Evaluation of MTBDR<i>sl</i> for detecting resistance in <i>Mycobacterium tuberculosis</i> to second-line drugs

SETTING: Patients with presumed multidrug-resistant tuberculosis (MDR-TB) and undergoing MDR-TB treatment from Rajasthan, India. OBJECTIVE: To compare the GenoType ® MTBDR sl v.1.0 (MTBDR sl ) assay capacity to detect resistance to ofloxacin, amikacin, capreomycin, kanamycin and ethambutol in Mycobacterium tuberculosis with phenotypic drug susceptibility testing (DST) using MGIT ™ 960™ in sputum samples and isolates. DESIGN: Fifty-three smear-positive sputum samples were tested directly by MTBDR sl and 205 MDR-TB isolates were processed using MTBDR sl and DST for five drugs on MGIT960. DNA sequencing was performed in isolates with discordance in the results between the two methods for the gyr A , gyr B and rrs genes . RESULT: Sensitivity and specificity of MTBDR sl was found to be respectively 93.1% and 100% for fluoroquinoline, respectively 75-78% and 100% for aminoglycosides/cyclopeptides, respectively 70% and 92% for ethambutol and respectively 92.3% and 100% for extensively drug-resistant (XDR) TB detection. On sequencing eight discordant isolates for quinolones, mutations were seen in 12.5% of the gyr B gene and among 20 discordant isolates for aminoglycosides/cyclopeptides in the rrs gene in 15% isolates. The turnaround time was 2 days for MTBDR sl vs. 10 days for MGIT960. CONCLUSIONS: MTBDR sl can be used as an initial rapid test for detecting XDR-TB, resistance to quinolones and aminogycosides/cyclopeptides in smear-positive sputum samples.