Evaluation of the MTBDRsl test for detection of second-line-drug resistance in Mycobacterium tuberculosis

Abstract

The MTBDRsl assay (Hain Lifescience GmbH, Germany) is a new line probe assay for the detection of extensively drug-resistant tuberculosis (XDR TB). The test simultaneously detects resistance to ethambutol, aminoglycosides/cyclic peptides, and fluoroquinolones through detection of mutations in the relevant genes. The assay format is identical to the MTBDR Hain assay. The assay was evaluated for the detection of second-line-drug resistance in Vietnamese isolates using two sample sets from the microbiology department of Pham Ngoc Thach Hospital, Ho Chi Minh City, Viet Nam, with existing conventional phenotypic drug susceptibility results for second-line drugs: 41 consecutive fluoroquinolone-resistant isolates and 21 consecutive multidrug-resistant but fluoroquinolone-sensitive isolates. The sensitivity for detection of fluoroquinolone resistance was 75.6% (31/41) (95% confidence interval [95% CI], 59.7% to 87.6%), and for kanamycin resistance, the sensitivity was 100% (5/5) (95% CI, 47.8% to 100%). The sensitivity of the test for detection of ethambutol resistance was low, consistent with previous reports, at 64.2% (34/53) (95% CI, 49.8% to 76.9%). The specificity of the test was 100% for all three drugs. These data suggest that the MTBDRsl assay is a rapid, specific test for the detection of XDR TB but should not be used exclusively to "rule out" second-line-drug resistance. Further operational evaluation is required and should be integrated with evaluations of the MTBDR test.

FIG. 1.

Representative patterns obtained by the MTBDRsl assay. Lane 1, negative control; lanes 2 and 3, FQ-, EMB-, and KAN-susceptible strains; lanes 4, 5, 6, and 7, resistant strains (lane 4, resistant to FQ and EMB; lane 5, resistant to FQ, AMP/CMP, and EMB; lane 6, resistant to EMB; lane 7, resistant to FQ and EMB); lanes 8, 9, 10, and 11, strains containing wild-type and FQ-resistant populations. Specific probes are as follows: CC, conjugate control; AC, amplification control; TUB, Mycobacterium tuberculosis complex control; gyrA, gyrA gene amplification control; gyrA WT1 to WT3, gyrA wild-type probes; gyrA MUT1, gyrA MUT2, and gyrA MUT3A to MUT3D, gyrA mutant probes for A90V, S91P, D94A, D94N, D94Y-D94G, and D94H, respectively; rrs, rrs amplification control; rrs WT1 and WT2, rrs wild-type probes; rrs MUT1 and MUT2, rrs mutant probes for A1401G and G1484T, respectively; embB, embB amplification control; embB WT1, embB wild-type probe I codon 306; embB MUT1A and embB MUT1B, embB mutant probes for M306I and M306V, respectively.