffering various nuclear activities or accidents. However, whether the radionuclides can affect the fate of antibiotic resistance in bacteria remains poorly understood. Here, the dynamics of ARB, three forms of ARGs-intracellular ARGs (iARGs), adsorbed extracellular ARGs (aeARGs), and free extracellular ARGs (feARGs)-and microbial communities were investigated following exposure to uranium (U), a representative radioactive heavy metal. The results showed that 90-d of U exposure at environmentally relevant concentrations of 0.05 mg/L or 5 mg/L significantly increased the ARB concentration in activated sludge (p < 0.05). Furthermore, 90-d of U exposure slightly elevated the absolute abundance of aeARGs (except tetO) and sulfonamide iARGs, but decreased tetracycline iARGs. Regarding feARGs, the abundance of tetC, tetO, and sul1 decreased after 90-d of U stress, whereas sul2 showed the opposite trend. Partial least-squares path model analysis revealed that the abundance of aeARGs and iARGs under U stress was predominantly driven by increased cell membrane permeability/intI1 abundance and cell membrane permeability/reactive oxygen species concentration, respectively. Conversely, the changes in feARGs abundance depended on the composition of the microbial community and the expression of efflux pumps. Our findings shed light on the variations of ARGs and ARB in activated sludge under U exposure, providing a more comprehensive understanding of antibiotic resistance risks aggravated by radioactive heavy metal-containing wastewater.

Characterization of heavy metal, antibiotic pollution, and their resistance genes in paddy with secondary municipal-treated wastewater irrigation

Secondary municipal-treated wastewater irrigation may introduce residual antibiotics into the agricultural systems contaminated with certain heavy metals, ultimately leading to the coexistence of antibiotics and heavy metals. The coexistence may induce synergistic resistance to both in the microbial community. Here, we investigated the effects of long-term municipal-treated irrigation for rice on the microbiome and resistome. The results showed that the target antibiotics were undetectable in edible grains, and the heavy metal concentrations did not exceed the standard in edible rice grains. Heavy metal resistance genes (MRGs) ruvB and acn antibiotic resistance genes (ARGs) sul1 and sul2 were the dominating resistant genes. The coexistence of antibiotics and heavy metals affected the microbial community and promoted metal and antibiotic resistance. Network analysis revealed that Proteobacteria were the most influential hosts for MRGs, ARGs, and integrons, and co-selection may serve as a potential mechanism for resistance maintenance. MRG czcA and ARG sul1 can be recommended as model genes to study the co-selection of ARGs and MRGs in environments. The obtained results highlight the importance of considering the co-occurrence of heavy metals and antibiotics while developing effective methods to prevent the transmission of ARGs. These findings are critical for assessing the possible human health concerns associated with secondary municipal-treated wastewater irrigation for agriculture and improving the understanding of the coexistence of heavy metals and antibiotics.

Toxic effects of long-term dual or single exposure to oxytetracycline and arsenic on Xenopus tropicalis living in duck wastewater

Direct discharge of aquaculture wastewater may have toxic effects, due to the presence of heavy metals, antibiotics, and even resistant pathogens, but little attention has been given. Here, tanks simulating a wild ecosystem were built to study the effects of long-term exposure to duck wastewater containing oxytetracycline (OTC) and/or arsenic (As) on the growth, physiological function, and gut microbiota evolution of Xenopus tropicalis. The results showed that duck wastewater had no apparent impact on X. tropicalis, but the impact increased significantly (P < 0.05) with exposure to OTC and/or As, especially the impact on body weight and growth rate. Biochemical indicators revealed varying degrees of oxidative stress damage, hepatotoxicity (inflammation, necrosis, and sinusoids), and collagen fibrosis of X. tropicalis in all treated groups after 72 days of exposure, which indirectly inhibited X. tropicalis growth. Moreover, 16S rDNA amplicon sequencing results showed that the gut microbiota structure and metabolic function were perturbed after chronic exposure, which might be the leading cause of growth inhibition. Interestingly, the abundance of intestinal resistance genes (RGs) increased with exposure time owing to the combined direct and indirect effects of stress factors in duck wastewater. Moreover, once the RGs were expressed, the resistance persisted for at least 24 days, especially that conferred by tetA. These results provide evidence of the toxic effects of DW containing OTC (0.1-4.0 mg/L) and/or As (0.3-3.5 µg/L) on amphibians and indicate that it is vital to limit the usage of heavy metals and antibiotics on farms to control the biotoxicity of wastewater.

Using bait microalga as an oral delivery vehicle of antimicrobial peptide for controlling Vibrio infection in mussels

In shellfish aquaculture, antibiotics are commonly used to address Vibrio infections. However, antibiotic abuse has increased the risk of environment pollution, which has also raised food safety concerns. Antimicrobial peptides (AMPs) are considered safe and sustainable alternatives to antibiotics. Hence, in this study, we aimed to develop a transgenic Tetraselmis subcordiformis line harboring AMP-PisL9K22WK for reducing the use of antibiotics in mussel aquaculture. Toward this, pisL9K22WK was assembled into nuclear expression vectors of T. subcordiformis. Post particle bombardment, several stable transgenic lines were selected after 6 months of herbicide resistance culture. Subsequently, Vibrio-infected mussels (Mytilus sp.) were orally fed transgenic T. subcordiformis to test the efficacy of this drug delivery system. The results showed that the transgenic line as an oral antimicrobial agent significantly improved the resistance of mussels to Vibrio. The growth rate of the mussels fed transgenic T. subcordiformis was considerably higher than that of mussels fed wild-type algae (10.35% versus 2.44%). In addition, the possibility of using the lyophilized powder of the transgenic line as drug delivery system was also evaluated; however, compared to that observed after feeding with live cells, the lyophilized powder did not improve the low growth rate caused by Vibrio infection, suggesting that fresh microalgae are more beneficial for the delivery of the PisL9K22WK to mussels than the lyophilized powder. In summary, this is a promising step toward the development of safe and environment-friendly antimicrobial baits.

A global perspective on compositions, risks, and ecological genesis of antibiotic resistance genes in biofilters of drinking water treatment plants

Antibiotic resistance genes (ARGs) in biofilters of drinking water treatment plants (DWTPs) are regarded to be a remarkable potential health risk to human. A global survey on ARGs in biofilters may help evaluate their risk features as a whole. This study aims to explore the compositions, risks, and ecological genesis of ARGs in the biofilters of DWTPs. In total, 98 metagenomes of DWTP biofilters were collected from Sequence Read Archive  (SRA)  of National center for Biotechnology Information (NCBI), and the main ARG types were recognized, with multidrug, bacitracin, and beta-lactam as the first three types. Source water types (surface water vs. groundwater) were found to significantly influence antibiotic resistome, overpassing biofilter media and locations. Although ARG abundances of surface water biofilters were approximately five times higher than that of groundwater biofilters, the risk pattern of ARGs was highly similar between surface water biofilters and groundwater biofilters, and up to 99.61% of the ARGs on average belong to the least risk and unassessed ranks, and only 0.23% the highest risk rank. Monobactam biosynthesis pathway and prodigiosin biosynthesis pathway, two antibiotics biosynthesis pathways, were observed to be positively correlated with several ARG types and total ARG abundance in samples of surface water and groundwater biofilters, respectively, suggesting their potential roles in ecological genesis of ARGs. Overall, the results of this study would deepen our understanding of the ARG risks in biofilters of DWTPs and shed light on their ecological genesis inside.

Multidrug-resistant Aeromonas bacteria prevalence in Nile tilapia broodstock

BACKGROUND

Aeromonas hydrophila is an opportunistic pathogen. Thus, it has received significant attention mainly in the fish sectors with high production scales. Nile tilapia broodstock confined in the environment of fish hatcheries can be stressed. Hence, they are vulnerable to A. hydrophila.

RESULTS

Sequencing of the gyr B gene revealed the presence of 18 different A. hydrophila strains (kdy 10,620-10,637), which were deposited in the NCBI under accession numbers ON745861-ON745878. The median lethal doses of the isolates ranged from 2.62 × 10⁴ to 3.02 × 10⁶ CFU/mL. Antibiotic resistant genes, sulfonamide (sul1) and tetracycline (tetA) were found in the eighteen isolates. Approximately 83.3% of A. hydrophila strains were sensitive to ciprofloxacin and florfenicol. Further, eight A. hydrophila strains had high MDR indices at 0.27-0.45. All isolates presented with hemolysin activity. However, only 72.22% of them had proteolytic activity, and only 61.11% could form biofilms. Bacterial isolates harbored different pattern virulence genes, the heat-stable cytotonic enterotoxin (ast), cytotoxic enterotoxin (act), and hemolysin (hly) genes were the most prevalent. Also, a trial to inhibit bacterial growth was conducted using titanium dioxide nanoparticles (TiO₂ NPs) with three sizes (13, 32, and 123 nm). If A. hydrophila strains with a high MDR index were tested against TiO₂ NPs (20 µg/mL) for 1, 12, and 24 h, those with a small size had a greater bactericidal action than large ones. Bacterial strains were inhibited at different percentages in response to TiO₂ NP treatment.

CONCLUSIONS

Nile tilapia broodstock, mortality is associated with different A. hydrophila strains, which harbored virulent and MDR genes. Furthermore, TiO₂ NPs had bactericidal activity, thereby resulting in a considerable reduction in bacterial load.

New insights into the effects of antibiotics and copper on microbial community diversity and carbon source utilization

Residual antibiotics (ABs) and heavy metals (HMs) are continuously released from soil, reflecting their intensive use and contamination of water and soil, posing an environmental problem of great concern. Relatively few studies exist of the functional diversity of soil microorganisms under the combined action of ABs and HMs. To address this deficiency, BIOLOG ECO microplates and the Integrated Biological Responses version 2 (IBRv2) method were used to comprehensively explore the effects of single and combined actions of copper (Cu) and enrofloxacin (ENR), oxytetracycline (OTC), and sulfadimidine (SM2) on the soil microbial community. The results showed that the high concentration (0.80 mmol/kg) compound group had a significant effect on average well color development (AWCD) and OTC showed a dose-response relationship. The results of IBRv2 analysis showed that the single treatment group of ENR or SM2 had a significant effect on soil microbial communities, and the IBRv2 of E1 was 5.432. Microbes under ENR, SM2, and Cu stress had more types of available carbon sources, and all treatment groups were significantly more enriched with microorganisms having D-mannitol and L-asparagine as carbon sources. This study confirms that the combined effects of ABs and HMs can inhibit or promote the function of soil microbial communities. In addition, this paper will provide new insights into IBRv2 as an effective method to evaluate the impacts of contaminants on soil health.

Evaluating the impact of heavy metals on antimicrobial resistance in the primary food production environment: A scoping review

Heavy metals are naturally occurring environmental compounds, which can influence antimicrobial resistance (AMR) dissemination. However, there is limited information on how heavy metals may act as a selective pressure on AMR in the primary food production environment. This review aims to examine the literature on this topic in order to identify knowledge gaps. A total of 73 studies, which met pre-established criteria, were included. These investigations were undertaken between 2008 and 2021, with a significant increase in the last three years. The majority of studies included were undertaken in China. Soil, water and manure were the most common samples analysed, and the sampling locations varied from areas with a natural presence of heavy metals, areas intentionally amended with heavy metals or manure, to areas close to industrial activity or mines. Fifty-four per cent of the investigations focused on the analysis of four or more heavy metals, and copper and zinc were the metals most frequently analysed (n = 59, n = 49, respectively). The findings of this review highlight a link between heavy metals and AMR in the primary food production environment. Heavy metals impacted the abundance and dissemination of mobile genetic elements (MGEs) and antimicrobial resistance genes (ARGs), with MGEs also observed as playing a key role in the spread of ARGs and metal resistance genes (MRGs). Harmonization of methodologies used in future studies would increase the opportunity for comparison between studies. Further research is also required to broaden the availability of data at a global level.

Heavy metal and antibiotic resistance in four Indian and UK rivers with different levels and types of water pollution

Heavy metal pollution can enhance the level of antibiotic resistance, posing concerns to ecosystem and public health. Here, we investigated heavy metal concentrations, heavy metal resistant bacteria and antibiotic resistant bacteria and their corresponding resistant genes, and integrons in four different river environments, i.e., low heavy metals and low wastewater, high heavy metals and low wastewater, low heavy metals and high wastewater, and high heavy metals and high wastewater levels. Heavy metals were found to show positive and significant correlations with heavy metal resistance and antibiotic resistance and integrons (r > 0.60, p < 0.05), indicating that heavy metal selective pressure can cause heavy metal and antibiotic resistance to be transmitted simultaneously via integrons, which can result in the development of multi-resistant bacteria in the heavy metal-polluted environments. Moreover, there were significant associations between heavy metal resistance and antibiotic resistance (r > 0.60, p < 0.05), demonstrating heavy metal and antibiotic resistance are connected via a same or related mechanism. Class 1 integrons were found to have strong correlations with heavy metals and heavy metal resistance and antibiotic resistance (r > 0.60, p < 0.05), indicating a higher occurrence of antibiotic resistance co-selection in the heavy metal-polluted environments.

Ecological mechanisms of sedimental microbial biodiversity shift and the role of antimicrobial resistance genes in modulating microbial turnover

The mechanisms of phylogenetic turnover of microbial communities to environmental perturbations in sediments remain unclear. In this study, the molecular mechanisms of phylogenetic turnover, and impact of antibiotics and antibiotic resistance genes (ARGs) on the modification of microbial assemblages were unravelled. We investigated 306 ARGs, 8 transposases, and 4 integron integrases, bacteria, and eukaryotic diversity through high-throughput quantitative PCR and illumina sequencing, 21 antibiotics and 3 tetracycline byproducts. The freshwater and estuary ecosystems were mainly dominated by genus Sulfurovum and colonised by closely related species compared with the estuary (closeness centrality = 0.42 vs. 0.46), which was dominated by genus Mycobacterium. Eighty-six percent of the ecological process in the bacterial community was driven by stochastic processes, while the rest was driven by deterministic processes. Environmental-related concentrations of antibiotics (0.15-32.53 ng/g) stimulated the proliferation of ARGs which potentially modulated the microbial community assembly. ARG acquisition significantly (P < 0.001) increased eukaryotic diversity through protection mechanisms. ARGs showed complex interrelationships with the microbial communities, and phylum arthropods and Nematea demonstrated the strongest ARG acquisition potential. This study provides key insights for environmental policymakers into understanding the ecological impact of antibiotics and the role of ARGs in modulating the phylogenetic turnover of microbial communities and trophic transfer mechanisms.

Leave No Trace? Ecological and anthropogenic determinants of antibiotic resistant bacteria in a recreational alpine environment

Antibiotic resistant bacteria (ARB) have been detected in remote environments, but the degree to which their presence is due to anthropogenic contamination remains unclear. Here, anthropogenic and ecological determinants of ARB were characterized in remote and highly visited areas of Rocky Mountain National Park in the United States. Soil and water samples were collected from 29 sites once a month for three months and measured for bacteria resistant to seven antibiotics with flow cytometry. A novel index of the likelihood of human presence (HPI) was generated for estimating human impact on ARB abundance. The HPI accounted for 44% of variation in ARB abundance in water samples (p < 0.0001) and 51% of variation in soil samples (p < 0.00001). Human presence index was illustrated as a reliable predictor of ARB abundance despite a tendency to underpredict at higher levels of human impact. Ecological determinants such as temperature, elevation, slope, and aspect were also found to be significantly associated with ARB abundance. These findings suggest that human presence drives the abundance of ARB in Rocky Mountain National Park, but ecological variables play a significant role in their presence and dispersal.

Damage and elimination of soil and water antibiotic and heavy metal pollution caused by livestock husbandry

The combination of antibiotics and heavy metals (HMs) increases the toxicity range of influence and requires additional research attention. This article analyzed the toxicity mechanisms and damage of combined pollution. Cross-resistance, co-resistance, and co-regulation are the primary toxicity mechanisms. Combined pollution increases antibiotic resistance genes (ARGs), increases bacterial resistance, and promotes the horizontal transfer of ARGs, affecting the types and distribution of microorganisms. The hazard of combined pollution varies with concentration and composition. The physicochemical and biological technologies for eliminating combined pollution are primarily elaborated. Adsorption, photocatalytic degradation, and microbial treatment show high removal rates and good recyclability, indicating good application potential. This review provides a basis and reference for the further study the elimination of combined antibiotic and HM pollution.

Antibiotic resistance bacteria and antibiotic resistance genes survived from the extremely acidity posing a risk on intestinal bacteria in an in vitro digestion model by horizontal gene transfer

Antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs) are emerging contaminants posing risk to human health. To investigate the pathogenic ARBs and the horizontal gene transfer (HGT) via both extracellular ARGs (eARGs) and intracellular ARGs (iARGs), an in vitro digestion simulation system was established to monitoring the ARB and ARGs passing through the artificial digestive tract. The results showed that ARB was mostly affected by the acidity of the gastric fluid with about 99% ARB (total population of 2.45 × 10⁹-2.54 × 10⁹) killed at pH 2.0 and severe damage of bacterial cell membrane. However, more than 80% ARB (total population of 2.71 × 10⁹-3.90 × 10⁹) survived the challenge when the pH of the gastric fluid was 3.0 and above. Most ARB died from the high acidity, but its ARGs, intI1 and 16 S rRNA could be detected. The eARGs (accounting for 0.03-24.56% of total genes) were less than iARGs obviously. The eARGs showed greater HGT potential than that of iARGs, suggesting that transformation occurred more easily than conjugation. The transferring potential followed: tet (100%) > sul (75%) > bla (58%), related to the high correlation of intI1 with tetA and sul2 (p < 0.01). Moreover, gastric juice of pH 1.0 could decrease the transfer frequency of ARGs by 2-3 order of magnitude compared to the control, but still posing potential risks to human health. Under the treatment of digestive fluid, ARGs showed high gene horizontal transfer potential, suggesting that food-borne ARBs pose a great risk of horizontal transfer of ARGs to intestinal bacteria.

Fate of antibiotic resistance genes and class 1 integrons during sludge treatment using pilot-scale anaerobic digestion with thermal hydrolysis pretreatment

This work evaluated the fate of antibiotic resistance genes (ARGs) and class 1 integron gene in sewage sludge before and after pilot-scale thermal hydrolysis pretreatment (THP) and subsequent mesophilic anaerobic digestion (AD) treatment. Variables investigated include THP temperatures, feedstock types, and AD solids retention times. Real-time polymerase chain reaction was performed to quantify the ARGs in feedstocks, THP and AD effluent. Results show that THP significantly (t test, p < 0.05) reduced the absolute abundances of most ARGs, with the reduction ranging from 0.03 to 3.09 log units. Rebound effects of ARGs in the subsequent AD were observed and were relevant with tested variables; shorter solids retention time (10 days) and higher THP temperature (165 ℃) can significantly reduce ARGs in AD effluent. These findings provide references about the effects of the THP and AD on the control of ARG spread from sewage sludge to environments.

Distribution of quinolone and macrolide resistance genes and their co-occurrence with heavy metal resistance genes in vegetable soils with long-term application of manure

The spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) has become an increasingly serious global public health issue. This study investigated the distribution characteristics and influencing factors of ARB and ARGs in greenhouse vegetable soils with long-term application of manure. Five typical ARGs, four heavy metal resistance genes (MRGs), and two mobile genetic elements (MGEs) were quantified by real-time quantitative polymerase chain reaction (qPCR). The amount of ARB in manure-improved soil greatly exceeded that in control soil, and the bacterial resistance rate decreased significantly with increases in antibiotic concentrations. In addition, the resistance rate of ARB to enrofloxacin (ENR) was lower than that of tylosin (TYL). Real-time qPCR results showed that long-term application of manure enhanced the relative abundance of ARGs in vegetable soils, and the content and proportion of quinolone resistance genes were higher than those of macrolide resistance genes. Redundancy analysis (RDA) showed that qepA and qnrS significantly correlated with total and available amounts of Cu and Zn, highlighting that certain heavy metals can influence persistence of ARGs. Integrase gene intI1 correlated significantly with the relative abundance of qepA, qnrS, and ermF, suggesting that intI1 played an important role in the horizontal transfer of ARGs. Furthermore, there was a weakly but not significantly positive correlation between specific detected MRGs and ARGs and MGEs. The results of this study enhance understanding the potential for increasing ARGs in manure-applied soil, assessing ecological risk and reducing the spread of ARGs.

Effects of heavy metals on the development and proliferation of antibiotic resistance in urban sewage treatment plants

Sewage treatment plants (STPs) are considered as "hotspots" for the emergence and proliferation of antibiotic resistance. However, the impact of heavy metals contamination on dispersal of antibiotic resistance in STPs is poorly understood. This study simultaneously investigated the effect of removal of metal and antibiotic resistance as well as mobile elements at different treatment units of STPs in Delhi, India. Results showed that treatment technologies used in STPs were inefficient for the complete removal of metal and antibiotic resistance, posing an ecological risk of co-selection of antibiotic resistance. The strong correlations were observed between heavy metals, metal and antibiotic resistance, and integrons, implying that antibiotic resistance may be exacerbated in the presence of heavy metals via integrons, and that metal and antibiotic resistance share a common or closely associated mechanism. We quantified an MRG rcnA, conferring resistance to Co and Ni, and identified that it was more abundant than all MRGs, ARGs, integrons, and 16S rRNA, suggesting rcnA could be important in antibiotic resistance dissemination in the environment. The associations between heavy metals, metal and antibiotic resistance, and integrons highlight the need for additional research to better understand the mechanism of co-selection as well as to improve the removal efficacy of current treatment systems.

Effects of heavy metals pollution on the co-selection of metal and antibiotic resistance in urban rivers in UK and India

Heavy metal pollution and the potential for co-selection of resistance to antibiotics in the environment is growing concern. However, clear associations between heavy metals and antibiotic resistance in river systems have not been developed. Here we investigated relationships between total and bioavailable heavy metals concentrations; metal resistance gene (MRG) and antibiotic resistance gene (ARG) abundances; mobile genetic elements; and the composition of local bacterial communities in low and high metal polluted rivers in UK and India. The results indicated that MRGs conferring resistance to cobalt (Co) and nickel (Ni) (rcnA), and Co, zinc (Zn), and cadmium (Cd) (czcA), and ARGs conferring resistance to carbapenem and erythromycin were the dominating resistant genes across the samples. The relative MRGs, ARGs, and integrons abundances tended to increase at high metal polluted environments, suggesting high metals concentrations have a strong potential to promote metal and antibiotic resistance by horizontal gene transmission and affecting bacterial communities, leading to the development of multi-metal and multi-antibiotic resistance. Network analysis demonstrated the positive and significant relationships between MRGs and ARGs as well as the potential for integrons playing a role in the co-transmission of MRGs and ARGs (r > 0.80, p < 0.05). Additionally, the major host bacteria of various MRGs and ARGs that could be accountable for greater MRGs and ARGs levels at high metal polluted environments were also identified by network analysis. Spearman's rank-order correlations and RDA analysis further confirm relationships between total and bioavailable heavy metals concentrations and the relative MRG, ARG, and integron abundances, as well as the composition of related bacterial communities (r > 0.80 (or < -0.80), p < 0.05). These findings are critical for assessing the possible human health concerns associated with metal-driven antibiotic resistance and highlight the need of considering metal pollution for developing appropriate measures to control ARG transmission.

New insight into the co-adsorption of oxytetracycline and Pb(II) using magnetic metal-organic frameworks composites in aqueous environment: co-adsorption mechanisms and application potentials

The present study aimed to investigate the co-adsorption and application of water stabilized Fe₃O₄@ZIF-8 composite with magnetic cubic crystal structure. This new material was successfully prepared by facile modification strategy and rational design, which was used for simultaneous adsorption of oxytetracycline (OTC) and Pb(II) in aqueous solution. The co-adsorption behavior and mechanism of the composite for OTC and Pb(II) were systematically investigated by characterization techniques and batch experiments, and its application potential was effectively evaluated. The results showed that the synthesized Fe₃O₄@ZIF-8 composite innovatively retained the cubic crystal structure of ZIF-8 and was successfully loaded on the surface of Fe₃O₄ particles with small particle size to form a core-shell structure. The Fe₃O₄@ZIF-8 composite possessed a large specific surface area (1722 m²/g), magnetic separation performance (13.4 emu/g), and rich functional groups. The co-adsorption of OTC and Pb(II) on Fe₃O₄@ZIF-8 had fast reaction kinetics (equilibrium within 90 min) and large adsorption capacity (310.29 mg/g and 276.06 mg/g respectively). The adsorption process for both contaminants followed pseudo-second order kinetics and Langmuir isotherm models and had synergistic and competitive effects at the same time. π-π stacking and electrostatic interaction were the main mechanisms of adsorption. Fe₃O₄@ZIF-8 had good adsorption performance after cyclic adsorption for 4 times and it performed well in the treatment of real waste water. This study provided a new sight for the control of combined pollution of OTC and Pb(II) and proved Fe₃O₄@ZIF-8 composites have great application potentials for complex wastewater treatment.

Recent progress in Fenton/Fenton-like reactions for the removal of antibiotics in aqueous environments

The frequent use of antibiotics allows them to enter aqueous environments via wastewater, and many types of antibiotics accumulate in the environment due to difficult degradation, causing a threat to environmental health. It is crucial to adopt effective technical means to remove antibiotics in aqueous environments. The Fenton reaction, as an effective organic pollution treatment technology, is particularly suitable for the treatment of antibiotics, and at present, it is one of the most promising advanced oxidation technologies. Specifically, rapid Fenton oxidation, which features high removal efficiency, thorough reactions, negligible secondary pollution, etc., has led to many studies on using the Fenton reaction to degrade antibiotics. This paper summarizes recent progress on the removal of antibiotics in aqueous environments by Fenton and Fenton-like reactions. First, the applications of various Fenton and Fenton-like oxidation technologies to the removal of antibiotics are summarized; then, the advantages and disadvantages of these technologies are further summarized. Compared with Fenton oxidation, Fenton-like oxidations exhibit milder reaction conditions, wider application ranges, great reduction in economic costs, and great improved cycle times, in addition to simple and easy recycling of the catalyst. Finally, based on the above analysis, we discuss the potential for the removal of antibiotics under different application scenarios. This review will enable the selection of a suitable Fenton system to treat antibiotics according to practical conditions and will also aid the development of more advanced Fenton technologies for removing antibiotics and other organic pollutants.

Antimicrobial Resistance and Transconjugants Characteristics of sul3 Positive Escherichia coli Isolated from Animals in Nanning, Guangxi Province

Sulfonamides are the second most popular antibiotic in many countries, which leads to the widespread emergence of sulfonamides resistance. sul3 is a more recent version of the gene associated with sulfonamide resistance, whose research is relatively little. In order to comprehend the prevalence of sul3 positive E. coli from animals in Nanning, a total of 146 strains of E. coli were identified from some farms and pet hospitals from 2015 to 2017. The drug resistance and prevalence of sul3 E. coli were analyzed by polymerase chain reaction (PCR) identification, multi-site sequence typing (MLST), drug sensitivity test, and drug resistance gene detection, and then the plasmid containing sul3 was conjugated with the recipient strain (C600). The effect of sul3 plasmid on the recipient was analyzed by stability, drug resistance, and competitive test. In this study, forty-six sul3 positive E. coli strains were separated. A total of 12 ST types were observed, and 1 of those was a previously unknown type. The ST350 is the most numerous type. All isolates were multidrug-resistant E. coli, with high resistant rates to penicillin, ceftriaxone sodium, streptomycin, tetracycline, ciprofloxacin, gatifloxacin, and chloramphenicol (100%, 73.9%, 82.6%, 100%, 80.4%, 71.7%, and 97.8%, respectively). They had at least three antibiotic resistance genes (ARGs) in addition to sul3. The plasmids transferred from three sul3-positive isolates to C600, most of which brought seven antimicrobial resistance (AMR) and increased ARGs to C600. The transferred sul3 gene and the plasmid carrying sul3 could be stably inherited in the recipient bacteria for at least 20 days. These plasmids had no effect on the growth of the recipient bacteria but greatly reduced the competitiveness of the strain at least 60 times in vitro. In Nanning, these sul3-positive E. coli had such strong AMR, and the plasmid carrying sul3 had the ability to transfer multiple resistance genes that long-term monitoring was necessary. Since the transferred plasmid would greatly reduce the competitiveness of the strain in vitro, we could consider limiting the spread of drug-resistant isolates in this respect.

Potential threat of antibiotics resistance genes in bioleaching of heavy metals from sediment

Bioleaching is considered a promising technology for remediating heavy metals pollution in sediments. During bioleaching, the pressure from the metals bioleached is more likely to cause the spread of antibiotic resistance genes (ARGs). The changes in abundance of ARGs in two typical heavy metal bioleaching treatments using indigenous bacteria or functional bacteria agent were compared in this study. Results showed that both treatments successfully bioleached heavy metals, with a higher removal ratio of Cu with functional bacteria agent. The absolute abundances of most ARGs decreased by one log unit after bioleaching, particularly tetR (p = 0.02) and tetX (p = 0.04), and intI1 decreased from 10⁶ to 10⁴ copies/g. As for the relative abundance, ARGs in the non-agent treatment increased from 3.90 × 10^-4 to 1.67 × 10^-3 copies/16S rRNA gene copies (p = 0.01), and in the treatment with agent, it reached 6.65 × 10^-2 copies/16S rRNA gene copies, and intI1 relative abundance was maintained at 10^-3 copies/16S rRNA gene copies. The relative abundance of ARGs associated with efflux pump mechanism and ribosomal protection mechanism increased the most. The co-occurrence network indicated that Cu bioleached was the environmental factor determining the distribution of ARGs, Firmicutes might be the potential hosts of ARGs. Compared to bioleaching with indigenous bacteria, the addition of functional bacteria agent engendered a decrease in microbial alpha diversity and an increase in the amount of Cu bioleached, resulting in a higher relative abundance of ARGs. Heavy metal pollution can be effectively removed from sediments using the two bioleaching treatments, however, the risk of ARGs propagation posed by those procedures should be considered, especially the treatment with functional bacteria agents. In the future, an economical and efficient green technology that simultaneously reduces both the absolute abundance and relative abundance of ARGs should be developed.

Effects of different oxygen conditions on pollutants removal and the abundances of tetracycline resistance genes in activated sludge systems

The individual and combined effects of tetracycline (TC) and divalent copper (Cu²⁺) on the performance of activated sludge systems and the abundances of tetracycline resistance genes (TRGs) in activated sludge, under both aerobic and anaerobic conditions, were studied. Activated sludge systems received TC (0.2 mg L^-1) and Cu²⁺ (5 mg L^-1) separately or jointly under either aerobic or anaerobic conditions. The addition of TC did not affect the performance of activated sludge systems and the addition of Cu²⁺ and mixed TC/Cu²⁺ inhibited biological phosphorus removal. The TC removal efficiencies in systems under aerobic and anaerobic conditions were 98.4%-99.7% and 96.8%-99.9%, respectively, and Cu²⁺ promoted TC removal in activated sludge systems. The TC degradation product was 4-epitetracycline (ETC) in activated sludge systems under both aerobic and anaerobic conditions. The total relative abundances of TRGs (tetA, tetC, tetE, tetM, tetO, tetW, tetX and tetB(P)) in activated sludge showed opposite development trends under the two oxygen conditions and aerobic condition was beneficial to the attenuation of high-risk TRGs. The results of this study might improve evaluation of the combined effects of antibiotics and heavy metals on wastewater biological treatment systems.

Co-selective Pressure of Cadmium and Doxycycline on the Antibiotic and Heavy Metal Resistance Genes in Ditch Wetlands

Abuse of heavy metals and antibiotics results in the dissemination of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). Ditch wetlands are important sinks for heavy metals and antibiotics. The relationships between bacterial communities and MRG/ARG dissemination under dual stresses of heavy metals and antibiotics remain unclear. The responses of MRGs and ARGs to the co-selective pressure of cadmium (Cd) and doxycycline (DC) in ditch wetlands were investigated after 7-day and 84-day exposures. In ecological ditches, residual rates of Cd and DC varied from 0.4 to –5.73% and 0 to –0.61%, respectively. The greatest total relative abundance of ARGs was observed in the Cd 5 mg L^–1 + DC 50 mg L^–1 group. A significant level of DC (50 mg L^–1) significantly reduced the total relative abundances of MRGs at a concentration of 5 mg L^–1 Cd stress. Redundancy analysis indicated that Cd and DC had strong positive effects on most ARGs and MRGs after a 7-day exposure. Meanwhile, the class 1 integron gene (intI1) exhibited strong positive correlations with most ARGs and cadmium resistance genes (czcA) after an 84-day exposure. Network analysis showed that Acinetobacter and Pseudomonas were the potential dominant host genera for ARGs and MRGs, and tetracycline resistance genes (tetA), czcA, and intI1 shared the same potential host bacteria Trichococcus after an 84-day exposure.

Do microplastic biofilms promote the evolution and co-selection of antibiotic and metal resistance genes and their associations with bacterial communities under antibiotic and metal pressures?

Microplastic (MP) biofilms with heterogeneous bacterial compositions and structure have become a hotspot of antibiotic resistance genes (ARGs) in aquatic environments. The evolutionary features of ARGs and their related factors including class 1 integron (intI1), metal resistance genes (MRGs), and bacterial communities in MP biofilms under exogenous pressures and how they compared with natural substrates (NS) are unclear. The individual and combined pressures of sulfamethoxazole, tetracycline, and zinc were used to drive the dynamic evolution of ARGs, intI1, MRGs, and bacterial communities in the MP and NS biofilms. The exogenous pressures from the combined selection of sulfamethoxazole, tetracycline, and zinc and their increasing concentrations both significantly enhanced the abundances of ARGs on the MP compared to the NS. Meanwhile, the selective pressures resulted in obvious dissimilarities between the MP and NS bacterial communities. The core bacterial taxa and the co-occurrence patterns of ARGs and bacterial genera in the biofilms of MP and NS were obviously different, and more potential ARG host bacteria selectively colonized the MP. Metal pressure also enhanced the enrichment of ARGs in the MP biofilms by promoting the spread of intI1 via the co-selection mechanism.

Landscape of genes in hospital wastewater breaking through the defense line of last-resort antibiotics

Hospital wastewater contains abundant antibiotics, antibiotic resistance genes (ARGs), and pathogens. Last-resort antibiotic resistance genes (LARGs) include the New Delhi metallo-β-lactamase gene blaNDM, mobile colistin resistance gene mcr and tigecycline resistance gene tet(X) which confers resistance to carbapenems, colistin and tigecycline. The presence and significance of LARGs in hospital wastewater treatment systems (HWTS) have not yet been systematically explored. Here, LARG variants were shown to be prevalent both influents and effluents of HWTS. A total of 989 Enterobacteriaceae isolates that confer resistance to last-resort antibiotics were collected from effluents and multiple genetic contexts of LARGs were analyzed. LARGs-carrying plasmids were confirmed to show high multidrug phenotypes and transferability. We also discovered the co-occurrence of plasmids harboring blaNDM-1 and mcr-1 in single Escherichia coli, as well as E. coli HM016 containing two unique mcr-1-carrying plasmids. This result might accelerate co-dissemination of LARGs under environmental selection pressure. Different core genetic arrangements in these strains suggest several evolutionary pathways in HWTS. The resistance functions of LARGs were confirmed in vitro and in vivo by mass spectrometry. This study provides novel insights into the diversity, genetic context and function of critical ARGs in HWTS. The results raise the concern that LARGs may further spread into the environment, thus, more stringent discharge standards and regulations for hospital wastewater are urgently needed.

Bloom of tetracycline resistance genes in mudflats following fertilization is attributed to the increases in the shared potential hosts between soil and organic fertilizers

A field experiment was carried out in mudflats adjacent to the Yellow Sea, China, amended with sewage sludge and vermicompost by one-time input at different rates to reveal the fates of tetracycline resistance genes (TRGs) and their potential hosts in the soils. Quantitative PCR results showed that soils added with either sludge or vermicompost had more abundant TRGs compared with the non-fertilized soil. This situation was more obvious in sludge fertilized soils especially at high application rates. Vermicompost exhibited a promising outlook for improvement of the mudflats. The abundances of intI1 in the non-fertilized soils were significantly higher than those in fertilizers and fertilized soils. The potential hosts for intI1 were not shared with other TRGs-contained hosts, indicating that intI1 had little effects on the dissemination of TRGs in the mudflats. Moreover, the exclusive hosts for TRGs in fertilizers were not higher than those in the non-fertilized soils, illustrating little effects of fertilization on the introduction of exogenous TRGs into soil. The shared hosts between soil and fertilizers were highest among four possible sources, contributing vastly to the bloom of TRGs following fertilization. It was also shown that different organic fertilizers caused distinct categories of shared potential hosts for TRGs. RDA analysis further indicated that the abundances of the shared potential hosts were affected by soil nutrients. These results suggested that the development of TRGs in soil following fertilization depended on the shared potential hosts with similar ecological niches between soil and fertilizers.

Occurrence of antibiotics and antibiotic resistance genes in cultured prawns from rice-prawn co-culture and prawn monoculture systems in China

Antibiotics and antibiotic resistance genes (ARGs) in the aquatic environment have raised great concerns, as the deleterious effects of residual antibiotics and the emergence of ARGs are challenges to aquaculture. This study analyzed feed, water, sediment and prawns' tissues from six culture ponds (integrated culture: rice-prawn pond; monoculture: prawn pond) in Tianjin, Northeast China. Eighteen types of antibiotics were detected in all ponds, which conferring to four classes of antibiotics including sulfonamides, tetracyclines, fluoroquinolones, macrolides. The mean log bioaccumulation factor (BAF) values for five antibiotics were analyzed in the hepatopancreas, muscle, and plasma, and we found the maximum Log BAF (1.45) for enrofloxacin in prawn plasma. Correlation analysis of antibiotic concentrations between the plasma and the other two tissues indicated that enrofloxacin, norfloxacin, and erythromycin levels in the hepatopancreas and muscle can be predicted by their plasma concentrations. We also conducted a hazard quotient analysis and found that the risk to human health of eating antibiotic-exposed prawns from the two types of aquaculture method was relatively low. Compared with monoculture, rice-prawn co-culture could significantly decrease the abundance of ARGs; additionally, significant correlations were detected among ARGs, antibiotics, and non-antibiotic environmental factors (e.g., total nitrogen, total ammonia nitrogen, and chemical oxygen demand) in prawn. The present study indicated that the rice-prawn co-culture system is more effective than monoculture for mitigating the bioaccumulation of antibiotics and the occurrence of ARGs in prawn.

Antibiotic residues in environment: antimicrobial resistance development, ecological risks, and bioremediation

The overuse of antibiotics and their disposal without processing are leading the environment and its inhabitants towards a serious health emergency. There is abundance of diverse antibiotic resistance genes and bacteria in environment, which demands immediate attention for the effective removal of antibiotics. There are physical and chemical methods for removal, but the generation of toxic byproducts has directed the efforts towards bioremediation for eco-friendly and sustainable elimination of antibiotics from the environment. Various effective and reliable bioremediation approaches have been used, but still antibiotic residues pose a major global threat. Recent developments in molecular and synthetic biology might offer better solution for engineering of microbe-metabolite biodevices and development of novel strains endowed with desirable properties. This review summarizes the impact of antibiotics on environment, mechanisms of resistance development, and different bioremediation approaches.

Effects of heavy metal contamination released by petrochemical plants on marine life and water quality of coastal areas

The present study attempts to assess the threat of water contamination in Persian Gulf by heavy metals (Fe, Cr, Pb, Cu, Zn, Cd, Se, and Ni) and its subsequent effects on five fish species including Scomberomorus guttatus (S. guttatus), Lethrinus nebulosus (L. nebulosus), Brachirus orientalis (B. orientalis), Pomadasys kaakan (P. kaakan), and Scomberomorus commerson (S. commerson). Water and fish samples from fourteen monitoring stations were obtained to determine the concentrations of contaminants in water and fish. Heavy metal pollution index (HMPI) and non-carcinogenic hazard quotient (NHQI) were employed to evaluate contamination level in water and fish muscle. The Kriging geostatistical method was employed to determine the spatial distribution of different heavy metals around petrochemical plants. The highest NHQI values for P. kaakan and B. orientalis species were 1.036 and 1.046, respectively. In both cases, the NHQI values were higher than the maximum allowable value of 1, indicating that both fish species were on the verge of contamination by heavy metals, which in turn makes the consumption of these fish highly hazardous to human health. The lowest NHQI value was observed in S. commerson species at a value of 0.394, indicating its harmlessness to human health. Overall, fish species living within the top 5 m of the water column (S. commerson and S. guttatus) were found to be less contaminated by heavy metals compared to species dwelling near the seafloor (P. kaakan and B. orientalis). Results also indicated the pollution absorption rate in S. commerson and S. guttatus were 0.45 and 3.4 mg/kg-year, while the corresponding values for the B. orientalis and L. nebulosus species were 6 and 2 mg/kg-year, respectively. P. kaakan species showed a pollution absorption rate of 3.2 mg/kg-year. High heavy metal concentrations of 4.8, 10, 9.8, 5.2, 9.4, and 6.7 mg/L were obtained for Cr, Zn, Pb, Ni, Fe, Cu, and Cd, respectively, in water samples obtained from stations nearby petrochemical plants. The HMPI index for the most contaminated stations was ten times that of the maximum allowable limit. Given the intense activity of oil, gas, and petrochemical plants in the Persian Gulf, defining safe fishing areas by management practices similar to contamination zoning maps presented in this study can substantially protect the public health from heavy metal contamination.

Comparison of the elimination effectiveness of tetracycline and AmpC β-lactamase resistance genes in a municipal wastewater treatment plant using four parallel processes

Municipal wastewater treatment plants (mWWTPs), considered reservoirs of antibiotic resistance genes (ARGs), are selected to compare the contributions of technology and process to ARG removal. Fifteen ARGs (tetA, tetB, tetC, tetE, tetG, tetL, tetM, tetO, tetQ, tetS, tetX, MOX, CIT, EBC, and FOX) and two integron genes (intI1, intI2) were tracked and detected in wastewater samples from a large-scale mWWTP with four parallel processes, including three biological technologies of AAO (anaerobic-anoxic-oxic), AB (adsorption-biodegradation), and UNITANK, two different disinfection technologies, and two primary sedimentation steps. The results showed that ARGs were widely detected, among which tetA and tetM had the highest detection rate at 100%. AAO was the most effective process in removing ARGs, followed by the AB and UNITANK processes, where the separation step was critical: 37.5% AmpC β-lactamase genes were reduced by the secondary clarifier. UV disinfection was more efficient than chlorination disinfection by 47.0% in ARG removal. Both disinfection and primary sedimentation processes could effectively remove integrons, and the swirling flow grit chamber was a more effective primary settling facility in total ARG removal than the aerated grit chamber. The tet genes and AmpC β-lactamase genes were significantly correlated with the water quality indexes of BOD5, CODCr, SS, TP, TOC, pH and NH4+-N (p < 0.05). In addition, the correlation between efflux pump genes and AmpC β-lactamase genes was strongly significant (r2 = 0.717, p < 0.01). This study provides a more powerful guide for selecting and designing treatment processes in mWWTPs with additional consideration of ARG removal.

Honeybee Exposure to Veterinary Drugs: How Is the Gut Microbiota Affected?

Several studies have outlined that a balanced gut microbiota offers metabolic and protective functions supporting honeybee health and performance. The present work contributes to increasing knowledge on the impact on the honeybee gut microbiota of the three most common veterinary drugs (oxytetracycline, sulfonamides, and tylosin). The study was designed with a semi-field approach in micro-hives containing about 500 honeybees. Micro-hives were located in an incubator during the day and moved outdoors in the late afternoon, considering the restrictions on the use of antibiotics in the open field but allowing a certain freedom to honeybees; 6 replicates were considered for each treatment. The absolute abundance of the major gut microbial taxa in newly eclosed individuals was studied with qPCR and next-generation sequencing. Antimicrobial resistance genes for the target antibiotics were also monitored using a qPCR approach. The results showed that the total amount of gut bacteria was not altered by antibiotic treatment, but qualitative variations were observed. Tylosin treatment determined a significant decrease of α- and β-diversity indices and a strong depletion of the rectum population (lactobacilli and bifidobacteria) while favoring the ileum microorganisms (Gilliamella, Snodgrassella, and Frischella spp.). Major changes were also observed in honeybees treated with sulfonamides, with a decrease in Bartonella and Frischella core taxa and an increase of Bombilactobacillus spp. and Snodgrassella spp. The present study also shows an important effect of tetracycline that is focused on specific taxa with minor impact on alfa and beta diversity. Monitoring of antibiotic resistance genes confirmed that honeybees represent a great reservoir of tetracycline resistance genes. Tetracycline and sulfonamides resistance genes tended to increase in the gut microbiota population upon antibiotic administration. IMPORTANCE This study investigates the impact of the three most widely used antibiotics in the beekeeping sector (oxytetracycline, tylosin, and sulfonamides) on the honeybee gut microbiota and on the spread of antibiotic resistance genes. The research represents an advance to the present literature, considering that the tylosin and sulfonamides effects on the gut microbiota have never been studied. Another original aspect lies in the experimental approach used, as the study looks at the impact of veterinary drugs and feed supplements 24 days after the beginning of the administration, in order to explore perturbations in newly eclosed honeybees, instead of the same treated honeybee generation. Moreover, the study was not performed with cage tests but in micro-hives, thus achieving conditions closer to real hives. The study reaches the conclusion that the most common veterinary drugs determine changes in some core microbiota members and that incidence of resistance genes for tetracycline and sulfonamides increases following antibiotic treatment.

Characteristics of bacterial community and ARGs profile in engineered goldfish tanks with stresses of sulfanilamide and copper

Abuse of antibiotics in aquaculture have been alarming and might aggravate spread of resistance genes in the environment. Holistic ARGs proliferation checks require deeper analyses of coupled absolute abundances in 16S rRNA bacteria communities at the phylum level to detect biomarkers. Sulfanilamide (sul) and copper II sulfate (CuSO₄ II) were, therefore, designed and added as separate or combined treatments in 9 replicate engineered goldfish tanks comprising 3 individual sul, 3 CuSO₄ II, 3 (sul + CuSO₄ II) combinations, and 3 controls within 180 days. The DNA from water and fish guts was sequenced under qPCR to determine 16S rRNA bacteria biomarkers co-occurring with the correspondent ARGs. Combined chemical addition at 0.8-1.5 mg sul + 0.5-1.0 mg CuSO₄ II/3 L of tank waters reduced sequenced 16S rRNA bacteria absolute abundances in fish gut and water samples while portraying the biomarkers. Absolute abundances of the entire 16S rRNA bacteria was higher in fish guts (3.4 × 10¹⁴-4.9 × 10⁸ copies/g) than water samples (1.5 × 10⁹-2.6 × 10¹⁵ copies/L), respectively. Much as sul 1(log) were dominant over intl 1(log) genes, and their fundamental profiles were also higher in the fish guts than water samples; the Spearman's correlation analyses revealed positive relationship (p < 0.01 and r = 0.873) among the biomarkers of both ARG pairs at the phylum level and the physicochemical parameters. In the fish gut and water samples ratios, Bacteroidetes (10-85:12-85%) > Proteobacteria (10-50:15-65%) > Planktomycetes (10-52:8-25%) featured prominently based on LEfSe use as the hot-spotted biomarkers, hence justifying its higher prospects towards innovative environmental microbiological and biotechnological studies.

Insight into the evolution of microbial community and antibiotic resistance genes in anammox process induced by copper after recovery from oxytetracycline stress

The influence of copper ion (Cu²⁺) on anaerobic ammonium oxidation (anammox) performance and microbial community structures after oxytetracycline (OTC) stress recovery were assessed. Experimental results demonstrated that anammox performance were stressed by 1.0 mg L^-1 Cu²⁺ and inhibitions were reversible with total nitrogen removal rate higher than 3.08 ± 0.2 kg N m^-3 d^-1. The residual OTC in the anammox sludge could combine with Cu²⁺ introduced and thereby retarded inhibition on performance in the presence of 2.0 mg L^-1 Cu²⁺. Moreover, the positive relation of dominant bacterium Ca. Anammoxoglobus with the abundance of functional genes and parts of antibiotic resistance genes were observed, suggesting that regain of performance was the results of the gradual domestication of latent resistant species after inhibition. This investigation reveals new insights into resistance of anammox performance for Cu²⁺ and OTC.

Deciphering of antibiotic resistance genes (ARGs) and potential abiotic indicators for the emergence of ARGs in an interconnected lake-river-reservoir system

This study aimed to decipher the patterns of antibiotic resistance genes (ARGs) and linkages of key abiotic indicators with ARGs in an interconnected lake-river-reservoir system. The results showed that seasonal variations in the relative abundance of ARGs and mobile gene elements (MGEs) were significant (KW, p < 0.05). ARGs representative of fecal pollution and natural environment were primarily distributed in the river and reservoir, respectively. The lake, river, and reservoir shared 54.5% of ARGs subtypes, most of which are multidrug resistance genes encoding for efflux pumps. Network results showed that ARGs conferring resistance to aminoglycoside frequently co-occurred with class 1 integrons and Limnohabitans. The resistance risks were low and associated with non-corresponding ARGs, and the highest resistance risk was caused by enrofloxacin in the Dianshan Lake. Fluorescence indices derived from two methods exhibited consistent positive correlations with abundance of individual genes (i.e. aada1 and aadA2-03) as well as total aminoglycoside resistance genes (Pearson, p < 0.05). Moreover, ARGs indicators of human and animal fecal pollution showed linkages with humic-like and fulvic-like indices (Pearson, p < 0.05). The results provide novel insights into the roles of abiotic factors on indicating dynamics of ARGs in aquatic environment impacted by anthropogenic activities.

Effectively reducing antibiotic contamination and resistance in fishery by efficient gastrointestine-blood delivering dietary millispheres

The overuse of antibiotics during the medication treatment is inevitable in the extensively-applied intensive and semi-intensive aquaculture mode; the accompanied antibiotic contamination and antimicrobial resistance pose threats to the ecosystems and cause great loss to the aquaculture industry. To solve the problem, this work introduced the antibiotic-laden dietary millispheres (DMSs) with internal porous structure for the high availability, attractiveness and digestibility to fish. Two types of antibiotics with distinct solubilities - tetracycline chloride (TCH) and sulfadiazine (SDZ) were made into the DMSs, individually, which were then directly adopted in the feeding of fish. Carassius auratus was chosen as the target fish in this work. The mesocosm study demonstrate that, compared with the regular way of oral administration (feeding the mixture of antibiotics and commercial feed pellets), the DMSs could use much less (i.e. one order of magnitude lower) antibiotic dose to reach the equivalent antibiotic concentration in gastrointestine and blood. As a robust alternative, either TCH- or SDZ-laden DMSs achieved efficient drug delivery in vivo, which importantly facilitated the source reduction of antibiotics, the alleviation of antibiotic contamination in fishery and the control of antibiotic resistance especially in sediments.

Improved reduction of antibiotic resistance genes and mobile genetic elements from biowastes in dry anaerobic co-digestion

This study investigated the performance of anaerobic co-digestion (AcoD) of pig manure and food waste on the reduction of antibiotic resistomes under wet and dry AcoD conditions. High-throughput quantitative PCR technology was utilized for a comprehensive assessment of the performances of the two processes. The results show that dry AcoD with a total solids (TS) content of 20% effectively reduced total antibiotic resistance genes (ARGs) by 1.24 log copies/g wet sample, while only 0.54 log copies/g wet sample was reduced in wet AcoD with a TS content of 5%. Dry AcoD was more efficient in reduction of aminoglycosides, multidrug and sulfonamide resistance genes compared with the reduction of other classes of ARGs. Dry AcoD caused a significant reduction of ARGs with resistance mechanisms of efflux pump and antibiotic deactivation. In contrast, there was no obvious difference in reductions of ARGs with different resistance mechanisms in wet AcoD. Network analysis showed that ARGs were significantly correlated with mobile genetic elements (MGEs) (Spearman's r > 0.8, P < 0.05), as well as microbial communities. Enrichment of ARGs and MGEs was found at the early period of AcoD processes, indicating some ARGs and MGEs increased during the hydrolysis and acidogenesis stages. But after a long retention time, their abundances were effectively reduced by dry AcoD in the subsequent stages.

Heavy metal pollution promotes antibiotic resistance potential in the aquatic environment

Water pollution is one of the main challenges and water crises, which has caused the existing water resources to be unusable due to contamination. To understand the determinants of the distribution and abundance of antibiotic resistance genes (ARGs), we examined the distribution of 22 ARGs in relation to habitat type, heavy metal pollution and antibiotics concentration across six lakes and wetlands of Iran. The concentration of 13 heavy metals was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) by Thermo Electron Corporation, and five antibiotics by online enrichment and triple-quadrupole LC-MS/MS were investigated. We further performed a global meta-analysis to evaluate the distribution of ARGs across global lakes compared with our studied lakes. While habitat type effect was negligible, we found a strong correlation between waste discharge into the lakes and the abundance of ARGs. The ARGs abundance showed stronger correlation with the concentration of heavy metals, such as Vanadium, than with that of antibiotics. Our meta-analysis also confirmed that overuse of antibiotics and discharge of heavy metals in the studied lakes. These data point to an increase in the distribution of ARGs among bacteria and their increasing resistance to various antibiotics, implying the susceptibility of aquatic environment to industrial pollution.