The increasing cases of multidrug-resistant tuberculosis (MDR-TB), caused by Mycobacterium tuberculosis resistant to isoniazid and rifampicin, and its extended resistance to other drugs are of great concern worldwide [1]. Treatment of drug-resistant TB relies on second-line drugs, which are more expensive, more toxic and less effective, resulting in longer treatment duration, thus reducing quality of life [2].

Preextensively drug-resistant TB (pre-XDR-TB) was classified as rifampicin-resistant-/MDR-TB with resistance to fluoroquinolones or second-line injectable drugs such as capreomycin, amikacin and kanamycin, while extensively drug-resistant-TB (XDR-TB) was rifampicin-resistant-/MDR-TB also resistant to both fluoroquinolones and second-line injectable drugs. In 2021, the World Health Organization (WHO) updated definitions of both pre-XDR- and XDR-TB, classifying pre-XDR-TB as caused by a rifampicin-resistant/MDR strain resistant to a fluoroquinolone, and XDR-TB as a rifampicin-resistant/MDR strain resistant to a fluoroquinolone and bedaquiline and/or linezolid [3]. Here, we apply the previous definitions of pre-XDR- and XDR-TB, because this study was performed before these updates.

WHO recommends the use of GenoType MTBDRsl (Bruker-Hain Lifescience, Nehren, Germany) for speeding up the detection of resistance to fluoroquinolones and second-line injectables, helping clinicians to manage drug-resistant TB treatment. The rapid detection of drug resistance also has an important impact by reducing drug-resistant-TB transmission within the community and minimizing the development of additional drug resistance [1,4].

GenoType MTBDRsl version (v.) 1.0 is a line probe assay (LPA) for genetic identification of the M. tuberculosis complex and its resistance to fluoroquinolones, aminoglycosides/cyclic peptides and ethambutol, by detecting the most frequent mutations in gyrA, rrs and embB genes, respectively. The assay can be performed directly in clinical specimens or cultured isolates [5,6].

In Brazil, a high TB burden country, drug susceptibility testing (DST) of M. tuberculosis to first- and second-line drugs is routinely performed by the proportion method in solid media or the automated BACTEC MGIT 960 (Becton Dickinson, Sparks, MD, USA). These phenotypic methodologies are time-consuming and delay the diagnosis of drug-resistant TB [7].

Very few studies using MTBDRsl on culture isolates in the routine of a high-throughput laboratory were conducted so far. Furthermore, information on second-line drug resistance-associated mutations in M. tuberculosis is scarce in our setting. Thus, we evaluated the performance of the MTBDRsl assay v. 1.0 compared to the phenotypic reference method of MGIT 960, for the detection of resistance to fluoroquinolones, aminoglycosides/cyclic peptides and ethambutol in MDR M. tuberculosis isolates.