Etude sérologique et bactériologique des mycoplasmoses aviaires dans la région du Cap Bon en Tunisie

Une enquête séroépidémiologique et bactériologique a été effectuée en Tunisie dans une région à forte concentration aviaire pour le dépistage des mycoplasmoses à Mycoplasma gallisepticum, M. synoviae chez la poule et chez la dinde. Au cours de l'enquête, 63 élevages ont été visités et 780 prélèvements de sang et écouvillons trachéaux ont été effectués et analysés pour la recherche sérologique d'anticorps anti-Mycoplasma gallisepticum, -M. synoviae et -M. meleagridis. La recherche bactériologique a porté sur M. gallisepticum et M. synoviae. Les taux d'infection des troupeaux déterminés par sérologie étaient de 36,5 % pour M. gallisepticum, de 19 % pour M. synoviae et de 0 % pour M. meleagridis. Les élevages positifs en bactériologie pour M. gallisepticum et M. synoviae étaient respectivement au nombre de 15 et 5, soit 23,8 et 7,9 % des élevages visités

Ageing phenomena and determination of the optical self absorption coefficient in PN junction

We have developed a model for the calculation of the induced current due to an electron beam with an extended generation profile. The analytical expression of the electron beam induced current (EBIC) is obtained by solving the steady-state continuity equation using the Green function method. In the case of a sulphur doped (Ga0.7Al0.3As:N+/Ga0.7Al0.3As:P) sample prepared by metalorganic vapour phase epitaxy (MOVPE) method, the experimental current profile, measured by SEM enabled us to calculate the diffusion length of the minority carriers (Lp = 1 μm in the N region and Ln = 1.80 μm in the P region of the ternary sample). Far from the depletion layer, the experimental current profile measured provided us the optical self absorption coefficient of this sample: ap = 1.483 μm−1 in the N region and an = 0.167 μm−1 in the P region. According to our EBIC model, the width of the depletion layer of this sample is about 0.8 μm, while at elaboration of the sample, 10 years ago, the width of the depletion layer deduced from the characteristic curve I(V) was about 300−400 Å. This widening of the depletion layer is due to the ageing of the diode

A Recombinant Antigen-Based ELISA for the Simultaneous Differential Serodiagnosis of Mycoplasma gallisepticum, Mycoplasma synoviae, and Mycoplasma meleagridis Infections

International audienceWe have previously identified species-specific DNA fragments, referred to as MS2/28 and Mm14, of Mycoplasma synoviae and Mycoplasma meleagridis, respectively. In the present study, we extended our analysis of the MS2/28 fragment that was found to encode a species-specific antigenic site, and we demonstrated the specificity of the Mycoplasma gallisepticum hemagglutinin protein encoded by pMGA1.2 (a member of the vlhA gene family). Then, we combined the Escherichia coli-expressed products of MS2/28, Mm14, and pMGA1.2, to develop a recombinant antigen-based enzyme-linked immunosorbent assay (recELISA), for the simultaneous and specific detection of antibodies to the three aforementioned major avian mycoplasma species. For comparative purposes, a novel in-house crude antigen capture ELISA (capELISA) was developed in parallel. In the latter protocol, the microtiter wells were enriched in species-specific antigens by capturing sonicated crude antigens on coated rabbit polyclonal antibodies that had been extensively adsorbed with the whole antigen of the heterologous species. With regard to rapid serum agglutination, both ELISA tests were highly specific, and they showed a significant correlation when field sera from naturally infected birds were tested. recELISA proved to be highly specific because absorbance values, with the heterologous species, were significantly lower (P<0.001) than those obtained with capELISA. Given its cost-effectiveness and simplicity, the recombinant antigen-based ELISA seems to represent a valid tool for the specific screening of the three major avian mycoplasma species. recELISA will be particularly useful with regard to trade control because a large number of samples from various fields could be rapidly processed

Duplex PCR To Differentiate between Mycoplasma synoviae and Mycoplasma gallisepticum on the Basis of Conserved Species-Specific Sequences of Their Hemagglutinin Genes

We developed a duplex PCR assay targeting the hemagglutinin multigene families, vlhA and pMGA, of Mycoplasma synoviae and Mycoplasma gallisepticum, respectively. The assay proved to be specific and sensitive enough to justify its use for the simultaneous detection of the two major avian mycoplasma species from field isolates

Minority carrier diffusion lengths and optical self-absorption coefficient in undoped GaN

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Determination of the diffusion length and the optical self absorption coefficient using EBIC model

We have developed a model of calculation of the induced current due to an electron beam. The expression for the electron beam induced current (EBIC) with an extended generation profile is obtained via the resolution of a steady state continuity equation by the Green function method, satisfying appropriated boundary conditions to the physical model. The generation profile takes into account the lateral diffusion, the effect of defects, dislocations and recombination surfaces besides the number of absorbed electrons and that of diffuse electrons as a function of the depth. In the case of a Schottky diode Au/GaAs obtained by metalorganic vapour phase epitaxy (MOVPE) method, the theoretical induced current profile is compared to the experimental one and to theoretical profiles whose analytical expressions are given by van Roosbroeck and Bresse. The minority carriers diffusion length Ln = 2 µm and the optical self-absorption coefficient a = 0.034 µm−1 can be deduced from the experimental current profile, measured by scanning electron microscopy. The theoretical curve, obtained from the proposed model is in a good agreement with the experimental one for surface recombination velocity 106 cm s−1 except for distances far from the depletion layer (x0 > 2.3 µm) where the photocurrent produced by the multiple process of the reabsorbed recombination radiation is preponderant. Our results are in agreement with those obtained by other experimental techniques on the same samples

Molecular cloning of a Mycoplasma meleagridis-specific antigenic domain endowed with a serodiagnostic potential

International audienceA recombinant phage library harbouring Mycoplasma meleagridis (MM) genomic DNA fragments was generated in the bacteriophage lambda gt11 expression vector. The library was screened for expression of MM specific antigens with a polyclonal antiserum that had been preadsorbed with antigens of the most common unrelated avian mycoplasma species. A 49-aminoacid antigenic domain unique to MM was isolated, expressed in Escherichia coli, and its serodiagnostic potential was demonstrated. An antiserum raised against this MM-specific antigenic domain recognized a cluster of seven membrane-associated MM proteins with molecular masses ranging from 34 to 75 kDa. Overall, this study resulted in the identification of a potent serodiagnostic tool and revealed the complex antigenic nature of MM. (c) 2006 Elsevier B.V. All rights reserved

Optical properties of GaN grown on porous silicon substrate

International audienceA photoluminescence (PL) study of GaN grown on Si(100) substrate using porous silicon (PS) as an intermediate layer is reported. The samples were characterized using PL for the temperature range 5-300 K under various excitation powers from 5 to 50 mW. For growth temperatures below 800 °C, the room temperature PL shows a broad peak located around cubic GaN emission. This is in clear contradiction with previous scanning electron microscopy and X-ray measurements. At low PL temperature, the observed lines located at 3.306 and 3.364 eV have a narrow full width at half maximum of about 6 and 10 meV, respectively. When the excitation power was varied, no peak shift was observed. These peaks were assigned as deeply localized excitons related to stacking faults near the PS/GaN interface. Quantum confinement (type I or II) due to the presence of nanometric cubic inclusions is another possible explanation for the low-temperature PL

Study of space charge in gallium nitride by the thermal step method

International audienceIn this paper, we report the electric investigation of thin nitride gallium films by the capacitance voltage technique and the thermal step method (TSM). The C-V analysis at 1 MHz of Au/GaN diode reveals MOS behaviour and shows strong capacitance hysteresis. This may be due to the presence of trapped charge in this structure. The space charge dynamics is studied by thermal step method at different applied voltages. The TS currents are reverted from negative ones to positive ones above inversion threshold of +0.2 V. This change corresponds to charge modulation from accumulation to the inversion one, in good agreement with the C-V characteristics. The stored charge in this sample is related to the nature of gallium nitride and to the manufacturing processes. The results confirm the possibility to apply the TSM for the measurement of the space charge in the semiconductor materials