Detection of mutations in quinolone resistance-determining regions in levofloxacin- and methicillin-resistant Staphylococcus aureus: effects of the mutations on fluoroquinolone MICs.
The minimum inhibitory concentrations (MICs) of 18 antibiotics were determined for 66 clinical isolates of staphylococci. Genotypes, mutations in the quinolone resistance-determining regions (QRDRs), and effect of efflux were determined in the 18 levofloxacin-resistant isolates, for which the MICs of levofloxacin were high (> or =8 microg/ml). The increased levofloxacin resistance mainly resulted from some combinations of mutations in the QRDRs, although NorA-mediated efflux may play a minor role in resistance. A combination of mutations in GrlA (Ser80Phe), GrlB (Pro451Ser), and GyrA (Ser84Leu) was found in 4 methicillin-resistant Staphylococcus aureus (MRSA) isolates that were unrelated genotypically. The mutations in grlA QRDR varied in the isolates classified as being in an identical pulsed-field gel electrophoresis (PFGE) group, although the grlB, gyrA, and gyrB QRDRs were the same. These results suggest that the patterns of amino acid mutations in the QRDRs can provide distinct epidemiologic information from PFGE genotypes in fluoroquinolone-resistant MRSA. A combination of at least three mutations in GrlA, GrlB, and/or GyrA is required to increase the MICs of fluoroquinolones, although all of the levofloxacin-resistant MRSA retained the MICs of sitafloxacin in the range of 1 to 2 microg/ml.
Horii
Toshinobu
T
Department of Laboratory Medicine, Hamamatsu University School of Medicine, 1-20-1 Handa-yama, Hamamatsu 431-3192, Japan. horiihm@hama-med.ac.jp
Suzuki
Yasuhiro
Y
Monji
Akio
A
Morita
Motoki
M
Muramatsu
Hideaki
H
Kondo
Yoko
Y
Doi
Matsuko
M
Takeshita
Akihiro
A
Kanno
Takashi
T
Maekawa
Masato
M
D000890:Anti-Infective Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000187:drug effects / Q000235:genetics; D001483:Base Sequence; D027081:DNA Gyrase; D018432:Drug Resistance, Multiple / Q000235:genetics*; D006801:Humans; D064704:Levofloxacin; D016106:Methicillin Resistance / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D015242:Ofloxacin / Q000494:pharmacology*; D010597:Pharmacogenetics; D016133:Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics
D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D064704:Levofloxacin; D015242:Ofloxacin; D027081:DNA Gyrase