*5.1.2 Fluoroquinolones*

They are bactericidal drugs. It functions by inhibiting the enzymes topoisomerase II (DNA gyrase, which is encoded by gyr A and gyr B genes) and topoisomerase IV (parC and parE) involved in winding—unwinding of the DNA. It is one of the most widely prescribed drugs due to easily available oral formulations. Fluoroquinolone resistance may be due to chromosomal mutations, plasmid mutations, alteration of outer membrane proteins causing decreased antibiotic uptake and presence of efflux pump systems.

Chromosomal mutation in DNA sequences of gyr A QRDRs i.e., quinolone resistance determining region is predominantly responsible for fluoroquinolone resistance. Resistance is also mediated via PMQR (plasmid-mediated quinolone resistance) genes which include qnr genes such as qnrA, qnr B and qnr C.
