A 24-year-old woman with acute uncomplicated cystitis is given ciprofloxacin. The bactericidal action of this drug results from inhibition of which bacterial enzyme?
- A DNA-dependent RNA polymerase
- B DNA topoisomerase IV and DNA gyrase ✓
- C DNA polymerase III holoenzyme
- D DnaB helicase
Correct answer: B. DNA topoisomerase IV and DNA gyrase
Explanation
Fluoroquinolones inhibit bacterial type II topoisomerases: DNA gyrase (topoisomerase II) in Gram-negative organisms and topoisomerase IV in Gram-positive organisms. These enzymes introduce transient double-strand breaks and use ATP to relieve positive supercoils ahead of the fork and decatenate daughter chromosomes, so their blockade arrests replication. Gyrase differs from mammalian topo II in being able to introduce negative supercoils, which explains selective toxicity.
Reference: Katzung Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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