Microplastics (MPs) are an emerging global concern as they are abundant in the environment and can act as vectors of various contaminants. However, whether and how MPs can be vectors of antibiotic resistance genes (ARGs), especially extracellular ARGs (eARGs), remains far from explicit. This study addresses the adsorption of both intracellular ARGs (iARGs) and eARGs by four types of MPs in municipal wastewater, and then explores the potential horizontal gene transfer of iARGs and eARGs exposed to MPs. Results indicate that though MPs significantly adsorbed both iARGs and eARGs, eARGs were adsorbed with a significantly higher fold enrichment (2.0–5.0 log versus 2.0–3.3 log) and rate (0.0056 min⁻¹ versus 0.0037 min⁻¹) than iARGs. While all four types of MPs adsorbed ARGs, polypropylene MPs showed the highest adsorption capacity for ARGs. Background constituents such as humic acid and antibiotics significantly inhibited adsorption of iARGs, but not eARGs on MPs. The presence of sodium chloride didn't significantly affect adsorption of iARGs or eARGs. The adsorption of ARGs was well explained by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) interaction energy profile. Higher eARG adsorption was attributed to a lower energy barrier between MPs and eARGs than that between MPs and iARGs. Exposure to MPs enhanced horizontal gene transfer of both iARGs and eARGs by 1.5 and 2.0 times, respectively. The improved contact potential between donors and recipients, as well as the increased cell permeability of recipients induced the improved horizontal gene transfer by MPs. This study underscores the need to address ARG propagation through adsorption to MPs.

Although concerns have been raised about co-selection for antibiotic resistance and various antibiotics and non-antibiotic agents, the data on their association in urban sludge is still limited. In addition, antibiotic contamination can result in not only the toxicity but also the antibiotic resistance. In this study, the first large-scale identification of antibiotics and non-antibiotic agents concern for co-selection of resistance against antibiotics was conducted in urban sludge. Co-occurrence analysis showed that antibiotic resistance genes (ARGs) had no significant correlation with the corresponding antibiotics. Therefore, the results of co-occurrence analysis based on antibiotic concentration and ARG abundance were always ambiguous and difficult to interpret. However, antibiotic resistance was positively correlated with highly toxic compounds such as diclofenac, enrofloxacin and nicotine, suggesting that environmental contaminants might influence antibiotic resistance while exerting toxicity through mechanisms such as changes in microbial community and enzyme activity. The close correlation between class 1 integrase gene (intI1) and diclofenac/enrofloxacin indicated that the co-selection scenario between environmental contaminants and ARGs was likely mediated via intI1. In total, the derived co-occurrence patterns improve our understanding of the co-selection between ARGs, antibiotics and non-antibiotic agents, and also reaffirm the importance of potential role of non-antibiotic agents in the global spread of antibiotic resistance.

Microplastics (MPs) serve as vectors for microorganisms and antibiotic resistance genes (ARGs) and contribute to the spread of pathogenic bacteria and ARGs across various environments. Patterns of microbial communities and ARGs in the biofilm on the surface of MPs, also termed as plastisphere, have become an issue of global concern. Although antibiotic resistome in the plastisphere has been detected, how watershed urbanization affects patterns of potential pathogens and ARGs in the microplastic biofilms is still unclear. Here, we compared the bacterial communities, the interaction between bacterial taxa, pathogenic bacteria, and ARGs between the plastisphere and their surrounding water, and revealed the extensive influence of urbanization on them. Our results showed that bacterial communities and interactions in the plastisphere differed from those in their surrounding water. Microplastics selectively enriched Bacteroidetes from water. In non-urbanized area, the abundance of Oxyphotobacteria was significantly (p < 0.05) higher in plastisphere than that in water, while α-Proteobacteria was significantly (p < 0.05) higher in plastisphere than those in water of urbanized area. Pathogenic bacteria, ARGs, and mobile genetic elements (MGEs) were significantly (p < 0.05) higher in the urbanized area than those in non-urbanized area. MPs selectively enriched ARG-carrying potential pathogens, i.e., Klebsiella pneumoniae and Enterobacter cloacae, and exhibited a distinct effect on the relative abundance of ARG and pathogens in water with different urbanization levels. We further found ARGs were significantly correlated to MGEs and pathogenic bacteria. These results suggested that MPs would promote the dissemination of ARGs among microbes including pathogenic bacteria, and urbanization would affect the impact of MPs on microbes, pathogens, and ARGs in water. A high level of urbanization could enhance the enrichment of pathogens and ARGs by MPs in aquatic systems and increase microbial risk in aquatic environments. Our findings highlighted the necessity of controlling the spread of ARGs among pathogens and the usage of plastic products in ecosystems of urban areas.

The presence of large amounts of antibiotic resistance genes (ARGs) in livestock manures poses an impending, tough safety risk to ecosystems. To investigate more comprehensively the mechanisms of ARGs removal from industrial-scale composting of livestock manure based on biochar addition, we tracked the dynamics of bacterial community and ARGs at various stages of aerobic composting of livestock manures with 10% biochar. There were no significant effects of biochar on the bacterial community and the profiles of ARGs. During aerobic composting, the relative abundance of ARGs and mobile genetic elements (MGEs) showed overall trends of decreasing and then increasing. The key factor driving the dynamics of ARGs was bacterial community composition, and the potential hosts of ARGs were Caldicoprobacter, Tepidimicrobium, Ignatzschineria, Pseudogracilibacillus, Actinomadura, Flavobacterium and Planifilum. The retention of the thermophilic bacteria and the repopulation of the initial bacteria were the dominant reasons for the increase in ARGs at maturation stage. Additionally, among the MGEs, the relative abundance of transposon gene was substantially removed, while the integron genes remained at high relative abundance. Our results highlighted that the suitability of biochar addition to industrial-scale aerobic composting needs to be further explored and that effective measures are needed to prevent the increase of ARGs content on maturation stage.

Recently, increasing attention has been paid to antibiotic resistance genes (ARGs) in urban stormwater runoff. However, there were little data on the diversity and distribution of ARGs associated with road sediments transported in runoff. The investigation of ARGs diversity showed that sulfonamide resistance genes (sul2 and sul3) occupied 61.7%–82.3% of total ARGs in runoff. The analysis of ARGs distribution in particulate matter (PM) implied that both tetQ and trbC existed mainly in PM with size of 150–300 μm, but other ARGs and mobile genetic elements (MGEs) were dominant in PM with size <75 μm. The discussion of potential hosts indicated that target genes (ermF, blaOXA1/blaOXA30, ermC, qnrA, sul2, tnpA-01, intI2, tetW, intI1, sul3, trbC) had the strongest subordinate relationship with Proteobacteria at phylum level and Enterobacter at genus level. The effect evaluation of ARGs distribution suggested that 13 kinds of ARGs were positively correlated with Pr/PS and Zeta potential, resulting in the more ARGs in PM with smaller size (<75 μm).

Irrational use of antibiotics produces a large number of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Wastewater treatment plants (WWTPs) act as important sources and sinks of ARGs, and play an important role in their generation, treatment, and dissemination. This study summarizes the types, concentrations, and factors of ARGs in WWTPs, investigates the sources of ARGs in wastewater, compares the removal efficiencies of different treatment processes on ARGs, and analyzes the potential risks of ARGs accumulation in effluent, sludge and their emission into the air. The results show that the main ARGs detected in the influent of WWTPs are the genes resistant to macrolides (ermB, ermF), tetracyclines (tetW, tetA, tetC), sulfonamides (sul1, sul2), and β-lactams (blaOXA, blaTEM). The concentrations of ARGs in the influent of the WWTPs are 2.23 × 10²–3.90 × 10⁹ copies/mL. Wastewater quality and microbial community are the dominant factors that affect the distribution characteristics of ARGs. The accumulation of ARGs in effluent, sludge, and aerosols pose potential risks to the regional ecological environment and human health. Based on these results, research trends with respect to ARGs in WWTPs are also prospected.

Manure application increases the transfer risk of antibiotic resistance to farmland. Especially, its impact remains unclear when it occurs in arsenic (As)-contaminated paddy soils, which is considered as a global environmental problem. In this work, we investigated the fate of antibiotic resistance genes (ARGs) in As-antibiotic co-contaminated paddy soils under the application of manure from different sources (pig manure, cow dung, and chicken manure). Differences in the aliphatic carbon and electron-donating capacities of these dissolved organic matters (DOM) regulated the transformation of iron and As by both biotic and abiotic processes. The regulation by pig manure was stronger than that by cow dung and chicken manure. DOM regulation increased the abundance of As-related functional genes (arsC, arrA, aioA, and arsM) in the soil and accelerated the transformation of As speciation, the highest proportion of As(III) being 45%–61%. Meanwhile, the continuous selection pressure provided by the highly toxic As(III) increased the risk of ARGs and mobile genetic elements (MGEs) via horizontal gene transfer. As-resistant bacteria, including Bacillus, Geobacter, and Desulfitobacterium, were finally considered as potential host bacteria for ARGs and MGEs. In summary, this study clarified the synergistic mechanism of As-antibiotic on the fate of ARGs in co-contaminated paddy soils, and provided practical guidance for the proper application of organic fertilizers.

The emergence of clinically relevant β-lactam-resistant bacteria poses a serious threat to human health and presents a major challenge for medical treatment. How opportunistic pathogenic bacteria acquire antibiotic resistance and the prevalence of antibiotic-resistant opportunistic pathogenic bacteria in the environment are still unclear. In this study, we further confirmed that the selective pressure of heavy metals contributes to the increase in ampicillin-resistant opportunistic pathogens in the Xiangjiang River. Four ampicillin-resistant opportunistic pathogenic bacteria (Pseudomonas monteilii, Aeromonas hydrophila, Acinetobacter baumannii, and Staphylococcus epidermidis) were isolated on Luria-Bertani (LB) agar plates and identified by 16S rRNA sequencing. The abundance of these opportunistic pathogenic bacteria significantly increased in the sites downstream of the Xiangjiang River that were heavily influenced by metal mining activities. A microcosm experiment showed that the abundance of β-lactam resistance genes carried by opportunistic pathogenic bacteria in the heavy metal (Cu²⁺ and Zn²⁺) treatment group was 2–10 times higher than that in the control. Moreover, heavy metals (Cu²⁺ and Zn²⁺) significantly increased the horizontal transfer of plasmids in pathogenic bacteria. Of particular interest is that heavy metals facilitated the horizontal transfer of conjugative plasmids, which may lead to the prevalence of multidrug-resistant pathogenic bacteria in the Xiangjiang River.

Triclosan (TCS), an emergent pollutant, is raising a global concern due to its toxic effects on organisms and aquatic ecosystems. The non-availability of proven treatment technologies for TCS remediation is the central issue stressing thorough research on understanding the underlying mechanisms of toxicity and assessing vital biomarkers in the aquatic organism for practical monitoring purposes. Given the unprecedented circumstances during COVID 19 pandemic, a several-fold higher discharge of TCS in the aquatic ecosystems cannot be considered a remote possibility. Therefore, identifying potential biomarkers for assessing chronic effects of TCS are prerequisites for addressing the issues related to its ecological impact and its monitoring in the future. It is the first holistic review on highlighting the biomarkers of TCS toxicity based on a comprehensive review of available literature about the biomarkers related to cytotoxicity, genotoxicity, hematological, alterations of gene expression, and metabolic profiling. This review establishes that biomarkers at the subcellular level such as oxidative stress, lipid peroxidation, neurotoxicity, and metabolic enzymes can be used to evaluate the cytotoxic effect of TCS in future investigations. Micronuclei frequency and % DNA damage proved to be reliable biomarkers for genotoxic effects of TCS in fishes and other aquatic organisms. Alteration of gene expression and metabolic profiling in different organs provides a better insight into mechanisms underlying the biocide's toxicity. In the concluding part of the review, the present status of knowledge about mechanisms of antimicrobial resistance of TCS and its relevance in understanding the toxicity is also discussed referring to the relevant reports on microorganisms.

Coastal tourist and industrial cities are most likely to have differential effects on the distance dilution of antibiotic resistance genes (ARGs) in an estuary system. This study used high-throughput fluorescence quantitative polymerase chain reaction to identify sediment ARGs in two typical estuaries of coastal tourist and industrial cities (Xiamen and Taizhou) in China. The distance dilution of ARGs and its relationship with key environmental factors were analysed. The results indicated that along the river inlet towards the sea, the distance dilution effect on ARG abundance in estuary sediments of Taizhou was approximately double that in Xiamen, and the macrolide, lincosamide, and streptogramin B (MLSB) and vancomycin genes were replaced by the fluoroquinolone, quinolone, florfenicol, chloramphenicol, and amphenicol (FCA) and β-lactam genes in Taizhou, whereas β-lactam genes succeeded the MLSB and sul genes in Xiamen. The abundance and number of ARGs and mobile genetic elements (MGEs) were positively correlated with the particle size and total organic carbon (TOC) contents of sediments, whereas they were negatively associated with the oxidation and reduction potential (Eₕ) and pH of sediments, as well as the seawater salinity. The sediment particle size (SPZ) was the dominant physicochemical factor affecting the abundance of ARGs (r = 0.826, p < 0.05) and MGEs (r = 0.850, p < 0.01). These findings suggest that although the distance dilution effect on the ARG abundance of estuary sediments of the industrial city is greater than that of the tourist city, the larger SPZ, higher TOC content, and lower salinity, pH, and Eₕ in estuary regions adjacent to the industrial city can more significantly facilitate the proliferation and propagation of ARGs in the sediments.