Faster lab test helps find drug-resistant TB in routine practice

Drug-resistant tuberculosis remains a major global health problem, and multidrug-resistant TB (MDR-TB) — resistance to at least rifampicin (RIF) and isoniazid (INH) — makes treatment harder and can drive further spread. To explore faster ways to find resistant TB, researchers tested a molecular platform in a routine reference laboratory setting. The study, led by corresponding author Juliana Maíra Watanabe Pinhata, evaluated the BD MAX™ Multi-Drug Resistant Tuberculosis (BD MAX) assay when used off-label on cultured clinical samples of Mycobacterium tuberculosis complex (MTBC). The goal was to see whether this fully automated real-time PCR platform, already recommended by the World Health Organization for direct testing of pulmonary samples, would still perform well when applied to isolates grown in the lab. The team first ran validation experiments with a mix of non-tuberculous mycobacteria (NTM) and MTBC isolates that had known resistance mutations, then moved on to a real-world comparison against a widely used line probe test to measure how well BD MAX identifies MTBC and detects resistance to RIF and INH under the pressures of high-volume testing.

The study began with targeted validation: BD MAX was challenged with NTM cultures and MTBC isolates that carried known resistance mutations. It correctly excluded MTBC from all NTM cultures, and among MTBC isolates with known mutations it identified 19 of 20 RIF-R isolates and 14 of 15 INH-R isolates. For real-world performance the team tested 1,440 clinical isolates prospectively and compared BD MAX results to the GenoType MTBDR plus assay. For MTBC detection BD MAX achieved 99.8% sensitivity (1,406/1,409), 100% specificity (31/31), and 99.8% overall accuracy (1,437/1,440). For drug resistance detection, concordance with MTBDR plus was 95.2% (40/42) for RIF, 96.8% (30/31) for INH, and 81.3% (13/16) for MDR. The study noted the main mismatches involved heteroresistant cases and situations where BD MAX returned unreportable resistance results because of infrequent mutations or low bacterial load.

Taken together, the results show BD MAX can be an accurate and reliable tool for both MTBC detection and drug resistance profiling when used on clinical isolates in a busy reference laboratory. Because BD MAX is fully automated and faster to run than a line probe assay like GenoType MTBDR plus, the study suggests it could simplify workflows and speed up results in high-volume settings, helping laboratories identify resistant TB more quickly. The authors also highlight limitations: BD MAX may miss or be unable to report resistance linked to rare mutations, and performance may fall when bacterial levels are low, so follow-up testing or complementary methods could still be needed in some cases. Overall, applying BD MAX off-label to cultured isolates offers a practical option to improve turnaround time for TB and drug-resistance testing in large laboratories, potentially aiding faster patient management and public health responses.