Ann Clin Microbiol 2025;28(4):26. Drug susceptibility testing for Mycobacterium tuberculosis: a narrative review

Download table
Table 1. Drug-resistant tuberculosis classifications
Drug-resistanceDescription
Isoniazid-resistant TB (rifampicin-susceptible) (Hr-TB)Tuberculosis caused by Mycobacterium tuberculosis strains that are resistant to isoniazid but remain susceptible to rifampicin.
Rifampicin-resistant TB (RR-TB)TB caused by strains resistant to rifampicin, with or without resistance to other first-line drugs.
Multidrug-resistant TB (MDR-TB)TB caused by strains resistant to at least both isoniazid and rifampicin.
Pre-extensively drug-resistant TB (pre-XDR-TB)RR-TB or MDR-TB with additional resistance to any fluoroquinolone.
Extensively drug-resistant TB (XDR-TB)RR-TB or MDR-TB with additional resistance to any fluoroquinolone and at least one Group A agent (e.g., bedaquiline or linezolid).

Abbreviation: TB, tuberculosis.