This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Mechanism of action of quinolones is: 
Select and explain. 
A. Inhibits DNA gyrase, B. Inhibits bacterial protein synthesis, C. Inhibits bacterial cell wall synthesis, D. Inhibits intake of folic acid
A: Inhibits DNA gyrase
Answer: A: Inhibits DNA gyrase 
Explanation: Mechanism of action of Fluoroquinolones
The FQs inhibit the enzyme bacterial DNA gyrase (primarily active in gram negative bacteria), which nicks double-stranded DNA, introduces negative supercoils and then reseals the nicked ends. This is necessary to prevent excessive positive supercoiling of the strands when they separate to permit replication or transcription.
Reference: Essentials of Medical Pharmacology Eighth Edition KD TRIPATHI page no 760