A Line Probe Assay (LPA — Hain GenoType MTBDRplus) performed on sputum from a tuberculosis patient detects a probe-hybridization pattern showing absence of the rpoB wild-type band WT8 and presence of MUT3 band. This finding indicates resistance to which drug?

• A Rifampicin ✓
• B Isoniazid
• C Pyrazinamide
• D Ethambutol

Explanation

The LPA MTBDRplus detects resistance to rifampicin (rpoB gene mutations) and isoniazid (katG and inhA mutations). The rpoB gene RRDR (Rifampicin Resistance Determining Region) contains wild-type probes (WT1–WT8) and mutation probes (MUT1–MUT3). Loss of the WT8 band with gain of MUT3 (corresponding to codon 531 Ser→Leu mutation — the most frequent rpoB mutation worldwide) signifies rifampicin resistance. isoniazid resistance is detected via katG (MUT1) and inhA (MUT1–MUT3) mutation probes. Pyrazinamide and ethambutol resistance are not detected by this version of LPA.

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

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