In vitro Pharmacodynamics of Enrofloxacin Against an Escherichia coli gyrA Mutant

The aim of this study was to investigate in vitro the pharmacodynamics of Enrofloxacin (ENR) against an Escherichia coli gyrA mutant (E. coli MT/128). Broth microdilution testing was used to determine the Minimum Inhibitory Concentration (MIC) and multi-step resistance selection was performed until reaching 1 mu g ML(-1) MIC. For time-kill experiments, colony counts were determined by plating each diluted sample onto Plate Count Agar and an integrated pharmacokinetic/pharmacodynamics area measure (log ratio area) was applied to all cfu data. A single C-T mutation was found in gyrA at codon 83. Concentration-dependent bacterial killing was observed for E. coli MT/128. Bactericidal activity for this strain was achieved within 4 h at concentrations >= 8 times the MIC with no significant regrowth by 24 h.