A Line Probe Assay (Hain LPA GenoType MTBDRplus) is performed on a sputum smear-positive specimen. The probe hybridisation pattern shows: absence of the WT2 band (rpoB region) and presence of the MUT3A band (rpoB S531L), plus absence of WT1 band (katG region) and presence of MUT1 band (katG S315T1). What drug resistance pattern is indicated?

• A INH mono-resistance only (katG mutation); rifampicin susceptible
• B MDR-TB — resistance to both rifampicin (rpoB S531L) and isoniazid (katG S315T1) ✓
• C Pre-XDR TB — additional fluoroquinolone resistance must be present for this designation
• D Rifampicin mono-resistance (rpoB); isoniazid susceptible

Explanation

The GenoType MTBDRplus LPA detects mutations in rpoB (rifampicin resistance) and katG/inhA promoter (isoniazid resistance). Absence of WT2 + presence of MUT3A (rpoB S531L) confirms rifampicin resistance. Absence of WT1 + presence of MUT1 (katG S315T1) confirms high-level isoniazid resistance (katG S315T mutation reduces INH activation by catalase-peroxidase). Both rifampicin AND isoniazid resistance together defines multidrug-resistant TB (MDR-TB). Pre-XDR requires additional resistance to fluoroquinolones (detected by GenoType MTBDRsl, not MTBDRplus).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.