**Core Concept**
Thoracic actinomycosis is a chronic bacterial infection caused by Actinomyces israelii, characterized by the formation of abscesses and granulomas in the thoracic cavity. The treatment of choice involves a combination of antibiotics and surgical intervention to manage the infection.

**Why the Correct Answer is Right**
The treatment of choice for thoracic actinomycosis is penicillin G, which is effective against Actinomyces species. Penicillin G works by inhibiting cell wall synthesis, ultimately leading to bacterial death. The recommended treatment duration is 6-12 weeks, and in some cases, surgical drainage may be necessary to manage the abscesses and granulomas. The use of penicillin G is critical in thoracic actinomycosis, as it is the most effective antibiotic against Actinomyces israelii.

**Why Each Wrong Option is Incorrect**
**Option A:** Other antibiotics like macrolides (e.g., erythromycin) may be used in penicillin-allergic patients, but they are not the first-line treatment for thoracic actinomycosis.
**Option B:** Surgical intervention alone is not sufficient to treat thoracic actinomycosis, as the infection is caused by a bacterial agent that requires antibiotic treatment.
**Option C:** Isoniazid is used to treat tuberculosis, not actinomycosis.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Actinomyces israelii can be found in the oral cavity and gastrointestinal tract, and the infection can spread to the thoracic cavity through inhalation of the bacteria.

**Correct Answer:** C. Isoniazid is used to treat tuberculosis, not actinomycosis