FIG. 3.

Lethal activities of fused-ring fluoroquinolones that have been used clinically. Survival of E. coli was measured as a function of the fluoroquinolone concentration expressed as a multiple of the MIC in the presence (filled symbols) or absence (open symbols) of chloramphenicol. The names of the compounds are indicated in each panel. Data for levofloxacin, for direct comparison, are shown in Fig. 2. Marbofloxacin is currently used in veterinary medicine. The error bars represent standard deviations of the means shown; similar results were observed with 2 additional, replicate experiments.