Assessment of the diagnostic potential of immuno-RCA in 96-well ELISA plates for foot-and-mouth disease virus.

The need for fast and very early detection of foot-and-mouth disease virus (FMDV) infection has yielded different types of diagnostic tools over the past decades: whereas very sensitive techniques such as virus isolation (VI) and more recently also real-time RT-PCR can provide evidence for the presence of low virus quantities, VI requires additional confirmation of the nature of the virus strain and both techniques (currently) lack the ability for direct serotyping. The latter usually depends on ELISA, which is a far less sensitive method and may require virus culturing. This paper elaborates on experimental efforts towards the development of an 'immuno-rolling circle amplification (RCA)' assay in 96-well plates, the aim being to increase the sensitivity of immunological FMDV detection and serotyping by means of RCA. The study attempts to explain the encountered hurdles and the complexity of the different setups tested. Conclusively, immuno-RCA in 96-well plates as a reliable diagnostic assay for FMDV seems very difficult to achieve.

Evaluation of antibody-ELISA and real-time RT-PCR for the diagnosis and profiling of bluetongue virus serotype 8 during the epidemic in Belgium in 2006.

In 2006 bluetongue (BT) emerged for the first time in North-Western Europe. Reliable diagnostic tools are essential in controlling BT but data on the diagnostic sensitivity (Se) and specificity (Sp) are often missing. This paper aims to describe and analyse the results obtained with the diagnostics used in Belgium during the 2006 BT crisis. The diagnosis was based on a combination of antibody detection (competitive ELISA, cELISA) and viral RNA detection by real-time RT-PCR (RT-qPCR). The performance of the cELISA as a diagnostic tool was assessed on field results obtained during the epidemic and previous surveillance campaigns. As the infectious status of the animals is unknown during an epidemic, a Bayesian analysis was performed. Both assays were found to be equally specific (RT-qPCR: 98.5%; cELISA: 98.2%) while the diagnostic sensitivity of the RT-qPCR (99.5%) was superior to that of the cELISA (87.8%). The assumption of RT-qPCR as standard of comparison during the bluetongue virus (BTV) epidemic proved valid based on the results of the Bayesian analysis. A ROC analysis of the cELISA, using RT-qPCR as standard of comparison, showed that the cut-off point with the highest accuracy occurred at a percentage negativity of 66, which is markedly higher than the cut-off proposed by the manufacturer. The analysis of the results was further extended to serological and molecular profiling and the possible use of profiling as a rapid epidemiological marker of the BTV in-field situation was assessed. A comparison of the serological profiles obtained before, during and at the end of the Belgian epidemic clearly showed the existence of an intermediate zone which appears soon after BTV (re)enters the population. The appearance or disappearance of this intermediate zone is correlated with virus circulation and provides valuable information, which would be entirely overlooked if only positive and negative results were considered.

Bluetongue in Belgium, 2006.

Bluetongue has emerged recently in Belgium. A bluetongue virus strain was isolated and characterized as serotype 8. Two new real-time reverse transcription-quantitative PCRs (RT-qPCRs) that amplified 2 different segments of bluetongue virus detected this exotic strain. These 2 RT-qPCRs detected infection earlier than a competitive ELISA for antibody detection.

Structural organization of the twin-arginine translocation system in Streptomyces lividans.

The twin-arginine translocation (Tat) system exports folded proteins across bacterial cytoplasmic membranes. Recently, genes encoding TatA, TatB and TatC homologues were identified in Streptomyces lividans and the functionality of the Tat pathway was demonstrated. Here, we have examined the localization and structural organization of the Tat components in S. lividans. Interestingly, besides being membrane-associated proteins, S. lividans TatA and TatB were also detected in the cytoplasm. TatC could only be detected in isolated membrane fractions. Whereas all TatC was found to be stably inserted in the membrane, part of membrane-associated TatA and TatB could be extracted following high salt, sodium carbonate or urea treatment suggesting a more loose association with the membrane. Finally, we have analyzed Tat complexes that could be purified from an S. lividans TatABC overproducing strain. From the cytoplasmic membrane, two types of high molecular mass Tat complexes could be isolated having a similar composition as those isolated from Escherichia coli. In the cytoplasm, TatA and TatB were detected as monomer or as homo-oligomeric complexes.