Evaluation of new GenoType® MTBDRplus for detection of resistance in cultures and direct specimens of Mycobacterium tuberculosis

S ETTIN G S: Molecular methods frequently used in laboratories Can now give US Useful information about low growth bacteria. OBJECTIVE: To evaluate the new GenoType (R) MTBDRplus assay for its ability to detect mutations in the 81-bp hotspot region of the rpoB gene, mutations In codon 315 of the katC, gene and alterations in the inhA promoter region. DESIGN: Prospective resistance to rifampicin (RMP) and isoniazid (INH) study using Mycobacterium tuberculosis positive specimens and cultures comparing the results of GenoType MTBDRplus with those obtained phenotypically with the Bactec MGIT (Mycobacterial Growth Indicator Tube) 960. RESULTS: In 59 specimens (18 smear microscopy Samples and 41 solid and liquid medium Cultures), mutations were detected in all of 36 M. tuberculosis strains phenotypically resistant to RMP(100%),and in 35 of 37 strains phenotypically resistant to INH (94.59%). The new assay prompted a 21.6% increase in the direct detection of INH resistance in the strains studied, due to the incorporation of inhA promoter region probes in the test. CONCLUSIONS: The GenoType MTBDRplus assay is a valid method for detecting the most common mutations in strains resistant to RMP and INK However, further phenotypic testing is required, as the assay failed to detect 100% of INH and RMP resistance.