Eth-A gene mutation can lead to cross resistance of Ethionamide with:
**Core Concept**
Ethionamide is an antibacterial medication used to treat tuberculosis. It works by inhibiting the synthesis of mycolic acid, a critical component of the Mycobacterium tuberculosis cell wall. The Eth-A gene encodes for the enzyme responsible for the activation of Ethionamide, and mutations in this gene can alter the drug's efficacy.
**Why the Correct Answer is Right**
A mutation in the Eth-A gene can lead to cross-resistance with other drugs that also rely on the same enzymatic pathway for activation. This is because the altered enzyme may not only affect Ethionamide but also other drugs that are substrates for the same enzyme. The correct answer is a drug that is metabolized by the same enzyme.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid - Isoniazid is metabolized by a different enzyme, InhA, and is not affected by Eth-A gene mutations.
**Option B:** Pyrazinamide - Pyrazinamide is also metabolized by a different enzyme, PZase, and is not affected by Eth-A gene mutations.
**Option C:** Streptomycin - Streptomycin is an aminoglycoside antibiotic that works by inhibiting protein synthesis and is not affected by Eth-A gene mutations.
**Clinical Pearl / High-Yield Fact**
It is essential to note that Ethionamide resistance is often associated with mutations in the Eth-A gene, which can lead to cross-resistance with other drugs. This highlights the importance of monitoring resistance patterns and adjusting treatment regimens accordingly.
**Correct Answer: C. Streptomycin. Streptomycin is not directly affected by Eth-A gene mutations, but it is often used in combination therapy for tuberculosis, and resistance to one drug in the regimen may indicate cross-resistance with other drugs.