Which molecular method is commonly used to assess drug susceptibility for second-line TB drugs?

• A. Chest radiograph
• B. Line Probe Assays
• C. Sputum smear
• D. Liver function test

Answer: (B)

Assessing susceptibility to second-line TB drugs is about detecting genetic changes that make the bacteria resistant. Line Probe Assays are the standard rapid molecular method for this, because they directly look for specific mutations linked to resistance to key second-line drugs—primarily fluoroquinolones (mutations in gyrA/gyrB) and injectable drugs (mutations in the rrs gene and in the eis promoter). By identifying these mutations in a sample, they tell you whether those drugs are likely to be effective, often within days rather than weeks of culture-based testing.

Other options listed don’t test drug resistance. Chest radiographs show the presence and extent of disease, sputum smears reveal bacterial load, and liver function tests monitor drug safety; none of these determine whether the TB bacteria will respond to particular second-line drugs.