A physician prescribes ciprofloxacin for a urinary tract infection. The dual bacterial targets of fluoroquinolones are:
- A DNA gyrase (topoisomerase II) in gram-negatives and topoisomerase IV in gram-positives ✓
- B RNA polymerase and DNA gyrase
- C Topoisomerase I and topoisomerase III
- D DNA polymerase III and DNA ligase
Correct answer: A. DNA gyrase (topoisomerase II) in gram-negatives and topoisomerase IV in gram-positives
Explanation
Fluoroquinolones trap the ternary complex of topoisomerase-DNA-drug, causing double-strand breaks. In gram-negative bacteria (including E. coli), DNA gyrase (topoisomerase II) is the primary target; in gram-positives (e.g., Staphylococcus), topoisomerase IV is the primary target. This dual-targeting mechanism explains why resistance requires mutations in both enzymes to achieve high-level resistance.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.