**Core Concept**
Pyrazinamide is a key antitubercular agent that exhibits sterilizing activity, particularly against dormant or semidormant tubercle bacilli in acidic environments. Its unique mechanism of action allows it to selectively target and kill these resistant organisms.

**Why the Correct Answer is Right**
Pyrazinamide's sterilizing action is primarily due to its ability to inhibit fatty acid synthase I, an enzyme essential for the synthesis of mycolic acid in Mycobacterium tuberculosis. This inhibition disrupts the bacterial cell wall, ultimately leading to the death of the organism. The acidic environment of the macrophage, where the bacteria reside, enhances pyrazinamide's activity, allowing it to exert its sterilizing effect.

**Why Each Wrong Option is Incorrect**
**Option A:** Rifampicin is a potent bactericidal agent that inhibits RNA synthesis by binding to the beta-subunit of RNA polymerase. While it is highly effective against actively growing tubercle bacilli, it does not exhibit significant sterilizing activity.

**Option B:** Isoniazid (INH) is a first-line antitubercular agent that inhibits mycolic acid synthase, leading to the disruption of the bacterial cell wall. However, its activity is primarily bactericidal against actively growing organisms, rather than sterilizing.

**Option D:** Streptomycin is an aminoglycoside antibiotic that inhibits protein synthesis by binding to the 30S subunit of the bacterial ribosome. It is bactericidal against actively growing tubercle bacilli but does not possess significant sterilizing activity.

**Clinical Pearl / High-Yield Fact**
Pyrazinamide's sterilizing action is most pronounced in the acidic environment of the macrophage, highlighting the importance of acidic pH in the pathogenesis of tuberculosis.

**✓ Correct Answer: C. Pyrazinamide**