Evaluation of the cobas MTB and MTB-RIF/INH assay in clinical samples for the detection of Mycobacterium tuberculosis in respiratory specimens

The aim of this study was to evaluate the performance of the automa ted cobas MTB-Real-Time PCR assay for the rapid direct detection of Mycobacterium tuberculosis complex (MTBC) in clinical specimens and the ability of the cobas MTBRIF/INH assay to correctly detect drug resistance to rifampin (RIF) and isoniazid (INH). The PCR assays were set up on the automated Cobas 6800 system, and the results were compared to liquid culture using BACTEC mycobacteria growth indicator tubes 960 TB system as the gold standard and line probe assays or sequencing results. A total of 500 N-acetyl-L-cysteine/sodium hydroxide (NALC-NaOH)-processed sputum samples were tested with the respective methods. The performance of MTBC detection in pulmonary specimens showed 91.8% sensitivity and 99.3% specificity in comparison to culture. The sensitivity for acid-fast bacteria (AFB) smear-positive specimens and for AFB smear-negative specimens was 100% and 85.1%, respectively. Due to the low prevalence of tuberculosis (TB) resistance in Germany, a collection of resistant TB strains with a wide variety of mutations was analyzed. The cobas MTB-RIF/INH assay detected 19 out of 21 INH-resistant and 22 out of 24 RIF-resistant TB strains. In conclusion, the cobas MTB and the cobas MTB-RIF/INH assays implemented on the automated cobas6800 instrument are reliable and versatile tools for the detection of MTB and RIF/INH resistance. IMPORTANCE Our manuscript addresses the WHO recommendation for the use of "moderate-complexity automated NAATs for detection of TB and resistance to rifampicin and isoniazid" as a part of the WHO End TB Strategy. Rapid detection of tuberculosis (TB) patients is essential to preventing TB transmission and finally reducing TB burden. In this study, we present data on the sensitivity and specificity of the novel cobas MTB assay for TB detection in a low-incidence country, demonstrating highly promising results. Additionally, by analyzing TB strains with various mutations conferring resistance to INH and/or RMP, we assess the opportunities and limitations of the cobas MTB-RIF/INH assay in reliably detecting drug resistance in sputum specimens, thereby facilitating the early onset of appropriate treatment.