A sputum culture from a patient with previously treated pulmonary TB grows M. tuberculosis resistant to isoniazid and rifampicin but susceptible to fluoroquinolones and injectable agents (amikacin/kanamycin). This drug resistance pattern defines:

• A Extensively drug-resistant TB (XDR-TB)
• B Pre-XDR TB
• C Rifampicin-resistant TB (RR-TB) without MDR classification
• D Multidrug-resistant TB (MDR-TB) ✓

Explanation

MDR-TB is defined as M. tuberculosis resistant to at least isoniazid and rifampicin (the two most potent first-line drugs), regardless of resistance to other agents. The updated WHO 2021 definitions: XDR-TB = MDR/RR-TB plus resistance to any fluoroquinolone AND at least one of bedaquiline or linezolid; Pre-XDR-TB = MDR/RR-TB resistant to a fluoroquinolone. Since this isolate is susceptible to fluoroquinolones, it is classified as MDR-TB. Treatment uses a BPaLM or BPaL regimen under NTEP guidelines.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.