Analysis, fate and effects of the antibiotic sulfadiazine in soil ecosystems

Effect of meddling ARBs on ARGs dynamics in fungal infested soil and their selective dispersal along spatially distant mycelial networks

During the recent times, environmental antibiotic resistance genes (ARGs) and their potential transfer to other bacterial hosts of pathogenic importance are of serious concern. However, the dissemination strategies of such ARGs are largely unknown. We tested that saprotrophic soil fungi differentially enriched antibiotic resistant bacteria (ARBs) and subsequently contributed in spatial distribution of selective ARGs. Wafergen qPCR analysis of 295 different ARGs was conducted for manure treated pre-sterilized soil incubated or not with selected bacterial-fungal consortia. The qPCR assay detected unique ARGs specifically found in the mycosphere of ascomycetous and basidiomycetous fungi. Both fungi exerted potentially different selection pressures on ARBs, resulting in different patterns of ARGs dissemination (to distant places) along their respective growing fungal highways. The relative abundance of mobile genetic elements (MGEs) was significantly decreased along fungal highways compared to the respective inoculation points. Moreover, the decrease in MGEs and ARGs (along fungal highways) was more prominent over time which depicts the continuous selection pressure of growing fungi on ARBs for enrichment of particular ARGs in mycosphere. Such data also indicate the potential role of saprotrophic soil fungi to facilitate horizontal gene transfer within mycospheric environmental settings. Our study, therefore, advocates to emphasize the future investigations for such (bacteria-fungal) interactive microbial consortia for potential (spatial) dissemination of resistance determinants which may ultimately increase the exposure risks of ARGs.

Elevated CO2 alleviated the dissemination of antibiotic resistance genes in sulfadiazine-contaminated soil: A free-air CO2 enrichment study

Climate change affects soil microbial communities and their genetic exchange, and subsequently modifies the transfer of antibiotic resistance genes (ARGs) among bacteria. However, how elevated CO₂ impacts soil antibiotic resistome remains poorly characterized. Here, a free-air CO₂ enrichment system was used in the field to investigate the responses of ARGs profiles and bacterial communities to elevated CO₂ (+200 ppm) in soils amended with sulfadiazine (SDZ) at 0, 0.5 and 5 mg kg^-1. Results showed that SDZ exposure induced the co-occurrence of beta-lactamase and tetracycline resistance genes, and SDZ at 5 mg kg^-1 enhanced the abundance of aminoglycoside, sulfonamide and multidrug resistance genes. However, elevated CO₂ weakened the effects of SDZ at 0.5 mg kg^-1 following an observed reduction in the total abundance of ARGs and mobile genetic elements. Additionally, elevated CO₂ significantly decreased the abundance of vancomycin resistance genes and alleviated the stimulation of SDZ on the dissemination of aminoglycoside resistance genes. Correlation analysis and structural equation models revealed that elevated CO₂ could directly influence the spread of ARGs or impose indirect effects on ARGs by affecting soil properties and bacterial communities. Overall, our results furthered the knowledge of the dissemination risks of ARGs under future climate scenarios.

Identification and characterization of Fe3O4/peroxodisulfate advanced oxidation products from sulfameter

Sulfonamides (SAs) are one of the most widely used antibiotics and their residuals in the environment could cause some negative environmental issues. Advanced oxidation such as Fenton-like reaction has been widely applied in the treatment of SAs polluted water. Degradation rates of 95%-99.7% were achieved in this work for the tested 8 SAs, including sulfisomidine, sulfameter (SME), phthalylsulfathiazole, sulfamethoxypyridazine, sulfamonomethoxine, sulfisoxazole, sulfachloropyridazine, and sulfadimethoxine, in the Fe₃O₄/peroxodisulfate (PDS) oxidation system after the optimization of PDS concentration and pH. Meanwhile, it was found that a lot of unknown oxidation products were formed, which brought up the uncertainty of health risks to the environment, and the identification of these unknown products was critical. Therefore, SME was selected as the model compound, from which the oxidation products were never elucidated, to identify these intermediates/products. With liquid chromatography-high resolution tandem mass spectrometry (LC-HRMS/MS), 10 new products were identified, in which 2-amino-5-methoxypyrimidine (AMP) was confirmed by its standard. The investigation of the oxidation process of SME indicated that most of the products were not stable and the degradation pathways were very complicated as multiple reactions, such as oxidation of the amino group, SO₂ extrusion, and potential cross-reaction occurred simultaneously. Though most of the products were not verified due to the lack of standards, our results could be helpful in the evaluation of the treatment performance of SAs containing wastewater.

Use of groundwater and reclaimed water for agricultural irrigation: Farmers' practices and attitudes and related environmental and health risks

Agricultural reuse of treated wastewater (TWW) for irrigation is widely practiced. Its conjunctive use with freshwater is becoming more common to guarantee food security, while the rationale behind and its sustainability are quite arguable. The objective of this study is to better understand the drivers of the conjunctive use of TWW and groundwater (GW) in Nabeul region, Tunisia, and the potential environmental and health impacts taking into account farmers' practices and attitudes toward reuse. TWW used for irrigation exhibited relatively high salinity and high microbiological load. GW has a very high salinity. TWW and GW showed low concentrations of heavy metals (Al, Cd, Co, Cu, Cr, Mn, Ni, Pb, and Zn). Concentrations of pharmaceutical compounds were between Limits of Quantification and 13 μg/L. In GW, values were relatively high, especially for caffeine, carbamazepine, ofloxacin, and ketoprofen. Farmers have a low perception of the polluting load of TWW and GW and of their potential long-term impacts on agricultural environment, human health, and agricultural productivity. GW availability has facilitated its conjunctive use with TWW, either to augment water quantity and/or to improve its quality. Despite its low quality, GW timeliness for irrigation was the main driver to guarantee a better yield and quality of produces. Soil microbial community, bacterial biomass, denitrifying potential and carbon oxidation profiles were similar under TWW, GW and their conjunctive use. Though an effect of the sampling period was observed with a high abundance of denitrifying bacteria in the wet season and a low carbon oxidation activity at the end of the dry season. The conjunctive use of TWW and GW is very likely unsustainable from health and environmental perspectives. Balancing farmers' economic profit against the preservation of agricultural activity, linked to cultural and natural heritage, remains one of the challenges for decision-makers and regional stakeholders.

Antibiotics in mariculture systems: A review of occurrence, environmental behavior, and ecological effects

Antibiotics are widely applied to prevent and treat diseases occurred in mariculture. The often-open nature of mariculture production systems has led to antibiotic residue accumulation in the culturing and adjacent environments, which can adversely affect aquatic ecosystems, and even human. This review summarizes the occurrence, environmental behavior, and ecological effects of antibiotics in mariculture systems based on peer-reviewed papers. Forty-five different antibiotics (categorized into ten groups) have been detected in mariculture systems around the world, which is far greater than the number officially allowed. Indiscriminate use of antibiotics is relatively high among major producing countries in Asia, which highlights the need for stricter enforcement of regulations and policies and effective antibiotic removal methods. Compared with other environmental systems, some environmental characteristics of mariculture systems, such as high salinity and dissolved organic matter (DOM) content, can affect the migration and transformation processes of antibiotics. Residues of antibiotics favor the proliferation of antibiotic resistance genes (ARGs). Antibiotics and ARGs alter microbial communities and biogeochemical cycles, as well as posing threats to marine organisms and human health. This review may provide a valuable summary of the effects of antibiotics on mariculture systems.

Sulfamethoxazole biodegradation and impacts on soil microbial communities in a Bolivian arid high altitude catchment

The processes controlling antibiotics fate in ecosystems are poorly understood, yet their presence can inhibit bacterial growth and induce the development of bacterial resistance. Sulfamethoxazole (SMX) is one of the most frequently detected sulfonamides in natural environments due to its low metabolism and molecular properties. This work presents pioneering results on SMX biodegradation and impact in high altitude soils (Bolivian Altiplano), allowing a better understanding of the persistence, spread and impact of this antibiotic at the global watershed scale. Our results showed significant dissipation of SMX in relation to its adsorption, hydrolysis and biotransformation. However, biodegradation appears to be lower in these mountain soils than in lowland soils as widely described in the literature. The half-life of SMX ranges from 12 to 346 days in non-sterile soils. In one soil, no biotic degradation was observed, indicating a likely high persistence. Biodegradation was related to OC content and to proximity to urban activities. Regarding the study of the impacts of SMX, the DGGE results were less sensitive than the sequencing. In general, SMX strongly changes the structure and composition of the studied soils at high altitudes, which is comparable to the observations of other authors in lowland soils. The phylum Actinobacter showed high sensitivity to SMX. In contrast, the abundance of ɣ-proteobacteria remained almost unchanged. Soil contamination with SMX did not lead to the development of the studied resistance genes (sul1 and sul2) in soils where they were absent at the beginning of the experiment. Thus, the presence of SMX resistance genes seems to be related to irrigation with wastewater carrying the studied resistance genes.

Effect of soil sulfamethoxazole on strawberry (Fragaria ananassa): Growth, health risks and silicon mitigation

The negative impact of antibiotic pollution on the agricultural system and human health is a hot issue in the world. However, little information is available on the antibiotics toxicity mechanism and the role of silicon (Si) to alleviate the antibiotics toxicity. In this study, strawberry (Fragaria ananassa) showed excitatory response to low-dose SMZ (1 mg L^-1), but strawberry root and photosynthetic efficiency were damaged under high level. When SMZ level exceeded 10 mg L^-1, H₂0₂, O₂^-, MDA and relative conductivity increased, while SOD and CAT activities first increased and then decreased. SMZ accumulated more in roots and fruits, but less in stems, and the accumulation increased with the increase of SMZ-dose. Under 1 mg L^-1 SMZ, the SMZ accumulation in fruits was 110.54 μg kg^-1, which exceeded the maximum residue limit. SMZ can induce the expression of sul1, sul2 and intI1, and intI1 had the highest abundance. Exogenous application of Si alleviated the toxicity of SMZ, which is mainly related to the degradation of SMZ in soil and the reduction of SMZ absorption by strawberry. In addition, Si relieved root damage, promoted the increase of photosynthetic efficiency, and improved the antioxidant system to resist SMZ toxicity.

Veterinary antibiotics in swine and cattle wastewaters of China and the United States: Features and differences

Veterinary antibiotics (VAs) have been widely used in livestock for disease prevention, treatment, and growth promotion. This study compared top 20 VAs in Chinese and US swine and cattle wastewater with published literatures. The sulfonamides (SAs) were found to be predominant, accounting for 62% of the top 20 VAs in Chinese swine wastewater, while tetracyclines (TCs) contributed to about 68.7% of the 18 VAs in US swine wastewater. The average concentration of the 20 major VAs in Chinese swine wastewater was estimated to be 1145 μg/L against 253.6 μg/L in the United States. On the other hand, the five major VAs in Chinese cattle wastewater were identified to be oxytetracycline, nafcillin, apramycin, lincomycin, and amikacin, while monensin was found to be dominant in US cattle wastewater. The average concentration of the top 20 VAs in Chinese and US cattle wastewaters were found to be 54.6 and 46.2 μg/L, respectively. These analyses suggested that VAs were probably over-used in Chinese swine industry, eventually causing the development and spreading of antibiotic resistant-bacteria and genes, which should be paid with attention. PRACTITIONER POINTS: Major veterinary antibiotics (VAs) in swine and cattle wastewater were identified. Top 20 VAs in swine and cattle wastewater of China and the United States were compared. VAs concentration in Chinese swine wastewater was 4.52 times that in the United States. VAs concentration in Chinese cattle wastewater was 1.18 times that of the United States.

Response of soil bacterial communities to sulfadiazine present in manure: Protection and adaptation mechanisms of extracellular polymeric substances

Extracellular polymeric substances (EPS) play a dominant role in protective biofilms. However, studies exploring the underlying protective mechanism of EPS have mainly focused on activated sludge, whereas their positive roles in protecting soil microbes from environmental stress have not been elucidated. In this study, we revealed the response of soil bacterial communities to various dosages of sulfadiazine (SDZ) present in manure, with a special emphasis on the role of EPS. Sequencing analysis showed that the bacterial community demonstrated stronger symbiotic relationships and weaker competitive interaction patterns to cope with disturbance induced by SDZ. EPS was mainly composed of tyrosine-like and tryptophan-like substances, and moreover, carboxyl, hydroxyl and ether groups were the main functional groups. An adaptation mechanism, namely the enhanced secretion of tryptophan-like substances, could help alleviate the SDZ stress effectively in the biofilms occurring in soil that experienced long-term manure application. Furthermore, the existence of EPS weakened the accumulation of antibiotic resistance genes (ARGs) in soil. Our results for the first time systematically uncover the joint action of biofilm tolerance and ARGs in resisting SDZ stress, which enhances understanding of the protective role of EPS and the underlying mechanisms governing biofilm functions in soil environments.

Modeling transport of antibiotic resistant bacteria in aquatic environment using stochastic differential equations

Contaminated sites are recognized as the "hotspot" for the development and spread of antibiotic resistance in environmental bacteria. It is very challenging to understand mechanism of development of antibiotic resistance in polluted environment in the presence of different anthropogenic pollutants. Uncertainties in the environmental processes adds complexity to the development of resistance. This study attempts to develop mathematical model by using stochastic partial differential equations for the transport of fluoroquinolone and its resistant bacteria in riverine environment. Poisson's process is assumed for the diffusion approximation in the stochastic partial differential equations (SPDE). Sensitive analysis is performed to evaluate the parameters and variables for their influence over the model outcome. Based on their sensitivity, the model parameters and variables are chosen and classified into environmental, demographic, and anthropogenic categories to investigate the sources of stochasticity. Stochastic partial differential equations are formulated for the state variables in the model. This SPDE model is then applied to the 100 km stretch of river Musi (South India) and simulations are carried out to assess the impact of stochasticity in model variables on the resistant bacteria population in sediments. By employing the stochasticity in model variables and parameters we came to know that environmental and anthropogenic variations are not able to affect the resistance dynamics at all. Demographic variations are able to affect the distribution of resistant bacteria population uniformly with standard deviation between 0.087 and 0.084, however, is not significant to have any biological relevance to it. The outcome of the present study is helpful in simplifying the model for practical applications. This study is an ongoing effort to improve the model for the transport of antibiotics and transport of antibiotic resistant bacteria in polluted river. There is a wide gap between the knowledge of stochastic resistant bacterial growth dynamics and the knowledge of transport of antibiotic resistance in polluted aquatic environment, this study is one step towards filling up that gap.

Salinity-independent dissipation of antibiotics from flooded tropical soil: a microcosm study

River deltas are frequently facing salinity intrusion, thus challenging agricultural production in these areas. One adaption strategy to increasing salinity is shrimp production, which however, heavily relies on antibiotic usage. This study was performed to evaluate the effect of increasing salinity on the dissipation rates of antibiotics in tropical flooded soil systems. For this purpose, paddy top soil from a coastal Vietnamese delta was spiked with selected frequently used antibiotics (sulfadiazine, sulfamethazine, sulfamethoxazole, trimethoprim) and incubated with flood water of different salt concentrations (0, 10, 20 g L^-1). Antibiotic concentrations were monitored in water and soil phases over a period of 112 days using liquid chromatography and tandem mass spectrometry. We found that sulfamethazine was the most persistent antibiotic in the flooded soil system (DT₅₀ = 77 days), followed by sulfadiazine (DT₅₀ = 53 days), trimethoprim (DT₅₀ = 3 days) and sulfamethoxazole (DT₅₀ = 1 days). With the exception of sulfamethoxazole, the apparent distribution coefficient increased significantly (p < 0.05) for all antibiotics in course of the incubation, which indicates an accumulation of antibiotics in soil. On a whole system basis, including soil and water into the assessment, there was no overall salinity effect on the dissipation rates of antibiotics, suggesting that common e-fate models remain valid under varying salinity.

Survey of selected antibiotic resistance genes in agricultural and non-agricultural soils in south-central Idaho

Improving our understanding of antibiotic resistance in soils is important for the protection of human, animal and ecological health. In south-central Idaho, antibiotic resistance genes (ARGs) [blaCTX-M-1, erm(B), sul1, tet(B), tet(M) and tet(X)] and a class 1 integron-integrase gene (intI1) were quantified in agricultural and non-agricultural soils (96 total sites) under various land use practices (cropland, forestland, inactive cropland, pastureland, rangeland, recreational, residential). We hypothesized that gene occurrence and abundance would be greater in intensively managed agricultural soils. The ARGs (except blaCTX-M-1) and intI1 gene were detected in many of the soils (15 to 58 out of 96 samples), with sul1 and intI1 being detected the most frequently (60% of samples). All of the genes were detected more frequently in the cropland soils (46 sites) and at statistically greater relative abundances (per 16S rRNA gene) than in soils from the other land use categories. When the cropland gene data was separated by sites that had received dairy manure, dairy wastewater, and/or biosolids (27 sites), it was revealed that the genes [except tet(B)] were found at statistically greater abundances (7- to 22-fold higher on average) than in soils that were not treated. The results from this study provide convincing evidence that manure/biosolids use in Idaho cropland soils increases the expansion of antibiotic resistance-related determinants.

Sulfadiazine Masquerading as a Natural Product from Scilla madeirensis (Scilloideae)

The structure of 2,4-(4'-aminobenzenamine)pyrimidine (1), a pyrimidine alkaloid previously isolated from the bulbs of Scilla madeirensis (Asparagaceae, synonym Autonoë madeirensis), has been revised. These conclusions were met via comparison of reported NMR and EIMS data with those obtained from synthetic standards. The corrected structure is the antibiotic sulfadiazine (2), which has likely been isolated as a contaminant from the site of collection. The reported bioactivity of 1 as an α1-adrenoceptor antagonist should instead be ascribed to sulfadiazine. Our findings appear to show another example of an anthropogenic contaminant being identified as a natural product and emphasize the importance of considering the biosynthetic origins of isolated compounds within a phylogenetic context.

Ecotoxicological effects of sulfonamide on and its removal by the submerged plant Vallisneria natans (Lour.) Hara

The extensive application of sulfonamides (SAs) raises concern regarding its negative environmental effects. In aquatic environments, macrophytes may not only be affected by various pollutants, they may also help to reduce the concentrations in the surrounding environment. We studied both the ecotoxicological effects of sulfonamide (SN) on and its removal by Vallisneria natans (Lour.) Hara, an important submerged macrophyte in Chinese lakes and rivers. The toxic effect and oxidative stress caused by SN resulted in a reduction of total chlorophyll (chl.a and b) and autofluorescence of chloroplast. Meanwhile, the levels of reactive oxygen species (ROS, including O₂^- and H₂O₂) and peroxidase (POD) increased with increasing SN concentration and duration of exposure. After 20 days' exposure, a reduction in the relative growth rate (RGR) and leaf length of V. natans was found under SN stress, but SN had only a weak effect on root length. Although high SN concentrations had toxic effects on the growth of V. natans, the plant was overall resistant to the SN doses that we used. We studied the effect of V. natans on sulfonamide removal in an additional 13-day exposure experiment with focus on the dynamics of dissolved oxygen (DO), the oxidation-reduction potential (ORP) and microbial communities in the water column, as well as in the periphyton on V. natans surfaces. The results show that presence of V. natans significantly improved the SN removal efficiency likely by increasing DO, ORP and bacterial diversity in the water column. The presence of V. natans led to higher relative abundances of Saccharimonadales and Rhizoniales. Lefse analysis showed that Saccharimonadales, Micrococcales, Sphingobacteriales, Bacteroidales, Obscuribacterales, Flavobacteriales, Pseudomonadaceae and Myxococcales, which are considered to be SN-resistant bacteria, increased significantly in the V + S+ (V. natans and SN) treatment compared with the V + S- (V. natans and no SN) treatment and V-S+ (no V. natans and SN) treatment. As far as we know, ours is the first study of the ecotoxicological effects of sulfonamide and its removal by submerged vascular plants (here V. natans). Thus, our results add to the understanding of the antibiotic removal mechanism of macrophytes in freshwater systems and help to clarify the linkages between antibiotics and macrophyte-microbe systems; thereby providing new insight into ecological-based removal of antibiotics in aquatic systems.

Sulfadiazine biodegradation by Phanerochaete chrysosporium: Mechanism and degradation product identification

Antibiotic contaminants have become a severe environmental problem in recent years and finding effective ways to deal with this issue is of great importance. In this study, Phanerochaete chrysosporium was used to degrade sulfadiazine (SDZ), which is frequently detected in the culture medium of isolates from soil and surface water systems. The results demonstrate that 10 mg L^-1 SDZ can be completely degraded by P. chrysosporium under conditions of pH 5.7 and 30 °C within 6 days. The Q-Exactive-MS/MS analysis identified and confirmed several different SDZ degradation intermediates, and four proposed degradation pathways of SDZ were deduced. Moreover, enzyme activity tests revealed that manganese peroxidase and ligninolytic peroxidase played important roles in SDZ degradation. Moreover, a transcriptome analysis method was performed to explore the mechanism and pathways of SDZ degradation by P. chrysosporium in greater detail. The results of GO and KEGG analysis strongly suggest that the metabolism pathway is significantly activated and plays an important role in antibiotic degradation. Further, this is the first study to identify SDZ degradation intermediates and two main intermediates were found to be involved in possible SDZ degradation pathways. This study is also the first report results from RNA sequencing to evaluate genome-wide changes of P. chrysosporium to further explore SDZ degradation mechanism.

Current progress in the adsorption, transport and biodegradation of antibiotics in soil

Antibiotic residues in soil may cause potential risks to human health and soil ecosystems. To avoid these potential risks, comprehensive study of the adsorption, transport and biodegradation of antibiotics in soil is very imperative. This review provided current views about the most recent studies, which have been conducted toward the adsorption, transport and biodegradation of antibiotics in soil. The influencing factors affecting the adsorption behaviors of antibiotics in soil, including the antibiotics properties (e.g., molecular structure, hydrophobicity, polarity, polarizability, and spatial configuration) and the soil characteristics (e.g., soil type, soil pH, coexisting ions, and soil organic matter), were discussed. The effects of fertilizer colloids, porous media, and pH of soil on the transport behaviors of antibiotics were analyzed. The biodegradation of antibiotics in soil were also highlighted by investigating the effects of soil microbiome, soil pH, soil temperature, and interactions between antibiotics. Prospects of antibiotics adsorption, transport and biodegradation were also proposed.

Sulfonamides removal under different redox conditions and microbial response to sulfonamides stress during riverbank filtration: A laboratory column study

Riverbank filtration (RBF) as a barrier of pathogenic microorganisms and organic micropollutants recently has been proven capable of removing sulfonamides. However, the study about the effect of redox conditions on biodegradation of common and persistent sulfonamides in RBF is limited and the response of microbial communities to sulfonamides stress during RBF is unknown. In this study, two column set-ups (with residence time 5 days and 11 days respectively), simulating different redox conditions of riverbank filtration systems, were operated for seven months to investigate 1) the long-term effect of redox conditions on ng∙L^-1 level sulfonamides (sulfapyridine, sulfadiazine, sulfamethoxazole, sulfamethazine, sulfaquinoxaline) removal, and 2) the microbial community evolution represented by the phylogenetic and metabolic function shift under non-lethal selective pressures of sulfonamides. The results showed that sulfonamides were more degradable under anoxic conditions than oxic and suboxic conditions. In the sulfonamides stressed community, the phylogenetic diversity increased slightly. Relative abundance of an intrinsic sulfonamides resistant bacteria Bacillus spp. increased, suggesting that sulfonamide resistance developed in specific bacteria under sulfonamides contamination pressure in RBF systems. At the same time, an activated transport function in the stressed microbial community was noticed. The predicted relative abundance of gene folP, which encodes dihydropteroate synthase, also increased significantly, indicating a detoxification mechanism and sulfonamides resistance potential under non-lethal selective pressures of sulfonamides in RBF systems.

Antibiotics in the Soil Environment-Degradation and Their Impact on Microbial Activity and Diversity

Antibiotics play a key role in the management of infectious diseases in humans, animals, livestock, and aquacultures all over the world. The release of increasing amount of antibiotics into waters and soils creates a potential threat to all microorganisms in these environments. This review addresses issues related to the fate and degradation of antibiotics in soils and the impact of antibiotics on the structural, genetic and functional diversity of microbial communities. Due to the emergence of bacterial resistance to antibiotics, which is considered a worldwide public health problem, the abundance and diversity of antibiotic resistance genes (ARGs) in soils are also discussed. When antibiotic residues enter the soil, the main processes determining their persistence are sorption to organic particles and degradation/transformation. The wide range of DT50 values for antibiotic residues in soils shows that the processes governing persistence depend on a number of different factors, e.g., physico-chemical properties of the residue, characteristics of the soil, and climatic factors (temperature, rainfall, and humidity). The results presented in this review show that antibiotics affect soil microorganisms by changing their enzyme activity and ability to metabolize different carbon sources, as well as by altering the overall microbial biomass and the relative abundance of different groups (i.e., Gram-negative bacteria, Gram-positive bacteria, and fungi) in microbial communities. Studies using methods based on analyses of nucleic acids prove that antibiotics alter the biodiversity of microbial communities and the presence of many types of ARGs in soil are affected by agricultural and human activities. It is worth emphasizing that studies on ARGs in soil have resulted in the discovery of new genes and enzymes responsible for bacterial resistance to antibiotics. However, many ambiguous results indicate that precise estimation of the impact of antibiotics on the activity and diversity of soil microbial communities is a great challenge.

Veterinary pharmaceutical residues from natural water to tap water: Sales, occurrence and fate

Veterinary pharmaceuticals (VPs) increasingly used in animal husbandry have led to their presence in aquatic environments -surface water (SW) or groundwater (GW) - and even in tap water. This review focuses on studies from 2007 to 2017. Sixty-eight different veterinary pharmaceutical residues (VPRs) have been quantified worldwide in natural waters at concentrations ranging from nanograms per liter (ng L^-1) to several micrograms per liter (μg L^-1). An extensive up-to-date on sales and tonnages of VPs worldwide has been performed. Tetracyclines (TCs) antibiotics are the most sold veterinary pharmaceuticals worldwide. An overview of VPRs degradation pathways in natural waters is provided. VPRs can be degraded or transformed by biodegradation, hydrolysis or photolysis. Photo-degradation appears to be the major degradation pathway in SW. This review then reports occurrences of VPRs found in tap water, and presents data on VPRs removal in drinking water treatment plants (DWTPs) at each step of the process. VPRs have been quantified in tap water at ng L^-1 concentration levels in four studies of the eleven studies dealing with VPRs occurrence in tap water. Overall removals of VPRs in DWTPs generally exceed 90% and advanced treatment processes (oxidation processes, adsorption on activated carbon, membrane filtration) greatly contribute to these removals. However, studies performed on full-scale DWTPs are scarce. A large majority of fate studies in DWTPs have been conducted under laboratory at environmentally irrelevant conditions (high concentration of VPRs (mg L^-1), use of deionized water instead of natural water, high concentration of oxidant, high contact time etc.). Also, studies on VPRs occurrence and fate in tap water focus on antibiotics. There is a scientific gap on the occurrence and fate of antiparatic drugs in tap waters.

Effect of sulfadiazine and trimethoprim on activated sludge performance and microbial community dynamics in laboratory-scale membrane bioreactors and sequencing batch reactors at 8°C

The effect of antibiotics sulfadiazine and trimethoprim on activated sludge operated at 8°C was investigated. Performance and microbial communities of sequencing batch reactors (SBRs) and Membrane Bioreactors (MBRs) were compared before and after the exposure of antibiotics to the synthetic wastewater. The results revealed irreversible negative effect of these antibiotics in environmentally relevant concentrations on nitrifying microbial community of SBR activated sludge. In opposite, MBR sludge demonstrated fast adaptation and more stable performance during the antibiotics exposure. Dynamics of microbial community was greatly affected by presence of antibiotics. Bacteria from classes Betaproteobacteria and Bacteroidetes demonstrated the potential to develop antibiotic resistance in both wastewater treatment systems while Actinobacteria disappeared from all of the reactors after 60 days of antibiotics exposure. Altogether, results showed that operational parameters such as sludge retention time (SRT) and reactor configuration had great effect on microbial community composition of activated sludge and its vulnerability to antibiotics. Operation at long SRT allowed archaea, including ammonium oxidizing species (AOA) such as Nitrososphaera viennensis to grow in MBRs. AOA could have an important role in stable nitrification performance of MBR-activated sludge as a result of tolerance of archaea to antibiotics. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2708, 2019.

Bacteria That Make a Meal of Sulfonamide Antibiotics: Blind Spots and Emerging Opportunities

The release of sulfonamide antibiotics into the environment is alarming because the existence of these antibiotics in the environment may promote resistance in clinically relevant microorganisms, which is a potential threat to the effectiveness of antibiotic therapies. Controllable biodegradation processes are of particular significance for the inexpensive yet effective restoration of sulfonamide-contaminated environments. Cultivation-based techniques have already made great strides in successfully isolating bacteria with promising sulfonamide degradation abilities, but the implementation of these isolates in bioremediation has been limited by unknown microbial diversity, vast population responsiveness, and the impact of perturbations from open and complex environments. Advances in DNA sequencing technologies and metagenomic analyses are being used to complement the information derived from cultivation-based procedures. In this Review, we provide an overview of the growing understanding of isolated sulfonamide degraders and identify shortcomings of the prevalent literature in this field. In addition, we propose a technical paradigm that integrates experimental testing with metagenomic analysis to pave the way for improved understanding and exploitation of these ecologically important isolates. Overall, this Review aims to outline how metagenomic studies of isolated sulfonamide degraders are being applied for the advancement of bioremediation strategies for sulfonamide contamination.

Interactions of 15N-Sulfadiazine and Soil Components As Evidenced by 15N-CPMAS NMR

The extensive use of sulfonamides (SNs) in animal husbandry has led to an unintentional widespread occurrence in several environmental compartments. The implementation of regulations and management recommendations to reduce the potential risk of development of antibiotic resistances necessitates detailed knowledge on their fate in soil. We present results from two independent incubation studies of ¹⁵N-labeled sulfadiazines (SDZ) which focused on identifying binding types in bound residues. In the first study ¹⁵N-amino labeled SDZ was incubated with two previously isolated humic acids in the presence and absence of Trametes versicolor laccase, while in the second study ¹⁵N-double-labeled SDZ was incubated with a typical agricultural Luvisol and the humic acid fraction isolated after sequential extraction of the soil. The freeze-dried humic acid fractions of both studies were then analyzed by ¹⁵N-CPMAS NMR and compared with the ¹⁵N-spectra of synthesized model compounds. In both studies amide bonds and Michael adducts were identified, while formation of imine bonds could be excluded. In the humic acid study, where less harsh extraction methods were applied, possible formation of H-bridging and sequestration were additionally detected.

Fungal networks serve as novel ecological routes for enrichment and dissemination of antibiotic resistance genes as exhibited by microcosm experiments

Antibiotic resistance genes (ARGs) in the environment and their subsequent acquisition by clinically important microorganisms are a serious concern. However, the spread of environmental ARGs remain largely unknown. We report, for the first time, the involvement of soil fungi in the distribution of bacteria with ARGs via soil microcosms. qPCR assay detected unique ARGs specifically found in the mycosphere of different fungi. Interestingly, the taxonomically and ecologically different fungi exerted different selection pressures on ARGs originating from the same source. Test fungi supported different antibiotic resistance bacteria enriched in the mycosphere and even transported to distant places. The relative abundance of the tnpA gene decreased, for manure, along mycelial networks of all fungi. While the fungal strain NFC-5 enriched the intI1 gene more, opposite to two other fungi at the migration front compared with the inoculation point for both sources. Such data indicate the differential effect of different fungi to facilitate horizontal gene transfer potential under fungal selection pressure. Our study provides the evidence that fungi can contribute ARGs, host bacterial diversity and abundance, and such interactive microbial consortia have the potential to disseminate the resistance determinants from one place to another, thus increasing the ARGs exposure risk to humans.

The potential implications of reclaimed wastewater reuse for irrigation on the agricultural environment: The knowns and unknowns of the fate of antibiotics and antibiotic resistant bacteria and resistance genes - A review

The use of reclaimed wastewater (RWW) for the irrigation of crops may result in the continuous exposure of the agricultural environment to antibiotics, antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In recent years, certain evidence indicate that antibiotics and resistance genes may become disseminated in agricultural soils as a result of the amendment with manure and biosolids and irrigation with RWW. Antibiotic residues and other contaminants may undergo sorption/desorption and transformation processes (both biotic and abiotic), and have the potential to affect the soil microbiota. Antibiotics found in the soil pore water (bioavailable fraction) as a result of RWW irrigation may be taken up by crop plants, bioaccumulate within plant tissues and subsequently enter the food webs; potentially resulting in detrimental public health implications. It can be also hypothesized that ARGs can spread among soil and plant-associated bacteria, a fact that may have serious human health implications. The majority of studies dealing with these environmental and social challenges related with the use of RWW for irrigation were conducted under laboratory or using, somehow, controlled conditions. This critical review discusses the state of the art on the fate of antibiotics, ARB and ARGs in agricultural environment where RWW is applied for irrigation. The implications associated with the uptake of antibiotics by plants (uptake mechanisms) and the potential risks to public health are highlighted. Additionally, knowledge gaps as well as challenges and opportunities are addressed, with the aim of boosting future research towards an enhanced understanding of the fate and implications of these contaminants of emerging concern in the agricultural environment. These are key issues in a world where the increasing water scarcity and the continuous appeal of circular economy demand answers for a long-term safe use of RWW for irrigation.

First molecular typing of Mycobacterium avium subspecies paratuberculosis identified in animal and human drinking water from dairy goat farms in Brazil

Mycobacterium avium subspecies paratuberculosis, the etiologic agent of Johne's disease or paratuberculosis, was identified by culture and/or polymerase chain reaction (PCR) in 50% and 30% of water samples for animal and human consumption, respectively, from ten dairy goat farms in Brazil. IS1311 restriction fragment length polymorphism analysis identified the isolates as cattle type C.

Distribution and incorporation mode of the herbicide MCPA in soil derived organo-clay complexes

The incorporation of xenobiotics into soil, especially via covalent bonds or sequestration has a major influence on the environmental behavior including toxicity, mobility, and bioavailability. The incorporation mode of 4-chloro-2-methylphenoxyacetic acid (MCPA) into organo-clay complexes has been investigated under a low (8.5 mg MCPA/kg soil) and high (1000 mg MCPA/kg soil) applied concentration, during an incubation period of up to 120 days. Emphasis was laid on the elucidation of distinct covalent linkages between non-extractable MCPA residues and humic sub-fractions (humic acids, fulvic acids, and humin). The cleavage of compounds by a sequential chemical degradation procedure (OH^-, BBr₃, RuO₄, TMAH thermochemolysis) revealed for both concentration levels ester/amide bonds as the predominate incorporation modes followed by ether linkages. A possible influence of the soil microbial activity on the mode of incorporation could be observed in case of the high level samples. Structure elucidation identified MCPA as the only nonextractable substance, whereas the metabolite 4-chloro-2-methylphenol was additionally found as bioavailable and bioaccessible compound.

Effect of different sulfadimidine addition methods on its degradation behaviour in swine manure

Sulfadimidine (SM2) is commonly used in the swine industry and enters the environment via faeces. In recent years, advances in the ecotoxicology of SM2 have become a popular research interest with two common research methods including swine manure collection from swine fed with a diet containing SM2 and directly adding SM2. The purpose of this experiment was to compare SM2 degradation behaviour in pig manure with two different SM2 addition methods. The results showed that the degradation half-lives of SM2 in manure from SM2-fed swine treatment were 33.2 and 32.0 days at the initial addition level of SM2 at 32.1 and 64.3 mg/kg, respectively. This was significantly longer than that in manure directly adding SM2 treatment with the half-lives of 21.4 and 14.8 days. The metabolite of SM2 N⁴-acetyl-sulfamethazine occurred in manure from SM2-fed swine treatment but was not detected in directly adding SM2 treatment. The pH in manure from SM2-fed swine treatment was significantly lower than that in directly adding SM2 treatment, but the values of organic carbon, total nitrogen, and electrical conductivity in manure from SM2-fed swine treatment were significantly higher than those in manure directly adding SM2 treatment. Meanwhile, although the copy number of bacteria had no significant difference between two treatments, there was a significant difference in bacteria diversity. Results of the present study demonstrated that the presence of the metabolites, chemical property, and microbial diversity might be the reason for different SM2 degradation behaviours on different addition methods. Thus, the method using manure with SM2 collected from swine could obtain more accurate results for the ecotoxicological study of SM2.

Effects of soil moisture depletion on vegetable crop uptake of pharmaceuticals and personal care products (PPCPs)

Agricultural crops have a long history of being irrigated with recycled wastewater (RW). However, its use on vegetable crops has been of concern due to the potential prevalence of microcontaminants, such as pharmaceuticals and personal care products (PPCPs) in the latter, which represents a possible health hazard to consumers. We investigated the uptake of three PPCPs (atenolol, diclofenac, and ofloxacin), at three different concentrations in irrigation water (0.5, 5, and 25 μg L^-1) in relation to three varying volumetric soil moisture depletion levels of 14 % (-4.26 kPa), 10 % (-8.66 kPa), and 7 % (-18.37 kPa) by various vegetable crop species. Experiments were conducted in a split-split block completely randomized design. PPCPs were extracted using a developed method of accelerated solvent extraction and solid phase extraction and analyzed via liquid chromatography mass spectrometry (LCMS). Results indicate that all treated crops were capable of PPCP uptake at nanogram per gram concentrations independent of the applied soil moisture depletion levels and PPCP concentrations. Ofloxacin was the chemical with the highest uptake amounts, followed by atenolol and then diclofenac. Although the results were not statistically significant, higher concentrations of PPCPs were detected in plants maintained under higher soil moisture levels of 14 % (-4.26 kPa).

Do antibiotics have environmental side-effects? Impact of synthetic antibiotics on biogeochemical processes

Antibiotic use in the early 1900 vastly improved human health but at the same time started an arms race of antibiotic resistance. The widespread use of antibiotics has resulted in ubiquitous trace concentrations of many antibiotics in most environments. Little is known about the impact of these antibiotics on microbial processes or "non-target" organisms. This mini-review summarizes our knowledge of the effect of synthetically produced antibiotics on microorganisms involved in biogeochemical cycling. We found only 31 articles that dealt with the effects of antibiotics on such processes in soil, sediment, or freshwater. We compare the processes, antibiotics, concentration range, source, environment, and experimental approach of these studies. Examining the effects of antibiotics on biogeochemical processes should involve environmentally relevant concentrations (instead of therapeutic), chronic exposure (versus acute), and monitoring of the administered antibiotics. Furthermore, the lack of standardized tests hinders generalizations regarding the effects of antibiotics on biogeochemical processes. We investigated the effects of antibiotics on biogeochemical N cycling, specifically nitrification, denitrification, and anammox. We found that environmentally relevant concentrations of fluoroquinolones and sulfonamides could partially inhibit denitrification. So far, the only documented effects of antibiotic inhibitions were at therapeutic doses on anammox activities. The most studied and inhibited was nitrification (25-100 %) mainly at therapeutic doses and rarely environmentally relevant. We recommend that firm conclusions regarding inhibition of antibiotics at environmentally relevant concentrations remain difficult due to the lack of studies testing low concentrations at chronic exposure. There is thus a need to test the effects of these environmental concentrations on biogeochemical processes to further establish the possible effects on ecosystem functioning.

Root Uptake of Pharmaceuticals and Personal Care Product Ingredients

Crops irrigated with reclaimed wastewater or grown in biosolids-amended soils may take up pharmaceuticals and personal care product ingredients (PPCPs) through their roots. The uptake pathways followed by PPCPs and the propensity for these compounds to bioaccumulate in food crops are still not well understood. In this critical review, we discuss processes expected to influence root uptake of PPCPs, evaluate current literature on uptake of PPCPs, assess models for predicting plant uptake of these compounds, and provide recommendations for future research, highlighting processes warranting study that hold promise for improving mechanistic understanding of plant uptake of PPCPs. We find that many processes that are expected to influence PPCP uptake and accumulation have received little study, particularly rhizosphere interactions, in planta transformations, and physicochemical properties beyond lipophilicity (as measured by Kow). Data gaps and discrepancies in methodology and reporting have so far hindered development of models that accurately predict plant uptake of PPCPs. Topics warranting investigation in future research include the influence of rhizosphere processes on uptake, determining mechanisms of uptake and accumulation, in planta transformations, the effects of PPCPs on plants, and the development of predictive models.

The fate of antibiotic resistance genes and class 1 integrons following the application of swine and dairy manure to soils

The goal of this study was to determine the fate of antibiotic resistance genes (ARGs) and class 1 integrons following the application of swine and dairy manure to soil. Soil microcosms were amended with either manure from swine fed subtherapeutic levels of antibiotics or manure from dairy cows that were given antibiotics only rarely and strictly for veterinary purposes. Microcosms were monitored for 6 months using quantitative PCR targeting 16S rRNA genes (a measure of bacterial biomass), intI1, erm(B), tet(A), tet(W) and tet(X). Swine manure had 10- to 100-fold higher levels of ARGs than the dairy manure, all of which decayed over time after being applied to soil. A modified Collins-Selleck model described the decay of ARGs in the soil microcosms well, particularly the characteristic in which the decay rate declined over time. By the completion of the soil microcosm experiments, ARGs in the dairy manure-amended soils returned to background levels, whereas the ARGs in swine manure remained elevated compared to control microcosms. Our research suggests that the use of subtherapeutic use of antibiotics in animal feed could lead to the accumulation of ARGs in soils to which manure is applied.

Ecotoxicological assessment of antibiotics: A call for improved consideration of microorganisms

Antibiotics play a pivotal role in the management of infectious disease in humans, companion animals, livestock, and aquaculture operations at a global scale. Antibiotics are produced, consumed, and released into the environment at an unprecedented scale causing concern that the presence of antibiotic residues may adversely impact aquatic and terrestrial ecosystems. Here we critically review the ecotoxicological assessment of antibiotics as related to environmental risk assessment (ERA). We initially discuss the need for more specific protection goals based on the ecosystem service concept, and suggest that the ERA of antibiotics, through the application of a mode of toxic action approach, should make more use of ecotoxicological endpoints targeting microorganisms (especially bacteria) and microbial communities. Key ecosystem services provided by microorganisms and associated ecosystem service-providing units (e.g. taxa or functional groups) are identified. Approaches currently available for elucidating ecotoxicological effects on microorganisms are reviewed in detail and we conclude that microbial community-based tests should be used to complement single-species tests to offer more targeted protection of key ecosystem services. Specifically, we propose that ecotoxicological tests should not only assess microbial community function, but also microbial diversity (‘species’ richness) and antibiotic susceptibility. Promising areas for future basic and applied research of relevance to ERA are highlighted throughout the text. In this regard, the most fundamental knowledge gaps probably relate to our rudimentary understanding of the ecological roles of antibiotics in nature and possible adverse effects of environmental pollution with subinhibitory levels of antibiotics.

Interactive effects of sulfadiazine and Cu(II) on their sorption and desorption on two soils with different characteristics

Antibiotics and heavy metals often coexist in soils due to land application of animal wastes and other sources of inputs. The aim of this study is to evaluate the interaction of Cu(II) and sulfadiazine (SDZ) regarding to their sorption and desorption on Brown soil (BS, luvisols) and Red soil (RS, Udic Ferrosols) using batch experiments. The presence of Cu(II) significantly enhanced sorption of SDZ on BS at pH>5.0, and this trend increased with increasing pH, which was mainly ascribed to the formation of ternary complexes of Cu-SDZ-soil and/or SDZ-Cu-soil. In contrast, Cu(II) only slightly increased SDZ sorption on RS at pH<5.0 due to the decrease of equilibrium solution pH, whereas it hardly affected SDZ sorption at pH>5.0 because RS had high oxides contents and low affinity for Cu(II). In addition, Cu(II) inhibited SDZ desorption from BS but promoted SDZ desorption from RS, which was related to their different sorption mechanisms. The presence of SDZ exerted no significant effect on the sorption of Cu(II) on the two soils at pH<6.5 because of its low sorption coefficients (Kd), while slightly decreased Cu(II) sorption at pH>6.5 by forming water-soluble complexes. Furthermore, SDZ had little effect on Cu(II) desorption from the two soils at natural pH. These results indicate that soil characteristics strongly influence the interactions of Cu(II) and SDZ on their sorption and desorption on soils.

High Concentrations of the Antibiotic Spiramycin in Wastewater Lead to High Abundance of Ammonia-Oxidizing Archaea in Nitrifying Populations

To evaluate the potential effects of antibiotics on ammonia-oxidizing microbes, multiple tools including quantitative PCR (qPCR), 454-pyrosequencing, and a high-throughput functional gene array (GeoChip) were used to reveal the distribution of ammonia-oxidizing archaea (AOA) and archaeal amoA (Arch-amoA) genes in three wastewater treatment systems receiving spiramycin or oxytetracycline production wastewaters. The qPCR results revealed that the copy number ratios of Arch-amoA to ammonia-oxidizing bacteria (AOB) amoA genes were the highest in the spiramycin full-scale (5.30) and pilot-scale systems (1.49 × 10(-1)), followed by the oxytetracycline system (4.90 × 10(-4)), with no Arch-amoA genes detected in the control systems treating sewage or inosine production wastewater. The pyrosequencing result showed that the relative abundance of AOA affiliated with Thaumarchaeota accounted for 78.5-99.6% of total archaea in the two spiramycin systems, which was in accordance with the qPCR results. Mantel test based on GeoChip data showed that Arch-amoA gene signal intensity correlated with the presence of spiramycin (P < 0.05). Antibiotics explained 25.8% of variations in amoA functional gene structures by variance partitioning analysis. This study revealed the selection of AOA in the presence of high concentrations of spiramycin in activated sludge systems.

Review: the important bacterial zoonoses in "one health" concept

An infectious disease that is transmitted from animals to humans, sometimes by a vector, is called zoonosis. The focus of this review article is on the most common emerging and re-emerging bacterial zoonotic diseases. The role of "One Health" approach, public health education, and some measures that can be taken to prevent zoonotic bacterial infections are discussed.

KEY POINTS

A zoonotic bacterial disease is a disease that can be very commonly transmitted between animals and humans. Global climate changes, overuse of antimicrobials in medicine, more intensified farm settings, and closer interactions with animals facilitate emergence or re-emergence of bacterial zoonotic infections.The global "One Health" approach, which requires interdisciplinary collaborations and communications in all aspects of health care for humans, animals, and the environment, will support public health in general.New strategies for continuous dissemination of multidisciplinary research findings related to zoonotic bacterial diseases are hence needed.

Sorption and desorption of sulfadimethoxine, sulfaquinoxaline and sulfamethazine antimicrobials in Brazilian soils

Adsorption and desorption are important processes that influence the transport, transformation and bioavailability of antimicrobials in soils. The adsorption-desorption characteristics of sulfadimethoxine, sulfaquinoxaline and sulfamethazine in Brazilian soils (sandy, sandy-clay and clay) were evaluated using the batch equilibrium method. The sulfonamides were quantified in the soil solutions by a previously in house validated HPLC-PAD method. The adsorption/desorption data for the sulfonamides in soils fit the Freundlich isotherms well in the logarithmic form. The Freundlich adsorption coefficients ranged from 1.4 to 19.0 μg(1-1/n)(cm(3))(1/n)g(-1), suggesting that all of the sulfonamides weakly adsorbed on the evaluated soils. The Freundlich desorption coefficients ranged from 0.85 to 24.8 μg(1-1/n)(cm(3))(1/n)g(-1), indicating that the sulfonamides tend to be leached from soils with high sand and low organic carbon contents, suggesting that there is high potential for surface and groundwater contamination.

Dynamics of soil bacterial communities in response to repeated application of manure containing sulfadiazine

Large amounts of manure have been applied to arable soils as fertilizer worldwide. Manure is often contaminated with veterinary antibiotics which enter the soil together with antibiotic resistant bacteria. However, little information is available regarding the main responders of bacterial communities in soil affected by repeated inputs of antibiotics via manure. In this study, a microcosm experiment was performed with two concentrations of the antibiotic sulfadiazine (SDZ) which were applied together with manure at three different time points over a period of 133 days. Samples were taken 3 and 60 days after each manure application. The effects of SDZ on soil bacterial communities were explored by barcoded pyrosequencing of 16S rRNA gene fragments amplified from total community DNA. Samples with high concentration of SDZ were analyzed on day 193 only. Repeated inputs of SDZ, especially at a high concentration, caused pronounced changes in bacterial community compositions. By comparison with the initial soil, we could observe an increase of the disturbance and a decrease of the stability of soil bacterial communities as a result of SDZ manure application compared to the manure treatment without SDZ. The number of taxa significantly affected by the presence of SDZ increased with the times of manure application and was highest during the treatment with high SDZ-concentration. Numerous taxa, known to harbor also human pathogens, such as Devosia, Shinella, Stenotrophomonas, Clostridium, Peptostreptococcus, Leifsonia, Gemmatimonas, were enriched in the soil when SDZ was present while the abundance of bacteria which typically contribute to high soil quality belonging to the genera Pseudomonas and Lysobacter, Hydrogenophaga, and Adhaeribacter decreased in response to the repeated application of manure and SDZ.

Cultivation-independent screening revealed hot spots of IncP-1, IncP-7 and IncP-9 plasmid occurrence in different environmental habitats

IncP-1, IncP-7 and IncP-9 plasmids often carry genes encoding enzymes involved in the degradation of man-made and natural contaminants, thus contributing to bacterial survival in polluted environments. However, the lack of suitable molecular tools often limits the detection of these plasmids in the environment. In this study, PCR followed by Southern blot hybridization detected the presence of plasmid-specific sequences in total community (TC-) DNA or fosmid DNA from samples originating from different environments and geographic regions. A novel primer system targeting IncP-9 plasmids was developed and applied along with established primers for IncP-1 and IncP-7. Screening TC-DNA from biopurification systems (BPS) which are used on farms for the purification of pesticide-contaminated water revealed high abundances of IncP-1 plasmids belonging to different subgroups as well as IncP-7 and IncP-9. The novel IncP-9 primer-system targeting the rep gene of nine IncP-9 subgroups allowed the detection of a high diversity of IncP-9 plasmid specific sequences in environments with different sources of pollution. Thus polluted sites are “hot spots” of plasmids potentially carrying catabolic genes.

Sorption and photodegradation processes govern distribution and fate of sulfamethazine in freshwater-sediment microcosms

The antibiotic sulfamethazine can be transported from manured fields to surface water bodies. We investigated the degradation and fate of sulfamethazine in pond water using (14)C-phenyl-sulfamethazine in small pond water microcosms containing intact sediment and pond water. We found a 2.7-day half-life in pond water and 4.2-day half-life when sulfamethazine was added to the water (5 mg L(-1) initial concentration) with swine manure diluted to simulate runoff. Sulfamethazine dissipated exponentially from the water column, with the majority of loss occurring via movement into the sediment phase. Extractable sulfamethazine in sediment accounted for 1.9-6.1% of the applied antibiotic within 14 days and then declined thereafter. Sulfamethazine was transformed mainly into nonextractable sediment-bound residue (40-60% of applied radioactivity) and smaller amounts of photoproducts. Biodegradation, as indicated by metabolite formation and (14)CO2 evolution, was less significant than photodegradation. Two photoproducts accounted for 15-30% of radioactivity in the water column at the end of the 63-day study; the photoproducts were the major degradates in the aqueous and sediment phases. Other unidentified metabolites individually accounted for <7% of radioactivity in the water or sediment. Less than 3% of applied radioactivity was mineralized to (14)CO2. Manure input significantly increased sorption and binding of sulfamethazine residues to the sediment. These results show concurrent processes of photodegradation and sorption to sediment control aqueous concentrations and establish that sediment is a sink for sulfamethazine and sulfamethazine-related residues. Accumulation of the photoproducts and sulfamethazine in sediment may have important implications for benthic organisms.

Column and batch tests of sulfonamide leaching from different types of soil

Sulfonamides (SAs) and their metabolites present severe hazards to human health and the environment, mainly because of antibiotic resistance. Knowledge of their bioavailability, including their sorption to soils and their impact on the soil-groundwater pathway, is crucial to their risk assessment. Laboratory batch and column leaching tests are important tools for determining the release potential of contaminants from soil or waste materials. Batch and column tests were carried out with soils differing in particle size distribution, organic matter content and pH, each spiked with sulfonamides (sulfadimethoxine (SDM), sulfaguanidine (SGD), sulfisoxazole (SX)). In order to test the applicability of leaching tests to polar contaminants batch and column tests were also compared. In the column tests, release was found to depend on the properties of both soil and sulfonamides. The fastest release was observed for coarse-grained soil with the smallest organic matter content (MS soil; 100% decrease in concentration until liquid-to-solid ratio (L/S) of 0.9 L kg(-1) for all SAs). The slowest release was established for sulfadimethoxine (24.5% decrease in concentration until L/S 1.22 L kg(-1)). The results of the batch and column tests were comparable to a large extent, with slightly higher concentrations being obtained in the column test experiments of fine-grained soils with a high organic matter content.

Biosolid-borne tetracyclines and sulfonamides in plants

Tetracyclines and sulfonamides used in human and animal medicine are released to terrestrial ecosystems from wastewater treatment plants or by direct manure application. The interactions between plants and these antibiotics are numerous and complex, including uptake and accumulation, phytometabolism, toxicity responses, and degradation in the rhizosphere. Uptake and accumulation of antibiotics have been studied in plants such as wheat, maize, potato, vegetables, and ornamentals. Once accumulated in plant tissue, organic contaminants can be metabolized through a sequential process of transformation, conjugation through glycosylation and glutathione pathways, and ultimately sequestration into plant tissue. While studies have yet to fully elucidate the phytometabolism of tetracyclines and sulfonamides, an in-depth review of plant and mammalian studies suggest multiple potential transformation and conjugation pathways for tetracyclines and sulfonamides. The presence of contaminants in the vicinity or within the plants can elicit stress responses and defense mechanisms that can help tolerate the negative effects of contaminants. Antibiotics can change microbial communities and enzyme activity in the rhizosphere, potentially inducing microbial antibiotic resistance. On the other hand, the interaction of microbes and root exudates on pharmaceuticals in the rhizosphere can result in degradation of the parent molecule to less toxic compounds. To fully characterize the environmental impacts of increased antibiotic use in human medicine and animal production, further research is essential to understand the effects of different antibiotics on plant physiology and productivity, uptake, translocation, and phytometabolism of antibiotics, and the role of antibiotics in the rhizosphere.

Effect of pH on the toxicity and bioconcentration of sulfadiazine on Daphnia magna

The antimicrobial sulfonamide sulfadiazine has in the last decades been detected in environmental water bodies, both surface and ground water. Since pH in the environment may vary considerably, this study examined the toxicity of the amphoter sulfadiazine towards Daphnia magna at pH levels of 6.0, 7.5 and 8.5, thus taking the impact of speciation into consideration, contrary to earlier eco-toxicity studies conducted at standard conditions. Toxicity tests were performed using the standard ISO 6341 test procedure modified to accommodate the three pH levels and the toxicity was expressed as EC50. After 48 h the EC50 was determined to be 27.2, 188 and 310 mg L(-1) at pH 6.0, 7.5 and 8.5, respectively, thus demonstrating a significant effect of pH on the toxicity of sulfadiazine. Furthermore, the bioconcentration factor (dry weight) was determined to be 50 and 36 at pH 6.0 and 8.5, respectively. The higher toxicity at the lower pHs was assumed to be caused by the higher fraction of un-ionized sulfadiazine at the lower pHs. However, the one and a half fold higher bioconcentration at pH 6.0 relative to pH 8.5 does not match the more than ten times higher toxicity at pH 6.0. When comparing the fraction of neutral compound to toxicity and bioconcentration results neither toxicity nor bioconcentration can be ascribed solely to the unionized fraction of sulfadiazine.

Short-term extractability of sulfadiazine after application to soils

The long-term environmental fate of the veterinary antibiotic sulfadiazine (SDZ) in soils is determined by a reversible sequestration into a residual fraction and an irreversible formation of non-extractable residues (NER), which can be described as first-order rate processes. However, the concentration dynamics of the resulting fractions of SDZ in soil show an unexplained rapid reduction of extractability during the first 24 h. We therefore investigated the short-term extractability of SDZ in two different soils under different SDZ application procedures over 24 h: with and without manure, for air-dried and for moist soils. In all batches, we observed an instantaneous loss of extractability on a time scale of minutes as well as kinetically determined sequestration and NER formation over 24 h. Data evaluation with a simple kinetic model led to the conclusion that application with manure accelerated the short-term formation of NER, whereas sequestration was very similar for all batches.