The source, fate and prospect of antibiotic resistance genes in soil: A review

Body size: A hidden trait of the organisms that influences the distribution of antibiotic resistance genes in soil

Body size is a key life-history trait of organisms, which has important ecological functions. However, the relationship between soil antibiotic resistance gene (ARG) distribution and organisms' body size has not been systematically reported so far. Herein, the impact of organic fertilizer on the soil ARGs and organisms (bacteria, fungi, and nematode) at the aggregate level was analyzed. The results showed that the smaller the soil aggregate size, the greater the abundance of ARGs, and the larger the body size of bacteria and nematodes. Further analysis revealed significant positive correlations of ARG abundance with the body sizes of bacteria, fungi, and nematodes, respectively. Additionally, the structural equation model demonstrated that changes in soil fertility mainly regulate the ARG abundance by affecting bacterial body size. The random forest model revealed that total phosphorus was the primary soil fertility factor influencing the body size of organisms. Therefore, these findings proposed that excessive application of phosphate fertilizers could increase the risk of soil ARG transmission by increasing the body size of soil organisms. This study highlights the significance of organisms' body size in determining the distribution of soil ARGs and proposes a new disadvantage of excessive fertilization from the perspective of ARGs.

Metagenomic investigation of antibiotic resistance genes and resistant bacteria contamination in pharmaceutical plant sites in China

Pharmaceutical plant sites play a significant role in the dissemination of antibiotic resistance genes (ARGs) into the environment. It is imperative to comprehensively monitor of ARGs across various environmental media at these sites. This study focused on three pharmaceutical plants, two located in North China and one in South China. Through metagenomic approaches, we examined the composition, mobility potential, and bacterial hosts of ARGs in diverse media such as process water, groundwater, topsoil, soil cores, and pharmaceutical fermentation residues across diverse environmental matrices, including topsoil, soil cores, process water, groundwater, and pharmaceutical fermentation residues. We identified a wide array of ARGs, comprising 21 types and 740 subtypes, with process water exhibiting the highest abundance and diversity. Treatment processes varied in their efficacy in eliminating ARGs, and the clinically relevant ARGs should also be considered when evaluating wastewater treatment plant efficiency. Geographical distinctions in groundwater ARG distribution between northern and southern regions were observed. Soil samples from the three sites showed minimal impact from pharmaceutical activity, with vancomycin-resistance genes being the most prevalent. High levels of ARGs in pharmaceutical fermentation residues underscore the necessity for improved waste management practices. Metagenomic assembly revealed that plasmid-mediated ARGs were more abundant than chromosome-mediated ARGs. Metagenome-assembled genomes (MAGs) analysis identified 166 MAGs, with 62 harboring multiple ARGs. Certain bacteria tended to carry specific types of ARGs, revealing distinct host-resistance associations. This study enhances our understanding of ARG dissemination across different environmental media within pharmaceutical plants and underscores the importance of implementing strict regulations for effluent and residue discharge to control ARG spread.

Impact of Soil Fertilization with Pig Slurry on Antibiotic Residues and Resistance Genes: A Longitudinal Study

The impact of soil fertilization with animal manure on the spread and persistence of antibiotic resistance in the environment is far from being fully understood. To add knowledge about persistence and correlations between antibiotic residues and antibiotic resistance genes (ARGs) in fertilized soil, a longitudinal soil mesocosm study was conducted. Soil samples were collected from the mesocosms immediately before spreading and then afterward at fifteen time points during a 320-day observation period. Eight ARGs (ermB, sul1, tetA, tetG, tetM, cfr, fexA, and optrA) and the class 1 integron-integrase gene, intI1, were determined in both pig slurry and soil, as well as residues of 36 antibiotics. Soil chemical and biochemical parameters were also measured. Twelve antibiotics were detected in the slurry in the range of 3 µg kg-1-3605 µg kg-1, with doxycycline, lincomycin, and tiamulin being the most abundant, whereas ermB, sul1, and tetM were the predominant ARGs. Before spreading, neither antibiotic residues nor ARGs were detectable in the soil; afterwards, their concentrations mirrored those in the slurry, with a gradual decline over the duration of the experiment. After about three months, the effect of the amendment was almost over, and no further evolution was observed.

Antibiotic-Resistant Bacteria Isolated from Street Foods: A Systematic Review

Street food may be a vehicle of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) to humans. Foods contaminated with ARB entail serious problems or challenges in the fields of medical care, animal husbandry, food industry, and public health worldwide. The objectives of this systematic review were to identify and evaluate scientific reports associated with ARB isolated from various street foods. "Preferred reporting items for systematic reviews and meta-analysis" (PRISMA) guidelines were followed. The bibliographic material covers a period from January 2015 to April 2024. Six electronic scientific databases were searched individually for full-text articles; only those papers that met the inclusion and exclusion criteria were selected. Seventeen papers were included in this systematic review. This study highlighted the wide distribution of ARB resistant to β-lactams and other antibiotics, posing significant health risks to consumers. High resistance levels were observed for antibiotics such as ampicillin, ceftriaxone, and tetracycline, while some antibiotics, such as ceftazidime, clavulanic acid, cefoperazone, cotrimoxazole, doxycycline, doripenem, fosfomycin, vancomycin, and piperacillin-tazobactam, demonstrated 100% susceptibility. The prevalence of ARB in street foods varied between 5.2% and 70.8% among different countries. The multiple resistance of various bacteria, including Escherichia coli, Staphylococcus, Salmonella, and Klebsiella, to multiple classes of antibiotics, as well as environmental factors contributing to the spread of antibiotic resistance (AR), emphasize the urgent need for comprehensive approaches and coordinated efforts to confront antimicrobial resistance (AMR) under the "One Health" paradigm.

Dynamics of antibiotic resistance genes and the association with bacterial community during pig manure composting with chitin and glucosamine addition

In modern ecological systems, the overuse and misuse of antibiotics have escalated the prevalence of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), positioning them as emerging environmental contaminants. Notably, composting serves as a sustainable method to recycle agricultural waste into nutrient-rich fertilizer while potentially reducing ARGs and MGEs. This study conducted a 47-day composting experiment using pig manure and corn straw, supplemented with chitin and N-Acetyl-D-glucosamine, to explore the impact of these additives on the dynamics of ARGs and MGEs, and to unravel the interplay between these genetic elements and microbial communities in pig manure composting. Results showed that adding 5% chitin into composting significantly postponed thermophilic phase, yet enhanced the removal efficiency of total ARGs and MGEs by over 20% compared to the control. Additionally, the addition of N-Acetyl-D-glucosamine significantly increased the abundance of tetracycline-resistant and sulfonamide-resistant genes, as well as MGEs. High-throughput sequencing revealed that N-Acetyl-D-glucosamine enhanced bacterial α-diversity, providing diverse hosts for ARGs and MGEs. Resistance mechanisms, predominantly efflux pumps and antibiotic deactivation, played a pivotal role in shaping the resistome of composting process. Co-occurrence network analysis identified the key bacterial phyla Proteobacteria, Firmicutes, Gemmatimonadota, and Myxococcota in ARGs and MGEs transformation and dissemination. Redundancy analysis indicated that physicochemical factors, particularly the carbon-to-nitrogen ratio emerged as critical variables influencing ARGs and MGEs. The findings lay a foundation for the developing microbial regulation method to reduce the risks of ARGs in animal manure composts.

Interplay of xenobiotic-degrading and antibiotic-resistant microorganisms among the microbiome found in the air, handrail, and floor of the subway station

Investigating the quality of the subway environment, especially regarding antibiotic resistance genes (ARGs) and xenobiotics, conveys ecological and health impacts. In this study, compositions and relations of microorganisms harboring ARGs and xenobiotic degradation and metabolism genes (XDGs) in the Sukhumvit subway station (MRT-SKV) in Bangkok was assessed by analyzing the taxonomic and genetic diversity of the microbiome in the air and on the surfaces of floor and handrail. The major bacteria in the MRT-SKV (including Moraxella, which was abundant in the bioaerosol and handrail samples, and Staphylococcus, which was abundant in the bioaerosol samples) were found to contain both ARGs and XDGs. The co-abundance correlation network revealed notable relationships among bacteria harboring antibiotic resistance genes (ARGs) and xenobiotic degradation genes (XDGs). Significant associations were observed between ARGs linked to glycopeptide and fluoroquinolone resistance and genes associated with benzoate, styrene, and atrazine degradation pathways, as well as between ARGs related to cephamycin, cephalosporin, and MLS resistance and XDGs associated with the cytochrome P450-dependent drug metabolism pathway. These correlations suggested that selective pressure exerted by certain xenobiotics and antibiotics can simultaneously affect both ARGs and XDGs in the environment and should favor correlations and co-survival among ARG- and XDG-containing bacteria in the environments. The correlations may occur via shared mechanisms of resistance to both xenobiotics and antibiotics. Finally, different correlation pairs were seen in different niches (air, handrail, floor) of the subway environment or different geolocations. Thus, the relationship between ARG and XDG pairs most likely depends on the unique characteristics of the niches and on the prominent types of xenobiotics and antibiotics in the subway environment. The results indicated that interactions and connections between microbial communities can impact how they function. These microorganisms can have profound effects on accumulation of xenobiotics and ARGs in the MRT-SKV.

Emerging environmental contaminants: Sources, effects on biodiversity and humans, remediation, and conservation implications

Ecosystems, biodiversity, and the human population all depend on a quality or uncontaminated environment. Quality environment provides people and wildlife access to nutrition, medications, dietary supplements, and other ecosystem services. The conservation of biodiversity-that is, species richness, abundance, heredities, and diversity-as well as the control of climate change are facilitated by such an uncontaminated environment. However, these advantages are jeopardized by newly emerging environmental chemical contaminants (EECCs) brought on by increased industrialization and urbanization. In developing countries, inadequate or poor environmental policies, infrastructure, and national standards concerning the usage, recycling, remediation, control, and management of EECCs hasten their effects. EECCs in these countries negatively affect biodiversity, ecological services and functions, and human health. This review reveals that the most deprived or vulnerable local communities in developing countries are those residing near mining or industrial areas and cultivating their crops and vegetables on contaminated soils, as is wildlife that forages or drinks in EECC-contaminated water bodies. Yet, people in these countries have limited knowledge about EECCs, their threats to human well-being, ecosystem safety, and the environment, as well as remediation technologies. Besides, efforts to efficiently control, combat, regulate, and monitor EECCs are limited. Thus, the review aims to increase public knowledge concerning EECCs in developing countries and present a comprehensive overview of the current status of EECCs. It also explores the sources and advancements in remediation techniques and the threats of EECCs to humans, ecosystems, and biodiversity.

Agroecological transition: towards a better understanding of the impact of ecology-based farming practices on soil microbial ecotoxicology

Alternative farming systems have developed since the beginning of industrial agriculture. Organic, biodynamic, conservation farming, agroecology and permaculture, all share a grounding in ecological concepts and a belief that farmers should work with nature rather than damage it. As ecology-based agricultures rely greatly on soil organisms to perform the functions necessary for agricultural production, it is thus important to evaluate the performance of these systems through the lens of soil organisms, especially soil microbes. They provide numerous services to plants, including growth promotion, nutrient supply, tolerance to environmental stresses and protection against pathogens. An overwhelming majority of studies confirm that ecology-based agricultures are beneficial for soil microorganisms. However, three practices were identified as posing potential ecotoxicological risks: the recycling of organic waste products, plastic mulching, and pest and disease management with biopesticides. The first two because they can be a source of contaminants; the third because of potential impacts on non-target microorganisms. Consequently, developing strategies to allow a safe recycling of the increasingly growing organic matter stocks produced in cities and factories, and the assessment of the ecotoxicological impact of biopesticides on non-target soil microorganisms, represent two challenges that ecology-based agricultural systems will have to face in the future.

Low-density polyethylene enhances the disturbance of microbiome and antibiotic resistance genes transfer in soil-earthworm system induced by pyraclostrobin

Non-antibiotic chemicals in farmlands, including microplastics (MPs) and pesticides, have the potential to influence the soil microbiome and the dissemination of antibiotic resistance genes (ARGs). Despite this, there is limited understanding of the combined effects of MPs and pesticides on microbial communities and ARGs transmission in soil ecosystems. In this study, we observed that low-density polyethylene (LDPE) microplastic enhance the accumulation of pyraclostrobin in earthworms, resulting in reduced weight and causing severe oxidative damage. Analysis of 16 S rRNA amplification revealed that exposure to pyraclostrobin and/or LDPE disrupts the microbial community structure at the phylum and genus levels, leading to reduced alpha diversity in both the soil and earthworm gut. Furthermore, co-exposure to LDPE and pyraclostrobin increased the relative abundance of ARGs in the soil and earthworm gut by 2.15 and 1.34 times, respectively, compared to exposure to pyraclostrobin alone. It correlated well with the increasing relative abundance of genera carrying ARGs. Our findings contribute novel insights into the impact of co-exposure to MPs and pesticides on soil and earthworm microbiomes, highlighting their role in promoting the transfer of ARGs. This knowledge is crucial for managing the risk associated with the dissemination of ARGs in soil ecosystems.

The role of water matrix on antibiotic resistance genes transmission in substrate layer from stormwater bioretention cells

Recently, extensive attention has been paid to antibiotic resistance genes (ARGs) transmission. However, little available literature could be found about ARGs transmission in stormwater bioretention cells, especially the role of water matrix on ARGs transmission. Batch experiments were conducted to investigate target ARGs (blaTEM, tetR and aphA) transmission behaviors in substrate layer from stormwater bioretention cells under different water matrices, including nutrient elements (e.g., carbon, nitrogen and phosphorus), water environmental conditions (dissolved oxygen (DO), pH and salinity, etc.) and pollution factors (like heavy metals, antibiotics and disinfectants), showing that ARGs conjugation frequency increased sharply with the enhancement of water matrices (expect DO and pH), while there were obvious increasing tendencies for all ARGs transformation frequencies under only the pollution factor. The correlation between dominant bacteria and ARGs transmission implied that conjugation and transformation of ARGs were mainly determined by Firmicutes, Bacteroidota, Latescibacterota, Chloroflexi and Cyanobacteria at the phylum level, and by Sphingomonas, Ensifer, IMCC26256, Rubellimicrobium, Saccharimonadales, Vicinamibacteraceae, Nocardioides, JG30-KF-CM66 at the genus level. The mentioned dominant bacteria were responsible for intracellular reactive oxygen species (ROS) and cell membrane permeability (CMP) in the substrate layer, where the amplification of intracellular ROS variation were the largest with 144 and 147 % under the condition of TP and salinity, respectively, and the one of CMP variation were the highest more than 165 % under various pollution factors. Furthermore, both increasing DO and reducing salinity could be potential approaches for the inhibition of ARGs transmission in bioretention cells taking into account the simultaneous removal of conventional pollutants.

Antibiotic resistance genes in integrated surface ice, cryoconite, and glacier-fed stream in a mountain glacier in Central Asia

Glacier ice, cryoconite, and glacier-fed streams are interconnected features that have important implications for the dynamics and distribution of abiotic and biotic materials. However, the presence and behavior of antibiotic resistance genes (ARGs) within these glacial environments remained largely unexplored. Addressing this gap, we hypothesized that ARGs are widely distributed and exhibit distinct yet interconnected patterns of diversity and dynamics in these glacial environments. Here, we investigated ARGs in a mountain glacier in Central Asia. A total of 944 ARGs, spanning 22 antibiotic classes, were identified, with 633 ARGs shared across all three environments. Cryoconite exhibited the highest ARG richness, followed by ice, while stream biofilm displayed the lowest value. Exploring ARG profiles, we observed a consistent pattern in terms of antibiotic class and resistance mechanism across all three environments. Beta-lactam resistance genes exhibited the highest diversity, followed by multidrug, glycopeptide, and MLS. The predominant mechanisms were antibiotic inactivation, antibiotic efflux, and target alteration. The most prevalent ARG is cls, followed by mdfA, ropB, fabI, and macB. The similarity in ARG profiles between surface ice and cryoconite samples was more pronounced than their resemblance to stream biofilm samples. The variations of ARG profiles between any pair of environments were largely contributed by turnover component. Further insights into microbial interactions revealed 2328 significant associations between 80 OTUs and 356 ARGs, indicating complex relationships. Certain OTUs, including those from the genera Polaromonas, Ferruginibacter, Hymenobacter, Phormidesmis, Novosphingobium, and Polymorphobacter, were speculated as potential hosts for a variety of ARGs. Our findings underscore the intricate dynamics of antibiotic resistance in glacial ecosystems, emphasizing the need for a holistic understanding of ARG distribution, diversity, and associations across diverse environmental compartments. This research contributes valuable insights into the potential ecological implications of antibiotic resistance dissemination in cold environments, particularly as influenced by increasing climate change.

Short-term evolution of antibiotic responses in highly dynamic environments favors loss of regulation

Microbes inhabit natural environments that are remarkably dynamic, with sudden environmental shifts that require immediate action by the cell. To cope with changing environments, microbes are equipped with regulated response mechanisms that are only activated when needed. However, when exposed to extreme environments such as clinical antibiotic treatments, complete loss of regulation is frequently observed. Although recent studies suggest that the initial evolution of microbes in new environments tends to favor mutations in regulatory pathways, it is not clear how this evolution is affected by how quickly conditions change (i.e. dynamics), or which mechanisms are commonly used to implement new regulation. Here, we perform experimental evolution on continuous cultures of E. coli carrying the tetracycline resistance tet operon to identify specific types of mutations that adapt drug responses to different dynamical regimens of drug administration. When cultures are evolved under gradually increasing tetracycline concentrations, we observe no mutations in the tet operon, but a predominance of fine-tuning mutations increasing the affinity of alternative efflux pump AcrB to tetracycline. When cultures are instead periodically exposed to large drug doses, all populations developed transposon insertions in repressor TetR, resulting in loss of regulation of efflux pump TetA. We use a mathematical model of the dynamics of antibiotic responses to show that sudden exposure to large drug concentrations can overwhelm regulated responses, which cannot induce resistance fast enough, resulting in fitness advantage for constitutive expression of resistance. These results help explain the loss of regulation of antibiotic resistance by opportunistic pathogens evolving in clinical environments. Our experiment supports the notion that initial evolution in new ecological niches proceeds largely through regulatory mutations and suggests that transposon insertions are a main mechanism driving this process.

Occurrence and prevalence of antibiotic resistance genes and pathogens in an industrial park wastewater treatment plant

Antibiotic resistance genes (ARGs) and pathogens are emerging environmental pollutants that pose a threat to human health and ecosystem. Industrial park wastewater treatment plants (WWTPs) treat large amounts of comprehensive wastewater derived from industrial production and park human activity, which is possible a source of ARGs and pathogens. Therefore, this study investigated the occurrence and prevalence of ARGs, ARGs hosts and pathogens and assesses the ARGs health risk in the biological treatment process in a large-sale industrial park WWTP using metagenomic analysis and omics-based framework, respectively. Results show that the major ARG subtypes are multidrug resistance genes (MDRGs), macB, tetA(58), evgS, novA, msbA and bcrA and the ARGs main hosts were genus Acidovorax, Pseudomonas, Mesorhizobium. In particular, all determined ARGs genus level hosts are pathogens. The total removal percentage of ARGs, MDRGs and pathogens were 12.77 %, 12.96 % and 25.71 % respectively, suggesting that the present treatment could not efficiently remove these pollutants. The relative abundance of ARGs, MDRGs and pathogens varied along biological treatment process that ARGs and MDRGs were enriched in activated sludge and pathogens were enriched in both secondary sedimentation tank and activated sludge. Among 980 known ARGs, 23 ARGs (e.g., ermB, gadX and tetM) were assigned into risk Rank I with characters of enrichment in the human-associated environment, gene mobility and pathogenicity. The results indicate that industrial park WWTPs might serve as an important source of ARGs, MDRGs, and pathogens. These observations invite further study of the origination, development, dissemination and risk assessment of industrial park WWTPs ARGs and pathogens.

Effects of freeze-thaw dynamics and microplastics on the distribution of antibiotic resistance genes in soil aggregates

This is the first study investigating the effects of freeze-thaw (FT) and microplastics (MPs) on the distribution of antibiotic resistance genes (ARGs) in soil aggregates (i.e., soil basic constituent and functional unit) via microcosm experiments. The results showed that FT significantly increased the total relative abundance of target ARGs in different aggregates due to the increase in intI1 and ARG host bacteria. However, polyethylene MPs (PE-MPs) hindered the increase in ARG abundance caused by FT. The host bacteria carrying ARGs and intI1 varied with aggregate size, and the highest number of hosts was observed in micro-aggregates (<0.25 mm). FT and MPs altered host bacteria abundance by affecting aggregate physicochemical properties and bacterial community and enhanced multiple antibiotic resistance via vertical gene transfer. Although the dominant factors affecting ARGs varied with aggregate size, intI1 was a co-dominant factor in various-sized aggregates. Furthermore, other than ARGs, FT, PE-MPs, and their integration promoted the proliferation of human pathogenic bacteria in aggregates. These findings suggested that FT and its integration with MPs significantly affected ARG distribution in soil aggregates. They amplified antibiotic resistance environmental risks, contributing to a profound understanding of soil antibiotic resistance in the boreal region.