What is the mechanism of action for fluoroquinolones?

• A. Inhibition of DNA polymerase
• B. Inhibition of DNA gyrase
• C. Interference with ribosomal function
• D. Inhibition of folic acid synthesis

Answer: (B)

Fluoroquinolones exert their antibacterial effects primarily through the inhibition of bacterial DNA gyrase. DNA gyrase is a type II topoisomerase that is crucial for bacterial DNA replication and transcription. It introduces negative supercoils into DNA, which helps relieve the torsional strain generated ahead of the replication fork during DNA unwinding. By inhibiting DNA gyrase, fluoroquinolones prevent the relaxation of supercoiled DNA, ultimately disrupting DNA replication and transcription processes. This action is specific to bacteria, making fluoroquinolones effective antibiotics.

The other mechanisms listed do not apply to fluoroquinolones. Inhibition of DNA polymerase, interference with ribosomal function, and inhibition of folic acid synthesis represent the actions of other classes of antibiotics. For example, DNA polymerase inhibitors target nucleic acid synthesis, ribosomal function interference characterizes aminoglycosides or macrolides, and folic acid synthesis inhibition is mainly associated with sulfonamides. Thus, the mechanism of action for fluoroquinolones distinctly focuses on the inhibition of DNA gyrase, which is essential for bacterial survival and proliferation.