Which of the following antibiotics are considered bactericidal agents?

• A. Trimethoprim
• B. Tetracyclines
• C. Sulfonamides
• D. Aminoglycosides

Answer: (D)

Bactericidal agents actively kill bacteria, whereas bacteriostatic ones merely halt growth and let the immune system clear the infection. Aminoglycosides kill by irreversibly binding to the 30S ribosomal subunit, causing misreading of mRNA and disruption of protein synthesis, which leads to bacterial death. They are also typically concentration-dependent killers, providing more rapid kill with higher drug levels. In contrast, trimethoprim and sulfonamides inhibit folate synthesis, which stops bacterial growth rather than directly killing cells, and tetracyclines prevent aminoacyl-tRNA from binding to the ribosome in a way that halts growth rather than causing immediate death. Thus, the class most reliably producing bacterial death is the aminoglycosides.