The Impact of Mutations in Topoisomerase Genes and the Plasmid-Mediated Quinolone Resistance (PMQR) Determinants on the Resistance to Fluoroquinolones in Klebsiella pneumoniae

Klebsiella pneumoniae causes a variety of infections including community acquired pneumonia and nosocomial infections.
The aim of this study was to determine the plasmid-associated quinolone-resistance (PMQR) genes and mutations in quinolone-resistance determining region (QRDR) of topoisomerase genes in K. pneumoniae.
One hundred clinical K. pneumoniae isolates were collected from Kermanshah hospitals for this study. The minimum inhibitory concentrations (MIC) for levofloxacin and ciprofloxacin was determined by broth microdilution method. The presence of PMQR genes (qnrA, qnrB, qnrS, aac (6´)-Ib, and qepA) among isolates resistant to fluoroquinolones was detected by PCR. All PCR products for topoisomerase genes (gyrA, gyrB and parC) were sequenced and analyzed.
Sequence analysis showed mutations in gyrA at codons 83 and 87 in 24 (85.7%) and 20 (71.4%) of isolates, respectively. For parC mutations were detected at codons 80 and 84 in 15 (53.6%) and 7 (25%) isolates, respectively. At the outside of QRDR in gyrA and gyrB, mutations were also observed. The mutation was not detected in the QRDR of gyrB. The qnrB, qnrS, and aac (6')-Ib-cr were found in 1 (3.6%), 11 (39.3%) and 25 (89.3%) of isolates, respectively. Howevr, the qnrA and qepA genes were not detected among isolates.
The resistance to fluoroquinolones is relatively high among K. pneumonia and mutations in QRDR of topoisomerase genes play an important role for this resistance. The plasmid-mediated genes also increase the level of resistance. The mutations outside the QRDR of topoisomerase genes also occur, but their exact role in resistance needs to be clarified.