Which of the following drugs is classified as a bactericidal antibiotic?

Penicillin is classified as a bactericidal antibiotic due to its mechanism of action, which involves inhibiting the synthesis of bacterial cell walls. This disruption leads to the lysis and death of the bacteria, making it effective in treating a variety of bacterial infections. As a member of the beta-lactam antibiotics, penicillin targets the enzymes involved in cell wall formation, particularly transpeptidases, which are essential for maintaining the structural integrity of the bacterial cell. When these enzymes are inhibited, the bacteria cannot maintain their cell wall, leading to osmotic instability and ultimately cell death.

In contrast, the other drugs listed—aspirin, ibuprofen, and acetaminophen—are primarily analgesics or anti-inflammatory medications and do not have antimicrobial properties. They are used to relieve pain and reduce inflammation but do not directly kill bacteria or prevent their growth. Therefore, penicillin is the only drug among the options that qualifies as a bactericidal antibiotic.