Insight into the mechanisms of trichloronitromethane formation by vacuum ultraviolet: QSAR model and FTICR-MS analysis.

Vacuum ultraviolet (VUV) photolysis is recognized as an environmental-friendly treatment process. Nitrate (NO3-) and natural organic matter (NOM) are widely present in water source. We investigated trichloronitromethane (TCNM) formation during chlorination after VUV photolysis, because TCNM is an unregulated highly toxic disinfection byproduct. In this study: (1) we found reactive nitrogen species that is generated under VUV photolysis of NO3- react with organic matter to form nitrogen-containing compounds and subsequently form TCNM during chlorination; (2) we found the mere presence of 0.1 mmol/L NO3- can result in the formation of up to 63.96 µg/L TCNM; (3) we found the changes in pH (6.0-8.0), chloride (1-4 mmol/L), and bicarbonate (1-4 mmol/L) cannot effectively diminish TCNM formation; and, (4) we established the quantitative structure-activity relationship (QSAR) model, which indicated a linear relationship between TCNM formation and the Hammett constant (σ) of model compounds; and, (5) we characterized TCNM precursors in water matrix after VUV photolysis and found 1161 much more nitrogen-containing compounds with higher aromaticity were generated. Overall, this study indicates more attention should be paid to reducing the formation risk of TCNM when applying VUV photolysis process at scale.

UV-induced activation of organic chloramine: Radicals generation, transformation pathway and DBP formation.

Organic chloramines of little disinfection efficacy commonly exist in disinfection process (chlor(am)ination) due to the wide presence of organic amines in water, of which N-chlorodimethylamine (CDMA) is a typical one. For the first time, UV photolysis for the activation of CDMA was investigated. UV photolysis caused the cleavage of N-Cl bond in CDMA to form Cl• and subsequently HO•, both of which are dominant contributors to the destruction of model contaminant bisphenol A (BPA). Typical spectra of HO• were detected by electron paramagnetic resonance (EPR) experiments, while spectra of reactive nitrogen species (RNS) were not detected during UV photolysis of CDMA. The increase of pH (6.0-8.0), HCO3-/CO32-, Cl- and nature organic matter inhibited the degradation of BPA. We proposed pathways of CDMA and BPA degradation based on the identified transformation products. UV photolysis of CDMA and BPA reduced the formation of N-nitrosodimethylamine (NDMA) at pH 8.0, but increased the formation of trichloronitromethane (TCNM) at pH 7.0 and 8.0. The increasing toxicity and the formation of TCNM and NDMA gave us a hint that formation of organic chloramines should be concerned.

The role of carbonate radicals on the kinetics, radical chemistry, and energy requirement of UV/chlorine and UV/H2O2 processes.

Quantitative insight into the HCO3--dependent degradation kinetics is critical to improve understanding of the UV processes for the most-cost effective application. In this study, we developed a kinetic model to precisely predict the kinetics in UV/H2O2 and UV/chlorine processes. The second-order rate constants of HO, Cl, ClO, Cl2-, and CO3- with carbamazepine (CBZ) were fitted as 1.3 × 109, 1.9 × 109, 1.8 × 106, 1.1 × 105, and 4.5 × 106 M-1 s-1, respectively. Based on the model, we investigated the significant impact of bicarbonate (HCO3-) and subsequently generated carbonate radical (CO3-) on CBZ degradation, radical chemistry, and energy requirement of UV/H2O2 and UV/chlorine processes. The presence of HCO3- inhibited CBZ degradation in UV/H2O2 and UV/chlorine processes to different degree. Contributions of HO, Cl, ClO, Cl2-, and CO3- to CBZ degradation in UV/H2O2 and UV/chlorine processes in the absence/presence of HCO3- were investigated. HO and CO3- make comparable contributions to CBZ degradation in UV/H2O2 process in the presence of HCO3- (2 mM), while ClO is always the main contributor at various HCO3- concentration of 0-2 mM. Furthermore, the presence of HCO3- in both processes increased the corresponding EE/O, when CBZ was degraded by an order of magnitude. Overall, HCO3- and CO3- influence the reactions and mechanism of UV/H2O2 and UV/chlorine processes, and have higher impact on UV/H2O2 process.

Computerized Pathway Generator for the UV/Free Chlorine Process: Prediction of Byproducts and Reactions.

The ultraviolet (UV)/free chlorine process is a very promising treatment technology to remove persistent organic contaminants (POCs, e.g., pharmaceutical and personal care products) from water. The radical chain reactions involved in the UV/free chlorine process are very complicated, and the reaction pathways for organic contaminants degradation are largely unknown. Therefore, we developed a computerized pathway generator that uses graph theory and experimentally determined reaction rules that were reported for the UV/free chlorine process. Our pathway generator predicts all possible intermediates, byproducts, and elementary reactions that are involved in the oxidation of organic contaminants. For example, the degradation of tricholoroethylene (TCE) produces 497 species (i.e., intermediates and byproducts) and 6608 elementary reactions. The predicted species from our pathway generator not only predict the major and stable byproducts that were observed in our experiments (e.g., CHCl2COOH, CHCl(OCl)COOH, etc.) but also include many other minor and toxic byproducts that were produced but not measured because they have a short lifetime. Overall, our pathway generator significantly improves our understanding of the reaction pathways that are involved in organic contaminant degradation in the UV/free chlorine process.

Simultaneous removal of chlorite and contaminants of emerging concern under UV photolysis: Hydroxyl radicals vs. chlorate formation.

It is well known that using chlorine dioxide (ClO2) as a disinfectant inevitably produces a common disinfection byproducts chlorite (ClO2‒). In this study, we found that UV photolysis after ClO2 disinfection can effectively eliminate both ClO2‒ and contaminants of emerging concern (CECs). However, the kinetic mechanisms of UV/ClO2‒ process destructing CECs, as well as transformation of ClO2‒ in UV/ClO2‒ system are not clear yet. Therefore, we systematically investigated the UV/ClO2‒ system to assist us appropriately design this process under optimal operational conditions. In this work, we first investigated the impact of water matrix conditions (i.e., pH, bicarbonate and natural organic matter (NOM)) and ClO2‒ dosage on the UV/ClO2‒ process. We found that bicarbonate and NOM have inhibition effects, while lower pH and higher ClO2‒ dosage have enhancement effects. Besides, hydroxyl radical (HO•) and reactive chlorine species (RCS) are generated from UV/ClO2‒ system, and RCS are main contributors to CBZ degradation. Then we proposed a possible degradation pathway of CBZ based on the determined products from experiments. Additionally, we found that photolysis of ClO2‒ resulted in the generation of chloride (Cl‒) and chlorate (ClO3‒). As the ClO2‒ dosage increases, the yield of ClO3‒ increased while that of Cl‒ decreased. Finally, we elucidated the second order rate constant of the target organic compound with HO• has a strong correlation with the formation of ClO3‒.

Development of a highly efficient electrochemical flow-through anode based on inner in-site enhanced TiO2-nanotubes array.

This paper reports on the development of macroporous flow-through anodes. The anodes comprised an enhanced TiO2 nanotube array (ENTA) that was grown on three macroporous titanium substrates (MP-Ti) with nominal pore sizes of 10, 20, and 50 µm. The ENTA was then covered with SnO2-Sb2O3. We refer to this anode as the MP-Ti-ENTA/SnO2-Sb2O3 anode. The morphology, pore structure, and electrochemical properties of the anode were characterized. Compared with the traditional NTA layer, we found that the MP-Ti-ENTA/SnO2-Sb2O3 anode has a service lifetime that was 1.56 times larger than that of MP-Ti-NTA/SnO2-Sb2O3. We used 2-methyl-4-isothiazolin-3-one (MIT), a common biocide, as the target pollutant. We evaluated the impact of the operating parameters on energy efficiency and the oxidation rate of MIT. Furthermore, the apparent rate constants were 0.38, 1.63, and 1.24 min-1 for the 10, 20, and 50 µm nominal pore sizes of the MP-Ti substrates, respectively, demonstrating the different coating-loading mechanisms for the porous substrate. We found that hydroxyl radicals were the dominant species in the MIT oxidation in the HO radical scavenging experiments. The radical and nonradical oxidation contributions to the MIT degradation for different current densities were quantitatively determined as 72.1%-74.8% and 25.2%-27.9%, respectively. Finally, we summarized the oxidation performance for MIT destruction for (1) the published literature on various advanced oxidation technologies, (2) the published literature on various anodes, and (3) our flow-by and -through anodes. Accordingly, we found that our flow-through anode has a much lower electrical efficiency per order value (0.58 kWh m-3) than the flow-by anodes (6.85 kWh m-3).

Non-negligible risk of chloropicrin formation during chlorination with the UV/persulfate pretreatment process in the presence of low concentrations of nitrite.

The UV/persulfate (PS) process is a promising water treatment technology, and it can not only effectively degrade contaminants of emerging concern, but also control formation of disinfection byproducts (DBPs). In this study, we investigated the potential and mechanisms of chloropicrin (i.e. trichloronitromethane, TCNM) formation during chlorination that followed UV/PS pretreatment in the presence of low concentrations of nitrite. We found that when nitrite was present in the UV/PS system, unexpected high concentrations of TCNM were formed. The formation potential of TCNM was impacted by operational conditions and water matrix components: (1) high pH enhanced TCNM formation; (2) high UV fluence inhibited TCNM formation; and (3) organic compounds containing phenolic groups enhanced TCNM formation. We discovered that electrophilic substitutions by reactive nitrogen species were favored for phenolic groups, and thus more nitrite-N was transformed to organic nitrogen. We also found that more TCNM was generated from natural organic matter than algal organic matter during chlorination following pretreatment using UV/PS. Accordingly, more attention needs to be paid to TCNM formation, if nitrite is present and the water is pretreated using UV/PS (when applied at upstream of chlorination). For example, we found that if monochloramine was used as a disinfectant downstream of the UV/PS process, the formation of TCNM was reduced.

Development of a Three-Dimensional Electrochemical System Using a Blue TiO2/SnO2-Sb2O3 Anode for Treating Low-Ionic-Strength Wastewater.

Reducing energy use is crucial to commercialize electrochemical oxidation technologies. We developed a three-dimensional (3-D) electrochemical system that can significantly reduce the applied voltage and effectively degrade organic contaminants in low-ionic-strength wastewaters. The 3-D system consisted of a composite wire mesh anode (composed of blue TiO2 nanotubes covered with SnO2-Sb2O3), a proton exchange membrane, and a stainless-steel wire mesh cathode, which were compressed firmly together. For the 3-D system, we placed the anode of a 3-D electrode toward the wastewater that flowed past the anode. Both the two-dimensional (2-D) and 3-D systems had the same anode and cathode. We found that the 3-D system could reduce the applied voltage by 75.7% and reduce the electrical efficiency per log order reduction (EE/O) by 73% for 0.001 M Na2SO4. For Na2SO4 concentrations greater than 0.05 M, the 2-D system had a slightly lower EE/O. We also compared the EE/O of electrochemical advanced oxidation processes (EAOPs) with that of other advanced oxidation processes (UV/H2O2, UV/persulfate, O3/H2O2, UV/ TiO2, and UV/chlorine). We found that EAOPs have a much higher EE/O for low BA concentrations (20 mg/L) and a much lower EE/O for high BA concentrations (2000 mg/L).

The individual and Co-exposure degradation of benzophenone derivatives by UV/H2O2 and UV/PDS in different water matrices.

Benzophenone derivatives, including benzophenone-1 (C13H10O3, BP1), benzophenone-3 (C14H12O3, BP3) and benzophenone-8 (C14H12O4, BP8), that used as UV filters are currently viewed as emerging contaminants. Degradation behaviors on co-exposure benzophenone derivatives using UV-driven advanced oxidation processes under different aqueous environments are still unknown. In this study, the degradation behavior of mixed benzophenone derivatives via UV/H2O2 and UV/peroxydisulfate (PDS), in different water matrices (surface water, hydrolyzed urine and seawater) were systematically examined. In surface water, the attack of BP3 by hydroxyl radicals (HO∙) or carbonate radicals (CO3∙-) in UV/H2O2 can generate BP8, which was responsible for the relatively high degradation rate of BP3. Intermediates from BP3 and BP8 in UV/PDS were susceptible to CO3∙-, bringing inhibition of BP1 degradation. In hydrolyzed urine, Cl- was shown the negligible effect for benzophenone derivatives degradation due to low concentration of reactive chlorine species (RCS). Meanwhile, BP3 abatement was excessively inhibited during co-exposure pattern. In seawater, non-first-order kinetic behavior for BP3 and BP8 was found during UV/PDS treatment. Based on modeling, Br- was the sink for HO∙, and the co-existence of Br- and Cl- was the sink for SO4∙-. The cost-effective treatment toward target compounds removal in different water matrices was further evaluated using EE/O. In most cases, UV/H2O2 process is more economically competitive than UV/PDS process.

Deactivation Mechanism of Multipoisons in Cement Furnace Flue Gas on Selective Catalytic Reduction Catalysts.

Increasing numbers of cement furnaces have applied selective catalytic reduction (SCR) units for advanced treatment of NO in the flue gas. However, the SCR catalysts may face various poisons, such as acidic, alkaline, and heavy metal species, in the fly ash. In this work, we studied the deactivation mechanisms of multipoisons (Ca, Pb, and S) on the CeO2-WO3/TiO2 catalyst, using the in situ diffuse reflectance infrared Fourier transform spectroscopy method. Calcium promoted the conversion of Ce(III) to Ce(IV) and, thus, (i) suppressed the redox cycle, (ii) decreased the NO adsorption (monodentate NO3- and bridged NO2-), and (iii) enriched the Lewis acid sites. Pb(IV) blocked Ce2(WO4)3, aggravating the electronegativity of W6+, which inhibited (i) the binding stability of tungsten and ammonia species, (ii) bridged NO3- (bonded to tungsten), and (iii) the Brønsted acid sites. The multipoisoning processes enriched O2- by repairing partial surface oxygen defects, which suppressed O22- and O-. Sulfur occupied the surface base sites and formed PbSO4 after Ce2(WO4)3 was saturated.

Oxidation Mechanisms of the UV/Free Chlorine Process: Kinetic Modeling and Quantitative Structure Activity Relationships.

Recently, the UV/free chlorine process has gained attention as a promising technology for destroying refractory organic contaminants in the aqueous phase. We have developed a kinetic model based on first-principles to describe the kinetics and mechanisms of the oxidation of organic contaminants in the UV/free chlorine process. Substituted benzoic acid compounds (SBACs) were chosen as the target parent contaminants. We determined the second-order rate constants between SBACs and reactive chlorine species (RCS; including [Formula: see text], [Formula: see text] and [Formula: see text]) by fitting our model to the experimental results. We then predicted the concentration profiles of SBACs under various operational conditions. We analyzed the kinetic data and predicted concentration profiles of reactive radicals ([Formula: see text] and RCS), we found that [Formula: see text] was the dominant radicals for SBACs destruction. In addition, we established quantitative structure activity relationships (QSARs) that can help predict the second-order rate constants for SBACs destruction by each type of reactive radicals using SBACs Hammett constants. Our first-principles-based kinetic model has been verified using experimental data. Our model can facilitate a design for the most cost-effective application of the UV/free chlorine process. For example, our model can determine the optimum chlorine dosage and UV light intensity that result in the lowest energy consumption.

Sulfadiazine destruction by chlorination in a pilot-scale water distribution system: Kinetics, pathway, and bacterial community structure.

Sulfadiazine (SDZ) has been frequently detected in surface waters in recent years. We evaluated the kinetics, mechanisms, intermediate products and bacterial community structure that result from the reaction of SDZ with free chlorine (HOCl/OCl-). We examined this in a pilot-scale water distribution system. Neutral pH had the fastest rate of destruction of SDZ. A second-order reaction constant for the destruction of SDZ by chlorine increased with increasing concentration of free chlorine (FC). For different pipe materials, the rate of SDZ degradation decreased as follows: stainless steel (SS) pipe > polyethylene (PE) pipe > ductile iron (DI) pipe. Based on the less complex bacterial diversity and more chlorine-resistant by 16S ribosomal ribonucleic acid (rRNA) gene analysis, SS pipe and PE pipe were more suitable in SDZ degradation in water distribution system (WDS) than DI pipe. In addition, the transformation products from SDZ chlorination were identified by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, and the products included SO2 extrusion products, haloacetic acids and trihalomethanes. Toxicity tests further confirmed that the toxicity of SDZ chlorination was higher both in low FC (0.7 mg/L) and high FC (1.3 mg/L) in WDS.

The role of reactive oxygen species and carbonate radical in oxcarbazepine degradation via UV, UV/H2O2: Kinetics, mechanisms and toxicity evaluation.

Oxcarbazepine (OXC) is ubiquitous in the aqueous environment. And due to its ecotoxicological effects and potential risks to human, an effective way to eliminate OXC from aqueous environment has aroused public concerns in recent years. Radical-based reactions have been shown to be an efficient way for OXC destruction, but the reactions of OXC with reactive oxygen species (ROS) and carbonate radical (CO3•-) are still unclear. In this study, we focused the degradation of OXC and ROS, CO3•- generation mechanism, and their roles in OXC degradation via UV and UV/H2O2. The triplet state of oxcarbazepine (3OXC∗) was found to play an important role in OXC degradation via UV. And hydroxyl radicals (•OH) and singlet oxygen (1O2) were found to be the dominant ROS in OXC degradation. Superoxide radical (O2•-) did not react with OXC directly, but it may react with intermediate byproducts. Generation of CO3•- played a positive role on OXC degradation for both UV and UV/H2O2. In addition to •OH, 3OXC* also contribute to CO3•- production. The second-order rate constants of OXC with •OH and CO3•- were 1.7 × 1010 M-1 s-1 and 8.6 × 107 M-1 s-1, respectively. Potential OXC degradation mechanisms by •OH were proposed and included hydroxylation, α-ketol rearrangement, and benzylic acid rearrangement. Compared with non-selective •OH, the reactions involving CO3•- are mainly electron transfer and hydrogen abstraction. And the acute toxicity of OXC was lower after UV/H2O2 and UV/H2O2/HCO3- treatments, which was confirmed by luminescent bacterial assay (Vibrio fischeri bacterium).

Impact of Chloride Ions on UV/H2O2 and UV/Persulfate Advanced Oxidation Processes.

Chloride ion (Cl-) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl- on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H2O2 processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl- is present to the rate when Cl- is not present (designated as rRCl-/ rR) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, rRCl-/ rR, can be no larger than 60%. Hence, Cl- significantly reduces the organic destruction rate in the UV/PS process. In the UV/H2O2 process, we found that Cl- has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is a reliable method for determining whether Cl- will adversely impact organic compounds destruction by the UV/PS and UV/H2O2 processes.

Oxidation of Microcystin-LR via Activation of Peroxymonosulfate Using Ascorbic Acid: Kinetic Modeling and Toxicity Assessment.

Advanced oxidation processes (AOPs) have been widely used for the destruction of organic contaminants in the aqueous phase. In this study, we introduce an AOP on activated peroxymonosulfate (PMS) by using ascorbic acid (H2A) to generate sulfate radicals (SO4•-). Sulfate radicals, hydroxyl radicals (HO•), and ascorbyl radicals (A•-) were found using electron spin resonance (ESR). But we found A•- is negligible in the degradation of microcystin-LR (MCLR) due to its low reactivity. We developed a first-principles kinetic model to simulate the MCLR degradation and predict the radical concentrations. The MCLR degradation rate decreased with increasing pH. The scavenging effect of natural organic matter (NOM) on SO4•- was relatively small compared to that for HO•. Considering both energy consumption and MCLR removal, the optimal H2A and PMS doses for H2A/PMS process were determined at 1.0 × 10-6 M and 1.6 × 10-5 M, respectively. In addition, we determined the toxicity using the protein phosphatase 2A (PP2A) test and the results showed that MCLR was readily detoxified and its oxidation byproducts were not hepatotoxic. Overall, our work provides a new type of AOP and a promising, efficient, and environmental-friendly method for removing microcystins in algae-laden water.

Degradation of dyes by peroxymonosulfate activated by ternary CoFeNi-layered double hydroxide: Catalytic performance, mechanism and kinetic modeling.

Ternary CoFeNi-layered double hydroxide (CoFeNi-LDH) was synthesized and initially applied to activate peroxymonosulfate (PMS) for the degradation of Congo red (CR) and Rhodamine B (RhB). The results show that the CoFeNi-LDH/PMS system can efficiently degrade nearly 100% of 20 mg/L CR or 20 mg/L RhB within 6- and 10-min reaction times, respectively. And the catalyst exhibits higher degradation efficiency on CR than on RhB under identical conditions, which is confirmed by electron clouds of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) performed by DFT calculations. Quenching tests reveal that SO4- is the dominant active species participating in the degradation process. Mechanism investigation demonstrates that Co(II)-Co(III)-Co(II) cycle is responsible for activating PMS to generate radicals for dyes degradation. A dynamic kinetic model is successfully developed to simulate the concentration profiles of CR and RhB degradation in CoFeNi-LDH/PMS system. The empirical second order rate constants between SO4- and CR (kSO4-/CR), HO and CR (kOH/CR), SO4- and RhB (kSO4-/RhB), HO and RhB (kHO/RhB) are determined to be 2.47 × 107, 3.44 × 106, 8.39 × 106 and 2.62 × 107 M-1s-1, respectively. In addition, toxic assessment using ECOSAR program suggests that the overall toxicity of CR and RhB decreased after treatment with CoFeNi-LDH/PMS system. Repeating tests and application of CoFeNi-LDH in different water sources give us adequate confidence that the as-synthesized CoFeNi-LDH is favorable for the purification of dye-contaminanted waters in practical.

Antagonist of thromboxane A2 receptor by SQ29548 lowers DOCA-induced hypertension in diabetic rats.

Diabetes is one of high risk factors for cardiovascular diseases, including atherosclerosis and hypertension. This study was conducted to elucidate whether and how thromboxane receptor (TPr) activation contributes to hypertension in diabetes. Human umbilical vein endothelial cells (HUVECs) were cultured. The phosphorylated levels of endothelial nitric oxide synthase (eNOS) and Akt were monitored by western blot. Endothelial function was determined by organ bath. High glucose (HG) or thromboxane A2 mimetic U46619 significantly reduced the levels of p-eNOS and p-Akt in cultured HUVECs, which were reversed by inhibition of TPr. HG/U46619-induced reductions of p-eNOS and p-Akt were accompanied with increases of total and phosphorylated tumor suppressor phosphatase and tensin homolog on chromosome 10 (PTEN). PTEN siRNA restored Akt-eNOS signaling in cells treated with HG. In rats, streptozotocin-induced hyperglycemia was associated with aortic PTEN upregulation and reductions of p-Akt and p-eNOS. TPr antagonist SQ29548 ablated these alterations and reduced blood pressure in rats with DOCA-induced hypertensive. In conclusion, hyperglycemia activates thromboxane A2 receptor to augment DOCA-induced high blood pressure in rats via the PTEN-Akt-eNOS signaling.

Escherichia coli isolates from sick chickens in China: changes in antimicrobial resistance between 1993 and 2013.

The use of antimicrobials for the control of infectious disease has increased in recent decades. Understanding trends in antimicrobial resistance provides clues about the relationship between antimicrobial use and the emergence of resistance. We examined the resistance of 540 Escherichia coli isolates to 19 antimicrobials that represent 11 classes of antimicrobial agents. The isolates were collected from chickens between 1993 and 2013 in China. Overall, >96.7% of the isolates were resistant to at least one of the tested compounds, and 87.2% of them displayed multidrug resistance (MDR) representing five to six antimicrobial classes. A high proportion of E. coli isolates were resistant to tetracycline (90.6%), nalidixic acid (80.6%), ampicillin (77.2%), trimethoprim-sulfamethoxazole (76.9%), and streptomycin (72.8%). Only 3.0% of the isolates were resistant to nitrofurantoin, and none was resistant to meropenem. Resistance to amikacin, ampicillin, aztreonam, ceftazidime, cefotaxime, cephalothin, chloramphenicol, ciprofloxacin, fosfomycin, levofloxacin, norfloxacin, nalidixic acid, piperacillin, and trimethoprim-sulfamethoxazole significantly increased from 1993 to 2013 (P <0.01). There was an increasing trend in MDR over the 20 year period.

[Prevalence and transmission of plasmid-mediated quinolone resistance qnrS gene among Escherichia coli isolates in a poultry farm].

OBJECTIVE: To investigate the prevalence and transmission of plasmid-mediated quinolone resistance qnrS gene among Escherichia coli isolates in a poultry farm and its environment. METHODS: E. coli isolates from fecal samples in a poultry farm and its environment from February to June 2010 were screened for the prevalence and dynamic changes of qnrS gene. Susceptibility testing, conjugant experiments, and pulsed field gel electrophoresis of qnrS-positive isolates were also performed. RESULTS: A total of 379 isolates were randomly obtained from feces samples of chickens, ducks and geese in a poultry farm and its environment. The qnrS positive strains were detected in all sources of isolates and two alleles of qnrS were prevalent on this farm. The positive rate of qnrS gene in environmental strains was 29.2%, which was significantly higher than that in the avian strains (13.4%). Chicken can quickly acquire qnrS gene after they live on this farm. Transconjugants of the qnrS gene can elevate ciprofloxacin Minimun inhibitory concentrations (MICs) by 16 - 32 fold compared with the recipient. Various determinants for resistance to other antimicrobial agents were also transferred with the qnrS plasmid. The Xba I PFGE analysis of the qnrS positive strains showed that the dissemination of qnrS was not mainly due to the clonal dissemination of positive strains. However, qnrS-positive strains with indistinguishable PFGE patterns were found in ducks and environment. CONCLUSION: Both horizontal gene transfer and clonal spread could be responsible for the dissemination of the qnrS gene in the poultry farm and its environment, but it is mainly disseminated by horizontal transmission.

Prevalence of qnr, aac(6')-Ib-cr, qepA, and oqxAB in Escherichia coli isolates from humans, animals, and the environment.

qnr, aac(6')-Ib-cr, qepA, and oqxAB genes were detected in 5.7%, 4.9%, 2.6%, and 20.2% of 1,022 Escherichia coli isolates from humans, animals, and the environment, respectively, collected between 1993 and 2010 in China. The prevalence of oqxAB in porcine isolates (51.0%) was significantly higher than that in other isolates. This is the first report of oqxAB-positive isolates from ducks and geese and as early as 1994 from chickens.