Fluoroquinolones exert their antibacterial effect by inhibiting DNA gyrase (topoisomerase II) and topoisomerase IV. In Gram-negative bacteria, the primary target is:

• A Topoisomerase IV
• B RNA polymerase β-subunit
• C DNA gyrase ✓
• D Dihydropteroate synthase

Explanation

In Gram-negative organisms, DNA gyrase (topoisomerase II) is the primary fluoroquinolone target, while in Gram-positive organisms, topoisomerase IV is the primary target. Mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene are the most common mechanism of fluoroquinolone resistance in Gram-negatives. RNA polymerase and DHPS are targets of rifampicin and sulfonamides respectively.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.