Effect of GrlA mutation on the development of quinolone resistance in Staphylococcus aureus in an in vitro pharmacokinetic model.
OBJECTIVE
To investigate the effect of GrlA mutation on the development of quinolone resistance in Staphylococcus aureus in an in vitro pharmacokinetic (PK) model and to examine the relationship between the emergence of resistance and PK/pharmacodynamic parameters.


METHODS
A wild-type and a GrlA mutant of S. aureus were exposed to the Japanese clinical dose of ciprofloxacin in an in vitro PK model, and the development of resistance was measured by population analysis. In addition, several doses of four quinolones (pazufloxacin, ciprofloxacin, levofloxacin and tosufloxacin) were tested against the GrlA mutant. All model simulations were single-dose design and were conducted over 24 h.


RESULTS
Four quinolones were tested against the GrlA mutant, and a resistant population emerged after treatment with 250 mg pazufloxacin intravenous drip infusion, 600 mg ciprofloxacin intravenous drip infusion, 200 mg levofloxacin oral dosing and 150 mg tosufloxacin oral dosing. The emergence of a resistant population was not induced by treatment with 500 mg pazufloxacin intravenous drip infusion, 2,400 mg ciprofloxacin intravenous drip infusion, 400 mg levofloxacin oral dosing and 600 mg tosufloxacin oral dosing. Treatment with the clinical dose of ciprofloxacin induced the development of resistance in the GrlA mutant, but not in the wild-type strain.


CONCLUSIONS
These data suggest that the frequency of acquisition of additional mutations differs between the wild-type and the GrlA mutant of S. aureus. Also, GrlA mutation predisposes S. aureus to develop high-level quinolone resistance.
Oonishi
Yoshimi
Y
Research Laboratories, Toyama Chemical Co., Ltd, Toyama, Japan. yoshimi_oonishi@toyama-chemical.co.jp
Mitsuyama
Junichi
J
Yamaguchi
Keizo
K
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D027101:DNA Topoisomerase IV / Q000235:genetics* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D015363:Quinolones / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics*; D013997:Time Factors