The Xpert MTB/RIF assay (GeneXpert) simultaneously detects M. tuberculosis complex and rifampicin resistance in under 2 hours. Rifampicin resistance is detected by identifying mutations in which region?
- A katG gene encoding catalase-peroxidase
- B rpoB gene — specifically mutations within the 81 bp Rifampicin Resistance Determining Region (RRDR) ✓
- C inhA gene encoding enoyl-ACP reductase
- D pncA gene encoding pyrazinamidase
Correct answer: B. rpoB gene — specifically mutations within the 81 bp Rifampicin Resistance Determining Region (RRDR)
Explanation
Xpert MTB/RIF detects M. tuberculosis complex by amplifying an IS6110 target and simultaneously uses probes covering the 81 base-pair RRDR (Rifampicin Resistance Determining Region) of the rpoB gene. Over 96% of clinically significant rifampicin resistance mutations fall within this region, most commonly at codon 450 (S450L, formerly S531L), 445 (H445Y), and 441 (L441P). katG mutations confer isoniazid resistance; inhA promoter mutations confer low-level isoniazid and ethionamide resistance; pncA is for pyrazinamide 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.