Comparison of mutant prevention concentrations of fluoroquinolones againstmethicillin-resistant and -susceptible Staphylococcus aureus isolated from animal
Abstract:ABSTRACT:In order to compare the capacity of the choosing on the resistant mutant strain of the 4 kinds of fluoroquinolones against methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) S. aureus Isolated from animal. The minimum inhibitory concentration (MIC) and MPC of ciprofloxacin, levofloxacin, gatifloxacin, and gemifloxacin for MSSA and MRSA were determined by agar plate dilution methods. The results showed that for 85 MSSA strains, the rank order of potency based on MPC90 values were ciprofloxacin (4 mg/l)>levofloxacin (2 mg/l) > gatifloxacin (0.5 mg/l) =gemifloxacin (0.5 mg/l). The selective index (MPC90/MIC90) of gatifloxacin was min. For 21 MRSA strains, the MPC90 of ciprofloxacin, levofloxacin, gatifloxacin and gemifloxacin were 128 mg/l,64 mg/l,16 mg/l and 8 mg/l respectively and the selective index of gemifloxacin was min. The ability of gatifloxacin for restricting the selection of MSSA resistant mutants were stronger than that of other fluoroquinolones. gatifloxacin and gemifloxacin may restrict the selective enrichment of resistant mutants among MSSA whenever they are administered as mono-therapy. But for MRSA strains, four fluoroquinolones will select resistant mutants whenever they are administered as mono-therapy.