**Core Concept**
Actinomycosis is a chronic bacterial infection caused by Actinomyces species, typically affecting the face and neck, lungs, or gastrointestinal tract. The treatment involves antibiotics that effectively penetrate the infected tissue and have a broad spectrum of activity against anaerobic bacteria.

**Why the Correct Answer is Right**
The drug of choice for actinomycosis is penicillin, specifically penicillin G, due to its ability to penetrate the infected tissue and its broad-spectrum activity against anaerobic bacteria. Penicillin G inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), ultimately leading to bacterial cell lysis and death. **Penicillin G is effective against Actinomyces israelii**, the most common species causing actinomycosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Macrolides, such as erythromycin, may be used as an alternative in penicillin-allergic patients, but they are not the first-line treatment.
* **Option B:** Tetracyclines have a broad spectrum of activity, but they are not the preferred choice for actinomycosis due to their lower efficacy against anaerobic bacteria.
* **Option C:** Clindamycin is a lincosamide antibiotic that is effective against anaerobic bacteria, but it is not the first-line treatment for actinomycosis.

**Clinical Pearl / High-Yield Fact**
Actinomycosis is often misdiagnosed as a tumor or a malignancy due to its chronic and painful nature, so a high index of suspicion is necessary for early diagnosis and treatment.

**Correct Answer: C. Clindamycin.**