What is the mechanism of action of fluoroquinolones?

• A. Inhibit protein synthesis by binding to ribosomes
• B. Inhibit DNA gyrase and topoisomerase IV
• C. Inhibit cell wall synthesis
• D. Inhibit folic acid synthesis

Answer: (B)

Fluoroquinolones exert their antibacterial effects primarily through the inhibition of bacterial enzymes known as DNA gyrase and topoisomerase IV. These enzymes play crucial roles in the processes of DNA replication, transcription, and repair.

DNA gyrase is involved in introducing negative supercoils into DNA, which is essential for relieving torsional stress that occurs ahead of the replication fork during DNA synthesis. Topoisomerase IV is vital for separating the interlinked daughter DNA strands that result from replication. By inhibiting these enzymes, fluoroquinolones effectively disrupt the proper function of bacterial DNA, leading to bacterial growth inhibition and eventual cell death.

This precise mechanism highlights the fluoroquinolones' role as broad-spectrum antibiotics against a variety of Gram-negative and Gram-positive bacteria. Their ability to target critical pathways in bacterial DNA handling distinguishes them from other classes of antibiotics, such as those that inhibit protein synthesis or cell wall synthesis.