Line probe assays are a rapid molecular DST used to detect resistance to which drug?

• A. Rifampin
• B. Ethambutol
• C. Isoniazid
• D. Pyrazinamide

Answer: (A)

Line probe assays are rapid molecular tests that look for specific genetic mutations in Mycobacterium tuberculosis associated with drug resistance. Their primary clinical use is to detect rifampicin resistance quickly by analyzing changes in the rpoB gene. Detecting rifampicin resistance is especially important because it serves as a strong indicator of multidrug-resistant TB, allowing clinicians to start appropriate regimens much sooner than with traditional culture-based testing. The assay works by amplifying the target gene regions and then using a strip with wild-type and mutant probes; a pattern of missing or shifted bands indicates resistance.

Some line probe assays also test for isoniazid resistance (via katG and inhA), but the drug resistance most characteristically identified rapidly by these tests is rifampicin resistance. Ethambutol and pyrazinamide resistance are typically assessed with other methods or genes, and are not the primary target of standard line probe assays.