Which of the following antibiotics is recommended for use against Gram-negative bacteria?

• A. Griseofulvin
• B. Polymyxin B
• C. Penicillin G
• D. Vancomycin

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the characteristics of Gram-negative bacteria, which have an outer membrane containing lipopolysaccharides that can act as a barrier to many antibiotics.
2. Step 2: Review the mechanism of action and spectrum of activity of each antibiotic option: Griseofulvin (antifungal, not antibacterial), Penicillin G (primarily effective against Gram-positive bacteria), Vancomycin (targets Gram-positive bacteria by inhibiting cell wall synthesis), and Polymyxin B (disrupts the outer membrane of Gram-negative bacteria).
3. Step 3: Identify which antibiotic specifically targets the outer membrane of Gram-negative bacteria, making it effective against them.
4. Step 4: Recognize that Polymyxin B binds to lipopolysaccharides and phospholipids in the outer membrane of Gram-negative bacteria, increasing membrane permeability and causing cell death.
5. Step 5: Conclude that Polymyxin B is the recommended antibiotic for use against Gram-negative bacteria based on its mode of action and spectrum.