Role of type II topoisomerase mutations and AcrAB efflux pump in fluoroquinolone-resistant clinical isolates of Proteus mirabilis.
OBJECTIVE
We conducted a study to determine the role played by amino acid mutations in DNA gyrase and topoisomerase IV, and the AcrAB efflux pump in resistance to fluoroquinolones in clinical isolates of Proteus mirabilis.


METHODS
Nine clinical isolates of P. mirabilis containing eight fluoroquinolone-resistant isolates and one fluoroquinolone-susceptible isolate as the causative pathogen were collected from different patients with urinary tract infections. Fluoroquinolone resistance was characterized by PCR and DNA sequencing. The role of the AcrAB efflux pump was investigated by semi-quantifying the transcriptional expression of the acrB gene.


RESULTS
Double mutations were found in GyrA, at S83I and E87K, and single mutations in GyrB (S464F) and ParC (S80I) in four isolates with ciprofloxacin MICs of 16 to >128 mg/L. In three isolates (ciprofloxacin MICs of >128 mg/L), the level of acrB expression was 2.1- to 3.2-fold higher than that in the wild-type control strain (ciprofloxacin MIC of < or =0.12 mg/L) and these isolates also had increased MICs of minocycline (>64 versus 8-16 mg/L) and chloramphenicol (>256 versus 4-8 mg/L) compared with the five other fluoroquinolone-resistant isolates.


CONCLUSIONS
Our findings demonstrate that two mechanisms--mutations in GyrA (at S83I and E87K), GyrB and ParC, and overproduction of the AcrAB efflux pump--might synergistically contribute to a highest level of resistance to fluoroquinolones in clinical isolates of P. mirabilis.
Saito
Ryoichi
R
Department of Infection Control and Prevention, The University of Tokyo Hospital, Tokyo, Japan. saito-lab@h.u-tokyo.ac.jp
Sato
Kenya
K
Kumita
Wakako
W
Inami
Natsuko
N
Nishiyama
Hiroyuki
H
Okamura
Noboru
N
Moriya
Kyoji
K
Koike
Kazuhiko
K
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D027081:DNA Gyrase / Q000235:genetics; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology*; D005798:Genes, Bacterial; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D011512:Proteus Infections / Q000188:drug therapy / Q000382:microbiology; D011513:Proteus mirabilis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D014552:Urinary Tract Infections / Q000188:drug therapy / Q000382:microbiology
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II