The most common DNA gyrase mutations found in MDR-TB samples are gyrA D94G and gyrA A90V and these mutations are strongly associated with fluoroquinolone resistance . These residues are part of the gyrA "quinolone resistance determining region" (QRDR), defined as gyrA codons 74 to 113 . However, again, not all mutations in this region confer resistance, leading to false positive resistance results in genotypic assays . Rarely seen DNA gyrase mutations in gyrB are also associated with fluoroquinolone resistance, and a gyrB QRDR from residues 461 to 501 has also been proposed . The residues of the two QRDR regions make up the fluoroquinolone binding pocket, and gyrB A642P is the only mutation significantly associated with an increase in minimum inhibitory concentration (MIC) to fluoroquinolones that was found outside this region .