Mutant Prevention Concentration Of Fluoroquinolones For Staphylococcus

Objectives: To defect minimal inhibitory concentrations (MIC), mutant prevention concentrations (MPC) and mutant selection window (MSW) of fluoroquinolones for ciprofloxacin-susceptible staphylococcus isolated from clinical samples and to compare the capacity of selection of fluoroquinolones to prevent the resistant mutant strain,and based on it to direct the rational use of drug in clinic.Methods: The MIC for 50% and for 90% of ciprofloxacin, 1evofloxacin, pazufloxacin, gatifloxacin, cadrofloxacin and moxifloxacin for staphylococcus were determined by the standard two fold agar dilution methods;The celles of 10¹⁰ colony forming units per milliliter staphylococcus were enriched in broth, and the MPC , MPC 50, MPC₉₀ and MSW of fluoroquinolones against strains were determined by agar plates dilution method . High–density cultures were prepared from overnight cultures grown in MH agar medium followed ofincubation with shaking at 37℃.Inoculated fluoroquinolone-impregnated plates were incubated for 72h , the MPC recorded as the lowest fluoroquinolone concentration completely inhibiting bacterial growth at this time.Using the SPSS statistics software to analyze the data.Results: (1) As for the MPC for 50% and for 90% of six fluoroquinolones for 36 staphylococcus aureus (S aureus)and 34 negative coagulase staphylococcus(CN-S), moxifloxacin was the lowest among the six drugs, then cadrofloxacin, gatifloxacin, while ciprofloxacin was the highest. The MPC for 50% and for 90% of six drugs for S aureus were all higher than for CN-S. No significant difference was found between the MPC of two sets of staphylococcus in every fluoroquinolone (P>0.05). (2) With regard to the MPC₅₀/MIC₅₀ and MPC₉₀/MIC₉₀ of fluoroquinolones for two sets staphylococcus, moxifloxacin was the lowest among the six drugs, ciprofloxacin was the highest. S aureus were all higher than CN-S on the MPC₅₀/MIC₅₀ and MPC₉₀/MIC₉₀ of six fluoroquinolones. No significant difference was found between the MPC/MIC of two sets staphylococcus in every fluoroquinolone (P>0.05). (3) No significant difference was found between the MPC of ciprofloxacin and of 1evofloxacin in all staphylococcus (P>0.05). Significant difference was found between the MPC of ciprofloxacin and 1evofloxacin and the MPC of pazufloxacin, gatifloxacin, cadrofloxacin and moxifloxacin in staphylococcus (P<0.05). Significant difference was found among the MPC of pazufloxacin, gatifloxacin, cadrofloxacin and moxifloxacin in staphylococcus (P<0.05). As same as no significant difference was found among the MPC/MIC of six fluoroquinolones in all staphylococcus (P>0.05). (4) By compare the MPC₉₀ for two sets of staphylococcus with the pharmacokinetic parameter sin vivo of fluoroquinolones. The MPC₉₀ of moxifloxacin for two sets of staphylococcus all less than the Cmax of moxifloxacin; the MPC₉₀ of gatifloxacin for S aureus less than the Cmax of gatifloxacin,but the MPC₉₀ of gatifloxacin for negative coagulase staphylococcus amount to the Cmax of gatifloxacin; The MPC₉₀ of ciprofloxacin and 1evofloxacin for two sets of staphylococcus were all higher than the Cmax of ciprofloxacin.Conclusions: The mutant prevention concentration and the mutant selection window of moxifloxacin and cadrofloxacin is the lowest in six fluoroquinolones, then the lower are pazufloxacin and gatifloxacin; the highest are ciprofloxacin and 1evofloxacin in sequence. The ability of new fluoroquinolones to restrict the selection of resistant mutants are stronger than traditional fluoroquinolones. No significant difference is found between the ability of fluoroquinolones to restrict the selection of resistant mutants for S aureus and for CN-S.