Lab Med Online.  2011 Jan;1(1):19-25.

Evaluation of the Performance of GenoType(R) MTBDRplus Assay for Rapid Detection of Multi-drug Resistant Mycobacterium tuberculosis in Sputum Specimens

Affiliations
  • 1Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea. mnkim@amc.seoul.kr
  • 2Department of Internal Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea.

Abstract

BACKGROUND
GenoType(R) MTBDRplus assay (Hain Lifescience, Germany) enables detection of the mutations prevalent in rpoB, katG, and inhA genes and identification of Mycobacterium tuberculosis complex (MTB). We evaluated the performance of the MTBDRplus assay in detecting multidrug resistant M. tuberculosis in sputum specimens by directly comparing it to the performance of conventional drug susceptibility testing (DST) with M. tuberculosis culture isolates.
METHODS
From December 2007 to July 2008, 40 patients with acid-fast bacilli (AFB) smear-positive and AFB culture-positive sputa, including 19 patients with rifampin (RIF)- or isoniazid (INH)-resistant MTB isolates, were enrolled. The MTBDRplus assay was performed using DNA extracted from respiratory specimens. DST of the culture isolates was performed using an absolute concentration method.
RESULTS
The result of the AFB smear test was +/-1 for 7 specimens, +1 for 8 specimens, +2 for 9 specimens, +3 for 9 specimens, and +4 for 7 specimens. The MTBDRplus assay revealed that 37 of the 40 specimens were positive for an MTB-specific band, 12 specimens were RIF-resistant, and 16 specimens were INH-resistant. The rpoB S531L mutation was detected in 58.3% of the RIF-resistant specimens, and the katG S315T1 and inhA C15T mutations were detected in 56.3% and 31.3% of the INH-resistant specimens, respectively. Compared to the sensitivity and specificity of DST, both sensitivity and specificity of MTBDRplus assay for RIF resistance were 100%, and the corresponding values for INH resistance were 82.4% and 90.0%. Discrepant MTBDRplus assay and DST results were obtained in 3 INH-resistant isolates without mutation and 2 INH-susceptible isolates with katG S315T1 and inhA C15T mutations.
CONCLUSIONS
The MTBDRplus assay can be applied for AFB smear-positive specimens with positivity +/- to 4+. The assay was reliable for predicting the RIF resistance of culture isolates, but DST was required for confirming INH resistance.

Keyword

GenoType(R) MTBDRplus assay; Rifampin; Isoniazid; Multi-drug resistant Mycobacterium tuberculosis
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