**Core Concept**
The question tests the student's understanding of the **antimicrobial spectrum** of ceftizoxime sodium, a third-generation **cephalosporin antibiotic**. Ceftizoxime is known for its broad-spectrum activity, particularly against **Gram-negative bacteria**.

**Why the Correct Answer is Right**
Ceftizoxime sodium has a broad spectrum of activity that includes many **Gram-negative** and some **Gram-positive** bacteria. However, its effectiveness against certain bacteria, especially those producing **beta-lactamase enzymes**, can be limited. The correct answer choice would be an organism against which ceftizoxime has limited or no activity.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice might be incorrect because ceftizoxime has activity against a wide range of bacteria.
**Option B:** Similarly, this choice could be incorrect as ceftizoxime is effective against many common pathogens.
**Option C:** This option might also be incorrect due to the broad-spectrum activity of ceftizoxime.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **third-generation cephalosporins** like ceftizoxime have limited activity against **MRSA (Methicillin-resistant Staphylococcus aureus)** and some **Enterococci**, making them less ideal choices for infections suspected to be caused by these organisms.

**Correct Answer:** D. Enterococcus faecalis.