Which antibiotic is commonly considered bactericidal?

• A. Tetracycline
• B. Penicillin
• C. Erythromycin
• D. Clindamycin

Answer: (B)

The distinction between bactericidal and bacteriostatic antibiotics is what this question targets. Penicillin kills bacteria by blocking the enzymes (PBPs) that form the peptidoglycan cell wall, so during active growth the cell wall weakens and the bacteria lyse. This direct disruption of a vital structural process makes penicillin bactericidal.

In contrast, the other common inhibitors—tetracycline and erythromycin (and clindamycin to a large extent)—primarily halt bacterial growth by interrupting protein synthesis, which is typically bacteriostatic rather than lethal. While some agents can be bactericidal against certain organisms at high concentrations, penicillin remains the classic bactericidal option among these.