[Mutant prevention concentrations of fluoroquinolones for Staphylococcus aureus]

Abstract

Objective: To establish a method to measure mutant prevention concentration (MPC) in vitro, and to measure MPC of fluoroquinolones for staphylococcus aureus.

Methods: The staphylococcus aureus strain ATCC25923 and 20 ciprofloxacin-susceptible clinical isolates were enriched in broth, and the bacterial concentrations were adjusted to 10(10) colony forming units per milliliter. The minimal inhibitory concentration (MIC), MIC for 99% of input cells (MIC99), provisional MPC (MPCpr) and MPC of moxifloxacin, gatifloxacin, pasufloxacin and ciprofloxacin for staphylococcus aureus were determined by agar plates dilution method.

Results: The MPC of moxifloxacin, gatifloxacin, pasufloxacin and ciprofloxacin for staphylococcus aureus strain ATCC25923 were 0.18, 0.3, 0.75 and 1.8 microg/ml, and the MPC/MIC99 were 9.0, 7.5, 8.0 and 10.6 respectively. The MPC for 90% of the isolates (MPCpr90) of moxifloxacin, gatifloxacin, pasufloxacin and ciprofloxacin for 20 staphylococcus aureus clinical isolates were 1, 1, 4 and 8 microg/ml, and the MPCpr90/MIC90 were 8, 8, 16 and 16 respectively.

Conclusion: The capacity of moxifloxacin and gatifloxacin for restricting the selection of staphylococcus aureus resistant mutants were stronger than that of pasufloxacin and ciprofloxacin. Combined with pharmacokinetic parameters, moxifloxacin and gatifloxacin may restrict the selective enrichment of resistant mutants among ciprofloxacin-susceptible staphylococcus aureus clinical isolates, and ciprofloxacin is expected to selectively enrich mutants easily.