**Core Concept**
Pseudomonas aeruginosa is a Gram-negative bacterium known for its ability to infect immunocompromised individuals and cause a range of opportunistic infections. Cetrimide agar is a selective and differential medium used for its isolation.

**Why the Correct Answer is Right**
Cetrimide agar contains cetrimide (cetyltrimethylammonium bromide), which inhibits the growth of most Gram-positive bacteria and some Gram-negative bacteria. Pseudomonas aeruginosa is resistant to the inhibitory effects of cetrimide due to its unique cell membrane structure, allowing it to grow on the agar. This selective medium also contains a pH indicator, which turns the medium yellow in the presence of Pseudomonas aeruginosa due to its production of pyocyanin.

**Why Each Wrong Option is Incorrect**
* **Option A:** Staphylococcus aureus - This bacterium is typically inhibited by the cetrimide in Cetrimide agar and would not grow on this medium.
* **Option B:** Escherichia coli - While E. coli is a Gram-negative bacterium, it is not resistant to cetrimide and would be inhibited on Cetrimide agar.
* **Option D:** Klebsiella pneumoniae - Similar to E. coli, Klebsiella pneumoniae is also a Gram-negative bacterium that is inhibited by cetrimide and would not grow on Cetrimide agar.

**Clinical Pearl / High-Yield Fact**
Pseudomonas aeruginosa is known for its resistance to multiple antibiotics, making it a challenging organism to treat. It is often isolated from hospital environments and can cause a range of infections, including pneumonia, urinary tract infections, and septicemia.

**Correct Answer: C. Pseudomonas aeruginosa**