Which antibacterial drug class does not work by inhibiting protein synthesis?

• A. Aminoglycosides
• B. Streptogramins
• C. Oxazolidinones
• D. Fluoroquinolones

Answer: (D)

Antibiotics can disrupt bacteria by targeting different essential processes. Here, the key idea is distinguishing those that stop protein synthesis from those that affect DNA replication. Fluoroquinolones do not interfere with the ribosome; instead, they inhibit DNA gyrase and topoisomerase IV, enzymes crucial for supercoiling and unwinding DNA during replication. By blocking these enzymes, they prevent bacterial DNA replication and growth, not protein production.

In contrast, the other listed classes interact with the ribosome to shut down protein synthesis: one binds the 30S subunit and causes misreading of mRNA; another prevents initiation at the 50S subunit, halting protein assembly; and the last blocks elongation on the 50S subunit. So fluoroquinolones are the one that does not work by inhibiting protein synthesis.