Genotype MTBDR assay for rapid detection of rifampin and isoniazid resistance in Mycobacterium tuberculosis isolates
Abstract number: 1733_1486
Cisterna R., Alava J., Unzaga M., Blanco R., Fernandez M., Morla A., Garcia L., Ezpeleta C.
Objectives: The rapid determination of drug resistance in clinical isolates of Mycobacterium tuberculosis is essential for the initiation of effective chemotherapy and preventing further spread of drug-resistant isolates. Drug susceptibility testing by conventional methods takes several weeks although some new liquid medium-based systems have been commercially introduced with a shortened incubation time. A commercially DNA strip assay (Genotype MTBDR assay (Hain Lifescience Nehren, Germany) based on a multiplex PCR in combination with reverse hybridisation to identify either wild type or most common mutations in M. tuberculosis katG and rpoB was evaluated.
Material and Methods: Genotype MTBDR assay was evaluated by investigating 53 strains isolated in Basurto Hospital. The results were compared to data obtained by BACTEC MGIT 960 Becton Dickinson Microbiology Systems, Sparks, MD). Both assays were performed as recommended by the manufacturer.
Results: According to the results of BACTEC MGIT 960, 49 were fully susceptible, 2 were resistant to high level isoniazid (0.4mg/mL) (INH), 2 WERE resistant to low level INH (0.1mg/mL), and two was Multidrug-resistant (MDR).
All the isolates that were phenotypically resistant to high level INH had a S315T1 mutation in katG codon 315. No mutation was found in the 2 strains which showed a low level of resistance. None of phenotypically INH-susceptible isolates had the codon 315 mutation.
No mutations were detected in the phenotypically RIF-susceptible.
One of MDR isolate had an rpoB S531L mutation but did not hybridised with the Genotype MTBDR test probe (S531L), although the test with the WT 5 probe was negative. The other one had an rpoB S531L mutation that hybridised with the mutation-specific probe (MUT3). In both of MDR the mutation in katG of MDR was the same than the mentioned in the other strains.
Conclusions: Genotype MTBDR assay allows rapid and specific detection to INH and RMP although it cannot totally replace traditional cultured-based methods basically due there is not molecular test established targets all possible genes o mechanism and thus a variable proportion of resistant strains will not be detected.
|Session name:||European Society of Clinical Microbiology and Infectious Diseases|
|Location:||ICC, Munich, Germany|
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