A sputum sample from a suspected TB patient is smear-negative but culture-positive. Line probe assay (LPA) on a subsequent sputum sample detects wild-type rpoB band absence and mutation in codon 531. What does this indicate?
- A Rifampicin resistance predicting MDR-TB ✓
- B Susceptibility to rifampicin
- C Isoniazid resistance only
- D Streptomycin resistance
Correct answer: A. Rifampicin resistance predicting MDR-TB
Explanation
LPA (e.g., GenoType MTBDRplus) detects rpoB mutations (codons 516, 526, 531) associated with rifampicin resistance; absence of wild-type band and presence of mutation band at codon 531 confirms rifampicin resistance. Because >90% of rifampicin-resistant strains are also isoniazid-resistant, rifampicin resistance is used as a proxy for MDR-TB (resistance to both rifampicin and isoniazid), necessitating second-line DST. Isoniazid resistance is detected via katG and inhA probes on the same LPA.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.