**Core Concept**
The management of abdominal sepsis involves the use of broad-spectrum antibiotics to cover a wide range of potential pathogens. This approach is based on the concept of empirical treatment, where antibiotics are chosen before the results of cultures and sensitivities are known.

**Why the Correct Answer is Right**
The combination of ampicillin and gentamicin is a common empirical treatment for abdominal sepsis. Ampicillin provides coverage against Gram-positive and some Gram-negative bacteria, including Listeria monocytogenes, while gentamicin offers broad-spectrum activity against a wide range of Gram-negative bacteria, including Pseudomonas aeruginosa. This combination allows for effective coverage against both aerobic and anaerobic bacteria, which are commonly involved in abdominal sepsis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the combination of ampicillin and gentamicin is not typically used to treat methicillin-resistant Staphylococcus aureus (MRSA), which requires vancomycin or linezolid.
* **Option B:** This option is incorrect because ceftriaxone and metronidazole may not provide adequate coverage against Pseudomonas aeruginosa, which is a common pathogen in abdominal sepsis.
* **Option C:** This option is incorrect because fluconazole is an antifungal agent and is not typically used as part of the empirical treatment for abdominal sepsis.

**Clinical Pearl / High-Yield Fact**
When choosing empirical antibiotics for abdominal sepsis, it's essential to consider the potential pathogens involved and the local antibiotic resistance patterns.

**Correct Answer:** D.