Optimization of the use of ciprofloxacin

Abstract Aims To compare mutant prevention concentration (MPC) of ciprofloxacin and time-killing curve with regards to 11 genotyped Escherichia coli. Method MICs were determined using the E-test method. Time-killing studies were performed in accordance with the NCCLS guidelines. The genes gyr A, gyr B, par C, par E and mar R were amplified by PCR and sequenced. The MPC was defined as the lowest antibiotic concentration preventing the growth of resistant colonies when 10 10  CFU/mL were spread on a solid medium. Results Strains with no genes gyr A, gyr B, par C, par E and mar R mutation presented MIC less or equal to 0.023 mg/L and MPC less or equal to 0.25 mg/L. Strains with two mutations ( gyr A and par C) presented MIC equal to 1.5 mg/L and MPC equal to 4 mg/L. Strains with one mutation ( gyr A) presented MIC less or equal to 0.75 mg/L, but MPC ranged from 0.5 to 6 mg/L depending of the MIC of ciprofloxacin. The time-killing curves for ciprofloxacin showed a bactericidal activity of 0.25 mg/L in 1 h for strains without mutation, compared with a bactericidal activity of 2 and 4 mg/L in 4 h for strains with one and two mutations, respectively. Conclusion For strains of E. coli resistant to nalidixic acid, it was necessary to evaluate the MIC of ciprofloxacin in order to asses the optimal dosage of ciprofloxacin.