Dynamics of oxytetracycline, sulfamerazine, and ciprofloxacin and related antibiotic resistance genes during swine manure composting

The fate of antibiotic resistance genes in cow manure composting: shaped by temperature-controlled composting stages

Current work for animal manure processing is not up to the required standards and hence are not supposed to reflect the actual performance in antibiotic resistance control. As a result, this study carried out temperature-controlled aerobic composting, with sulfamethoxazole (SMX) as a typical antibiotic. The results of four different treatments demonstrated that temperature, water content, C/N ratio, EC, and pH showed no significant (p > 0.05) difference. Antibiotic resistance genes (ARGs) significantly decreased in the initial 10 days of the thermophilic phase, but the abundance of sul1 and sul2 increased greatly after 30 days. Moreover, ARGs were closely related with each other during the late stages of composting. A noteworthy effect of composting properties, especially temperature on bacterial community, which then had a positive effect on ARGs abundances. These findings provided evidence that the standard composting was still insufficient to control antibiotic resistance.

Adsorption, desorption and coadsorption behaviors of sulfamerazine, Pb(II) and benzoic acid on carbon nanotubes and nano-silica

In this study, nano-silica (Nano-SiO₂), oxidized (O-CNTs) and graphitized multi-walled carbon nanotubes (G-CNTs) were applied as model adsorbents to study the adsorption, desorption and coadsorption behaviors of sulfamerazine (SMR), Pb(II) and benzoic acid (BA). The results showed that charge assisted H-bond (CAHB) formation played an important role in adsorption of SMR and BA on O-riched nanomaterials. The adsorption capacities of Pb(II) on CNTs were 21.46- 26.77 times higher than that on Nano-SiO₂, which was mainly attributed to surface complexation and cation-π interaction. The fraction of Pb²⁺ adsorbed in the inside channel of CNTs should not be ignored. In coexisting systems, the absolute sorption inhibition of the SMR (ΔQ_e^SMR) was compared with the amount of competitor adsorbed. Competitive sorption was observed as indicated by adding Pb(II) decreased adsorption of SMR on Nano-SiO₂ (ΔQ_e^SMR > 0), but hardly affected SMR adsorption on CNTs (ΔQ_e^SMR ≈ 0) which was attributed to cation-π interaction. In addition, CAHB formed between SMR and Nano-SiO₂ (ΔpK_a ≈ 4.34) was weaker than that formed between SMR and O-CNTs (ΔpK_a ≈ 3.15), which also consequently resulted in stronger competition of Pb(II) to SMR on Nano-SiO₂ than that on O-CNTs. Moreover, coexisting BA increased adsorption of SMR on Nano-SiO₂ and G-CNTs (ΔQ_e^SMR < 0), but did not result in an apparent competition on SMR adsorption by O-CNTs (ΔQ_e^SMR ≈ 0). These results emphasize that the environmental behaviors of a certain pollutant should be assessed carefully by considering the presence of other pollutants.

Enhanced Sulfamerazine Removal via Adsorption–Photocatalysis Using Bi2O3–TiO2/PAC Ternary Nanoparticles

The presence of sulfonamides (SAs) in water has received increasing attention due to the risk to ecosystems. The adsorption and photocatalysis performance for sulfamerazine (SMZ) of Bi2O3–TiO2 supported on powdered activated carbon (Bi2O3–TiO2/PAC) nanoparticles was evaluated. The amount of doped Bi2O3 not only influenced the photocatalytic performance but also impacted the adsorption capacity. The adsorption mass transfer mechanism of Bi2O3–TiO2/PAC was elucidated and is further discussed in combination with the photocatalytic mechanism. It was indicated that Bi2O3–TiO2/PAC(10%–700 °C) performed best, and the SMZ removal by the adsorption–photocatalysis of Bi2O3–TiO2/PAC(10%–700 °C) reached 95.5%. Adsorption onto active sites was a major adsorption step, and external diffusion was assisted. Superoxide radical (●O2−) and hole (h+) were identified as the major reactive oxygen species (ROS) for SMZ removal. Benzene ring fracture, SO2 extrusion and nitrogenated SMZ were proposed as the main pathways for photocatalysis. Meanwhile, alkaline conditions enhanced photocatalytic performance, while contrary effects were observed for adsorption. The adsorption–photocatalysis removal performance for SMZ in lake water was better than that for river water. It can be generalized for the potential application of photocatalysis coupling with adsorption to remove refractory antibiotics in water.

Potential of industrial composting and anaerobic digestion for the removal of antibiotics, antibiotic resistance genes and heavy metals from chicken manure

Composting and anaerobic digestion techniques are widely used for manure recycling, but these methods have shown conflicting results in the removal of antibiotics, antibiotic resistance genes (ARGs), and heavy metals. In the present study, anaerobically digested chicken manure and various types of composted chicken manure were investigated on an industrial scale. Antibiotics, ARGs, and heavy metals had shown inconsistent results for anaerobic digestion and composting. The different composting processes either declined or completely removed the blaCTX-M, intl1 and oqxB genes. In addition, composting processes decreased the absolute abundance of aac6'-Ib and aadA genes, while increased the absolute abundance of qnrD, sul1, and tet(A) genes. On the other hand, anaerobic digestion of chicken manure increased the absolute abundance of ere(A) and tet(A). High throughput sequencing showed that Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria dominated the total bacterial composition of composted and anaerobically digested samples. Network analysis revealed the co-occurrence of ARGs and intl1. The redundancy analysis showed a significant correlation between some heavy metals and ARGs. Similarly, the bacterial composition showed a positive correlation with the prevalence of ARGs in treated manure. These findings suggest that bacterial community, heavy metals, and mobile genetic elements can play a significant role in the abundance and variation of ARGs during composting and anaerobic digestion. In conclusion, anaerobic digestion and composting methods at industrial scale need to be improved for the effective removal of antibiotics, ARGs and heavy metals from chicken manure.

Changes in microbial community structure during pig manure composting and its relationship to the fate of antibiotics and antibiotic resistance genes

Animal manure containing veterinary antibiotics is a significant source of microbial antibiotic resistance genes (ARGs). Composting of animal manure with wheat straw and sawdust was explored as a means to reduce ARGs load in the final material. The effects of ciprofloxacin, oxytetracycline, sulfamerazine on the bacterial community composition, and how this then affected the removal of seven tetracycline resistance genes (TARGs), four sulfonamide resistance genes (SARGs), and two fluoroquinolone resistance genes (QARGs) were investigated. Treatments receiving either ciprofloxacin or the three mixed antibiotics had reduced bacterial alpha-diversity and displayed shifts in the abundance of Proteobacteria and Firmicutes. This demonstrated that different antibiotics played an important role in bacterial community composition. Furthermore, variation in the physicochemical properties of compost, particularly pH and temperature, was also strongly linked to shifts in bacterial composition over time. Based on network analysis, the reduction of TARGs were associated with loss of Pseudomonas, Pseudoxanthomonas, Pusillimonas, Aquamicrobium, Ureibacillus, Lysinibacillus, Bacillus and Brachybacterium during the thermophilic stage. However, QARGs and SARGs were more strongly affected by the presence of multiple antibiotics. Our results have important implications for reducing the spread of certain ARGs by controlling the composting temperature, pH or the antibiotics species used in husbandry.

Long-term alkaline conditions inhibit the relative abundances of tetracycline resistance genes in saline 4-chlorophenol wastewater treatment

Considering the occurrence and spread of antibiotic resistance genes (ARGs) pose significant risks to public health, the effects of long-term exposure to alkaline conditions on the relative abundances of tetracycline resistance genes (TRGs) were studied in saline 4-chlorophenol (4-CP) wastewater treatment. Alkaline conditions were maintained by supplying the co-metabolic carbon source of sodium acetate. Results showed that except for the 4-CP, the removal of pollutants was significantly inhibited, and the relative abundances of the most TRGs were repressed. In addition, the removal of pollutants and the relative abundances of TRGs were moderately affected by the NaCl addition. The proteins in the extracellular polymeric substances (EPS) played key roles in reducing the relative abundances of TRGs, which were altered by the microbial diversity. In conclusion, for the pollutants removal and ARGs reduction in refractory industrial wastewater treatment, alkaline conditions should be maintained by selecting suitable co-metabolic carbon sources.

Effects of multiple antibiotics on greenhouse gas and ammonia emissions during swine manure composting

Antibiotics are commonly used in intensive farming, leading to multiple antibiotic residue in livestock waste. However, the effects of multiple antibiotics on the emissions of greenhouse gas and ammonia remain indistinct. This paper selects sulfamethoxazole and norfloxacin to represent two different types of antibiotics to explore their effects on gaseous emissions. Four treatments including CK (control), SMZ (spiked with 5 mg kg^-1 DW sulfamethoxazole), NOR (spiked with 5 mg kg^-1 DW norfloxacin), and SN (spiked with 5 mg kg^-1 DW sulfamethoxazole and 5 mg kg^-1 DW norfloxacin) were composted for 65 days. Coexistence of sulfamethoxazole and norfloxacin facilitated the biodegradation of organic carbon, and significantly (p < 0.05) increased the cumulative CO₂ emission by 31.9%. The cumulative CH₄ emissions were decreased by 6.19%, 23.7%, and 27.6% for SMZ, NOR, and SN, respectively. The total NH₃ volatilization in SMZ and NOR rose to 1020 and 1190 mg kg^-1 DW, respectively. The individual existence of sulfamethoxazole significantly (p < 0.05) ascended the N₂O emission rate in the first 7 days due to the increase of NO₂^--N content. In addition, coexistence of sulfamethoxazole and norfloxacin notably dropped the total greenhouse gas emission (subtracting CO₂) by 15.5%.

Insight into the effects of sulfamethoxazole and norfloxacin on nitrogen transformation functional genes during swine manure composting

The effects of sulfamethoxazole and norfloxacin on nitrogen functional genes were investigated in four composting treatments of swine manure: CK (no antibiotics), SMZ (spiked with 5 mg kg^-1 dry weight (DW) sulfamethoxazole), NOR (spiked with 5 mg kg^-1DW norfloxacin), and SN (spiked with 5 mg kg^-1DW sulfamethoxazole and 5 mg kg^-1DW norfloxacin). Antibiotics decreased relative abundance of bacterial amoA and nxrA, while increased nosZ/nirK. The decline in amoA/16S rRNA increased the total NH₃ emission in SMZ and NOR from 1027.05 to 1144.39 and 1278.22 mg kg^-1DW. The decrease of nxrA/16S rRNA enhanced the NO₂^--N content and N₂O emission in SMZ in the initial composting. Additionally, the increase in nosZ/nirK probably was the main reason for the lower N₂O emission in SN than other treatments in the cooling phase. The inhibition on nitrification process and increase in NH₃ emission resulted from antibiotics is worthy of attention in the future.

Effects of macroporous adsorption resin on antibiotic resistance genes and the bacterial community during composting

Swine manure is considered a reservoir for antibiotic resistance genes (ARGs), which may enter the soil and then the food chain to endanger human health. This study investigated the effects of adding 0%, 5%, and 15% (w/w) macroporous adsorption resin (MAR) on ARGs and the bacterial community during composting. The results showed that the addition of MAR reduced the abundances of ARGs (14.14-99.44%) and mobile genetic elements (MGEs) (47.83-99.48%) after swine manure composting. Significant positive correlations were detected between ARGs and MGEs, and thus the variations in MGEs may have led to the changes in ARGs. Redundancy analysis showed that MGEs had stronger effects on ARGs than environmental factors and the bacterial community. Network analysis suggested that ARGs and MGEs co-existed in common host bacteria. In conclusion, the results showed that adding 5% MAR can reduce the risk of ARG transmission.

Application of humic acid changes the microbial communities and inhibits the expression of tetracycline resistance genes in 4-chlorophenol wastewater treatment

The occurrence and spread of antibiotic resistance genes (ARGs) are concerns that have threatened public health for many years. However, the effects of humic acid (HA) application on the expression of ARGs in chlorophenols wastewater treatment are rarely reported. In this study, we investigated the sludge performance, including the removal of pollutants, changes in the microbial communities, and the expression of tetracycline resistance genes (TRGs), to explore the function of HA in 4-chlorophenol (4-CP) wastewater treatment at different HA concentrations. The results showed that HA application did not significantly stimulate the removal of pollutants, other than the removal of PO₄^3--P. High-throughput sequencing analysis indicated that the application of HA influenced the microbial communities and changed the expression level of TRGs. Quantitative real-time PCR analysis showed that the expression of numerous TRGs (tetC, tetG, tetW, tetX, and intI1) was significantly inhibited by the application of HA (25 mg L^-1) during 4-CP wastewater treatment. In summary, HA application played an important role in treating chlorophenols wastewater and reducing the expression of TRGs. This work aimed to provide an efficient method of reducing the expression level of ARGs in industrial wastewater treatment, which has inevitable environmental significance.

The correlation between antibiotic resistance gene abundance and microbial community resistance in pig farm wastewater and surrounding rivers

Antimicrobial resistance gene (ARG) abundance and microbial resistance (MR) are often used as important indicators of pollution risk; however, the relationship between ARGs abundance and MR in pig farm wastewater remains unknown. In this study, the raw pig farm wastewater, effluent water, upstream river water, domestic wastewater and downstream river water samples were collected. The concentration of 20 subtypes of ARGs and 2 integrons, minimal inhibit concentration (MIC), and bacterial communities were investigated. In this study, 20 subtypes of ARGs and integrons were detected in all sampling sites. The highest abundance of 17 of the 20 subtypes of ARGs was detected in raw pig farm wastewater, and ermA had the maximum average abundance of 10⁸ copies/mL, with up to 2.41 ± 0.12 × 10⁸ copies/mL. There was no significant correlation between MR to three antibiotics (ciprofloxacin, streptomycin and tetracycline hydrochloride) and the abundance of their corresponding ARGs (P > 0.05), and a large difference was detected between the types of ARGs co-occur bacteria and resistance co-occur bacteria in the 5 sampling sites. And the pig farm wastewater treatment (WWT) could effectively reduce the ARGs and MR to the 3 antibiotics. The results presented here show that there may be no obvious correlation between ARGs and MCR in pig farm wastewater and surrounding rivers, which may be due to various environmental factors, highlighting the urgent need for a comprehensive evaluation of relationship between ARGs abundance and MR.

Exploring the persistence and spreading of antibiotic resistance from manure to biocompost, soils and vegetables

The main avenue in which antibiotic resistance enters soils is through the application of livestock manure. However, whether antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) persist and spread to vegetables with the application of manure and manure products is still unclear. This study assessed seven kinds of cultured ARB, 221 ARGs subtypes and three transposon genes in the vegetable production chain (from manure to biocompost, soils and vegetables). Results showed that at least 80% of ARB, ARGs and transposon genes were removed after aerobic composting. However, aerobic composting did not reduce the diversity of ARGs in pig and chicken manure. A total of 19 ARGs subtypes still persisted during aerobic composting. Compared to the temperature-thermophilic stage, the number of bacteria resistant to erythromycin, the relative abundance of ARGs and IS613 increased 1.7-4.9 times at the temperature-decreasing stage. Direct application of biocompost introduced 11 ARGs subtypes to pakchoi, but these ARGs did not present in biocompost-amended soil. A transposon gene tnpA was also detected in the biocompost-amended soil, but surprisingly was found in the control vegetable. This demonstrated that the transposon gene is intrinsic in pakchoi. Bacterial community analysis and network analysis revealed that a specific genus Terrisporobacter carrying tetO, tetW ermB and tnpA persisted in the vegetable production chain, which may generate a potential risk in the following production. Our study illuminates the persistence and spreading of antibiotic resistance in the vegetable production chain which could help manage the ecological risks arising from antibiotic resistance in manure sources.

High removal efficiency of antibiotic resistance genes in swine wastewater via nanofiltration and reverse osmosis processes

Swine wastewater treatment plant has become one of the main sources of antibiotic resistance genes (ARGs). Membrane treatment processes are promising solutions for removal of the emerging contaminants. However, limited studies have investigated the effects of nanofiltration and reverse osmosis treatment in removing ARGs in swine wastewater. In this study, the presence and the fate of common ARGs including sul1, sul2, tetA, tetM and tetW, as well as intI1 and 16S rRNA gene, were investigated in a medium-sized (6500) pig farm wastewater treatment plant (WWTP) equipped with conventional biological treatment and advanced membrane processing system. All of the genes were detected with highly abundance in the raw sewage. The biological treatments of the swine wastewater treatment plant did not reduce the quantity of the ARGs. As expected, nanofiltration and reverse osmosis treatment reduced the absolute gene copy number of ARGs efficiently (4.98-9.52 logs removal compared to raw sewage). Compared to the reverse osmosis effluent, however, the absolute abundance of ARGs in the artificial wetland increased by 1.00-2.06 logs. Meanwhile, the relative abundance of sulfonamide resistant genes were basically unchanged, while tetracycline resistance genes (tetA, tetM and tetW) decreased by 0.88, 3.47, 2.51 log, respectively. The results demonstrated that advanced membrane treatments are capable of removing various kinds of ARGs efficiently, as well as some common nitrogen and phosphorus contaminants. This study suggested a mature alternative method for the removal of ARGs from livestock wastewater.