**Core Concept**
The underlying principle in this scenario is the concept of antibiotic resistance and the need to identify the causative organism of the abscess to select the appropriate antibiotic therapy. The patient's clinical presentation suggests that the current antibiotic regimen is ineffective, and further investigation is necessary to determine the cause of treatment failure.

**Why the Correct Answer is Right**
The failure of the abscess to regress despite high-dose antibiotics may indicate the presence of a resistant organism. This can occur due to various mechanisms, including beta-lactamase production, altered cell wall permeability, or efflux pumps. The correct approach is to obtain cultures from the abscess to identify the causative organism and determine its antibiotic susceptibility pattern. This will guide the selection of an alternative antibiotic regimen or the addition of an antibiotic with a different mechanism of action.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ordering a CT scan or MRI may provide additional information on the extent of the abscess, but it will not address the issue of antibiotic resistance.
* **Option B:** Increasing the dose of the current antibiotic may not be effective if the organism is resistant.
* **Option C:** Discontinuing antibiotics altogether may lead to worsening of the infection and potentially life-threatening consequences.

**Clinical Pearl / High-Yield Fact**
In cases of treatment failure, it is essential to obtain cultures from the site of infection to guide antibiotic therapy. This approach can help prevent the spread of resistant organisms and ensure effective treatment.

**Correct Answer: C. Discontinuing antibiotics altogether may lead to worsening of the infection and potentially life-threatening consequences.**