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FAST-XDR-DETECT


Development of a two-approach plate system for the fast and simultaneous detection of MDR and XDR M. tuberculosis
 
 
Framework programme:
 7
Contract/Grant agreement number:
201690
EC contribution:
2.700.000 €
Duration:
48 months
Funding scheme:
Collaborative Project
Starting date:
01/02/2008
Web-site:
https://room.projectcoordinator.net/~oligocolor
 
 

Keywords: tuberculosis, drug resistance, MDR, XDR, rapid methods

Background

The HIV/AIDS pandemic and the emergence of drug resistance are hindering the control of tuberculosis (TB). Associated with drug resistance is the emergence of multidrug-resistant (MDR) strains of Mycobacterium tuberculosis, defined as strains resistant to (at least) isoniazid and rifampicin, the most valuable drugs for treatment of the disease. More recently, the appearance of extensively drug-resistant (XDR) strains has been reported. These strains, in addition to being MDR, are also resistant to key second-line drugs. Patients, especially HIV patients, harbouring XDR strains, have virtually no treatment options.

Detection of drug resistance in M. tuberculosis has traditionally been performed by cumbersome methodologies. Based on the detection of M. tuberculosis growth on solid media, these require several weeks to give results. Newer automated culture systems, although accurate and reliable, have been mainly evaluated for first-line anti-TB drugs and, due to their high cost, remain out of reach for most TB laboratories in middle- and low-income countries.

Molecular assays have also been proposed for the detection of drug resistance in M. tuberculosis. They follow a two-step procedure with nucleic acid amplification by polymerase chain reaction (PCR) and subsequent identification of specific mutations known to be associated with drug resistance. Two commercially available tests are based on hybridisation of amplified DNA from cultured isolates or sputum samples to several probes immobilised on a nitrocellulose strip covering the core region of rpoB for detecting resistance to RIF or katG and inhA for detecting resistance to INH. The limitation of these assays is that they only detect resistance to these two drugs. Sequencing DNA of PCR-amplified products has been the most widely used method; it is accurate and reliable and it has become the reference standard for mutation detection in M. tuberculosis. However, it would be rather difficult to implement DNA sequencing routinely for detection of drug resistance to several drugs, such as those responsible for MDR- and XDR-TB simultaneously, since it would involve multiple reactions for each isolate, making their cost high.

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