Detection of Escherichia coli O157:H7 in cattle feces using a polymerase chain reaction-based fluorogenic 5' nuclease (TaqMan) detection assay after secondary enrichment.

Currently, methods for recovering and identifying Escherichia coli O157:H7 from cattle feces are inconsistent and hindered by their inability to specifically and rapidly detect small numbers of organisms from this complex and highly variable matrix. A standard approach for isolating and characterizing E. coli O157:H7 from cattle feces was compared with a polymerase chain reaction (PCR)-based 5' nuclease assay specific for E. coli O157:H7 that included a secondary enrichment step. The PCR-based method proved a better indicator of the presence of the organism than the culture procedure. Retests indicated that the inclusion of a secondary enrichment step and the subsequent analysis by the 5' nuclease assay were reproducible and specific. Escherichia coli O157:H7 could be detected in fecal samples that were otherwise negative after a primary enrichment step, immunomagnetic separation, and plating onto sorbitol MacConkey agar plates containing cefixime and tellurite (CT-SMAC). In samples that were initially identified as culture positive but PCR negative, retesting of the culture isolates on CT-SMAC indicated that the sorbitol fermentation interpretations could frequently not be repeated in retests, whereas retesting using the 5' nuclease assay on the original samples demonstrated a high level of agreement with the initial PCR conclusions. These results indicate the necessity of confirmatory evaluation of isolates culturally recovered by standard cultural methods that involve the interpretation of CT-SMAC. The high level of disagreement between initial culture results and retests, and the high level of agreement between initial PCR results and retests, indicates the advantages of a gene-based detection system for identifying E. coli O157:H7 in cattle feces. Screening large numbers of fecal samples for E. coli O157:H7 would appear to be feasible by integrating the use of enrichment media in serial rounds of incubation with a PCR-based fluorogenic detection procedure in high throughput detection systems that had automated liquid-handling capabilities.     

扬州古运河生态环境林建设研究

从建设中国森林生态网络体系工程的角度 ,结合扬州市古运可综合治理建设 ,就营建扬州古运河生态环境林的指导思想、建设目标、建设原则 ,主要建设模式、建设要求及建设的主要景点和相关研究作了论述     

母马生长激素细胞和催乳激素细胞的形态计测学研究

利用免疫组织化学和形态计测学的方法 ,观察了 1 8匹成熟雌性蒙古马的脑垂体前叶生长激素细胞和催乳激素细胞的数量和面积 ,同时利用放射免疫分析方法检测了这两种激素的血浆水平。结果表明 ,每个马脑垂体前叶中 ,生长激素细胞的平均数量为 6 .42× 1 8,每个细胞的平均面积为 82 .40μm2 ;催乳激素细胞的平均数量为 6 .0 7× 1 0 8,每个细胞的平均面积为 47.31μm2 。生长激素的血浆含量平均为 2 .84ng/ m L,但个体差异较大 ,变异系数高达 78.5 % ,催乳激素的血浆含量平均为 7.2 6 ng/ m L。本研究结果揭示 :母马脑垂体生长激素细胞和催乳激素细胞的数量和面积并不是决定母马这两种激素血中浓度的唯一重要因素 ;生长激素血中浓度上的个体差异 ,可能与其搏动性分泌形式有关     

Coincident scrapie infection and nephritis lead to urinary prion excretion

Prion infectivity is typically restricted to the central nervous and lymphatic systems of infected hosts, but chronic inflammation can expand the distribution of prions. We tested whether chronic inflammatory kidney disorders would trigger excretion of prion infectivity into urine. Urinary proteins from scrapie-infected mice with lymphocytic nephritis induced scrapie upon inoculation into noninfected indicator mice. Prionuria was found in presymptomatic scrapie-infected and in sick mice, whereas neither prionuria nor urinary PrP(Sc) was detectable in prion-infected wild-type or PrP(C)-overexpressing mice, or in nephritic mice inoculated with noninfectious brain. Thus, urine may provide a vector for horizontal prion transmission, and inflammation of excretory organs may influence prion spread.     

Deterministic coupling of single quantum dots to single nanocavity modes

We demonstrate a deterministic approach to the implementation of solid-state cavity quantum electrodynamics (QED) systems based on a precise spatial and spectral overlap between a single self-assembled quantum dot and a photonic crystal membrane nanocavity. By fine-tuning nanocavity modes with a high quality factor into resonance with any given quantum dot exciton, we observed clear signatures of cavity QED (such as the Purcell effect) in all fabricated structures. This approach removes the major hindrances that had limited the application of solid-state cavity QED and enables the realization of experiments previously proposed in the context of quantum information processing.     

Defective telomere lagging strand synthesis in cells lacking WRN helicase activity

Cells from Werner syndrome patients are characterized by slow growth rates, premature senescence, accelerated telomere shortening rates, and genome instability. The syndrome is caused by the loss of the RecQ helicase WRN, but the underlying molecular mechanism is unclear. Here we report that cells lacking WRN exhibit deletion of telomeres from single sister chromatids. Only telomeres replicated by lagging strand synthesis were affected, and prevention of loss of individual telomeres was dependent on the helicase activity of WRN. Telomere loss could be counteracted by telomerase activity. We propose that WRN is necessary for efficient replication of G-rich telomeric DNA, preventing telomere dysfunction and consequent genomic instability.     

Indian Ocean climate and an absolute chronology over Dansgaard/Oeschger events 9 to 13

Oxygen-isotope ratios of a stalagmite from Socotra Island in the Indian Ocean provide a record of changes in monsoon precipitation and climate for the time period from 42 to 55 thousand years before the present. The pattern of precipitation bears a striking resemblance to the oxygen-isotope record from Greenland ice cores, with increased tropical precipitation associated with warm periods in the high northern latitudes. The largest change, at the onset of interstadial 12, occurred very rapidly, in about 25 years. The chronology of the events found in our record requires a reevaluation of previously published time scales for climate events during this period.