Interlaboratory validation of the Vidas SET2 kit for detection of staphylococcal enterotoxins in milk products

An earlier intralaboratory validation study based on the EN ISO 16140 Standard conducted by the Community Reference Laboratory for coagulase-positive staphylococci including Staphylocococcus aureus showed that, after an extraction step using dialysis concentration, the Vidas SET2 detection kit could be used to screen staphylococcal enterotoxins in milk and milk products. In order to fully validate Vidas SET2, an interlaboratory study was organized. Six freeze-dried samples and 3 ready-to-use concentrated extracts were analyzed by 21 laboratories according to the method, including a detection with Vidas SET2. Results did not show false-positive or -negative results. Accordance and concordance parameters were equal to 100%, corresponding to a concordance odds ratio of 1. This interlaboratory study confirmed the satisfactory outcome of the preliminary tests and of the intralaboratory study performed previously. The Vidas SET2 detection kit can be used as a method for the detection of staphylococcal enterotoxins in milk and milk products as well as the Transia Plate SET detection kit in the European screening method for official control purposes, after an extraction step followed by dialysis concentration.     

Paramagnetic pyrrole-based semiconductor molecular material

The electrochemical oxidation of hexa-N-pyrrolylbenzene in organic media leads, via intramolecular coupling of the pyrrole residues, to the deposition of a molecular semiconductor film on an electrode surface. In situ electron spin resonance–electrochemical experiments reveal that the semiconductor is endowed with both properties of conducting polymers (i.e., reversible oxidation) and polyaromatic molecular materials (i.e., highly paramagnetic). The material, which is easy to process as soft homogeneous thin film, shows a tunable 0 to 1 spin concentration per molecule at room temperature by controlling the electrochemical potential. Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on the Electrochemical–Chemical Reactivity of Metastable Materials, Warsaw, 17th–21st September, 2007. An erratum to this article can be found at     

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the ground X1Sigma+ state. Copyright 1999 Academic Press.     

Spectral analysis of 208Pb muonic atom

We have applied to the ²⁰⁸Pb muonic atom a series of recurrence relations relating the moments of the ground-state density and the energy differences between the 1s level and the states of the line. The large amount of precise experimental data and the electromagnetic character of the interaction allow a detailed test of the method for determining the ground-state density and reconstructing the local equivalent potential. Though the present work is limited to the study of the efficiency for a given trial density, it results in a semi-quantitative analysis with an accuracy better than 1%. Received: 18 December 2000 / Accepted: 18 April 2001     

Generalized Bertlmann-Martin inequalities and power-law potentials

In the three-dimensional Schrödinger equation, the generalized Bertlmann-Martin inequalities connect the moments of the ground state density to the energy differences between the lowest level of each angular momentum ? and the ground state. They are discussed in the case of the power-law potentials, as well as the lnr potential. Use is made of the derived moments to reconstruct the form factor F(q), i.e., the Fourier transform of the ground state density. Padé approximants are used to describe the high q behavior of the form factor when only a limited number of low order moments are known. The estimate of the ground state density at the origin is also discussed.     

Identification of iron(III) peroxo species in the active site of the superoxide reductase SOR from Desulfoarculus baarsii

The active site of superoxide reductase SOR consists of an Fe2+ center in an unusual [His4 Cys1] square-pyramidal geometry. It specifically reduces superoxide to produce H2O2. Here, we have reacted the SOR from Desulfoarculus baarsii directly with H2O2. We have found that its active site can transiently stabilize an Fe3+-peroxo species that we have spectroscopically characterized by resonance Raman. The mutation of the strictly conserved Glu47 into alanine results in a stabilization of this Fe3+-peroxo species, when compared to the wild-type form. These data support the hypothesis that the reaction of SOR proceeds through such a Fe3+-peroxo intermediate. This also suggests that Glu47 might serve to help H2O2 release during the reaction with superoxide.     

Protein purification using combined streptavidin (or avidin)-Sepharose and thiopropyl-Sepharose affinity chromatography.

The major problem usually encountered in the application of the (strept)avidin-biotin system to the purification of proteins (or other biological molecules) lies in the difficult reversion of the interaction between immobilized (strept)avidin and the adsorbed biotinylated protein. Among the proposed solutions is the selective biotinylation of the entity to be purified by a disulphide-containing biotinylated reagent which allows its recovery from (strept)avidin gels by dithiothreitol (DTT) treatment. As emphasized by the example of angiotensin II receptor purification, achieved using this strategy, optimum reduction of this disulphide bridge may require improvement of its accessibility using denaturating agents such as sodium dodecyl sulphate or urea. However, these agents release important amounts of (strept)avidin. Two general ways of solving this problem are proposed. One solution takes advantage of the absence of cysteine in the streptavidin sequence: the protein to be purified is selectively readsorbed to thiopropyl-Sepharose through the thiol function generated on DTT cleavage of the biotinylated reagent. The other solution is an empirical approach to make possible the use of avidin, which possesses cysteine residues: combined avidin-Sepharose and thiopropyl-Sepharose chromatography proved efficient when carried out in the presence of urea as denaturing agent.     

Modeling 1-D elastic P-waves in a fractured rock with hyperbolic jump conditions

The propagation of elastic waves in a fractured rock is investigated, both theoretically and numerically. Outside the fractures, the propagation of compressional waves is described in the simple framework of 1-D linear elastodynamics. The focus here is on the interactions between the waves and fractures: for this purpose, the mechanical behavior of the fractures is modeled using nonlinear jump conditions deduced from the Bandis–Barton model classically used in geomechanics. Well-posedness of the initial-boundary value problem thus obtained is proved. Numerical modeling is performed by coupling a time-domain finite-difference scheme with an interface method accounting for the jump conditions. The numerical experiments show the effects of contact nonlinearities. The harmonics generated may provide a nondestructive means of evaluating the mechanical properties of fractures.