Mechanism of self-supporting montmorillonite composite material for bio-enhanced degradation of chlorotetracycline: Electron transfer and microbial response.

The efficient degradation of antibiotics holds significant implications for mitigating environmental pollution. This study synthesized a montmorillonite chitosan composite material (MMT-CS) using the gel template method. Subsequently, a bio-enhanced reactor was constructed to facilitate the degradation of chlorotetracycline (CTC). The addition of MMT-CS composite material enables the degradation of different concentrations of CTC. MMT-CS, a conductive carrier, effectively promotes microbial adhesion and boosts the metabolic activity of functional microorganisms. Additionally, it facilitates the maintenance of microbial activity under CTC pressure by promoting the secretion of extracellular polymeric substances, increasing critical enzyme activity, and enhancing the electron transfer capacity within the system. In this MMT-CS bio-enhanced process, Paracoccus (11.4%) and Bacillus (3.9%) are utilized as essential bacteria genes. The results of metabolic pathways prediction indicated significant enhancements in membrane-transport, nucleotide-metabolism, replication-repair, and lipid-metabolism. Thus, the developed self-supporting MMT-CS bio-enhanced process ensured the stability of the system during the removal of antibiotics.

Effects of oleanolic acid on acute liver injury triggered by lipopolysaccharide in broiler chickens.

1. Infectious injury caused by lipopolysaccharide (LPS), a metabolite of gram-negative bacteria, can induce stress responses in animals and is a significant cause of morbidity and mortality in young birds. The purpose of this study was to investigate the effects of dietary supplementation with oleanolic acid (OA) on acute liver injury in broiler chickens challenged with LPS.2. In total, 120 broiler chickens were randomly divided into six groups and fed a basal diet containing 0, 50, 100, or 200 mg/kg OA or 100 mg/kg aureomycin. On d 15, broiler chickens were injected with either LPS or an equivalent volume of normal saline. Six hours after LPS injection, two broiler chicks were randomly selected for sampling in each replicate.3. The results indicated that dietary aureomycin was ineffective in alleviating LSP-associated liver injury, but protected broiler chickens from LPS-induced liver damage. This promoted a significant reduction in the levels of malondialdehyde and an increase in the levels of superoxide dismutase in liver. In addition, OA was found to cause significant reductions in the relative expression of IL-1ß, IL-6, and TNF-α in broiler liver tissues, whereas the relative expression of IL-10 was significantly increased.4. In conclusion, oleanolic acid can alleviate oxidative stress and injury in the livers of broiler chickens induced by lipopolysaccharide. Consequently, oleanolic acid has potential utility as a novel anti-inflammatory and antioxidant feed additive.

Crystal structure determination of the halogenase CtcP from Streptomyces aureofaciens.

Chlortetracycline (CTC), a derivative of tetracycline (TC), is a broadly used antibiotic that inhibits the synthesis of bacterial proteins by competing with the A-site tRNA on ribosomes. A recent study showed that during the biosynthesis of CTC in Streptomyces aureofaciens, the halogenase CtcP catalyzes the final chlorination reaction and transforms TC into CTC. However, the structure of this fundamental enzyme is still lacking. Here, selenomethionine-derivatized CtcP from S. aureofaciens was overexpressed and purified and its structure was determined at 2.7 Šresolution. The structure of CtcP reveals the conserved monooxygenase domain shared by all flavin-dependent halogenases and a unique C-terminal domain. Although FAD was not observed in the structure, the monooxygenase domain has a conserved FAD-binding pocket and active center. The C-terminal domain displays an α-helical bundle fold, which could contribute to substrate specificity. This work provides a molecular basis for enzyme engineering to improve the industrial production of CTC.

G protein-coupled estrogen receptor promotes acrosome reaction via regulation of Ca2+ signaling in mouse sperm†.

G protein-coupled estrogen receptor (GPER), a seven-transmembrane G protein-coupled receptor, mediates the rapid pre-genomic signaling actions of estrogen and derivatives thereof. The expression of GPER is extensive in mammal male reproductive system. However, the functional role of GPER in mouse sperm has not yet been well recognized. This study revealed that GPER was expressed at the acrosome and the mid-flagellum of the mouse sperm. The endogenous GPER ligand 17ß-estradiol and the selective GPER agonist G1 increased intracellular Ca2+ concentration ([Ca2+]i) in mouse sperm, which could be abolished by G15, an antagonist of GPER. In addition, the G1-stimulated Ca2+ response was attenuated by interference with the phospholipase C (PLC) signaling pathways or by blocking the cation channel of sperm (CatSper). Chlortetracycline staining assay showed that the activation of GPER increased the incidence of acrosome-reacted sperm. Conclusively, GPER was located at the acrosome and mid-flagellum of the mouse sperm. Activation of GPER triggered the elevation of [Ca2+]i through PLC-dependent Ca2+ mobilization and CatSper-mediated Ca2+ influx, which promoted the acrosome reaction of mouse sperm.

Antibiotic Chlortetracycline Causes Transgenerational Immunosuppression via NF-κB.

The extensive and increasing global use of antibiotics results in the ubiquitous presence of antibiotics in the environment, which has made them "pseudo persistent organic contaminants." Despite numerous studies showing wide adverse effects of antibiotics on organisms, the chronic environmental risk of their exposure is unknown, and the molecular and cellular mechanisms of antibiotic toxicity remain unclear. Here, we systematically quantified transgenerational immune disturbances after chronic parental exposure to environmental levels of a common antibiotic, chlortetracycline (CTC), using zebrafish as a model. CTC strongly reduced the antibacterial activities of fish offspring by transgenerational immunosuppression. Both innate and adaptive immunities of the offspring were suppressed, showing significant perturbation of macrophages and neutrophils, expression of immune-related genes, and other immune functions. Moreover, these CTC-induced immune effects were either prevented or alleviated by the supplementation with PDTC, an antagonist of nuclear factor-κB (NF-κB), uncovering a seminal role of NF-κB in CTC immunotoxicity. Our results provide the evidence in fish that CTC at environmentally relevant concentrations can be transmitted over multiple generations and weaken the immune defense of offspring, raising concerns on the population hazards and ecological risk of antibiotics in the natural environment.

Persistence and fate of chlortetracycline in the aquatic environment under sub-tropical conditions: generation and dissipation of metabolites.

The persistence of chlortetracycline in the aquatic environment, including the generation and dissipation of its metabolites, were investigated over a period of 90 days using microcosm experiments, with a view to establishing the metabolites generated and their persistence under conditions closely resembling the actual aquatic environment in terms of chemical and microbial composition. The concentrations of chlortetracycline and its metabolites were monitored in the water phase as well as the sediment phase. Data are presented showing that the degradation of chlortetracycline in each phase conforms to a triphasic linear rate law, confirming the existence of three speciation forms in each phase, attributed to one free dissolved form, and two colloidal particle adsorbed forms. Data are also presented showing that the two adsorbed forms are the most persistent, with life-times of 204.1 and 20.3 days respectively in the water phase, and 215.1 and 19.8 days respectively in the sediment phase. Life-times of 5.01 and 3.7 days respectively were obtained for the free dissolved forms in the water phase and sediment phase respectively. Data are further presented showing that of the several metabolites of chlortetracycline reported previously, only 4-epi-chlortetracycline and iso-chlortetracycline could be detected, and that these two degradation products undergo microbial mineralization without transformation to other intermediate degradation products in significant or detectable amounts.

Effects of lime amendment on the organic substances changes, antibiotics removal, and heavy metals speciation transformation during swine manure composting.

Aerobic composting has been used for a long time for bioconversion of manure wastes, however, its application has been limited due to slow transition of organic matters and influence of heavy metals and antibiotics residues. Compost with lime addition can speed up the composting process, while its effects on the evolution of organic matters, heavy metals and antibiotics need to be further investigated. In this research, the effects of lime amendment on organic substances changes was assessed by the spectroscopic characteristics. Besides, chlortetracycline (CTC) removal and Cu, Zn chemical speciation transformation were also evaluated. Results showed that the humic acid-like substances region of fluorescence regional integration (FRI-EEM) increased from 20.5% to 40.9% and 20.6%-32.6%, respectively, in lime addition treatment and control after 15 days of composting, indicating that the addition of lime remarkably improved the transition of organic matter and accelerated the maturity process. Besides, 94.04% of CTC in the manure was removed when lime was added, higher than 86.10% in the control group. The transformation of zinc from exchangeable and reducible into oxidizable and residual fractions was improved while the transformation of copper was affected slightly. Therefore, lime is a suitable amendment material for manure composting, which can accelerate the transition of organic matters due to the regulation of composting pH, as well as eliminate harmful CTC and bioavailable heavy metal, thus promoting the further utilizing of organic substance.

Research on the Impact and Mechanism for the Inhibition of Micrococcus Catalase Activity by Typical Tetracyclines.

As potential inhibitors target to biological enzymes, antibiotics may have certain impacts on the biochemical treatment process. With micrococcus catalase (CAT) served as the target molecule, the impact and inhibition mechanism for typical tetracyclines (TCs) were evaluated. Toxicity experiments showed that TCs had significant inhibition on CAT in the sequence of tetracycline>chlortetracycline>oxytetracycline>doxycycline. To clarify the inhibition mechanism between TCs and CAT which was explored with the assistance of fluorescence spectroscopy and MOE molecule simulation. According to fluorescence analysis, TCs quenched the fluorescence signal of CAT by the mode of static quenching. Combined with toxicity data, it could be presumed that TCs combined with the catalytic active center and thus inhibited CAT. Above presumption was further verified by the molecular simulation data. When TCs combined with the catalytic center of CAT, the compounds have increased combination areas and prominent energy change (compared with the compounds formed by TCs and noncatalytic center recommend by MOE software). IBM SPSS statistics showed that TC toxicity positively correlated with the hydrogen bonds such as O13→Glu252, O1←Arg195, and O6→Asp249, but negatively correlated with the hydrogen bonds such as O10→Pro363, O10→Lys455, and O12 â†’ Asn127. TC toxicity also positively correlated with the ion bonds ofN4-Glu252, but negatively correlated with the ion bonds of N4-Asp379. Hydrogen bonds and ion bonds for above key sites were closely related to the inhibition effect of TCs on CAT.

The enhanced degradation and detoxification of chlortetracycline by Chlamydomonas reinhardtii.

Nowadays, numerous studies have focused on the newly developed technologies for the thorough removal of tetracyclines (TCs). However, it is often ignored that the parent TCs have limited stability in aquatic environments. Thus, this study selected green alga Chlamydomonas reinhardtii with high chlorophyll content to rapidly degrade chlortetracycline (CTC) into products with low toxicity. As the results shown, the half-life times of CTC (1 × 10-6 mol/L) decreased from 10.35 h to 2.55 h by the presence of C. reinhardtii at 24±1 °C with 12/12 h dark/light cycle. The main transformation products were iso-chlortetracycline (ICTC), 4-epi-iso-chlortetracycline (EICTC), and other degradation products with lower molecular weight. The toxicity evaluation shows that the negative effects of CTC on growth rate and soluble protein content of green algae were significantly alleviated after the enhanced degradation treatment, while the generation of reactive oxygen species (ROS) and antioxidant response in algal cells returned to normal levels. The chlorophyll of algae played an important role of photosensitizer, which catalyzed the photo-induced electron/energy transfer of CTC degradation. The ROS generation of algae also was also inseparable from the enhanced degradation of CTC, especially when the chlorophyll was damaged at the high CTC concentration. Based on these results, we can better select suitable algal species to further strengthen the degradation of antibiotics and effectively reduce the environmental risk of CTC in aqueous system.

Anaerobic digestion of livestock and poultry manures spiked with tetracycline antibiotics.

We investigated the anaerobic degradation of tetracycline antibiotics (tetracycline [TC], oxytetracycline [OTC] and chlortetracycline [CTC]) in swine, cattle, and poultry manures. The manures were anaerobically digested inside polyvinyl chloride batch reactors for 64 days at room temperature. The degradation rate constants and half-lives of the parent tetracyclines were determined following first-order kinetics. For CTC the fastest degradation rate was observed in swine manure (k = 0.016 ± 0.001 d-1; half-life = 42.8 days), while the slowest degradation rate was observed in poultry litter (k = 0.0043 ± 0.001 d-1; half-life = 161 days). The half-lives of OTC ranged between 88.9 (cattle manure) and 99.0 days (poultry litter), while TC persisted the longest of the tetracycline antibiotics studied with half-lives ranging from 92.4 days (cattle manure) to 330 days (swine manure). In general, the tetracyclines were found to degrade faster in cattle manure, which had the lowest concentrations of organic matter and metals as compared to swine and poultry manures. Our results demonstrate that tetracycline antibiotics persist in the animal manure after anaerobic digestion, which can potentially lead to emergence and persistence of antibiotic resistant bacteria in the environment when anaerobic digestion byproducts are land applied for crop production.

Azoxystrobin dissipation and its effect on soil microbial community structure and function in the presence of chlorothalonil, chlortetracycline and ciprofloxacin.

The residual characteristics and the adsorption-desorption behaviors of azoxystrobin (AZO) as well as the soil ecological effects in the individual repeated treatments of AZO and its combination with chlorothalonil (CTL), chlortetracycline (CTC) and ciprofloxacin (CIP) were systematically studied in organic manure (OM)-amended soil under laboratory conditions. The presence of CTL, CTC, and CIP, both individually and combined, decreased the sorption affinity of AZO with the Freundlich adsorption and desorption coefficient decreasing by 0.3-24.2%, and CTC and CIP exhibited greater adverse effects than CTL. AZO dissipated slowly and the residues significantly accumulated during ten repeated treatments. The dissipation of AZO was inhibited to different degrees in the combined treatments. Biolog analysis revealed that the soil microbial functional diversity in the OM-soil + AZO and OM-soil + AZO + CTL treatments was higher than that in the OM-soil treatment during the former three repeated treatments, but which was inhibited during the latter seven repeated treatments. The soil microbial functional diversity in the OM-soil + AZO + CTC, OM-soil + AZO + CIP and OM-soil + AZO + CTL + CTC + CIP treatments was inhibited during the ten repeated treatments compared with OM-soil treatment. Metagenomic results showed that all repeated treatments significantly increased the relative abundance of Actinobacteria, but significantly decreased that of Proteobacteria and Firmicutes during the ten repeated treatments. Furthermore, the relative abundance of soil dominant bacterial genera Rhodococcus, Mycobacterium and Arthrobacter in all the repeated treatments significantly increased by 1.5-1283.9% compared with the OM-soil treatment. It is concluded that coexistence of CTL, CTC and CIP, both individually and combined, with AZO can inhibit the dissipation of AZO, reduce the adsorption affinity of AZO on soil, and alter the soil microbial community structure and functional diversity.

Abiotic transformation products of tetracycline and chlortetracycline in salt solutions and manure.

Tetracyclines belong to the group of the most applied antibiotics in veterinary medicine worldwide. Due to their incomplete absorption and/or metabolism in the animal gut, tetracyclines are frequently detected in manure samples. Within the matrix, an elimination of these compounds has been reported in several studies. However, only little information about potential transformation products of tetracyclines in manure and the environment is available. Therefore, the fate of tetracycline (TC) and chlortetracycline (CTC) was investigated in aqueous solutions and manure. Abiotic incubation of TC in phosphate buffer led to a remarkable red-brown coloring of the solution. Subsequent compound isolation and structure elucidation by MS/MS and NMR techniques revealed the formation of seco-cycline A, a compound formerly described as a fungal biotransformation product of TC. For CTC, two comparable products were identified which were derived from its isomeric form isoCTC. All transformation products showed no antimicrobial activity for concentrations up to 500 mg L-1. When TC and CTC were incubated in cow manure for 7 d, the above mentioned three transformation products were also formed in this complex matrix (up to 5.1 mg kg-1). Manure, soil and leachate samples from Lower Saxony revealed the presence of seco-cycline A in manure and soil, but not in water. To obtain a better insight in the fate of tetracyclines in environmental matrices, future analytical and ecotoxicological studies dealing with this subject should include the analysis especially of seco-cycline A.

Chlortetracycline and melanin biopolymer - The risk of accumulation and implications for phototoxicity: An in vitro study on normal human melanocytes.

Tetracyclines belong to antimicrobial classes with the highest consumption in veterinary medicine and agriculture, which leads to the contamination of the environment and food products, as well as to antibiotic resistance and adverse drug reactions. Chloro-derivatives of tetracyclines are thought to be relatively more phototoxic than others and belong to the most frequently cited drugs as photosensitizers. Melanins are heterogenous biopolymers determining skin, hair and eye colour. They are biosynthesized in a multistep process in melanocytes. Melanins, besides photoprotective and antioxidant properties, may also contribute to adverse skin drug reactions, which involve e.g. hyperpigmentation disorders and phototoxic reactions. Furthermore, they have the ability to form a drug-melanin complex, which leads to deposition of the drug or its metabolites in pigmented tissues. The aim of the study was to examine the ability of chlortetracycline to form a complex with melanin, as well as the effect of the drug on viability, antioxidant defence system and melanogenesis in normal human epidermal melanocytes exposed to the UVA radiation. The obtained results show for the first time that chlortetracycline forms a complex with melanin polymers, which creates a possibility of the drug accumulation in pigmented tissues. A simultaneous exposition of normal melanocytes to chlortetracycline and to the UVA radiation decreases cell viability, proportionally to the drug concentration and the irradiation time. The phototoxic effect appears to be related to the induction of oxidative stress in melanocytes, mainly through an increase of SOD and a decrease of the CAT activity. Chlortetracycline itself does not influence the melanin content or the activity of tyrosinase. The UVA radiation appeared to be a conditioning factor stimulating melanogenesis, whereas the presence of the drug augmented this effect.

Degradation of tetracyclines in manure-amended soil and their uptake by litchi (Litchi chinensis Sonn.).

The environmental and human health risk posed by veterinary antibiotics is of global concern. Antibiotic uptake by herbal plants has been studied, but little is known about perennial woody fruit crops. Litchi (Litchi chinensis Sonn.), a longevial fruit tree, is routinely fertilized with animal manure and, therefore, may be at risk of antibiotic uptake into its fruits. This study investigated the degradation of chlortetracycline and doxycycline present in manure used to amend orchard soil, and their subsequent assimilation by litchi plant, as affected by manure application rate. The results show that half-lives of chlortetracycline and doxycycline in soil were decreased by increased manure rate, with an average of 27 and 59 days, respectively. Chlortetracycline was readily transported to litchi shoots and increased with the growth of litchi plants. Doxycycline predominantly remained in the roots, and underwent growth dilution in the plants. The two tetracyclines could not be detected in fruits from litchi trees when applied with manures, at various rates, over 2 years. For litchi, chlortetracycline may pose human health risk through manure application, but doxycycline is unlikely to do so. Long-term field experiments are required to monitor antibiotic accumulation in fruits of perennial fruit trees fertilized with animal manure.

Occurrence and transformation of veterinary antibiotics and antibiotic resistance genes in dairy manure treated by advanced anaerobic digestion and conventional treatment methods.

Manure treatment technologies are rapidly developing to minimize eutrophication of surrounding environments and potentially decrease the introduction of antibiotics and antibiotic resistant genes (ARGs) into the environment. While laboratory and pilot-scale manure treatment systems boast promising results, antibiotic and ARG removals in full-scale systems receiving continuous manure input have not been evaluated. The effect of treatment on ARGs is similarly lacking. This study examines the occurrence and transformation of sulfonamides, tetracyclines, tetracycline degradation products, and related ARGs throughout a full-scale advanced anaerobic digester (AAD) receiving continuous manure and antibiotic input. Manure samples were collected throughout the AAD system to evaluate baseline antibiotic and ARG input (raw manure), the effect of hygenization (post-pasteurized manure) and anaerobic digestion (post-digestion manure) on antibiotic and ARG levels. Antibiotics were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the ARGs tet(O), tet(W), sul1 and sul2 were analyzed by quantitative polymerase chain reaction (Q-PCR). Significant reductions in the concentrations of chlortetracycline, oxytetracycline, tetracycline and their degradation products were observed in manure liquids following treatment (p < 0.001), concomitant to significant increases in manure solids (p < 0.001). These results suggest sorption is the major removal route for tetracyclines during AAD. Significant decreases in the epimer-to-total residue ratios for chlortetracycline and tetracycline in manure solids further indicate degradation is desorption-limited. Moreover, sul1 and sul2 copies decreased significantly (p < 0.001) following AAD in the absence of sulfonamide antibiotics, while tetracyclines-resistant genes remained unchanged. A cross-sectional study of dairy farms utilizing natural aeration and liquid-solid separation treatments was additionally performed to compare levels of antibiotics and ARGs found in AAD with the levels in common manure management systems. The concentration of antibiotics in raw manure varied greatly between farms while minimal differences in ARGs were observed. However, significant (p < 0.01) differences in the levels of antibiotics and ARGs (except tet(W)) were observed in the effluents from the three different manure management systems.

Uptake of the veterinary antibiotics chlortetracycline, enrofloxacin, and sulphathiazole from soil by radish.

Veterinary antibiotics are available for uptake by the plants through sources such as manure, irrigation, and atmospheric interaction. The present study was conducted to estimate the half-lives of three veterinary antibiotics, chlortetracycline (CTC), enrofloxacin (ENR), and sulphathiazole (STZ), in soil and experimentally explore their uptake from contaminated soil to radish roots and leaves. Samples were extracted using a modified citrate-buffered version of the quick, easy, cheap, effective, rugged, and safe "QuEChERS" method followed by liquid chromatography coupled with tandem mass spectrometric analysis (LC-MS/MS) in the positive ion mode. Good linearity was observed for the three tested antibiotics in soil and plants (roots and leaves) with high coefficients of determination (R2≥0.9922). The average recovery rates at two spiking levels with three replicates per level ranged between 77.1 and 114.8%, with a relative standard deviation (RSD)≤19.9% for all tested drugs. In a batch incubation experiment (in vitro study), the half-lives of CTC, ENR, and STZ ranged from 2.0-6.1, 2.2-4.5, and 1.1-2.2days, respectively. Under greenhouse conditions, the half-lives of the three target antibiotics in soil with and without radishes were 2.5-6.9 and 2.7-7.4; 4.7-16.7 and 10.3-14.6; and 4.4-4.9 and 2.5-2.8days, respectively. Trace amounts of the target antibiotics (CTC, ENR, and STZ) were taken up from soil via roots and entered the leaves of radishes. The concentration of CTC was lower than 2.73%, ENR was 0.08-3.90%, and <1.64% STZ was uptaken. In conclusion, the concentrations of the tested antibiotics decreased with time and consequently lower residues were observed in the radishes. The rapid degradation of the tested antibiotics in the present study might have only little impact on soil microorganisms, fauna, and plants.

Effects of In-Feed Chlortetracycline Prophylaxis in Beef Cattle on Animal Health and Antimicrobial-Resistant Escherichia coli.

Concerns have been raised that in-feed chlortetracycline (CTC) may increase antimicrobial resistance (AMR), specifically tetracycline-resistant (TETr) Escherichia coli and third-generation cephalosporin-resistant (3GCr) E. coli We evaluated the impact of a 5-day in-feed CTC prophylaxis on animal health, TETr E. coli, and 3GCr E. coli A control group of cattle (n = 150) received no CTC, while a CTC group (n = 150) received in-feed CTC (10 mg/lb of body weight/day) from the 5th to the 9th day after feedlot arrival. Over 25% (38/150) of the animals in the control group developed illnesses requiring therapeutic treatment with antimicrobials critically important to human medicine. Only two animals (1.3%) in the CTC group required such treatments. Fecal swab and pen surface occurrences of generic E. coli (isolated on media that did not contain antimicrobials of interest and were not isolated based on any specific resistance), TETr E. coli, and 3GCr E. coli were determined on five sampling occasions: arrival at the feedlot, 5 days posttreatment (5 dpt), 27 dpt, 75 dpt, and 117 dpt. On 5 dpt, TETr E. coli concentrations were higher for the CTC group than the control group (P < 0.01). On 27 dpt, 75 dpt, and 117 dpt, TETr E. coli concentrations did not differ between groups. 3GCr E. coli occurrences did not differ between control and CTC groups on any sampling occasion. For both groups, generic, TETr, and 3GCr E. coli occurrences were highest on 75 dpt and 117 dpt, suggesting that factors other than in-feed CTC contributed more significantly to antimicrobial-resistant E. coli occurrence. IMPORTANCE: The occurrence of human bacterial infections resistant to antimicrobial therapy has been increasing. It has been postulated that antimicrobial resistance was inevitable, but the life span of the antimicrobial era has been prematurely compromised due to the misuse of antimicrobials in clinical and agricultural practices. Direct evidence relating the use of antimicrobials in livestock production to diminished human health outcomes due to antimicrobial resistance is lacking, and the U.S. Food and Drug Administration has taken an approach to maximize therapeutic efficacy and minimize the selection of resistant microorganisms through judicious use of antimicrobials. This study demonstrated that prophylactic in-feed treatment of chlortetracycline administered for 5 days to calves entering feedlots is judicious, as this therapy reduced animal morbidity, reduced the use of antimicrobials more critical to human health, and had no long-term impact on the occurrence of antimicrobial-resistant E. coli.

Changes in soil microbial community structure and function associated with degradation and resistance of carbendazim and chlortetracycline during repeated treatments.

The degradation characteristics of carbendazim (CBD) and chlortetracycline (CTC) in individual and combined treatments, and dynamics of soil microbial structural and functional diversity as well as their potential relations were studied during three repeated treatments using different concentrations. The results showed that the degradation half-life of CBD at concentrations of 3mg/kg and 6mg/kg obviously increased, but that of CTC at levels of 1mg/kg and 10mg/kg decreased with increasing treatment frequency. Soil microbial activity and functional diversity displayed the suppression trend in CBD treatment and the suppression-recovery-stimulation trend in CTC and CBD+CTC treatments, which were consistent with the findings of decreased degradation rate of CBD and increased degradation rate of CTC. 16S amplicon sequencing analysis revealed five potentially dominant CTC-resistant microbial genera including Bacillus, Actinobacillus, Pseudomonas, Mycobacterium, and Corynebacterium, which may mainly carry major facilitator superfamily transporter protein, ribosomal protection protein, and other proteins encoded by tetA, tetB, tetC, tetH, tetL, tetM, tetO, tetV, tetW, tetX, tetZ, tet33, and tet39. These five dominant genera may jointly contribute to the elevated bacterial community resistance to CTC. Our findings provided a better understanding of microbial community structure and function changes in repeatedly treated soils with CBD and CTC.

Effects of anaerobic digestion on chlortetracycline and oxytetracycline degradation efficiency for swine manure.

Manure containing antibiotics is considered a hazardous substance that poses a serious health risk to the environment and to human health. Anaerobic digestion (AD) could not only treatment animal waste but also generate valuable biogas. However, the interaction between antibiotics in manure and the AD process has not been clearly understood. In this study, experiments on biochemical methane potential (BMP) were conducted to determine the inhibition of the AD process from antibiotics and the threshold of complete antibiotic removal. The thresholds of the complete antibiotic removal were 60 and 40mg/kg·TS for CTC and OTC, respectively. CTC and OTC with concentrations below thresholds could increase the BMP of manure. When the CTC and OTC concentrations exceeded the thresholds, they inhibited manure fermentation, and the CTC removal rate declined exponentially with concentration (60-500mg/kg·TS). The relationship between OTC antibiotic concentration and its removal rate in AD treatment was described with exponential (40-100mg/kg·TS) and linear equations (100-500mg/kg·TS).

Ozonation of chlortetracycline in the aqueous phase: Degradation intermediates and pathway confirmed by NMR.

Chlortetracycline (CTC) degradation mechanism in aqueous phase ozonation was evaluated for degradation mechanism and its correlation with the biodegradability and mineralization. CTC was removed within 8 and 4 min of ozonation at pH 2.2 and 7.0, respectively. At pH 2.2, HPLC-triple quadrupole mass spectrometry (MS) detected 30 products. The structures for some of these products were proposed on the basis of ozonation chemistry, CTC structure and MS data; these structures were then confirmed by nuclear magnetic resonance (NMR) spectra. Double bond cleavages, dimethyl amino group oxidation, opening and removal of the aromatic ring and dechlorination, mostly direct ozonation reactions, gave products with molecular weights (m.w.) 494, 510, 524, 495 and 413, respectively. Subsequent degradations gave products with m.w. 449, 465, 463 and 415. These products were arranged into a degradation pathway. At pH 7.0, the rate of reaction was increased, though the detected products were similar. Direct ozonation at pH 2.2 increased the biodegradability by altering the structures of CTC and its products. Nevertheless, direct ozonation alone remained insufficient for the mineralization, which was efficient at pH 7.0 due to the production of free radicals.