In phenotypic drug susceptibility testing (DST) for Mycobacterium tuberculosis using the proportion method on Lowenstein-Jensen medium, what is the critical concentration of ethambutol used to define resistance?

• A 0.2 µg/mL
• B 2.0 µg/mL ✓
• C 5.0 µg/mL
• D 10.0 µg/mL

Explanation

The critical concentration of ethambutol for DST on LJ medium is 2.0 µg/mL. Isoniazid is 0.2 µg/mL, rifampicin is 40 µg/mL, and streptomycin is 4.0 µg/mL. Resistance is defined if growth on the drug medium exceeds 1% of growth on the drug-free medium.

Reference: Tuberculosis: National Technical Guidelines for Diagnosis and Treatment, 2023 ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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