Evaluation of Mycobacterium tuberculosis drug susceptibility in clinical specimens from Nigeria using genotype MTBDRplus and MTBDRsl assays.

The incidence of tuberculosis (TB) and especially multidrug-resistant TB (MDR) continues to increase alarmingly worldwide, and reliable and fast diagnosis of MDR is essential for the adequate treatment of patients. In contrast to the standard culture methods, nucleid acid amplification tests (NAATs) provide information about presence of Mycobacterium tuberculosis complex (MTBC) DNA and a potential resistance pattern within hours. We analyzed specimens of 110 patients from Nigeria comparing culture-based drug susceptibility testing (DST) to NAAT assays detecting isoniazid (INH), rifampicin (RMP) (GenoType MTBDRplus), and ethambutol (EMB) (GenoType MTBDRsl) resistance. Compared to DST, the GenoType MTBDRplus and MTBDRsl showed a specificity of 100% (86.3-100) and a sensitivity of 86% (42.1-99.6%) for detection of INH and a specificity of 100% (86.3-100) and a sensitivity of 83% (35.9-99.6%) for detection of RMP, and a sensitivity 100% (47.8-100%) for EMB resistance. However, in two strains, the NAAT assays provided false susceptible results as the mutations causing resistance were in genomic regions not covered by the probes of the GenoType MTBDRplus assay. We show that, in combination to DST, application of the GenoType MTBDRplus and GenoType MTBDRsl assays might be a useful additional tool to allow a rapid and safe diagnosis of MDR and extensively drug-resistant (XDR) MTBC.