Penicillin is best described as which spectrum?

Penicillin is best described as which spectrum?

• A. Broad-spectrum, active against Gram-positive and Gram-negative bacteria
• B. Narrow-spectrum, active primarily against Gram-positive bacteria
• C. Narrow-spectrum, active primarily against Gram-negative bacteria
• D. Not an antibiotic

Answer: (B)

Antibiotic spectrum describes the range of bacteria that an antibiotic can effectively inhibit. Penicillin, especially the original forms like penicillin G, is best described as narrow-spectrum because its activity is strongest against Gram-positive bacteria. This stems from how penicillin targets cell wall synthesis and the structural differences between bacteria: Gram-positive bacteria have a thick peptidoglycan layer and are more accessible to penicillin, while Gram-negative bacteria have an outer membrane that limits penicillin’s entry and often possess mechanisms that resist its action. Therefore, penicillin is primarily effective against Gram-positive organisms, with broader activity only seen in later derivatives designed to reach some Gram-negatives. Not an antibiotic is incorrect, and broad-spectrum activity would imply substantial Gram-negative coverage, which classic penicillin lacks.

Antibiotic spectrum describes the range of bacteria that an antibiotic can effectively inhibit. Penicillin, especially the original forms like penicillin G, is best described as narrow-spectrum because its activity is strongest against Gram-positive bacteria. This stems from how penicillin targets cell wall synthesis and the structural differences between bacteria: Gram-positive bacteria have a thick peptidoglycan layer and are more accessible to penicillin, while Gram-negative bacteria have an outer membrane that limits penicillin’s entry and often possess mechanisms that resist its action. Therefore, penicillin is primarily effective against Gram-positive organisms, with broader activity only seen in later derivatives designed to reach some Gram-negatives. Not an antibiotic is incorrect, and broad-spectrum activity would imply substantial Gram-negative coverage, which classic penicillin lacks.