**Core Concept**
The combination of a beta-lactam antibiotic with a beta-lactamase inhibitor is used to enhance its spectrum of activity and prevent inactivation by beta-lactamase enzymes produced by certain bacteria, including Pseudomonas aeruginosa. This concept is crucial in treating infections caused by multidrug-resistant organisms.

**Why the Correct Answer is Right**
Piperacillin is a broad-spectrum penicillin antibiotic that is often used in combination with tazobactam, a beta-lactamase inhibitor. This combination is particularly effective against Pseudomonas aeruginosa, a common cause of hospital-acquired infections, due to the inhibitory effect of tazobactam on beta-lactamases produced by this organism. The addition of tazobactam to piperacillin enhances its stability against beta-lactamase degradation, allowing it to effectively target a broader range of bacteria, including those producing beta-lactamases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a correct combination of a beta-lactam antibiotic with a beta-lactamase inhibitor. The combination of amoxicillin with clavulanic acid is another example of a beta-lactam antibiotic with a beta-lactamase inhibitor, but it is not used against Pseudomonas aeruginosa.
**Option B:** Metronidazole is an antibiotic effective against anaerobic bacteria and protozoa, but it is not a beta-lactam antibiotic and is not used in combination with tazobactam.
**Option C:** Ceftriaxone is a third-generation cephalosporin with broad-spectrum activity, but it is not typically used in combination with tazobactam for anti-Pseudomonas activity.
**Option D:** This option is not a correct combination of a beta-lactam antibiotic with a beta-lactamase inhibitor. The combination of cefepime with a beta-lactamase inhibitor is not a commonly used or recommended regimen.

**Clinical Pearl / High-Yield Fact**
When treating infections caused by Pseudomonas aeruginosa, it is essential to use antibiotics that are specifically effective against this organism, such as piperacillin-tazobactam. Remember that the addition of a beta-lactamase inhibitor can enhance the spectrum of activity of a beta-lactam antibiotic, making it a valuable strategy in treating multidrug-resistant infections.

**Correct Answer: C. Piperacillin**