The effect and mechanism of urban fine particulate matter (PM2.5) on horizontal transfer of plasmid-mediated antimicrobial resistance genes

Airborne antibiotic resistome from sludge dewatering systems: Mobility, pathogen accessibility, cross-media migration propensity, impacting factors, and risks

Bioaerosol contamination was considered as a potential health threat in sludge dewatering systems (SDSs), while emission and risk of airborne antibiotic resistome remain largely unclear. Herein, seasonal investigations of fine particulate matter (PM2.5) were conducted using metagenomics-based methods within and around different SDSs, together with an analysis of sewage sludge. Featured with evident seasonality, antibiotic resistance genes (ARGs) in SDS-PM2.5 also possessed greater accumulation, transfer, and pathogen accessibility than those in ambient air PM2.5. Mobile ARGs in SDS-PM2.5 mainly encoded resistance to tetracycline, and most were flanked by integrase. Some pathogenic antibiotic resistant bacteria (PARB), including Enterobacter asburiae, Escherichia coli, Enterococcus faecium, and Staphylococcus aureus, also carried mobile genetic elements in SDS-PM2.5. Dewatering behavior actuated > 50.56% of ARG subtypes and > 42.86% of PARB in sewage sludge to aerosolize into air. Relative humidity, temperature, and PM2.5 concentration collectively drove the evolution of bacterial community and indirectly promoted the antibiotic resistance of SDS-PM2.5. SDS-PM2.5 posed more serious resistome risks than sewage sludge and ambient air PM2.5, and the highest levels were discovered in winter. These findings underline the role of dewatering behavior in facilitating resistome's aerosolization, and the need to mitigate this potential air pollution.

Ketoprofen promotes the conjugative transfer of antibiotic resistance among antibiotic resistant bacteria in natural aqueous environments

The emergence and spread of antibiotic resistance in the environment pose a serious threat to global public health. It is acknowledged that non-antibiotic stresses, including disinfectants, pharmaceuticals and organic pollutants, play a crucial role in horizontal transmission of antibiotic resistance genes (ARGs). Despite the widespread presence of non-steroidal anti-inflammatory drugs (NSAIDs), notably in surface water, their contributions to the transfer of ARGs have not been systematically explored. Furthermore, previous studies have primarily concentrated on model strains to investigate whether contaminants promote the conjugative transfer of ARGs, leaving the mechanisms of ARG transmission among antibiotic resistant bacteria in natural aqueous environments under the selective pressures of non-antibiotic contaminants remains unclear. In this study, the Escherichia coli (E. coli) K12 carrying RP4 plasmid was used as the donor strain, indigenous strain Aeromonas veronii containing rifampicin resistance genes in Taihu Lake, and E. coli HB101 were used as receptor strains to establish inter-genus and intra-genus conjugative transfer systems, examining the conjugative transfer frequency under the stress of ketoprofen. The results indicated that ketoprofen accelerated the environmental spread of ARGs through several mechanisms. Ketoprofen promoted cell-to-cell contact by increasing cell surface hydrophobicity and reducing cell surface charge, thereby mitigating cell-to-cell repulsion. Furthermore, ketoprofen induced increased levels of reactive oxygen species (ROS) production, activated the DNA damage-induced response (SOS), and enhanced cell membrane permeability, facilitating ARG transmission in intra-genus and inter-genus systems. The upregulation of outer membrane proteins, oxidative stress, SOS response, mating pair formation (Mpf) system, and DNA transfer and replication (Dtr) system related genes, as well as the inhibition of global regulatory genes, all contributed to higher transfer efficiency under ketoprofen treatment. These findings served as an early warning for a comprehensive assessment of the roles of NSAIDs in the spread of antibiotic resistance in natural aqueous environments.

Different paths, same destination: Bisphenol A and its substitute induce the conjugative transfer of antibiotic resistance genes

Antibiotic resistance genes are primarily spread through horizontal gene transfer in aquatic environments. Bisphenols, which are widely used in industry, are pervasive contaminants in such environments. This study investigated how environmentally relevant concentrations of bisphenol A and its substitute (bisphenol S, Bisphenol AP and Bisphenol AF) affect the spread of antibiotic resistance genes among Escherichia coli. As a result, bisphenol A and its three substitutes were found to promote the RP4 plasmid-mediated conjugative transfer of antibiotic resistance genes with different promotive efficiency. Particularly, bisphenol A and bisphenol S were found to induce more than double the incidence of conjugation at 0.1 nmol/L concentration. They therefore were selected as model compounds to investigate the involved mechanisms. Surprisingly, both slightly inhibited bacterial activity, but there was no significant increase in cell death. Bisphenols exposure changed the polymeric substances excreted by the bacteria, increased the permeability of their cell membranes, induced the secretion of antioxidant enzymes and generated reactive oxygen species. They also affected the expression of genes related to conjugative transfer by upregulating replication and DNA transfer genes and downregulating global regulatory genes. It should be noted that gene expression levels were higher in the BPS-exposed group than in the BPA-exposed group. The synthesis of bacterial metabolites and functional components was also significantly affected by bisphenols exposure. This research has helped to clarify the potential health risks of bisphenol contamination of aquatic environments.

Masks As a New Hotspot for Antibiotic Resistance Gene Spread: Reveal the Contribution of Atmospheric Pollutants and Potential Risks

The consumption of disposable surgical masks (DSMs) considerably increased during the coronavirus pandemic in 2019. Herein, we explored the spread of antibiotic resistance genes (ARGs) and the potential risks of antibiotic resistant bacteria (ARB) on DSMs. At environmentally relevant concentrations, the conjugate transfer frequency (CTF) of ARGs increased by 1.34-2.37 folds by 20 μg/m3 of atmospheric water-soluble inorganic ions (WSIIs), and it increased by 2.62-2.86 folds by 80 ng/m3 of polycyclic aromatic hydrocarbons (PAHs). Total suspended particulates (TSP) further promoted the CTF in combination with WSIIs or PAHs. Under WSII and PAH exposure, gene expression levels related to oxidative stress, cell membrane, and the adenosine triphosphate (ATP) were upregulated. WSIIs predominantly induced cellular contact, while PAHs triggered ATP formation and membrane damage. Molecular dynamics simulations showed that WSIIs and PAHs reduced membrane lipid fluidity and increased membrane permeability through interactions with the phosphatidylcholine bilayer. DSM filtering performance decreased, and the CTF of ARGs increased with the wearing time. The gut simulator test showed that ARB disrupted the human gut microbial community and increased total ARG abundance but did not change the ARG abundance carried by ARB themselves. A mathematical model showed that long-term WSII and PAH exposure accelerated ARG dissemination in DSMs.

Understanding Stimulation of Conjugal Gene Transfer by Nonantibiotic Compounds: How Far Are We?

A myriad of nonantibiotic compounds is released into the environment, some of which may contribute to the dissemination of antimicrobial resistance by stimulating conjugation. Here, we analyzed a collection of studies to (i) identify patterns of transfer stimulation across groups and concentrations of chemicals, (ii) evaluate the strength of evidence for the proposed mechanisms behind conjugal stimulation, and (iii) examine the plausibility of alternative mechanisms. We show that stimulatory nonantibiotic compounds act at concentrations from 1/1000 to 1/10 of the minimal inhibitory concentration for the donor strain but that stimulation is always modest (less than 8-fold). The main proposed mechanisms for stimulation via the reactive oxygen species/SOS cascade and/or an increase in cell membrane permeability are not unequivocally supported by the literature. However, we identify the reactive oxygen species/SOS cascade as the most likely mechanism. This remains to be confirmed by firm molecular evidence. Such evidence and more standardized and high-throughput conjugation assays are needed to create technologies and solutions to limit the stimulation of conjugal gene transfer and contribute to mitigating global antibiotic resistance.

Carbonaceous particulate matter promotes the horizontal transfer of antibiotic resistance genes

There is growing concern about the transfer of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in airborne particulate matter. In this study, we investigated the effects of various types of carbonaceous particulate matter (CPM) on the transfer of ARGs in vitro. The results showed that CPM promoted the transfer of ARGs, which was related to the concentration and particle size. Compared with the control group, the transfer frequency was 95.5, 74.7, 65.4, 14.7, and 3.8 times higher in G (graphene), CB (carbon black), NGP (nanographite powder), GP1.6 (graphite powder 1.6 micron), and GP45 (graphite powder 45 micron) groups, respectively. Moreover, the transfer frequency gradually increased with the increase in CPM concentration, while there was a negative relationship between the CPM particle size and conjugative transfer frequency. In addition, the results showed that CPM could promote the transfer of ARGs by increasing ROS, as well as activating the SOS response and expression of conjugative transfer-related genes (trbBp, trfAp, korA, kroB, and trbA). These findings are indicative of the potential risk of CPM for the transfer of ARGs in the environment, enriching our understanding of environmental pollution and further raising awareness of environmental protection.

Priority establishment of soil bacteria in rhizosphere limited the spread of tetracycline resistance genes from pig manure to soil-plant systems based on synthetic communities approach

The spread of antibiotic resistance genes (ARGs) in agroecosystems through the application of animal manure is a global threat to human and environmental health. However, the adaptability and colonization ability of animal manure-derived bacteria determine the spread pathways of ARG in agroecosystems, which have rarely been studied. Here, we performed an invasion experiment by creating a synthetic communities (SynCom) with ten isolates from pig manure and followed its assembly during gnotobiotic cultivation of a soil-Arabidopsis thaliana (A. thaliana) system. We found that Firmicutes in the SynCom were efficiently filtered out in the rhizosphere, thereby limiting the entry of tetracycline resistance genes (TRGs) into the plant. However, Proteobacteria and Actinobacteria in the SynCom were able to establish in all compartments of the soil-plant system thereby spreading TRGs from manure to soil and plant. The presence of native soil bacteria prevented the establishment of manure-borne bacteria and effectively reduced the spread of TRGs. Achromobacter mucicolens and Pantoea septica were the main vectors for the entry of tetA into plants. Furthermore, doxycycline stress promoted the horizontal gene transfer (HGT) of the conjugative resistance plasmid RP4 within the SynCom in A. thaliana by upregulating the expression of HGT-related mRNAs. Therefore, this study provides evidence for the dissemination pathways of ARGs in agricultural systems through the invasion of manure-derived bacteria and HGT by conjugative resistance plasmids and demonstrates that the priority establishment of soil bacteria in the rhizosphere limited the spread of TRGs from pig manure to soil-plant systems.

The effect of triclosan on intergeneric horizontal transmission of plasmid-mediated tigecycline resistance gene tet(X4) from Citrobacter freundii isolated from grass carp gut

The transmission of antibiotic resistance genes (ARGs) in pathogenic bacteria affects culture animal health, endangers food safety, and thus gravely threatens public health. However, information about the effect of disinfectants - triclosan (TCS) on ARGs dissemination of bacterial pathogens in aquatic animals is still limited. One Citrobacter freundii (C. freundii) strain harboring tet(X4)-resistant plasmid was isolated from farmed grass carp guts, and subsequently conjugative transfer frequency from C. freundii to Escherichia coli C600 (E. coli C600) was analyzed under different mating time, temperature, and ratio. The effect of different concentrations of TCS (0.02, 0.2, 2, 20, 200 and 2000 μg/L) on the conjugative transfer was detected. The optimum conditions for conjugative transfer were at 37 °C for 8h with mating ratio of 2:1 or 1:1 (C. freundii: E. coli C600). The conjugative transfer frequency was significantly promoted under TCS treatment and reached the maximum value under 2.00 μg/L TCS with 18.39 times that of the control group. Reactive oxygen species (ROS), superoxide dismutase (SOD) and catalase (CAT) activities, cell membrane permeability of C. freundii and E. coli C600 were obviously increased under TCS stress. Scanning electron microscope showed that the cell membrane surface of the conjugative strains was wrinkled and pitted, even broken at 2.00 μg/L TCS, while lysed or even ruptured at 200.00 μg/L TCS. In addition, TCS up-regulated expression levels of oxidative stress genes (katE, hemF, bcp, hemA, katG, ahpF, and ahpC) and cell membrane-related genes (fimC, bamE and ompA) of donor and recipient bacteria. Gene Ontology (GO) enrichment demonstrated significant changes in categories relevant to pilus, porin activity, transmembrane transporter activity, transferase activity, hydrolase activity, material transport and metabolism. Taken together, a tet(X4)-resistant plasmid could horizontal transmission among different pathogens, while TCS can promote the propagation of the resistant plasmid.

Urbanization influences the indoor transfer of airborne antibiotic resistance genes, which has a seasonally dependent pattern

Over the last few years, the cumulative use of antibiotics in healthcare institutions, as well as the rearing of livestock and poultry, has resulted in the accumulation of antibiotic resistance genes (ARGs). This presents a substantial danger to human health worldwide. The characteristics of airborne ARGs, especially those transferred from outdoors to indoors, remains largely unexplored in neighborhoods, even though a majority of human population spends most of their time there. We investigated airborne ARGs and mobile genetic element (MGE, IntI1), plant communities, and airborne microbiota transferred indoors, as well as respiratory disease (RD) prevalence using a combination of metabarcode sequencing, real-time quantitative PCR and questionnaires in 72 neighborhoods in Shanghai. We hypothesized that (i) urbanization regulates ARGs abundance, (ii) the urbanization effect on ARGs varies seasonally, and (iii) land use types are associated with ARGs abundance. Supporting these hypotheses, during the warm season, the abundance of ARGs in peri-urban areas was higher than in urban areas. The abundance of ARGs was also affected by the surrounding land use and plant communities: an increase in the proportion of gray infrastructure (e.g., residential area) around neighborhoods can lead to an increase in some ARGs (mecA, qnrA, ermB and mexD). Additionally, there were variations observed in the relationship between ARGs and bacterial genera in different seasons. Specifically, Stenotrophomonas and Campylobacter were positively correlated with vanA during warm seasons, whereas Pseudomonas, Bacteroides, Treponema and Stenotrophomonas positively correlated with tetX in the cold season. Interstingly, a noteworthy positive correlation was observed between the abundance of vanA and the occurrence of both rhinitis and rhinoconjunctivitis. Taken together, our study underlines the importance of urbanization and season in controlling the indoor transfer of airborne ARGs. Furthermore, we also highlight the augmentation of green-blue infrastructure in urban environments has the potential to mitigate an excess of ARGs.

Synergistic Enhancement of Carrier Migration by SnO2/ZnO@GO Heterojunction for Rapid Degradation of RhB

Organic dyes in natural waters jeopardize human health. Whether semiconductor materials can effectively degrade dyes has become a challenge for scientific research. Based on this, this study rationally prepared different nanocomposites to remove organic dyes effectively. Pure SnO2 quantum dots, ZnO nanosheets, and SnO2/ZnO (ZS) binary nanocomposites are prepared using the hydrothermal method. Subsequently, SnO2/ZnO@GO (ZSG) ternary composites containing different amounts of GO, i.e., ZSG-5, ZSG-15, and ZSG-25, are synthesized by an ultrasonic water bath method, in which ZS was coupled with GO to form Z-type heterojunctions. The ZSG-15 ternary composites exhibited excellent photocatalytic activity for the degradation of rhodamine B by simulating sunlight. The test results show that the degradation rate of ZSG-15 is about 7.6 times higher than ZnO. The increase in photocatalytic activity is attributed to the synergistic effect of SnO2 and GO to improve the separation efficiency of photogenerated carriers in ZnO. Notably, the large specific surface area of GO increases the reactive sites. Compared with binary nanocomposites, ZSG-15 broadens the response range to light while further accelerating the electron transport rate and improving the photoelectric stability.

Association between particulate matter (PM)2·5 air pollution and clinical antibiotic resistance: a global analysis

BACKGROUND

Antibiotic resistance is an increasing global issue, causing millions of deaths worldwide every year. Particulate matter (PM)2·5 has diverse elements of antibiotic resistance that increase its spread after inhalation. However, understanding of the contribution of PM2·5 to global antibiotic resistance is poor. Through univariate and multivariable analysis, we aimed to present the first global estimates of antibiotic resistance and burden of premature deaths attributable to antibiotic resistance resulting from PM2·5 pollution.

METHODS

For this global analysis, data on multiple potential predictors (ie, air pollution, antibiotic use, sanitation services, economics, health expenditure, population, education, climate, year, and region) were collected in 116 countries from 2000 to 2018 to estimate the effect of PM2·5 on antibiotic resistance via univariate and multivariable analysis. Data were obtained from ResistanceMap, European Centre for Disease Prevention and Control Surveillance Atlas (antimicrobial-resistance sources), and PLISA Health Information Platform for the Americas. Future global aggregate antibiotic resistance and premature mortality trends derived from PM2·5 in different scenarios (eg, 50% reduced antibiotic use or PM2·5 controlled to 5 μg/m3) were projected until 2050.

FINDINGS

The final dataset included more than 11·5 million tested isolates. Raw antibiotic-resistance data included nine pathogens and 43 types of antibiotic agents. Significant correlations between PM2·5 and antibiotic resistance were consistent globally in most antibiotic-resistant bacteria (R2=0·42-0·76, p<0·0001), and correlations have strengthened over time. Antibiotic resistance derived from PM2·5 caused an estimated 0·48 (95% CI 0·34-0·60) million premature deaths and 18·2 (13·4-23·0) million years of life lost in 2018 worldwide, corresponding to an annual welfare loss of US$395 (290-500) billion due to premature deaths. The 5 μg/m3 target of concentration of PM2·5 in the air quality guidelines set by WHO, if reached in 2050, was estimated to reduce antibiotic resistance by 16·8% (95% CI 15·3-18·3) and avoid 23·4% (21·2-25·6) of premature deaths attributable to antibiotic resistance, equivalent to a saving of $640 (580-671) billion.

INTERPRETATION

This analysis is the first to describe the association between PM2·5 and clinical antibiotic resistance globally. Results provide new pathways for antibiotic-resistance control from an environmental perspective.

FUNDING

National Natural Science Foundation of China, Fundamental Research Funds for the Central Universities, Zhejiang University Global Partnership Fund, and China Postdoctoral Science Foundation.

Augmented dissemination of antibiotic resistance elicited by non-antibiotic factors

The emergence and rapid spread of antibiotic resistance seriously compromise the clinical efficacy of current antibiotic therapies, representing a serious public health threat worldwide. Generally, drug-susceptible bacteria can acquire antibiotic resistance through genetic mutation or gene transfer, among which horizontal gene transfer (HGT) plays a dominant role. It is widely acknowledged that the sub-inhibitory concentrations of antibiotics are the key drivers in promoting the transmission of antibiotic resistance. However, accumulating evidence in recent years has shown that in addition to antibiotics, non-antibiotics can also accelerate the horizontal transfer of antibiotic resistance genes (ARGs). Nevertheless, the roles and potential mechanisms of non-antibiotic factors in the transmission of ARGs remain largely underestimated. In this review, we depict the four pathways of HGT and their differences, including conjugation, transformation, transduction and vesiduction. We summarize non-antibiotic factors accounting for the enhanced horizontal transfer of ARGs and their underlying molecular mechanisms. Finally, we discuss the limitations and implications of current studies.

Development of ZnO/SnO2/rGO hybrid nanocomposites for effective photocatalytic degradation of toxic dye pollutants from aquatic ecosystems

The impact of ZnO/SnO₂/reduced graphene oxide nanocomposites (ZnO/SnO₂/rGO NCs) for improved photocatalytic degradation of organic dye pollution is examined in this study. The developed ternary nanocomposites had a variety of characteristics that were detected, such as crystallinity, recombination of photogenerated charge carriers, energy gap, and surface morphologies. When rGO was added to the mixture, the optical band gap energy of ZnO/SnO₂ was lowered, which improved the photocatalytic activity. Additionally, in comparison to ZnO, ZnO/rGO, SnO₂/rGO samples, the ZnO/SnO₂/rGO nanocomposites demonstrated exceptional photocatalytic effectiveness for the destruction of orange II (99.8%) and reactive red 120 dye (97.02%), respectively after 120 min exposure to sunlight. The high electron transport properties of the rGO layers, which make it feasible to efficiently separate electron-hole pairs, are attributed to the enhanced photocatalytic activity of the ZnO/SnO₂/rGO nanocomposites. According to the results, synthesized ZnO/SnO₂/rGO nanocomposites are a cost-efficient option for removing dye pollutants from an aqueous ecosystem. Studies show that ZnO/SnO₂/rGO nanocomposites are effective photocatalysts and may one day serve as the ideal material to reduce water pollution.

Effect of sulfamethazine on the horizontal transfer of plasmid-mediated antibiotic resistance genes and its mechanism of action

As a new type of environmental pollutant, antibiotic resistance genes (ARGs) pose a huge challenge to global health. Horizontal gene transfer (HGT) represents an important route for the spread of ARGs. The widespread use of sulfamethazine (SM2) as a broad-spectrum bacteriostatic agent leads to high residual levels in the environment, thereby increasing the spread of ARGs. Therefore, we chose to study the effect of SM2 on the HGT of ARGs mediated by plasmid RP4 from Escherichia coli (E. coli) HB101 to E. coli NK5449 as well as its mechanism of action. The results showed that compared with the control group, SM2 at concentrations of 10 mg/L and 200 mg/L promoted the HGT of ARGs, but transfer frequency decreased at concentrations of 100 mg/L and 500 mg/L. The transfer frequency at 200 mg/L was 3.04 × 10^-5, which was 1.34-fold of the control group. The mechanism of SM2 improving conjugation transfer is via enhancement of the mRNA expression of conjugation genes (trbBP, trfAP) and oxidative stress genes, inhibition of the mRNA expression of vertical transfer genes, up regulation of the outer membrane protein genes (ompC, ompA), promotion of the formation of cell pores, and improvement of the permeability of cell membrane to promote the conjugation transfer of plasmid RP4. The results of this study provide theoretical support for studying the spread of ARGs in the environment.

Fungicide exposure accelerated horizontal transfer of antibiotic resistance genes via plasmid-mediated conjugation

Co-pollution of soil with pesticide residues and antibiotic resistance genes (ARGs) is increasing due to the substantial usage of pesticides and organic fertilizers in greenhouse-based agricultural production. Non-antibiotic stresses, including those from agricultural fungicides, are potential co-selectors for the horizontal transfer of ARGs, but the underlying mechanism remains unclear. Intragenus and intergenus conjugative transfer systems of the antibiotic resistant plasmid RP4 were established to examine conjugative transfer frequency under stress from four widely used fungicides: triadimefon, chlorothalonil, azoxystrobin, and carbendazim. The mechanisms were elucidated at the cellular and molecular levels using transmission electron microscopy, flow cytometry, RT-qPCR, and RNA-seq techniques. The conjugative transfer frequency of plasmid RP4 between Escherichia coli strains increased with the rising exposure concentrations of chlorothalonil, azoxystrobin, and carbendazim, but was suppressed between E. coli and Pseudomonas putida by a high fungicide concentration (10 µg/mL). Triadimefon did not significantly affect conjugative transfer frequency. Exploration of the underlying mechanisms revealed that: (i) chlorothalonil exposure mainly promoted generation of intracellular reactive oxygen species, stimulated the SOS response, and increased cell membrane permeability, while (ii) azoxystrobin and carbendazim primarily enhanced expression of conjugation-related genes on the plasmid. These findings reveal the fungicide-triggered mechanisms associated with plasmid conjugation and highlight the potential role of non-bactericidal pesticides on the dissemination of ARGs.

Effects and mechanisms of plant growth regulators on horizontal transfer of antibiotic resistance genes through plasmid-mediated conjugation

A vast number of bacteria occur in both soil and plants, with some of them harboring antibiotic resistance genes (ARGs). When bacteria congregate on the interface of soil particles or on plant root surfaces, these ARGs can be transferred between bacteria via conjugation, leading to the formation of antibiotic-resistant pathogens that threaten human health. Plant growth regulators (PGRs) are widely used in agricultural production, promoting plant growth and increasing crop yields. However, until now, little information has been known about the effects of PGRs on the horizontal gene transfer (HGT) of ARGs. In this study, with Escherichia coli DH5α (carrying RP4 plasmid with Tet^R, Amp^R, Kan^R) as the donor and E. coli HB101 as the recipient, a series of diparental conjugation experiments were conducted to investigate the effects of indoleacetic acid (IAA), ethel (ETH) and gibberellin (GA₃) on HGT of ARGs via plasmid-mediated conjugation. Furthermore, the mechanisms involved were also clarified. The results showed that all three PGRs affected the ARG transfer frequency by inducing the intracellular reactive oxygen species (ROS) formation, changing the cell membrane permeability, and regulating the gene transcription of traA, traL, trfAp, trbBp, kilA, and korA in plasmid RP4. In detail, 50-100 mg⋅L^-1 IAA, 20-50 mg⋅L^-1 ETH and 1500-2500 mg⋅L^-1 GA₃ all significantly promoted the ARG conjugation. This study indicated that widespread use of PGRs in agricultural production could affect the HGT of ARGs via plasmid-mediated conjugation, and the application of reasonable concentrations of PGRs could reduce the ARG transmission in both soil environments and plants.

Short-term inhalation exposure evaluations of airborne antibiotic resistance genes in environments

Antibiotic resistance is a sword of Damocles that hangs over humans. In regards to airborne antibiotic resistance genes (AARGs), critical knowledge gaps still exist in the identification of hotspots and quantification of exposure levels in different environments. Here, we have studied the profiles of AARGs, mobile genetic elements (MGEs) and bacterial communities in various atmospheric environments by high throughput qPCR and 16S rRNA gene sequencing. We propose a new AARGs exposure dose calculation that uses short-term inhalation (STI). Swine farms and hospitals were high-risk areas where AARGs standardised abundance was more abundant than suburbs and urban areas. Additionally, resistance gene abundance in swine farm worker sputum was higher than that in healthy individuals in other environments. The correlation between AARGs with MGEs and bacteria was strong in suburbs but weak in livestock farms and hospitals. STI exposure analysis revealed that occupational intake of AARGs (via PM₁₀) in swine farms and hospitals were 110 and 29 times higher than in suburbs, were 1.5 × 10⁴, 5.6 × 10⁴ and 5.1 × 10² copies, i.e., 61.9%, 75.1% and 10.7% of the overall daily inhalation intake, respectively. Our study comprehensively compares environmental differences in AARGs to identify high-risk areas, and forwardly proposes the STI exposure dose of AARGs to guide risk assessment.

Detection and various environmental factors of antibiotic resistance gene horizontal transfer

Bacterial antibiotic resistance in water environments is becoming increasingly severe, and new antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have also attracted the attention of researchers. The horizontal transfer of ARGs in water environments is considered one of the main sources of bacterial resistance in the natural environment. Horizontal gene transfer (HGT) mainly includes conjugation, natural transformation, and transduction, and conjugation has been investigated most. Several studies have shown that there are a large number of environmental factors that might affect the horizontal transfer of ARGs in water environments, such as nanomaterials, various oxidants, and light; however, there is still a lack of systematic and comprehensive reviews on the detection and the effects of the influence factors of on ARG horizontal transfer. Therefore, this study introduced three HGT modes, analysed the advantages and disadvantages of current methods for monitoring HGT, and then summarized the influence and mechanism of various factors on ARG horizontal transfer, and the possible reasons for the different effects caused by similar factors were mainly critically discussed. Finally, existing research deficiencies and future research directions of ARG horizontal transfer in water environments were discussed.

Effects of hematite on the dissemination of antibiotic resistance in pathogens and underlying mechanisms

The dissemination of antibiotic resistance genes (ARGs) in pathogens is becoming a pervasive global health threat, to which the importance of the environment attracts more and more attention. However, how natural minerals affect ARGs transfer in pathogens is still unclear. In this study, the concentration and size effects of hematite on the ARGs conjugative transfer to a common zoonotic pathogen Escherichia coli O157:H7 and underlying mechanisms were explored. Results revealed that bulk hematite reduced the conjugation of resistant plasmids by inhibiting cell growth at any concentration (1-100 mg/L), different from nano-hematite. Low concentrations of nano-hematite (≤ 25 mg/L) induced significant increases in conjugative transfer frequency of 1.83-4.49 folds, while its high concentrations (50 and 100 mg/L) showed no impact, compared with the control group. This low-concentration effect was likely attributed to the increased intracellular ROS level, the reduced intercellular repulsion by increasing the extracellular polymeric substances production and cell surface hydrophobicity, the formation of transfer channels and the increased membrane permeability evidenced by significant changes in gene expression level, and the increased proton motive force by increasing the transmembrane potential of recipients. These findings shed light on potential health risks caused by nano minerals-mediated ARGs dissemination in pathogens in the environment.

Low-concentration of trichloromethane and dichloroacetonitrile promote the plasmid-mediated horizontal transfer of antibiotic resistance genes

Disinfection by-products (DBPs) are one of the unintended consequences of water disinfection that are commonly detected in various water environments. Although DBPs are known to induce antimicrobial resistance via stimulation of chromosomal mutations, it remains unclear whether low-concentration of DBPs could stimulate the conjugative transfer of antibiotic resistance genes (ARGs). The present study aimed to investigate the effect of two typical DBPs, namely trichloromethane (TCM) and dichloroacetonitrile (DCAN), on the conjugative transfer of RP4 plasmid in Escherichia coli genera. The results of the study demonstrated that exposure to low concentrations of TCM and DCAN significantly stimulated conjugative transfer of ARGs, wherein application of 25 μg/L of TCM and 10 μg/L of DCAN resulted in maximum fold change of ~5.5- and ~6.0-fold, respectively, at 16 h of exposure. Further, assessment of underlying mechanisms revealed the involvement of intracellular reactive oxygen species generation, SOS response, increase in cell membrane permeability, upregulation of expression of genes and proteins related to pilus generation, ATP synthesis, and RP4 gene expression. Our findings provided a better understanding of the hidden biological effects and the ecological risks of DBPs in the water environment, especially concerning their effect on the spread of antibiotic resistance.

Seasonal disparities and source tracking of airborne antibiotic resistance genes in Handan, China

The transmission of airborne antibiotic resistance genes (ARGs) loaded on particle is a significant global public health concern. Up to date, the dispersal pattern of airborne ARGs remains unclear despite their critical role in multiregional transmission. In this study, airborne ARGs loaded on fine particulate matter (PM_2.5) and source tracking based on the airflow trajectories were performed by the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) model. The results show that the absolute abundance of ARG subtypes were generally twice times higher in the winter season than that in the summer season, which could be attributable to winter haze events with high particulate matter concentrations in Handan. Exogenous input from serious haze events and local release of ARGs loaded on PM_2.5 of air masses may cause higher levels of ARGs in the winter. Moreover, based on the positive correlation between the abundance of ARGs and PM_2.5 concentration, a source tracing model of airborne ARGs was proposed to the estimate of ARGs release and dissemination. This study highlights airborne ARGs transmission loaded on PM_2.5 of air masses, which facilitating the global spread of antibiotic resistance.

Spread of antibiotic resistance genes and microbiota in airborne particulate matter, dust, and human airways in the urban hospital

Antimicrobial resistance is an increasingly serious threat to public health worldwide. The presence of antibiotic resistance genes (ARGs) in human airways and relevant environments has not received significant attention. In this study, abundances of ARGs and microbes from airborne particulate matter, dust, and human airways in a hospital were profiled using high-throughput qPCR and 16S rRNA gene sequencing. More diverse ARGs and microbes in indoor dust and higher levels of ARGs in particulate matter PM₁₀ and PM_2.5 were observed. Macrolides and aminoglycoside resistance genes were the most abundant ARGs in the airway and environmental samples, respectively. Moreover, the co-occurrences of priority pathogens, ARGs, and mobile genetic elements (MGEs) were shown by the Network analysis. Campylobacter spp. and Staphylococcus spp. positively correlated with fluoroquinolone (vatC-02, mexD) and β-lactams (blaZ, mecA) resistance genes, respectively. In this regard, based on SourceTracker analysis, inhalable particles contributed to 4.0% to 5.5% of ARGs in human airway samples, suggesting an important exchange between airborne inhalable particles and human commensals. This study may advance knowledge about ARGs in airborne particulate matter and dust associated environments, reveal their potential link between environments and humans, and provide a new sight and fundamental data for ARG risk assessment.

Continuous measurement of reactive oxygen species inside and outside of a residential house during summer

Reactive oxygen species (ROS) are an important contributor to adverse health effects associated with ambient air pollution. Despite infiltration of ROS from outdoors, and possible indoor sources (eg, combustion), there are limited data available on indoor ROS. In this study, part of the second phase of Air Composition and Reactivity from Outdoor aNd Indoor Mixing campaign (ACRONIM-2), we constructed and deployed an online, continuous, system to measure extracellular gas- and particle-phase ROS during summer in an unoccupied residence in St. Louis, MO, USA. Over a period of one week, we observed that the non-denuded outdoor ROS (representing particle-phase ROS and some gas-phase ROS) concentration ranged from 1 to 4 nmol/m³ (as H₂ O₂ ). Outdoor concentrations were highest in the afternoon, coincident with peak photochemistry periods. The indoor concentrations of particle-phase ROS were nearly equal to outdoor concentrations, regardless of window-opening status or air exchange rates. The indoor/outdoor ratio of non-denuded ROS (I/O_ROS ) was significantly less than 1 with windows open and even lower with windows closed. Combined, these observations suggest that gas-phase ROS are efficiently removed by interior building surfaces and that there may be an indoor source of particle-phase ROS.

Solar photon-Fenton process eliminates free plasmid DNA harboring antimicrobial resistance genes from wastewater

This work aimed to assess the elimination and inactivation of resistance-conferring plasmids (RCPs) present in suspension in secondary wastewater by solar photo-Fenton as these are important vectors for the dissemination of antimicrobial resistance. Experiments were performed in synthetic secondary wastewater (SWW) and municipal wastewater treatment plant effluent (MWWTPE). Solar photo-Fenton (50 mg L-1 of H2O2 and 30 mg L-1 of Fe2+) was carried out for 60 min at neutral pH by applying the intermittent iron addition strategy. The removal of RCPs was assessed by Real-Time Polymerase Chain Reaction (qPCR). The transformation of competent non-resistant E. coli was used to evaluate the inactivation of target RCPs harboring antibiotic resistance genes (ARGs) to ampicillin (pSB1A2) or kanamycin (pSB1K3) after treatment and controls. Solar photo-Fenton completely removed RCPs initially present in both matrixes (SWW and MWWTPE), showing enhanced performance compared to the dark Fenton process. Both RCPs were inactivated after 30 min of solar photo-Fenton treatment, while 60 min were necessary to achieve the same effect for the dark Fenton reaction under similar conditions. These results indicate the potential of solar photo-Fenton to improve wastewater quality and reduce the spread of antimicrobial resistance in the environment by hampering the discharge of cell-free RCPs present in suspension in MWWTP onto environmental waters.

Biochanin A alleviates oxidative damage caused by the urban particulate matter

Urban particulate matter (UPM), an air pollutant-absorbing toxic substance, can access alveoli, leading to pulmonary diseases. Studies have shown that the water-soluble components of UPM (WS-UPM), containing main toxic substances, can induce oxidative damage in lung cells. In this study, the UPM particle size and composition were detected via instrumental analysis. The isoflavones (biochanin A (BCA), formononetin and daidzein) from chickpeas possess biological antioxidant properties. The present study aimed to investigate the mechanism of the oxidative damage induced by WS-UPM, and the protective role of isoflavones in human alveolar basal epithelial cells. The antioxidant activity of BCA, formononetin and daidzein was investigated through the total reduction capacity, diphenylpicrylhydrazine radical (DPPH), superoxide radical, and hydroxyl radical scavenging capacity detection. We also established cell models in vitro to further explore the BCA-protective mechanism. BCA presented a significant protection, and increased the levels of antioxidant makers including superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH). The effects were also reflected as the reduction of malondialdehyde (MDA) and nitric oxide (NO). Moreover, results obtained from RT-PCR and western blot techniques revealed that MEK5/ERK5 played an indispensable role in regulating the antioxidant effect of BCA, alleviating WS-UPM-induced lung injury. Furthermore, BCA mitigated WS-UPM-exposed damage through upregulating the Nrf2 signaling pathway to enhance the antioxidase expression downstream of Nrf2. In summary, our findings indicated that the WS-UPM-induced pulmonary disease was involved in oxidative stress and the MEK5/ERK5-Nrf2 signaling pathway, and BCA regulated the WS-UPM-induced lung damage via upregulation of the MEK5/ERK5-Nrf2 pathway.

Copper Ions Facilitate the Conjugative Transfer of SXT/R391 Integrative and Conjugative Element Across Bacterial Genera

Copper can persist stably in the environment for prolonged periods. Except for inducing antibiotic resistance in bacteria, copper ions (Cu²⁺) can facilitate the horizontal transfer of plasmid DNA. However, whether and how Cu²⁺ can accelerate the conjugative transfer of SXT/R391 integrative and conjugative element (ICE) is still largely unknown. In this study, Proteus mirabilis ChSC1905, harboring an SXT/R391 ICE that carried 21 antibiotic resistance genes (ARGs), was used as a donor, and Escherichia coli EC600 was used as a recipient. Cu²⁺, at subinhibitory and environmentally relevant concentrations (1–10 μmol/L), significantly accelerated the conjugative transfer of SXT/R391 ICE across bacterial genera (from P. mirabilis to E. coli) (p < 0.05). The combined analyses of phenotypic tests and genome-wide sequencing indicated that reactive oxygen species (ROS) production and cell membrane permeability were critical in the enhanced conjugative transfer of SXT/R391 ICE. Furthermore, the expression of genes related to cell adhesion and ATP synthesis was also significantly upregulated on exposure to Cu²⁺ at a concentration of 5 μmol/L. This study clarified the potential mechanisms of Cu²⁺ to promote the conjugative transfer of SXT/R391 ICE, revealing the potential risk imposed by Cu²⁺ on the horizontal transfer of SXT/R391 ICE-mediated ARGs.

Prevalence of multi-resistant plasmids in hospital inhalable particulate matter (PM) and its impact on horizontal gene transfer

Antibiotic resistance is exacerbated by the exchange of antibiotic resistance genes (ARGs) between microbes from diverse habitats. Plasmids are important ARGs mobile elements and are spread by horizontal gene transfer (HGT). In this study, we demonstrated the presence of multi-resistant plasmids from inhalable particulate matter (PM) and its effect on gene horizontal transfer. Three transferable multi-resistant plasmids were identified from PM in a hospital, using conjugative mating assays and nanopore sequencing. pTAir-3 contained 26 horizontal transfer elements and 10 ARGs. Importantly pTAir-5 harbored carbapenem resistance gene (blaOXA) which shows homology to plasmids from human and pig commensal bacteria, thus indicating that PM is a media for antibiotic resistant plasmid spread. In addition, 125 μg/mL PM_2.5 and PM₁₀ significantly increased the conjugative transfer rate by 110% and 30%, respectively, and augmented reactive oxygen species (ROS) levels. Underlying mechanisms were revealed by identifying the upregulated expressional levels of genes related to ROS, SOS, cell membranes, pilus generation, and transposition via genome-wide RNA sequencing. The study highlights the airborne spread of multi-resistant plasmids and the impact of inhalable PM on the horizontal transfer of antibiotic resistance.

Insects, Rodents, and Pets as Reservoirs, Vectors, and Sentinels of Antimicrobial Resistance

This paper reviews the occurrence of antimicrobial resistance (AMR) in insects, rodents, and pets. Insects (e.g., houseflies, cockroaches), rodents (rats, mice), and pets (dogs, cats) act as reservoirs of AMR for first-line and last-resort antimicrobial agents. AMR proliferates in insects, rodents, and pets, and their skin and gut systems. Subsequently, insects, rodents, and pets act as vectors that disseminate AMR to humans via direct contact, human food contamination, and horizontal gene transfer. Thus, insects, rodents, and pets might act as sentinels or bioindicators of AMR. Human health risks are discussed, including those unique to low-income countries. Current evidence on human health risks is largely inferential and based on qualitative data, but comprehensive statistics based on quantitative microbial risk assessment (QMRA) are still lacking. Hence, tracing human health risks of AMR to insects, rodents, and pets, remains a challenge. To safeguard human health, mitigation measures are proposed, based on the one-health approach. Future research should include human health risk analysis using QMRA, and the application of in-silico techniques, genomics, network analysis, and ’big data’ analytical tools to understand the role of household insects, rodents, and pets in the persistence, circulation, and health risks of AMR.

Ultraviolet/peroxydisulfate degradation of ofloxacin in seawater: Kinetics, mechanism and toxicity of products

The ultraviolet/peroxydisulfate (UV/PDS) system was used to degrade ofloxacin (OFL) in fresh water, synthetic marine aquaculture water and synthetic seawater. The comparison of the reaction degradation rate constants proved that the order of reaction rate was the following: synthetic seawater (0.77 min^-1) > synthetic marine aquaculture water (0.74 min^-1) > freshwater (0.30 min^-1). Bromide (Br^-) and bicarbonate (HCO₃^-) promote the degradation of OFL, whereas chloride (Cl^-) inhibits the degradation. The piperazine ring of OFL was the main reactive group, and atoms N1, C6, C7 and N2 were identified as the reaction sites. Based on the intermediate and final products, the possible degradation pathways of OFL in the three kinds of water were proposed. Additionally, during the UV/PDS treatment of synthetic marine aquaculture water containing Cl^- and Br^-, the oxidation products of OFL showed a slight toxicity to Chlorella pyrenoidosa (C. pyrenoidosa) and Priacanthus tayenus (P. tayenus). The maximum growth inhibition rate of the products to C. pyrenoidosa was 9.72%. The products also caused liver cells of P. tayenus to be damaged and reduced the species richness and diversity of intestinal microorganism. Nevertheless, compared with the products degraded by traditional disinfection methods using NaClO, the biological toxicities were much lower. UV/PDS can be used for seawater as a new alternative disinfection method.

Maternal exposure to fine particle matters cause autophagy via UPR-mediated PI3K-mTOR pathway in testicular tissue of adult male mice in offspring

Epidemiological studies have shown that particulate matters are closely related to human infertility. However, the long-term risk of particulate matters exposure in early life is rarely considered. For the first time this study is designed to explore and elucidate the mechanism of maternal exposure to fine particle matters (PM_2.5) on autophagy in spermatogenic cells of adult offspring. Pregnant C57BL/6 mice were randomly divided into four groups. The 4.8 mg/kg.b.w group and the 43.2 mg/kg.b.w group were administered with different doses of PM_2.5. The membrane control group was administered with PM_2.5 sampling membrane and the control group received no treatment. The exposure was performed every three days from the day after vaginal plug was checked until delivery for a total of 6 times. The results showed that sperms motility and sperms concentration decreased, and sperm deformity increased in adult male offspring. The expression of SOD decreased and MDA increased. Moreover, the level of GRP78/ATF6 and P62 was upregulated, and the expression of PI3K/Akt/mTOR/p-mTOR was down-regulated. This suggests that early-life exposure to PM_2.5 can induce autophagy through the PI3K/Akt/mTOR pathway mediated by unfolded protein response in adult testicular tissue. PM_2.5 may pose a significant role and long-term threat to adult after early-life exposure.