Comparative killing rates of gatifloxacin and ciprofloxacin against 14 clinical isolates: impact of bacterial strain and antibiotic concentration

The influence of bacterial strain and antibiotic concentration on the time to achieve in vitro bactericidal activity was determined for gatifloxacin and ciprofloxacin using time-kill methodology. Killing rates were significantly affected by bacterial strain, antibiotic concentration, and type of fluoroquinolone. The most rapid bactericidal activity was seen against members of the Enterobacteriaceae and with fluoroquinolone concentrations of 8-16X MIC. In general, gatifloxacin demonstrated faster killing against Acinetobacter baumanii, Legionella pneumophila, Staphylococcus aureus, and Streptococcus pneumoniae.