Operating conditions influence microbial community structures, elimination of the antibiotic resistance genes and metabolites during anaerobic digestion of cow manure in the presence of oxytetracycline

Enterobacteria in anaerobic digestion of dairy cattle wastewater: Assessing virulence and resistance for one health security

Samples from a dairy cattle waste-fed anaerobic digester were collected across seasons to assess sanitary safety for biofertilizer use. Isolated enterobacteria (suggestive of Escherichia coli) were tested for susceptibility to biocides, antimicrobials, and biofilm-forming capability. Results revealed a decrease in total bacteria, coliforms, and enterobacteria in biofertilizer compared to the effluent. Among 488 isolates, 98.12 % exhibited high biofilm formation. Biofertilizer isolates exhibited a similar biofilm formation capability as effluent isolates in summer, but greater propensity in winter. Resistance to biocides and antimicrobials varied, with tetracycline resistance reaching 19 %. Of the isolates, 25 were multidrug-resistant (MDR), with 64 % resistant to three drugs. Positive correlations were observed between MDR and increased biofilm formation capacity in both samples, while there was negative correlation between MDR and increased biocide resistance. A higher number of MDR bacteria were found in biofertilizer compared to the effluent, revealing the persistence of E. coli resistance, posing challenges to food safety and public health.

A review on the effects of discharging conventionally treated livestock waste to the environmental resistome

Globally, animal production has developed rapidly as a consequence of the ongoing population growth, to support food security. This has consequently led to an extensive use of antibiotics to promote growth and prevent diseases in animals. However, most antibiotics are not fully metabolized by these animals, leading to their excretion within urine and faeces, thus making these wastes a major reservoir of antibiotics residues, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the environment. Farmers normally depend on conventional treatment methods to mitigate the environmental impact of animal waste; however, these methods are not fully efficient to remove the environmental resistome. The present study reviewed the variability of residual antibiotics, ARB, as well as ARGs in the conventionally treated waste and assessed how discharging it could increase resistome in the receiving environments. Wherein, considering the efficiency and environmental safety, an addition of pre-treatments steps with these conventional treatment methods could enhance the removal of antibiotic resistance agents from livestock waste.

Biochar-assisted degradation of oxytetracycline by Achromobacter denitrificans and underlying mechanisms

Contamination of the environment with large amounts of residual oxytetracycline (OTC) and the corresponding resistance genes poses a potential threat to natural ecosystems and human health. In this study, an effective OTC-degrading strain, identified as Achromobacter denitrificans OTC-F, was isolated from activated sludge. In the degradation experiment, the degradation rates of OTC in the degradation systems with and without biochar addition were 95.01-100% and 73.72-99.66%, respectively. Biochar promotes the biodegradation of OTC, particularly under extreme environmental conditions. Toxicity evaluation experiments showed that biochar reduced biotoxicity and increased the proportion of living cells by 17.36%. Additionally, biochar increased the activity of antioxidant enzymes by 34.1-91.0%. Metabolomic analysis revealed that biochar promoted the secretion of antioxidant substances such as glutathione and tetrahydrofolate, which effectively reduced oxidative stress induced by OTC. This study revealed the mechanism at the molecular level and provided new strategies for the bioremediation of OTC in the environment.

Improvement of carbon source composition reduces antibiotic resistance genes in the ectopic fermentation system

Effectively reduce antibiotic resistance genes (ARGs) in ectopic fermentation system (EFS) is essential for practical production. In this study, three experiments were performed to explore how to remove ARGs in EFS effectively. Results demonstrated that ARGs were easily enriched in rice-husk-sawdust padding; simultaneous addition of laccase and cellulase suppressed the ARGs, mainly by increasing soluble carbohydrate concentration and promoting humic acid concentration; addition of corn stalks into rice-husk-sawdust decreased the abundance of ARGs by improving the carbon source structure and enhancing cellulase activity. In conclusion, the present study provides a guidance to reduce the threat of ARGs in EFS, which paved a potential pathway to safely utilize manure resources.

The Antibiotics Degradation and Its Mechanisms during the Livestock Manure Anaerobic Digestion

Antibiotics are administered to livestock at subtherapeutic levels to promote growth, and their degradation in manure is slow. High antibiotic concentrations can inhibit bacterial activity. Livestock excretes antibiotics via feces and urine, leading to their accumulation in manure. This can result in the propagation of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs). Anaerobic digestion (AD) manure treatment technologies are gaining popularity due to their ability to mitigate organic matter pollution and pathogens, and produce methane-rich biogas as renewable energy. AD is influenced by multiple factors, including temperature, pH, total solids (TS), substrate type, organic loading rate (OLR), hydraulic retention time (HRT), intermediate substrates, and pre-treatments. Temperature plays a critical role, and thermophilic AD has been found to be more effective in reducing ARGs in manure compared to mesophilic AD, as evidenced by numerous studies. This review paper investigates the fundamental principles of process parameters affecting the degradation of ARGs in anaerobic digestion. The management of waste to mitigate antibiotic resistance in microorganisms presents a significant challenge, highlighting the need for effective waste management technologies. As the prevalence of antibiotic resistance continues to rise, urgent implementation of effective treatment strategies is necessary.

Exploration of machine learning algorithms for predicting the changes in abundance of antibiotic resistance genes in anaerobic digestion

The land application of digestate from anaerobic digestion (AD) is considered a significant route for transmitting antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) to ecosystems. To date, efforts towards understanding complex non-linear interactions between AD operating parameters with ARG/MGE abundances rely on experimental investigations due to a lack of mechanistic models. Herein, three different machine learning (ML) algorithms, Random Forest (RF), eXtreme Gradient Boosting (XGBoost), and Artificial Neural Network (ANN), were compared for their predictive capacities in simulating ARG/MGE abundance changes during AD. The models were trained and cross-validated using experimental data collected from 33 published literature. The comparison of model performance using coefficients of determination (R²) and root mean squared errors (RMSE) indicated that ANN was more reliable than RF and XGBoost. The mode of operation (batch/semi-continuous), co-digestion of food waste and sewage sludge, and residence time were identified as the three most critical features in predicting ARG/MGE abundance changes. Moreover, the trained ANN model could simulate non-linear interactions between operational parameters and ARG/MGE abundance changes that could be interpreted intuitively based on existing knowledge. Overall, this study demonstrates that machine learning can enable a reliable predictive model that can provide a holistic optimization tool for mitigating the ARG/MGE transmission potential of AD.

Migration of antibiotic resistance genes and evolution of flora structure in the Xenopus tropicalis intestinal tract with combined exposure to roxithromycin and oxytetracycline

The intestinal flora is one of the most important environments for antibiotic resistance development, owing to its diverse mix of bacteria. An excellent medicine model organism, Xenopus tropicalis, was selected to investigate the spread of antibiotic resistance genes (ARGs) in the intestinal bacterial community with single or combined exposure to roxithromycin (ROX) and oxytetracycline (OTC). Seventeen resistance genes (tetA, tetB, tetE, tetM, tetO, tetS, tetX, ermF, msrA, mefA, ereA, ereB, mphA, mphB, intI1, intI2, intI3) were detected in the intestines of Xenopus tropicalis living in three testing tanks (ROX tanks, OTC tanks, ROX + OTC tanks) and a blank tank for 20 days. The results showed that the relative abundance of total ARGs increased obviously in the tank with single stress but decreased in the tank with combined stress, and the genes encoding the macrolide antibiotic efflux pump (msrA), phosphatase (mphB) and integron (intI2, intI3) were the most sensitive. With the aid of AFM scanning, DNA was found to be scattered short chain in the blank, became extended or curled and then compacted with the stress from a single antibiotic, and was compacted and then fragmented with combined stress, which might be the reason for the variation of the abundance of ARGs with stress. The ratio of Firmicutes/Bacteroides related to diseases was increased by ROX and OTC. The very significant correlation between intI2 and intI3 with tetS (p ≤ 0.001) hinted at a high risk of ARG transmission in the intestines. Collectively, our results suggested that the relative abundance of intestinal ARGs could be changed depending on the intestinal microbiome and DNA structures upon exposure to antibiotics at environmental concentrations.

Identification of factors affecting removal of antibiotic resistance genes in full-scale anaerobic digesters treating organic solid wastes

Efficiencies of removing antibiotic resistance genes (ARGs) and intI1 were explored using eight full-scale anaerobic digesters. The digesters demonstrated different characteristics on the basis of substrate types (food waste, manure or sludge); configuration (single or two-stage); temperature (psychrophilic, mesophilic or thermophilic); hydraulic retention time (HRT) (9.7-44 days); and operation mode (continuous stirred tank reactor or plug flow reactor). Digesters' configuration or operating parameters showed a greater effect on abundance of ARGs than the type of input substrate. Redundancy analysis (RDA) accounted for 85.2% of the total variances and digesters with the same configuration and operational conditions showed similar performance for removal of ARGs. The highest efficiencies of removing ARGs (99.99%) were observed in two-stage thermophilic digesters with relatively long HRTs (32 days). The lowest removal efficiency (97.93%) was observed in single-stage mesophilic with relatively short HRTs (9.7 days), likely due to vertical and horizontal gene transfer.

Impact of oxytetracycline exposure on the digestive system microbiota of Daphnia magna

Antibiotics are used to treat serious illness, but may also be used extraneously or as a preventative measure in many farm animals. This usage increases the potential for unintentional exposure to a variety of organisms. When antibiotics enter aquatic environments, Daphnia magna are especially vulnerable as they filter-feed in freshwater environments. Oxytetracycline (OTC) is a commonly-used broad-spectrum antibiotic used to treat a variety of mammalian diseases. In this study, the impact of OTC on D. magna mortality and gut biota were studied using both cultivation and sequencing-based approaches. Mortality rates were extremely low with the LD50 >2,000ppm. However, OTC impacted abundance and species diversity of intestinal microorganisms in the gut of the D. magna in abundance as well as species diversity. In control organisms, Pseudomonas putida and Aeromonas hydrophila were both present while only P. putida was found in OTC-exposed organisms. Disruption of the intestinal biota in D. magna could have implications on long-term survival, energy expenditure, and reproduction.

Effect of low levels of oxytetracycline on anaerobic digestion of cattle manure

Cattle manure is rich in organic matter and nutrients, but it may also contain harmful substances such as residual antibiotics and other toxic compounds. Oxytetracycline (OTC) is a widely used veterinary antibiotic and its presence in manure can affect the subsequent anaerobic digestion process. This study evaluated the effect of OTC concentrations viz. 0.12, 0.3, 0.6, 1.2, 3, 6 and 12 mg L^-1 on batch mesophilic anaerobic digestion of cattle manure. The results showed that cumulative biogas yield decreased by 25, 29 and 55% at 3, 6 and 12 mg OTC L^-1 in contrast to control. Volatile solids removal was 39% for control which reduced to 13% in 12 mg L^-1 OTC spiked reactor. Effect on stability parameters was significant at OTC concentrations from 1.2 to 12 mg L^-1. Two different kinetic models were used for biogas data validation and the modified Gompertz model best fitted to the experimental data.

A meta-analysis reveals that operational parameters influence levels of antibiotic resistance genes during anaerobic digestion of animal manures

Anaerobic digestion (AD) has shown the potential to reduce the numbers and types of antibiotic-resistance genes (ARG) present in animal manures. However, the variability of the results has limited the ability to draw solid conclusions. To address this issue, we performed a series of meta-analyses to evaluate how AD of pig, cattle, and dairy manures affects ARG levels and how different parameters, such as temperature, pH, digestion times, and the addition of other substances (e.g., solids, antibiotics) influence ARG changes. Twenty studies with enough details on changes in ARG levels during the AD process were identified and used for the meta-analyses. The results suggested that AD could significantly reduce ARG levels regardless of the conditions of the process. Also, thermophilic AD was more effective than mesophilic AD at reducing ARGs, although this difference was only significant for pig manures. The results also suggested that long digestion times (>50 days) yielded better ARG reduction rates, and that the addition of solids from an external source (co-digestion) negatively affected the efficiency of ARG reduction. In general, the results suggested that ARG changes during AD could be linked to the abundance and activity of hydrolytic communities.

A comprehensive review on biodegradation of tetracyclines: Current research progress and prospect

The release of tetracyclines (TCs) in the environment is of significant concern because the residual antibiotics may promote resistance in pathogenic microorganisms, and the transfer of antibiotic resistance genes poses a potential threat to ecosystems. Microbial biodegradation plays an important role in removing TCs in both natural and artificial systems. After long-term acclimation, microorganisms that can tolerate and degrade TCs are retained to achieve efficient removal of TCs under the optimum conditions (e.g. optimal operational parameters and moderate concentrations of TCs). To date, cultivation-based techniques have been used to isolate bacteria or fungi with potential degradation ability. Moreover, the biodegradation mechanism of TCs can be unveiled with the development of chemical analysis (e.g. UPLC-Q-TOF mass spectrometer) and molecular biology techniques (e.g. 16S rRNA gene sequencing, multi-omics sequencing, and whole genome sequencing). In this review, we made an overview of the biodegradation of TCs in different systems, refined functional microbial communities and pure isolates relevant to TCs biodegradation, and summarized the biodegradation products, pathways, and degradation genes of TCs. In addition, ecological risks of TCs biodegradation were considered from the perspectives of metabolic products toxicity and resistance genes. Overall, this article aimed to outline the research progress of TCs biodegradation and propose future research prospects.

A systematic review of antibiotics and antibiotic resistance genes in estuarine and coastal environments

Antibiotics and antibiotic resistance genes (ARGs) are prevalent in estuarine and coastal environments due to substantial terrestrial input, aquaculture effluent, and sewage discharge. In this article, based on peer-reviewed papers, the sources, spatial patterns, driving factors, and environmental implications of antibiotics and ARGs in global estuarine and coastal environments are discussed. Riverine runoff, WWTPs, sewage discharge, and aquaculture, are responsible for the prevalence of antibiotics and ARGs. Geographically, pollution due to antibiotics in low- and middle-income countries is higher than that in high-income countries, and ARGs show remarkable latitudinal variations. The distribution of antibiotics is driven by antibiotic usage and environmental variables (heavy metals, nutrients, organic pollutants, etc.), while ARGs are affected by antibiotics residues, environmental variables, microbial communities, and mobile genetic elements (MGEs). Antibiotics and ARGs alter microbial communities and biogeochemical cycles, as well as pose threats to marine organisms and human health. Our results provide comprehensive insights into the transport and environmental behaviors of antibiotics and ARGs in global estuarine and coastal environments.

CFD Modeling of a Stirred Anaerobic Digestion Tank for Evaluating Energy Consumption through Mixing

The anaerobic digestion process is an effective means to eliminate the detrimental impacts of cattle manure discharge into the environment, i.e., biochemical contamination and substantial methane emissions, the latter leading to global warming. For proper operation of anaerobic digesters, an efficient mixing provides a relatively homogenous mixture of the feedstock within the tank. This study aims to investigate the mixing process and the total energy consumption needed for stirring by using an asymmetrical mixer. A further objective is to analyze the formation of stagnant volume and the velocity gradient in the digester in order to assure the mixing efficiency of the mixer type. The computational model is implemented as the finite volume method, and the rheological properties of the feedstock are considered. The results are validated by comparing the on-site power consumption of the mixer with the values obtained by the numerical torque. At various mixer speeds, the dead volume does not exceed 0.5% of the digester tank; however, with the increase of the mixer rotation speed, the energy consumption of the mixer increases drastically.

Distribution of genetic elements associated with antibiotic resistance in treated and untreated animal husbandry waste and wastewater

Animal breeding for meat production based on swine, cattle, poultry, and aquaculture is an activity that generates several impacts on the environment, among them the spread of antibiotic resistance. There is a worldwide concern related to the massive use of antibiotics, which causes selective pressure on the microbial community, triggering bacteria that contain "antibiotic resistance genes." According to the survey here presented, antibiotic resistance-related genes such as tetracyclines (tet), erythromycin (erm), and sulfonamides (sul), as well as the genetic mobile element interferon (int), are the most reported genetic elements in qualitative and quantitative studies of swine, cattle, poultry, and aquaculture manure/wastewater. It has been observed that biological treatments based on waste composting and anaerobic digestion are effective in ARG removal, particularly for tet, bla, erm, and qnr (quinolone) genes. On the other hand, sul and intI genes were more persistent in such treatments. Tertiary treatments, such advanced oxidative processes, are suitable strategies to improve ARG reduction. In general temperature, hydraulic retention time, and penetration of sunlight are the main operational parameters for ARG reduction in treatments applied to animal waste, and therefore attention should be addressed to optimize their efficacy regarding ARG removal. Despite being reduced, the presence of ARG in treated effluents and in biosolids indicates that there is a potential risk of antibiotic resistance spread in nature, especially through the release of treated livestock waste into the environment.

Variation of Metagenome From Feedstock to Digestate in Full-Scale Biogas Plants

Anaerobic digestion (AD) has been widely used to resolve the problem of organic wastes worldwide. Previous studies showed that the types of feedstock have a great influence on the AD microbiome, and a huge number of AD populations are migrated from upstream feedstocks. However, the changes of microbial compositions from feedstock to AD digestate are still less understood. We collected feedstock samples from 56 full-scale biogas plants, generated 1,716 Gb feedstock metagenomic data in total, and constructed the first comprehensive microbial gene catalog of feedstock containing 25.2 million genes. Our result indicated that the predominant phyla in feedstock are Firmicutes, Bacteroidetes, and Proteobacteria, which is similar to that in AD digestate, and the microbial diversity of feedstock samples is higher than that of AD digestate samples. In addition, the relative abundance of most genes involved in methanogenesis increase from feedstock to AD digestate. Besides, the amount of antibiotic resistance genes (ARGs) and pathogenic bacteria in AD are effectively reduced compared to feedstocks. This study provides a comprehensive microbial gene catalog of feedstock, and deepens the understanding of variation of microbial communities from feedstock to AD digestate of full-scale AD. The results also suggest the potential of AD to reduce the level of ARGs and pathogens in animal manure.

Review on the fate of antimicrobials, antimicrobial resistance genes, and other micropollutants in manure during enhanced anaerobic digestion and composting

While manure has been used as nutrient-rich fertilizer for centuries, anaerobic digestion (AD) of manure has only been recognized recently as a promising renewable energy source for producing methane-rich biogas. Various forms of AD have been evaluated for the removal of manure contaminants, such as antimicrobials, antimicrobial resistance genes (ARGs), hormones, and pesticides that pose risks to human health and the environment. Increasing demand for cleaner energy prompts examination of the fate of manure contaminants in conventional and advanced AD techniques. This review reveals that removal of contaminants differs based on type (e.g. antimicrobials vs hormones) or class (e.g. tetracyclines vs sulfonamides) of chemicals being treated. Increasingly, pre-treatment techniques are incorporated into AD systems to enhance biogas production and degrade manure contaminants. For instance, activated carbon with microwave pretreatment removed 87-95% of ARGs. Advanced anaerobic digestion and solid-state anaerobic digestion reduced various ARGs associated with sulfonamides, macrolides, and tetracyclines. Further, total hormone reduction improved using high-temperature pretreatment prior to mesophilic AD. Finally, several studies revealed partial removal of antimicrobials and ARGs during managed composting. Although AD can independently decrease manure contaminants prior to use as fertilizer, augmenting AD with composting and other physical treatment processes can further enhance their removal.

Kinetic study of oxytetracycline and chlortetracycline inhibition in the anaerobic digestion of dairy manure

This study was aimed to investigate the mechanisms of oxytetracycline (OTC) and chlortetracycline (CTC) inhibition in anaerobic digestion (AD) using four kinetic models. The results showed that the inhibition rate of OTC was faster than CTC at OTC and CTC between 0.04 and 1.28 g/L. Hydrolysis rate constant was linearly and positively correlated with OTC and increased from 0.172 to 0.193 d^-1, 0.164 to 0.179 d^-1 and 0.251 to 0.285 d^-1 using first-order kinetic, Fitzhugh and Cone models, respectively, while the maximum specific methane production rate was linearly and negatively correlated with CTC and decreased from 0.028 to 0.016 L/gVS. Cone model was found to give the most satisfactory fitting results followed in descending order by first-order kinetic, Fitzhugh and modified Gompertz models. The kinetic modeling of methane yield helped explain the mechanism of OTC and CTC inhibition in the AD process and provided essential information for further process improvement.

Effect of mesophilic anaerobic digestion on the resistome profile of dairy manure

The effect of mesophilic anaerobic digestion (AD) on the resistome profile of manures from two different dairy farms was evaluated using a metagenomic approach. A total of 187 unique Antibiotic resistance genes (ARGs) for 17 different classes of antibiotics were detected in raw (undigested) manures. The results indicate that regardless of the origin of the dairy manure, mesophilic AD was capable of reducing or enriching the relative abundance of some ARGs. The main driver of these changes was strongly correlated with the evolution of the microbial community during the AD process. Putative ARG hosts were suggested by analyses of the co-occurrence of microbial groups and ARGs. Finally, network analyses revealed that mesophilic AD could also reduce the co-occurrence of different groups of ARGs potentially located in the same genetic elements. Our results provide valuable insights into the microbial mechanisms driving the diversity and abundance of ARGs during mesophilic AD.

In search of the optimal inoculum to substrate ratio during anaerobic co-digestion of spent coffee grounds and cow manure

The inoculum to substrate (I:S) ratio is a crucial operating parameter during the start-up period of anaerobic digestion (AD) processes and this ratio shows high differentiation with respect to substrate composition. While spent coffee grounds (SCG) have started to gain attraction in AD as a co-substrate due to their vast production and promising methane potential, there is still not enough information on the operative environment of SCG-based biogas reactors. This study investigated the optimal I:S ratio during anaerobic co-digestion of SCG and cow manure. Biochemical methane potential tests were conducted at mesophilic conditions and the influence of I:S ratio on methane production and digestion stability was evaluated at a wide range of I:S ratios from 0.5:1 to 4:1 (volatile solids (VS) basis). Methane yields increased gradually starting from the I:S ratio of 0.5:1 up to 3:1 and the highest methane yield (225 mlCH₄ gVS^-1) was achieved at the I:S ratio of 3:1. Comparatively lower methane yields were obtained at the ratios of 3.5:1 and 4:1. Instable AD conditions were established at the lowest I:S ratio examined (0.5:1), which caused volatile fatty acid (VFA) accumulation. The results highlighted that anaerobic co-digestion of SCG and cow manure is a promising approach, while the I:S ratio should be well-maintained due to the high potential risk of rapid and/or excess VFA production of these feedstocks.

Exploring the Animal Waste Resistome: The Spread of Antimicrobial Resistance Genes Through the Use of Livestock Manure

Antibiotic resistance is a public health problem of growing concern. Animal manure application to soil is considered to be a main cause of the propagation and dissemination of antibiotic residues, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the soil-water system. In recent decades, studies on the impact of antibiotic-contaminated manure on soil microbiomes have increased exponentially, in particular for taxonomical diversity and ARGs’ diffusion. Antibiotic resistance genes are often located on mobile genetic elements (MGEs). Horizontal transfer of MGEs toward a broad range of bacteria (pathogens and human commensals included) has been identified as the main cause for their persistence and dissemination. Chemical and bio-sanitizing treatments reduce the antibiotic load and ARB. Nevertheless, effects of these treatments on the persistence of resistance genes must be carefully considered. This review analyzed the most recent research on antibiotic and ARG environmental dissemination conveyed by livestock waste. Strategies to control ARG dissemination and antibiotic persistence were reviewed with the aim to identify methods for monitoring DNA transferability and environmental conditions promoting such diffusion.

Development of a new SLE-SPE-HPLC-MS/MS method for the determination of selected antibiotics and their transformation products in anthropogenically altered solid environmental matrices

The presence of antibiotic residues, their bioactive metabolites and other transformation products in the environment may adversely affect the organisms that live in the environment and may also contribute to increasing the antibiotic resistance of bacteria. It is particularly difficult to determine the types of contaminants in solid samples, in particular, those that are anthropogenically changed, e.g., as a result of controlled biochemical processes. Therefore, the aim of this research was to develop of a new method for the determination of twelve antibiotics belonging to different groups, such as penicillins, sulfonamides, tetracyclines, quinolones, imidazoles and cefalosporins, in digested manure and activated sludge samples, which were used as examples of anthropogenically altered environmental solid samples. The analyses were performed using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The solid-liquid extraction (SLE) method to isolate analytes from digested manure and activated sludge was developed and optimized, the same as clean-up procedure followed by solid phase extraction (SPE). The recovery ranged from 45 to 85%. Finally, the validated method was applied to the determination of the selected antibiotics in manure and activated sludge samples after an anaerobic digestion process.. An additional aim of the study was to verify whether the developed method allows simultaneous detection of transformation products of the studied antibiotics in solid samples. The study showed that by optimizing the analysis conditions, it is possible to simultaneously determine the selected antibiotics and their transformation products (including their epimeric forms), which can significantly improve the ability to control the efficiency of the biological processes used in this area. In practice, this means that the developed methodology may be particularly useful in the context of research and other works related to the anaerobic digestion of activated sludge, manure or other solid substrates of environmental origin.

Effects of copper salts on performance, antibiotic resistance genes, and microbial community during thermophilic anaerobic digestion of swine manure

This study investigated methane production and ARGs reduction during thermophilic AD of swine manure with the addition of different Cu salts (cupric sulfate, cupric glycinate, and the 1:1 mixture of these two salts). Results showed methane production was increased by 28.78% through adding mixed Cu salts. The mixed Cu group effectively reduced total ARGs abundance by 26.94%, suggesting mixed Cu salts did not promote the potential ARGs risk. The positive effects of mixed Cu salts on AD performance and ARGs removal might be ascribed to the low bioavailability. Microbial community analysis indicated the highest abundances of Clostridia_MBA03 and Methanobacterium in the mixed Cu group might cause the increased methane production. Spearman's rank correlation analysis elucidated the succession in microbial community induced by environmental factors was the main driver for shaping ARGs profiles. Thus, mixed Cu salts could be an alternative to replace the inorganic Cu salt in animal feed additives.

How methane yield, crucial parameters and microbial communities respond to the stimulating effect of antibiotics during high solid anaerobic digestion

To comprehensively understand how antibiotics affect anaerobic digestion, their stimulating effects on methane production cannot be ignored; however, few studies have evaluated these effects. This study investigated the stimulating effects of three typical antibiotics (oxytetracycline, sulfadimethoxine, and norfloxacin) on high solid anaerobic digestion. The results showed that 100 mg/L antibiotics exhibited a strong stimulating effect on CH₄ yield; while other external carbon sources had no obvious effects. The stimulating effect was more obvious under low inoculation ratios, which could improve the system processing capacity of feed sludge. Lower lag phases were given by the modified Gompertz model when stimulating effects occurred. The variations of physicochemical parameters and microbial Venn maps both showed that day 5 was a critical point for digestion time. The relative abundance of Methanosarcina was enhanced when the stimulating effect occurred, whereas Methanoculleus decreased. Different microbial characteristics were obtained for different samples from the heat maps.

Fate of antibiotic resistance genes during anaerobic digestion of sewage sludge: Role of solids retention times in different configurations

In this study, three anaerobic digestion experiments were established to investigate the effects of solids retention times (SRT) on the fate of antibiotic resistance genes (ARGs) including anaerobic digestion of sewage sludge (CK), one-stage anaerobic digestion of microwave pretreatment sludge (MW) and two-stage anaerobic digestion of microwave pretreatment sludge (Acid stage and CH₄ stage). The response of ARGs to the SRT varied significantly from ARG types and reactor configurations. Shorter SRT could avail the ARGs reduction for CK and two-stage digestion, while MW need longer SRT for the ARGs reduction. Concerning the variance of microbial community caused by reactor configurations, the role of SRT was limited. The partial redundancy analysis and structural equation models analysis indicated that the role of SRT on the ARGs fate could be attributed the most to the co-selection from heavy metals.

Pressurized liquid extraction of six tetracyclines from agricultural soils

Veterinary antibiotics used in agriculture can be introduced into the environment through land application of animal manure, accumulating in soils and groundwaters and posing a significant risk to human health and animal well-being. As the analysis of tetracyclines in soil is challenging due to their strong interaction with soil minerals and organic carbon, the objective of this study was to develop a reliable and reproducible method for quantitative analysis of chlortetracycline and oxytetracycline, and their respective metabolites in soils. A method based on pressurized liquid extraction (PLE) with in-cell clean-up was developed for the extraction of chlortetracycline and oxytetracycline and four likely metabolites from a set of four soils. Optimized conditions included a cell size of 22 mL, soil loading of 5 g, pH of 8.0, methanol:water ratio of 3:1, 50 °C, and two cycles. Soil extracts were analysed by high-performance liquid chromatography (HPLC) coupled with ion trap mass spectrometry (MS). Recoveries of seven tetracyclines from soil ranged from 41% to 110%. The limits of detection for tetracyclines were 0.08-0.3 µg g^-1 soil, and intra- and inter-day variation ranged from 0.12-0.34%. The proposed PLE method is suitable for quantification of tetracyclines in agricultural soils at typical concentrations expected in contaminated environments.

Responses and successions of sulfonamides, tetracyclines and fluoroquinolones resistance genes and bacterial community during the short-term storage of biogas residue and organic manure under the incubator and natural conditions

Biogas residue and organic manure are frequently used for crop planting. However, the evaluation of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and bacterial community before their applications to fields is still lacking. This study monitored the variations of bacteria resistant to sulfadiazine, tetracycline and norfloxacin, 57 resistance genes for sulfonamides, tetracyclines and fluoroquinolones as well as the bacterial community during the 28-day aerobic storage of biogas residue and organic manure by using viable plate counts, high-throughput qPCR and Illumina MiSeq sequencing methods. Then two storage conditions, incubator (25 °C) and natural environment, were used to assess the responses of ARB and ARGs to the environmental factors. Results showed that a total of 35 and 21 ARGs were detected in biogas residue and organic manure, respectively. ARB and ARGs were enriched up to 8.01-fold in biogas residue after the 28-day storage, but varied in a narrow range during the storage of organic manure. Compared with the incubator condition, the proliferation of ARB and ARGs in biogas residue under the natural condition was relatively inhibited by the varied and complicated environmental factors. However, we found that there was no significant difference of ARB and ARGs in organic manure between the incubator and natural conditions. Bacterial community was also shifted during the storage of biogas residue, especially Bacteroidetes_VC2.1_Bac22, Aequorivita, Luteimonas and Arenimonas. Network analysis revealed that the relationship in biogas residue was much more complicated than that in organic manure, which ultimately resulted in large successions of ARB and ARGs during the short-term storage of biogas residue. Therefore, we suggest that further measures should be taken before the application of biogas residue to fields.

Degradation of oxytetracycline under autotrophic nitrifying conditions in a membrane aerated biofilm reactor and community fingerprinting

Pharmaceuticals in waterbodies are a growing concern due to their extensive uses and adverse effects on aquatic life. Oxytetracycline (OTC) is one of tetracycline antibiotic group used for treatment of animals and humans. This study evaluates the simultaneous oxidation of OTC and ammonium under autotrophic nitrifying conditions by using a membrane aerated biofilm reactor (MABR) as it provides an appropriate environment for the antibiotic-degrading bacteria. The results showed that MABR achieved fluxes of 1.62 mg OTC/m².d and 1117 mg N/m².d while the fluxes of O₂ (J_OTC-O2) utilized for OTC and NH₄-N (J_NH4-N-_O2) oxidation were calculated to be 2.94 and 5105 mg O₂/m².d, respectively. Three transformation products, 4-Epi-OTC, α-Apo-OTC and β-Apo-OTC, were identified and measured at ppb levels. The biofilm community comprised of Bacteria environmental samples, b-proteobacteria, CFB group bacteria, g-proteobacteria, d-proteobacteria and a-proteobacteria.