Detection of Verotoxigenic Escherichia coli O157 and O26 in food by plating methods and LAMP method: a collaborative study

In order to establish a rapid and sensitive method for the detection of Verotoxigenic Escherichia coli O157 and O26, a collaborative study was conducted focusing on a comparison of the efficiency of loop-mediated amplification (LAMP) assay targeting the Verocytotoxin (also called Shiga toxin) gene, utilizing a direct plating method and a plating method with immunomagnetic separation (IMS-plating method) using various agar media. In combination with enrichment with the modified EC supplemented with novobiocin, E. coli O157 was detected in most samples of ground beef and alfalfa sprouts by LAMP assay, the direct plating method and the IMS-plating method. E. coli O26 was detected in approximately 100% of the food samples by LAMP assay. However, the IMS-plating and direct plating methods recovered 80 and 50% in ground beef samples, respectively. As a result, it was demonstrated the LAMP assay is superior to the IMS-plating method. Based on these results, it appears LAMP assay is effective as a screening assay to detect E. coli O157 and O26 from positive samples.     

Factors of hetero space charge generation in XLPE under dc electric field of 20 kV/mm

This report deals with the mechanism of space charge accumulation in cross‐linked polyethylene (XLPE) under dc electric field. Space charge was measured by the pulsed‐electroacoustic method with applying dc stress of 20 kV/mm. A large amount of hetero space charge accumulated in fresh XLPE samples. Factors influencing the space charge accumulation were analyzed in regard to cross‐linking by‐products and antioxidant. No space charge was seen when the fresh sample was degassed to remove cross‐linking by‐products. Introducing acetophenone, one of the cross‐linking by‐products, in a degassed sample produces no space charge, suggesting that acetophenone itself could not be the direct factor of space charge formation. However, heating this sample up to 150 °C results in formation of hetero space charges as in virgin samples. Hence, it is concluded that hetero space charges may be formed when impurities, such as an antioxidant, dissociate thermally with the help of acetophenone and that the dissociated products are attracted toward both electrodes under a dc field to form the hetero space charges. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 13–21, 1999     

Development of a quantitative real-time PCR method to enumerate total bacterial counts in ready-to-eat fruits and vegetables

A newly developed real-time PCR assay rapidly quantifies the total bacterial numbers in contaminated ready-to-eat vegetables and fruits compared with the standard plate count method. Primers targeting the rpoB gene, which encodes for the beta subunit of the bacterial RNA polymerase and which is common to most bacterial species, was used instead of the 16S rRNA gene, which has multiple copies and varies among bacterial species. A primer pair specific for rpoB was confirmed to amplify rpoB in a wide range of bacterial species after we assessed 49 strains isolated from five kinds of fruits and vegetables. We purchased fruits and vegetables from retail shops and enumerated the bacteria associated with them by use of real-time PCR and compared this to the number found by the culture method. We found a high correlation between the threshold PCR cycle number when compared with the plate count culture number. The real-time PCR assay developed in this study can enumerate the dominant bacterial species in ready-to-eat fruits and vegetables.     

Hydrodechlorination of para-substituted chlorobenzenes over a ruthenium/carbon catalyst

The hydrodechlorination (HDC) of chlorobenzene (abbreviated as CLB) and seven types of para-substituted chlorobenzenes (para-amino, -methoxy, -methyl, -chloro, -trifluoromethyl, -acetyl and -cyano: abbreviated as CLAN, CLAS, CLTN, DCLB, CLTF, CLAP and CLBN, respectively) were performed over 5%-ruthenium/carbon (Ru/C) under a hydrogen pressure of 0.5–1.5 MPa at 523 K.In the HDC of these model compounds, except for CLAP and CLBN, reductive cleavage between the carbon and chlorine atoms took place and dechlorinated compounds were produced preferentially. In the reaction of CLAP and CLBN, on the other hand, hydrogenation and/or hydrogenolysis of the substituent coincided with the HDC and a wide variety of products was observed accompanying the HDC product.For the chlorobenzenes of the simple HDC, the HDC reaction rate constants decreased in the orders of CLAN  CLB ≈ CLTN ≈ CLAS and CLB > DCLB  CLTF, respectively.In the reaction of the chlorobenzenes of the electron-donating substituent, the reaction constant (ln k/k₀) has no relevance to the Hammett substituent constant (). In the case of the chlorobenzenes possessing the electron-withdrawing substituent, on the other hand, it was indicated that the electron-withdrawing substituent suppressed the HDC reactivity of chlorobenzenes, although no proportional relationship was observed between the reaction rate constant and the Hammett substituent constant.To explore the factors affecting the HDC reactivity, quantum calculation according to the DFT method (B3LYP/LANL2DZ) was applied to the “chlorobenzenes-Ru₁₀” complex. As a result of the calculation, chlorobenzenes were adsorbed through a chlorine atom on the edge atom of the Ru₁₀ cluster. The magnitude of the adsorption energy, moreover, decreased in the order of CLAN > CLAS ≈ CLB ≈ CLTN and CLB > DCLB > CLTF, respectively. These orders of adsorption energy are similar to that of the HDC reaction rate constant. It was concluded that adsorption energy is a useful parameter for the reactivity index of the HDC.     

Long-range ordered single-crystal graphene on high-quality heteroepitaxial Ni thin films grown on MgO(111)

Large-area single crystal monolayer graphene is synthesized on Ni(111) thin films, which have flat terraces and no grain boundaries. The flat single-crystal Ni films are heteroepitaxially grown on MgO(111) substrates using a buffer layer technique. Low-energy electron diffraction and various spectroscopic methods reveal the long-range single crystallinity and uniform monolayer thickness of the graphene. When transferred onto an insulating wafer, continuous millimeter-scale single domain graphene is obtained.     

Wear Behavior of Al-Si Alloy Impregnated Graphite Composite

Pin-on-disk type unidirectional sliding wear experiments for an Al-Si alloy impregnated graphite composite (pin) in contact with a bearing steel (disk) were conducted at various contact loads in wet and dry air to investigate the wear behaviors in detail. The pin-lifting phenomena of the composite as observed. The height was constant at lower loads and increased with load. The entrance of wear particles into the contacting surfaces brought about the pin lifting. Mixtures of graphite powder and wear particles adhered to the sliding surface of the bearing steel, resulting in the formation of wide, compacted surface films. The mean thickness of the films increased with load to a few micrometers. The composite exhibited better wear resistance than the matrices in wet air and the wear rate decreased especially at high loads. The wide, compacted films together with the pin-lifting phenomena prevent metal-to-metal contact, achieving a good anti-wear condition. On the other hand, the surface films that adhere in a scaled fashion in dry air have little wear reduction effect.