Which of the following antibacterials is most effective against Pseudomonas aeruginosa?

• A. Vancomycin
• B. Amoxicillin
• C. Piperacillin-tazobactam
• D. Erythromycin

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the characteristics of Pseudomonas aeruginosa, which is a Gram-negative, opportunistic pathogen known for its resistance to many antibiotics due to its efflux pumps and impermeable outer membrane.
2. Step 2: Review the spectrum of activity of each antibacterial listed: Vancomycin is primarily effective against Gram-positive bacteria; Amoxicillin is a broad-spectrum penicillin but generally less effective against Pseudomonas; Erythromycin is a macrolide mainly targeting Gram-positive and some atypical bacteria.
3. Step 3: Recognize that Piperacillin is an extended-spectrum penicillin with activity against Pseudomonas aeruginosa, and when combined with tazobactam (a beta-lactamase inhibitor), it overcomes resistance mechanisms by inhibiting beta-lactamase enzymes.
4. Step 4: Compare the mechanisms of action and resistance profiles to conclude that Piperacillin-tazobactam is the most effective option against Pseudomonas aeruginosa among the choices given.
5. Step 5: Summarize that the choice of antibacterial depends on the bacterial species and its resistance mechanisms, and Piperacillin-tazobactam is specifically designed to target resistant Gram-negative bacteria like Pseudomonas aeruginosa.