Enterotoxigenic Escherichia coli detected in foods by PCR and an enzyme-linked oligonucleotide probe

A polymerase chain reaction (PCR) and an enzyme-linked oligonucleotide probe hybridization assay were developed for the detection of enterotoxigenic Escherichia coli (ETEC) in ground beef, chicken, pork and raw milk. Two synthetic primers, one of which was biotinylated, were used in the PCR to amplify a fragment of the E. coli heat-labile enterotoxin (LT) gene. The identity of the amplified products was confirmed by liquid hybridization using a horseradish peroxidase-linked internal oligonucleotide probe in a 96-well microplate coated with streptavidin. The final quantitation of the PCR products was performed by a colorimetric reaction. Under established conditions (including l min at 60 °C for primer annealing and extension in PCR cycles), this method detected all 7 LT-producing E. coli pathogenic for humans, but did not detect all 7 LT-positive E. coli of animal origin, 3 E. coli strains that do not produce LT, and 9 other bacteria. Under less stringent PCR conditions (55 °C for annealing and extension), 2 strains of LT-producing E. coli of porcine origin were detected while the results of other bacterial strains remained unchanged. In pure cultures, the detection limit of the method was 1.4 colony forming units (CFU). Prior to PCR amplification, all food samples inoculated with an LT-producing ETEC, were subjected to enrichment in brain heart infusion broth for 8 h at 37 °C. From these cultures, 10 μ1 was heated at 95 °C for 10 min and directly used in the PCR. An initial inoculum of as few as 1.2 to 12 CFU of the LT-producing ETEC per 25 g (or ml) of food sample gave a positive reaction.     

Intracellular localization of dietary and naked DNA in intestinal tissue of Atlantic salmon, Salmo salar L. using in situ hybridization

There is a continuing interest in the fate of DNA from genetically modified organisms (GMO) in the food chain including the uptake of DNA by intestinal cells from dietary sources containing GM feed ingredients. The objective of this study was to elucidate the uptake and persistence of foreign DNA in the intestinal tract of Atlantic salmon Salmo salar L. using in situ hybridization (ISH) that enables the intracellular localization of the DNA, and polymerase chain reaction (PCR) to verify the ISH results qualitatively. Two salmon intestinal models were employed for the investigations; intestinal tissues were sampled in two models namely (a) in vivo from salmon-fed diets containing 30% GM soybeans or 30% nonGM (nGM) soybeans, and (b) ex vivo from intestinal sleeves incubated using different concentrations of PCR-amplified test DNAs (211 and 305 bp) designed from the 35S promoter/plant DNA junction of the RoundupReady soybean (RRS) genome. Additionally, for the incubation study, the effect of a mucolytic agent dithiothreitol (DTT) and a permeability enhancer sodium deoxycholate (SDA) on DNA uptake were investigated. Both treatments were found to enhance DNA uptake ex vivo. Dietary DNA and PCR-amplified DNA could be visualized by ISH in the salmon intestine with more frequently observed signals in the ex vivo model compared to the in vivo model. All results could be verified by PCR. Dietary DNA was localized in the cell vacuolar system and in lamina propria of the mid intestine. Thus, based on the investigated DNA fragment lengths, this study shows that foreign DNA, can be taken up by Atlantic salmon intestinal tissue.     

萘系衍生物核磁共振碳谱模拟研究

从分子二维拓扑结构出发,应用原子电性作用矢量(AEIV)和原子杂化状态指数(AHSI)对35种萘系衍生物共计375个等价碳原子进行结构表征,分别以多元线性回归和逐步回归方法建立13C核磁共振化学位移定量结构波谱关系模型,通过严格检验,所得2个回归模型的复相关系数R分别为:0.978、0.978,留一法交互检验复相关系数Rcv分别为:0.977、0.978。结果表明,AEIV和AHSI具有表征能力强、物化意义明确等优点,所建模型具有良好的稳定性和估计能力。     

Analysis of Photoelectric Hybridization Measurementon Shearing Force for Flat Shearer

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Ultra‐Specific Zeptomole MicroRNA Detection by Plasmonic Nanowire Interstice Sensor with Bi‐Temperature Hybridization

MicroRNAs (miRNAs) are emerging new biomarkers for many human diseases. To fully employ miRNAs as biomarkers for clinical diagnosis, it is most desirable to accurately determine the expression patterns of miRNAs. The optimum miRNA profiling method would feature 1) highest sensitivity with a wide dynamic range for accurate expression patterns, 2) supreme specificity to discriminate single nucleotide polymorphisms (SNPs), and 3) simple sensing processes to minimize measurement variation. Here, an ultra‐specific detection method of miRNAs with zeptomole sensitivity is reported by applying bi‐temperature hybridizations on single‐crystalline plasmonic nanowire interstice (PNI) sensors. This method shows near‐perfect accuracy of SNPs and a very low detection limit of 100 am (50 zeptomole) without any amplification or labeling steps. Furthermore, multiplex sensing capability and wide dynamic ranges (100 am –100 pm ) of this method allows reliable observation of the expression patterns of miRNAs extracted from human tissues. The PNI sensor offers combination of ultra‐specificity and zeptomole sensitivity while requiring two steps of hybridization between short oligonucleotides, which could present the best set of features for optimum miRNA sensing method.     

C20富勒烯分子及C±20富勒烯离子特性分析与比较

以C1对称C20富勒烯分子为模型,在Gussion03上做了结构优化、频率计算以及自然键轨道理论(NBO)计算,并在同样的方法和基组下分别对C20分子得失一个电子的情况做了计算,并进行了分析和比较.结果表明:C1对称C20富勒烯分子不稳定,易于得失电子而以离子形式存在.C20,C+20,C-20三者的能量关系为:EC2...     

Floc-based sequential partial nitritation and anammox at full scale with contrasting N2O emissions

New Activated Sludge (NAS^®) is a hybrid, floc-based nitrogen removal process without carbon addition, based on the control of sludge retention times (SRT) and dissolved oxygen (DO) levels. The aim of this study was to examine the performance of a retrofitted four-stage NAS^® plant, including on-line measurements of greenhouse gas emissions (N₂O and CH₄). The plant treated anaerobically digested industrial wastewater, containing 264 mg N L⁻¹, 1154 mg chemical oxygen demand (COD) L⁻¹ and an inorganic carbon alkalinity of 34 meq L⁻¹. The batch-fed partial nitritation step received an overall nitrogen loading rate of 0.18-0.22 kg N m⁻³ d⁻¹, thereby oxidized nitrogen to nitrite (45-47%) and some nitrate (13-15%), but also to N₂O (5.1-6.6%). This was achieved at a SRT of 1.7 d and DO around 1.0 mg O₂ L⁻¹. Subsequently, anammox, denitrification and nitrification compartments were followed by a final settler, at an overall SRT of 46 d. None of the latter three reactors emitted N₂O. In the anammox step, 0.26 kg N m⁻³ d⁻¹ was removed, with an estimated contribution of 71% by the genus Kuenenia, which constituted 3.1% of the biomass. Overall, a nitrogen removal efficiency of 95% was obtained, yielding a dischargeable effluent. Retrofitting floc-based nitrification/denitrification with carbon addition to NAS^® allowed to save 40% of the operational wastewater treatment costs. Yet, a decrease of the N₂O emissions by about 50% is necessary in order to obtain a CO₂ neutral footprint. The impact of emitted CH₄ was 20 times lower.     

聚酰亚胺基复合材料在电池电极中的研究进展

聚酰亚胺(Polyimide,PI)是一种以二酐和二胺为原料,热亚胺化后合成的聚合物。PI作为电池电极材料,具有理论容量高、机械强度大和易于回收的优点,但是它的绝缘性限制了内部活性位点的利用率,导致电池的倍率性能较差。本文综述了通过构建共轭结构来提高结构稳定性和引入羰基结构增加PI氧化还原中心(C=O)位点,以获得更高电池容量的研究策略,介绍了碳化PI和与石墨烯、碳纳米管的杂化以及使用静电纺丝工艺对PI作为电池电极的电化学性能的改进,对基于PI的其他复合材料的研究进行了总结,并对目前PI的研究方向进行了展望。