Evaluation of the GenoType MTBDRplus assay for detection of rifampicin- and isoniazid-resistant Mycobacterium tuberculosis isolates in central Ethiopia

Objective/Background: Multidrug-resistant tuberculosis (MDR-TB) is growing globally and becoming a major challenge for national TB control programs. Therefore, rapid identification of MDR strains of Mycobacterium tuberculosis and monitoring their transmission could contribute significantly to the control of TB. The GenoType MTBDRplus assay has been recommended by the World Health Organization to identify rifampicin (RIF)- and isoniazid (INH)-resistant M. tuberculosis isolates. This study was carried out to evaluate the performance of the GenoType MTBDRplus assay for the detection of RIF- and INH-resistant M. tuberculosis isolates in central Ethiopia. Methods: A total of 279 M. tuberculosis strains isolated from active TB cases in central Ethiopia were evaluated for their drug sensitivity by the conventional drug-susceptibility test (DST) and compared with data derived from the GenoType MTBDRplus assay. The DST served as the gold standard for evaluating the GenoType MTBDRplus assay. Results: The sensitivity and specificity of the GenoType MTBDRplus assay for the detection of RIF-resistant M. tuberculosis isolates were 80.0% and 99.6%, respectively. Its sensitivity and specificity for the detection of INH-resistant M. tuberculosis isolates were 82.7% and 99.6%, respectively, whereas they were 75.0% and 100%, respectively, for the detection of MDR M. tuberculosis strains. The concordances of the GenoType MTBDRplus assay and the conventional DST for the detection of RIF and INH susceptibility were 80% (8/10) and 86.2% (25/29), respectively. Furthermore, the concordance of the two tests for the detection of MDR M. tuberculosis strains was 75%. Specific mutations were detected in 55.6% (5/9) of the RIF-resistant isolates, with the highest mutation rate (33.3%) for the rpoB gene (Codon S531L). For INH-resistant isolates, the highest mutation rate (88.8%) related to a katG mutation (Codon S315T1). Conclusion: The findings of this study revealed that the GenoType MTBDRplus assay has high sensitivity and specificity for the detection of RIF and INH resistance. These preliminary data support the notion that the assay should be considered as an alternative to the DST for the characterization of MDR in M. tuberculosis isolates and the control of TB.