Why are penicillins often more effective against gram-positive bacteria than gram-negative bacteria?

• A. Penicillins are unable to bind to the cell wall of gram-positive bacteria.
• B. Gram-negative bacteria have a thick outer membrane that prevents penicillins from reaching the peptidoglycan layer.
• C. Gram-positive bacteria have a thick peptidoglycan layer that is easily accessible to penicillins.
• D. Gram-negative bacteria lack peptidoglycan in their cell walls.

Answer: (C)

Verified step by step guidance

1. Understand the structure of bacterial cell walls: Gram-positive bacteria have a thick peptidoglycan layer, while gram-negative bacteria have a thinner peptidoglycan layer but possess an additional outer membrane.
2. Recognize the mechanism of action of penicillins: Penicillins inhibit the synthesis of peptidoglycan, which is essential for bacterial cell wall integrity.
3. Analyze why penicillins are more effective against gram-positive bacteria: The thick peptidoglycan layer in gram-positive bacteria is exposed and accessible, allowing penicillins to bind and inhibit cell wall synthesis effectively.
4. Consider the barrier in gram-negative bacteria: The outer membrane in gram-negative bacteria acts as a protective barrier that limits the penetration of penicillins to the peptidoglycan layer, reducing their effectiveness.
5. Evaluate the incorrect statements: Penicillins do bind to gram-positive bacteria cell walls, and gram-negative bacteria do have peptidoglycan, just less accessible due to the outer membrane.