In vitro antibacterial activity of AM-1155, a novel 6-fluoro-8-methoxy quinolone

The in vitro antibacterial activity of AM-1155 against a wide variety of clinical isolates was compared with those of other fluoroquinolones. The MICs of AM-1155 for 90% of Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus faecalis isolates tested were 0.10, 0.39, and 0.78 microgram/ml, respectively. The antibacterial activity of AM-1155 against gram-positive bacteria and anaerobes was comparable to those of sparfloxacin and tosufloxacin. AM-1155 inhibited 90% of most species of the family Enterobacteriaceae at a concentration of 0.39 microgram/ml. AM-1155 generally had activity comparable to that of sparfloxacin against gram-negative bacteria. AM-1155 showed moderate activity against methicillin- and quinolone-resistant S. aureus. AM-1155 demonstrated bactericidal activity at the MIC. The frequency of occurrence of spontaneous mutants resistant to four times the MIC of AM-1155 was < 1 x 10(9) for S. aureus, Escherichia coli, and Pseudomonas aeruginosa. AM-1155 strongly inhibited the supercoiling activities of DNA gyrases purified from E. coli and S. aureus.