Enrichment Of Antibiotic Resistance Genes Research Articles

Do microplastic biofilms promote the evolution and co-selection of antibiotic and metal resistance genes and their associations with bacterial communities under antibiotic and metal pressures?

Microplastic (MP) biofilms with heterogeneous bacterial compositions and structure have become a hotspot of antibiotic resistance genes (ARGs) in aquatic environments. The evolutionary features of ARGs and their related factors including class 1 integron (intI1), metal resistance genes (MRGs), and bacterial communities in MP biofilms under exogenous pressures and how they compared with natural substrates (NS) are unclear. The individual and combined pressures of sulfamethoxazole, tetracycline, and zinc were used to drive the dynamic evolution of ARGs, intI1, MRGs, and bacterial communities in the MP and NS biofilms. The exogenous pressures from the combined selection of sulfamethoxazole, tetracycline, and zinc and their increasing concentrations both significantly enhanced the abundances of ARGs on the MP compared to the NS. Meanwhile, the selective pressures resulted in obvious dissimilarities between the MP and NS bacterial communities. The core bacterial taxa and the co-occurrence patterns of ARGs and bacterial genera in the biofilms of MP and NS were obviously different, and more potential ARG host bacteria selectively colonized the MP. Metal pressure also enhanced the enrichment of ARGs in the MP biofilms by promoting the spread of intI1 via the co-selection mechanism.

Tracing Antibiotic Resistance Genes along the Irrigation Water Chain to Chive: Does Tap or Surface Water Make a Difference?

Irrigation water is well known as potential source of pathogens in fresh produce. However, its role in transferring antibiotic resistance determinants is less well investigated. Therefore, we analyzed the contribution of surface and tap water to the resistome of overhead-irrigated chive plants. Field-grown chive was irrigated with either surface water (R-system) or tap water (D-system), from planting to harvest. Water along the two irrigation chains as well as the respective plants were repeatedly sampled and screened for 264 antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), using high-capacity qPCR. Differentially abundant (DA) ARGs were determined by comparing the two systems. On R-chive, β-lactam ARGs, multidrug-resistance (MDR) determinants, and MGEs were most abundant, while D-chive featured DA ARGs from the vancomycin class. Diversity and number of DA ARGs was the highest on young chives, strongly diminished at harvest, and increased again at the end of shelf life. Most ARGs highly enriched on R- compared to D-chive were also enriched in R- compared to D-sprinkler water, indicating that water played a major role in ARG enrichment. Of note, blaKPC was detected at high levels in surface water and chive. We conclude that water quality significantly affects the resistome of the irrigated produce.

Unveiling the Gut Microbiota and Resistome of Wild Cotton Mice, Peromyscus gossypinus, from Heavy Metal- and Radionuclide-Contaminated Sites in the Southeastern United States.

ABSTRACTThe prevalence of antibiotic resistance genes (ARGs) can be driven by direct selection from antibiotic use and indirect selection from substances such as heavy metals (HMs). While significant progress has been made to characterize the influence of HMs on the enrichment and dissemination of ARGs in the environment, there is still much we do not know. To fill this knowledge gap, we present a comprehensive analysis of gut bacteria associated with wild cotton mice (Peromyscus gossypinus) trapped from several areas affected by legacies of HM and radionuclide contamination. We explore how these contaminants affect gut microbial community (GMC) composition and diversity and the enrichment of antibiotic, biocide, and metal resistance genes. Although we were able to identify that a myriad of co-occurring antimicrobial and HM resistance genes appear in mice from all areas, including those without a history of contamination, the proportions of co-occurring ARGs and metal resistance genes (MRGs) are higher in sites with radionuclide contamination. These results support those from several previous studies and enhance our understanding of the coselection process, while providing new insights into the ubiquity of antimicrobial resistance in the resistome of wild animals.IMPORTANCE Antimicrobial resistance is a serious global public health concern because of its prevalence and ubiquitous distribution. The rapid dissemination of antibiotic resistance genes is thought to be the result of the massive overuse of antibiotics in agriculture and therapeutics. However, previous studies have demonstrated that the spread of antibiotic resistance genes can also be influenced by heavy metal contamination. This coselection phenomenon, whereby different resistance determinants are genetically linked on the same genetic element (coresistance) or a single genetic element provides resistance to multiple antimicrobial agents (cross-resistance), has profound clinical and environmental implications. In contrast to antibiotics, heavy metals can persist in the environment as a selection pressure for long periods of time. Thus, it is important to understand how antibiotic resistance genes are distributed in the environment and to what extent heavy metal contaminants may be driving their selection, which we have done in one environmental setting.

Distribution and Influence on the Microbial Ecological Relationship of Antibiotic Resistance Genes in Soil at a Watershed Scale

Antibiotic resistance genes (ARGs) are ubiquitous in the environment, with previous studies mainly focusing on the terrestrial ecosystem, which is prone to higher antibiotic application. However, the characteristics, distribution pattern, and driving factors of soil ARGs at the macro scale are still unclear. In this study, the soil ARGs, antibiotics, mobile genetic elements (MGEs), soil properties, toxic metals, polycyclic aromatic hydrocarbons (PAHs), and bacterial community in the Taipu River Basin were analyzed to investigate the distribution and dissemination of ARGs at a watershed scale. The results revealed that ARGs were widespread in the soils along the Taipu River, and that ARG profiles varied greatly with different types of land use, but showed regional similarities. The characteristics were mainly determined by antibiotic input and the ARG transmission mediated by MGEs. The order of the contribution of environmental factors to ARG distribution was toxic metals > PAHs > soil properties. Toxic metal pollution was coupled with ARGs through MGE mediation, while PAHs and soil properties were most likely to affect the ARG distribution by shifting the bacterial community. The microbial–ecological relationship changed significantly with the enrichment of ARGs, and its impact may extend to the watershed scale. Transposon IS1247 can be used as an indicator of the ARGs impact on the microbial ecological relationship in the soils of the Taipu River Basin.

Antibiotic Resistance Genes in Lemur Gut and Soil Microbiota Along a Gradient of Anthropogenic Disturbance

The overuse of man-made antibiotics has facilitated the global propagation of antibiotic resistance genes in animals, across natural and anthropogenically disturbed environments. Although antibiotic treatment is the most well-studied route by which resistance genes can develop and spread within host-associated microbiota, resistomes also can be acquired or enriched via more indirect routes, such as via transmission between hosts or via contact with antibiotic-contaminated matter within the environment. Relatively little is known about the impacts of anthropogenic disturbance on reservoirs of resistance genes in wildlife and their environments. We therefore tested for (a) antibiotic resistance genes in primate hosts experiencing different severities and types of anthropogenic disturbance (i.e., non-wildlife animal presence, human presence, direct human contact, and antibiotic treatment), and (b) covariation between host-associated and environmental resistomes. We used shotgun metagenomic sequencing of ring-tailed lemur (Lemur catta) gut resistomes and associated soil resistomes sampled from up to 10 sites: seven in the wilderness of Madagascar and three in captivity in Madagascar or the United States. We found that, compared to wild lemurs, captive lemurs harbored greater abundances of resistance genes, but not necessarily more diverse resistomes. Abundances of resistance genes were positively correlated with our assessments of anthropogenic disturbance, a pattern that was robust across all ten lemur populations. The composition of lemur resistomes was site-specific and the types of resistance genes reflected antibiotic usage in the country of origin, such as vancomycin use in Madagascar. We found support for multiple routes of ARG enrichment (e.g., via human contact, antibiotic treatment, and environmental acquisition) that differed across lemur populations, but could result in similar degrees of enrichment. Soil resistomes varied across natural habitats in Madagascar and, at sites with greater anthropogenic disturbance, lemurs and soil resistomes covaried. As one of the broadest, single-species investigations of wildlife resistomes to date, we show that the transmission and enrichment of antibiotic resistance genes varies across environments, thereby adding to the mounting evidence that the resistance crisis extends outside of traditional clinical settings.

Optimization of Tidal-Combined Flow Constructed Wetland System and Its Removal Effect on Antibiotic Resistance Genes

Antibiotic resistance genes (ARGs) pose a serious threat to environmental biology and public health, along with the discharge and spread of wastewater. The advanced treatment of ARGs in wastewater therefore deserves special attention. In our previous study, we found that tidal flow constructed wetlands can effectively remove multiple ammonia from wastewater. In this study, we further optimized tidal flow constructed wetland systems by adding baffles and cultivating plants; we investigated the influence of process optimization on the removal of ARGs and the influence of functional microorganism distribution on nitrogen removal. The results show that the addition of baffles and plants can effectively improve the removal efficiency of ARGs, with the maximum removal rate of 21 resistance genes, in 7 categories, reaching 83.82%-100.0% with the simultaneous addition of baffles and plants. These removal rates were significantly higher than the increase resulting from a single baffle or plant group. From the comparison of the absolute abundance of ARGs in the substrate and plants, it is clear that the baffles can promote the enrichment of ARGs in the wetland substrate, while uptake by plants is also a way of removing ARGs. Combined with the results of nitrogen-cycle functional gene sequencing, system optimization can increase the diversity and richness of nitrification and denitrification functional microorganisms in the substrate, which is consistent with the higher removal rate of nitrification and total nitrogen in wastewater.

Evaluating the interaction of soil microorganisms and gut of soil fauna on the fate and spread of antibiotic resistance genes in digested sludge-amended soil ecosystem

Earthworms have shown their effectiveness in reducing the abundances of antibiotic resistance genes (ARGs) from solid waste. However, the mechanisms of the reduced ARGs by earthworm and whether the solid waste would affect the ARGs profile in earthworm gut were poorly understood. Herein, the patterns of ARGs and microbial communities in digested sludge-amended soil and earthworm gut after 80-day cultivation were investigated. Results show that the enrichment of ARGs (e.g., tetA, tetQ, and sulII) in soil caused by digested sludge-amendment was temporary and would recover to their original levels before amendment. In addition, earthworms could contribute to the further reduction of ARG abundances, which was mainly attributed to their gut digestion via shifting the microbial community (e.g., attenuating the anaerobes). However, the amended soil could significantly increase ARGs abundance in the earthworm gut, which may enhance the potential risk of ARGs spread via the food chain. These findings may provide a new sight on the control of ARGs occurrence and dissemination in sludge-amended soil ecosystem with consideration of earthworms.

Profiling the antibiotic resistome in soils between pristine and human-affected sites on the Tibetan Plateau

With increasing pressure from anthropogenic activity in pristine environments, the comprehensive profiling of antibiotic resistance genes (ARGs) is essential to evaluate the potential risks from human-induced antibiotic resistance in these under-studied places. Here, we characterized the microbial resistome in relatively pristine soil samples collected from four distinct habitats on the Tibetan Plateau, using a Smart chip based high-throughput qPCR approach. We compared these to soils from the same habitats that had been subjected to various anthropogenic activities, including residential sewage discharge, animal farming, atmospheric deposition, and tourism activity. Compared to pristine samples, an average of 23.7% more ARGs were detected in the human-affected soils, and the ARGs enriched in these soils mainly encoded resistances to aminoglycoside and beta-lactam. Of the four habitats studied, soils subjected to animal farming showed the highest risks of ARG enrichment and dissemination. As shown, the number of ARGs enriched (a total of 42), their fold changes (17.6 fold on average), and the co-occurrence complexity between ARGs and mobile genetic elements were all the highest in fecal-polluted soils. As well as antibiotics themselves, heavy metals also influenced ARG distributional patterns in Tibetan environments. However, compared to urban areas, the Tibetan Plateau had a low potential for ARG selection and exhibited low carriage of ARGs by mobile genetic elements, even in environments impacted by humans, suggesting that these ARGs have a limited capacity to disseminate. The present study examined the effects of multiple anthropogenic activities on the soil resistomes in relatively pristine environments.

Microbial responses underlying the denitrification kinetic shifting exposed to ng/L- and μg/L-level lomefloxacin in groundwater

The emerging co-contaminant of antibiotics and nitrate has acquired great concerns worldwide, which poses a potential impact on denitrification in the ecological environment, but little is known about the groundwater system at lower antibiotic concentration, especially ng/L-level. Herein the frequently detected Lomefloxacin (LOM) in groundwater was selected to explore its influences on denitrification kinetics and microbial dynamic responses. The NO3−-N removals in ng/L–μg/L LOM-amended reactors (8.7–44.9%) performed far lower than that in control (76.1%). LOM can inhibit denitrification even at ng/L-level. The kinetic characteristic shifted from zero- to first-order once inhibition occurred. This observation is the synergistic effects of microbial community, enzyme activity, and antibiotic resistance genes (ARGs). The enzyme activities were inhibited immediately, whereas microbial community and ARGs exhibited hysteresis responses at ng/L-level. The enrichment of non-corresponding ARG types suggested LOM's co-selection effects. Brevundimonas were potential antibiotic resistant bacteria. Exposed to μg/L-level LOM, denitrification underwent a 6-d lag phase. The more sensitive enzyme activities and microbial community and the enrichment of ARGs with less abundance were investigated. These findings clarify the microbial response mechanism underlying the denitrification kinetic shifting exposed to low-concentrations of LOM, which is the potential process for heightening nitrate accumulation in groundwater.

Soil type shapes the antibiotic resistome profiles of long-term manured soil

Animal manure fertilization facilitates the proliferation and dissemination of antibiotic resistance genes (ARGs) in soil, posing high risks to humans and ecosystem health. Although studies suggest that soil types could shape the ARG profiles in greenhouse soil, there is still a lack of comparative studies on the fate of ARGs in different types of manured soils under field trials. Thus, a metagenomic approach was used to decipher the fate of ARGs in 12-year long-term fertilized (inorganic fertilizer, compost manure and a mix of them) acidic, near-neutral and alkaline soils. A total of 408 unique ARG subtypes with multidrug, glycopeptide, beta-lactam and aminoglycoside resistance genes were identified as the most universal ARG types in all soil samples. Genes conferred to beta-lactam was the predominant ARG type in all the manure-amended soils. Genomic and statistical analyses showed that manure application caused the enrichment of 98 and 91 ARG subtypes in acidic and near-neutral soils, respectively, and 8 ARG subtypes in alkaline soil. The abundances of Proteobacteria (acidic and near-neutral soils) and Actinobacteria (alkaline soil), which are the potential hosts of ARGs, were clearly increased in manured soils. Random forest modelling and Pearson correlation analysis revealed that the soil properties (pH and bio-available Zn) and mobile genetic elements had considerable impacts on the transmission of ARGs. A structural equation model further indicated that soil types shaped the ARG profiles by significantly (P < 0.01) influencing the soil properties, bacterial abundance and bacterial diversity, where bacterial abundance was the major factor influencing the ARG profiles. This study systematically explored the mechanisms shaping the ARG profiles of long-term manured soils, and this information could support strategies to manage the dissemination of ARGs in different soil types.

Improved reduction of antibiotic resistance genes and mobile genetic elements from biowastes in dry anaerobic co-digestion

This study investigated the performance of anaerobic co-digestion (AcoD) of pig manure and food waste on the reduction of antibiotic resistomes under wet and dry AcoD conditions. High-throughput quantitative PCR technology was utilized for a comprehensive assessment of the performances of the two processes. The results show that dry AcoD with a total solids (TS) content of 20% effectively reduced total antibiotic resistance genes (ARGs) by 1.24 log copies/g wet sample, while only 0.54 log copies/g wet sample was reduced in wet AcoD with a TS content of 5%. Dry AcoD was more efficient in reduction of aminoglycosides, multidrug and sulfonamide resistance genes compared with the reduction of other classes of ARGs. Dry AcoD caused a significant reduction of ARGs with resistance mechanisms of efflux pump and antibiotic deactivation. In contrast, there was no obvious difference in reductions of ARGs with different resistance mechanisms in wet AcoD. Network analysis showed that ARGs were significantly correlated with mobile genetic elements (MGEs) (Spearman’s r > 0.8, P < 0.05), as well as microbial communities. Enrichment of ARGs and MGEs was found at the early period of AcoD processes, indicating some ARGs and MGEs increased during the hydrolysis and acidogenesis stages. But after a long retention time, their abundances were effectively reduced by dry AcoD in the subsequent stages.

Enrichment of antibiotic resistance genes (ARGs) in polyaromatic hydrocarbon-contaminated soils: a major challenge for environmental health.

Polyaromatic hydrocarbons (PAHs) are widely spread ecological contaminants. Antibiotic resistance genes (ARGs) are present with mobile genetic elements (MGE) in the bacteria. There are molecular evidences that PAHs may induce the development of ARGs in contaminated soils. Also, the abundance of ARGs related to tetracycline, sulfonamides, aminoglycosides, ampicillin, and fluoroquinolones is high in PAH-contaminated environments. Genes encoding the efflux pump are located in the MGE and, along with class 1 integrons, have a significant role as a connecting link between PAH contamination and enrichment of ARGs. The horizontal gene transfer mechanisms further make this interaction more dynamic. Therefore, necessary steps to control ARGs into the environment and risk management plan of PAHs should be enforced. In this review, influence of PAH on evolution of ARGs in the contaminated soil, and its spread in the environment, has been described. The co-occurrence of antibiotic resistance and PAH degradation abilities in bacterial isolates has raised the concerns. Also, presence of ARGs in the microbiome of PAH-contaminated soil has been discussed as environmental hotspots for ARG spread. In addition to this, the possible links of molecular interactions between ARGs and PAHs, and their effect on environmental health has been explored.

Enrichment of antibiotic resistance genes after sheep manure aerobic heap composting

In this study, physio-chemical properties, 45 antibiotics, 6 heavy metals, 42 antibiotic resistance genes (ARGs), 3 mobile genetic elements, and the bacterial community structure were investigated to analyze the fate of ARGs during sheep manure aerobic heap composting. Results showed that sheep manure heap composting could produce mature compost. The degradation processes reduced the total antibiotics content by 85%. The abundance of ARGs and mobile genetic elements (MGEs) were enriched 9-fold, with the major increases to sul and tet genes (sulI, sulII, tetQ, and tetX). Tetracycline and sulfonamide resistance genes were the most abundant ARGs after composting (more than 88% of all genes). The genes tetA, tetX and sulI were related to the most diverse bacteria that were most able to proliferate during heap composting. Therefore, sulI and tetX are the major ARGs to be controlled, and Actinobacteria and Bacteroidetes may be the major host bacteria.

Amazon deforestation enriches antibiotic resistance genes

The expansion of livestock production and agriculture is responsible for the increase of deforestation rates in the Amazon rainforest, with consequences to climate and micro and macro biodiversity. Although many studies have evaluated the effects of deforestation on the microbiome, its effect on the soil resistome remains unknown. Considering that antibiotic resistance genes (ARGs) are a threat to global health and food security, here we evaluated how land-use change in the Amazon region impacts the soil resistome. Our analysis revealed that several antibiotic resistance mechanisms and genes are common to both the native forest and the altered areas; however, deforestation and subsequent conversion to other land-use systems increased the diversity and abundance of these genes. The enrichment of ARGs is correlated to increased microbial diversity in response to deforestation, along with changes in soil chemical properties, such as pH and aluminum. Our findings demonstrated that Amazon deforestation enriched ARGs in soil and how anthropogenic disturbances may exert selective pressure on the microbial communities expanding the soil resistome. Further investigation is still needed to understand if the ARGs can be transferred via the food chains (e.g. agricultural soils) to humans, jeopardizing antibiotic treatment effectiveness and compromising public health.

Microplastics act as vectors for antibiotic resistance genes in landfill leachate: The enhanced roles of the long-term aging process.

Microplastics (MPs) are found to be ubiquitous and serve as vectors for other contaminants, and the inevitable aging process changes MP properties and fates. However, whether the MPs in aging process affects the fates of antibiotic resistance gene (ARGs) in aquatic environments is poorly understood. Herein, the physicochemical property alteration of MPs being aged in landfill leachate, an important reservoir of MPs and ARGs, was investigated, and microbial community evolution and ARGs occurrence of MP surface during the aging process were analyzed. Aging process remarkably altered surface properties, including increasing specific surface areas, causing the formation of oxygen-containing groups, and changing surface morphology, which further increased the probability of microbial colonization. The bacterial assemblage on MPs showed higher biofilm-forming and pathogenic potential compared to leachate. ARGs quantification results suggested that MPs exhibited selective enrichment for ARGs in a ratio of 5.7-103 folds, and the aging process enhanced the enrichment potential. Further co-occurrence networks suggested that the existence of non-random, closer and more stable ARGs-bacterial taxa relations on MP surface affected the ARG transmission. The study of ARG partitioning on MPs indicated that extracellular DNA was a nonnegligible reservoir of ARGs attached on MP surface, and that biofilm bacterial community influenced ARGs partitioning pattern during the aging process. This study confirmed that the aging process could enhance the potential of MPs as vectors for ARGs, which would promote the holistic understanding of MP behavior and risk in natural environments.

Simultaneous reduction of antibiotics and antibiotic resistance genes in pig manure using a composting process with a novel microbial agent

In recent years, in order to promote animal growth and reduce the risk of disease, a variety of antibiotics are frequently added to the animal feed of livestock and poultry. However, these antibiotics can not be fully digested by animals and most of them are excreted with feces, consequently causing the enrichment of antibiotic resistance genes (ARGs) and huge environmental risks. Nowadays, composting is a better option to solve these problems. Accordingly, this study explored the effects of co-composting swine manure with different inoculants dominated by Phanerochaete chrysosporium (p), Aspergillus niger (a), and Bacillus licheniformis (b) on the simultaneous removal of multiple antibiotics and resistance genes and evolution of the bacterial community. The results showed that the highest removal extent of tetracycline and oxytetracycline occurred in pile D (p:b:a=1:5:5, biomass) reaching 89.2% and 87.8%, respectively, while the highest removal extent of doxycycline and enrofloxacin occurred in pile A (p:b:a=1:0:0, biomass) reaching 98.6% and 89%, respectively. Compared with the levels in pile B (control check), in pile D, ARGs, except those for sulfonamides, decreased by 1.059 × 10−3–6.68 × 10−2 gene copies/16S rRNA copies. Inoculation with p alone effectively reduced intI1 and intI2. Canonical correspondence analysis (CCA) that microbial community structure evolution had a greater influence on ARGs than environmental factors. In summary, this study provided a feasible way to efficiently remove the antibiotics and antibiotic resistance genes in pig manure.

Cyanobacterial blooms contribute to the diversity of antibiotic-resistance genes in aquatic ecosystems

Cyanobacterial blooms are a global ecological problem that directly threatens human health and crop safety. Cyanobacteria have toxic effects on aquatic microorganisms, which could drive the selection for resistance genes. The effect of cyanobacterial blooms on the dispersal and abundance of antibiotic-resistance genes (ARGs) of concern to human health remains poorly known. We herein investigated the effect of cyanobacterial blooms on ARG composition in Lake Taihu, China. The numbers and relative abundances of total ARGs increased obviously during a Planktothrix bloom. More pathogenic microorganisms were present during this bloom than during a Planktothrix bloom or during the non-bloom period. Microcosmic experiments using additional aquatic ecosystems (an urban river and Lake West) found that a coculture of Microcystis aeruginosa and Planktothrix agardhii increased the richness of the bacterial community, because its phycosphere provided a richer microniche for bacterial colonization and growth. Antibiotic-resistance bacteria were naturally in a rich position, successfully increasing the momentum for the emergence and spread of ARGs. These results demonstrate that cyanobacterial blooms are a crucial driver of ARG diffusion and enrichment in freshwater, thus providing a reference for the ecology and evolution of ARGs and ARBs and for better assessing and managing water quality.

Long-term biogas slurry application increased antibiotics accumulation and antibiotic resistance genes (ARGs) spread in agricultural soils with different properties

Animal manures are commonly applied to soil which possibly promote the spread of antibiotic resistance from soil to human beings via food chains. Biogas slurry is an end product of anaerobic digestion of animal manures, which has been widely applied as fertilizers in the agricultural soil. However, effect of long-term biogas slurry application on the soil antibiotic resistance and the associated mechanism still remains unclear. The present study characterized antibiotics, antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and bacterial community, in different agricultural soils unamended (BS-) and amended (BS+) with biogas slurry (8–18 years) in five field experiments. Our results indicated that long-term application of biogas slurry largely increased the concentrations of tetracyclines in soils, and greatly increased the abundances of ARGs, transposase gene (Tn916/1545) and ARGs-associated bacteria. Long-term application of biogas slurry led to tetracyclines accumulation and ARGs enrichment in agricultural soil, and the selection pressure from tetracyclines and the increase of Tn916/1545 abundace become potential contributors for the increase of soil antibiotic resistance via promoting the enrichment of ARG-associated bacteria. The results of the present study should be taken into consideration to develop policy and practice for mitigating the enrichment and spread of antibiotic resistance during the recycling of biogas slurry into agricultural soil.

Changes and distributions of antibiotic resistance genes in liquid and solid fractions in mesophilic and thermophilic anaerobic digestion of dairy manure

This study mainly explored the changes and distributions of antibiotic resistance genes (ARGs) in liquid fraction (LF) and solid fraction (SF) in anaerobic digestion (AD) of dairy manure. After mesophilic and thermophilic AD, the copy numbers of ARGs in LF decreased by 0.06–1.80 logs while those in SF increased by 0.08–7.85 logs, suggesting the enrichment of ARGs in SF. Statistical analysis elucidated that high total solids promoted the enrichment of ARGs in SF. The increased abundances of genera such as Ruminofilibacter, Treponema and Sphaerochaeta in SF were responsible for the enrichment of most ARGs. These insights demonstrated the digested solid had the potential risks to promote the spread of ARGs in the environment, and the digested solid of livestock manure should be post-treated before the application.

Effect of ultrasonic and ozone pretreatment on the fate of enteric indicator bacteria and antibiotic resistance genes, and anaerobic digestion of dairy wastewater

In this study, the effect of ultrasound (US), ozone and US combined with ozone (US/ozone) pretreatments on the fate of enteric indicator bacteria and antibiotic resistance genes (ARGs), and anaerobic digestion (AD) of dairy wastewater was investigated. The pretreatment conditions included US power 200 W, ozone concentration 4.2 mg O3/L, and pretreatment time 0–30 min. The results showed that US/ozone pretreatment was effective in the inactivation of enteric indicator bacteria. Total coliforms and enterococci were reduced by 99% and 92% after 30 min US/ozone pretreatment. Pretreatments could not decrease ARGs in absolute concentration, but could decrease ARGs in relative abundance. In the subsequent AD process, methane production increased more than 10% with 20 min ozone or 20 min US/ozone pretreatments. Pretreatment-AD together obviously inhibited the enrichment of ARGs in relative abundance. This study provided a pretreatment way to enhance methane production and to prevent the enrichment of ARGs.