GenoType MTBDRplus assay for molecular detection of rifampin and isoniazid resistance in Mycobacterium tuberculosis strains and clinical samples

Abstract

The purpose of this study was to evaluate the GenoType MTBDRplus assay (Hain Lifescience GmbH, Nehren, Germany) for its ability to detect resistance to rifampin (RIF) and isoniazid (INH) in Mycobacterium tuberculosis clinical strains and directly in clinical samples. A total of 62 clinical strains characterized with the Bactec 460TB system were included. For the INH-resistant strains, the MIC was measured and sequencing was performed. Sixty-five clinical samples from 28 patients (39 smear-positive samples and 26 smear-negative samples) were also tested directly. The corresponding isolates of the clinical specimens were studied with the Bactec 460TB system. The overall rates of concordance of the MTBDRplus assay and the Bactec 460TB system for the detection of RIF and INH susceptibility in clinical strains were 98.3% (61/62) and 79% (49/62), respectively. The rate of concordance between the Bactec 460TB system and the MTBDRplus test for the detection of INH resistance in the group of 27 strains with low-level resistance was 62.9% (17/27), and that for the detection of INH resistance in the group of 21 strains with high-level resistance was 85.71% (18/21). Valid test results were obtained for 78.45% (51/65) of the clinical samples tested. The rates of concordance between both assays for the detection of drug resistance in these samples were 98% (50/51) for RIF and 96.2% (49/51) for INH. Taking into account only one sample per patient, the overall rate of concordance between both tests was 92.85% (26/28). The GenoType MTBDRplus assay is easy to perform and is a useful tool for the management of tuberculosis, as it allows the detection of resistance to RIF and INH in M. tuberculosis strains and also in clinical samples.

FIG. 1.

Representative DNA patterns obtained by the MTBDRplus assay. Examples of invalid results are also included. Lane 1, example of a pattern of RIF^s and INH^s; lane 2, example of a pattern of RIF^r and INH^r; lane 3, example of a pattern of RIF^s and INH^r; lanes 4 to 9, examples of invalid results. The positions of the oligonucleotides and the control probes are given on the left. The targeted genes and the specific probes lines are shown from top to bottom, as follows: conjugate control (CC); amplification control (AC); M. tuberculosis complex-specific control (TUB); rpoB amplification control; rpoB wild-type probes WT1 to WT8 (505 to 533); four rpoB mutant probes (probes MUT1, MUT2A, MUT2B, and MUT3) in codons D516V, D526Y, H526D, and S531L, respectively; katG amplification control; katG codon 315 wild-type probe; two katG codon 315 mutant probes (probes MUT1 and MUT2) with AGC-ACC (S315T1) and AGC-ACA (S315T2) mutations, respectively; inhA amplification control; inhA wild-type probes WT1 and WT2 covering positions −15 and −16 of the gene regulatory region; four inhA mutant probes (probes MUT1, MUT2, MUT3A, and MUT3B) with mutations C→T at position −15, A→G at position −16, T→C at position −8, and T→A at position −8, respectively. M, colored marker.

FIG. 2.

Distribution of MTBDRplus assay results according to the results obtained with the Bactec 460TB system for the 62 clinical strains.

FIG. 3.

Distribution of MTBDRplus assay results according to the results obtained with the Bactec 460TB system for the 51 clinical specimens with a valid result.