The CBNAAT (Xpert MTB/RIF) assay simultaneously detects M. tuberculosis DNA and resistance to rifampicin by probing which gene?
- A katG (isoniazid resistance gene)
- B rpoB (RNA polymerase beta subunit gene) ✓
- C gyrA (DNA gyrase A gene)
- D embB (ethambutol resistance gene)
Correct answer: B. rpoB (RNA polymerase beta subunit gene)
Explanation
The Xpert MTB/RIF assay (CBNAAT) uses real-time PCR to detect M. tuberculosis-specific rpoB gene sequences and simultaneously identifies mutations in an 81-bp 'hotspot' region of rpoB associated with >95% of rifampicin-resistant strains. Since rifampicin resistance is a reliable surrogate marker for MDR-TB, a single test can flag MDR-TB risk. katG mutations cause isoniazid resistance; gyrA mutations cause fluoroquinolone resistance; embB mutations cause ethambutol resistance.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.