Antibacterial activity of ofloxacin and its mode of action.

The antibacterial activity of ofloxacin against Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus influenzae, Branhamella catarrhalis, and Neisseria gonorrhoeae was comparable to norfloxacin and enoxacin, and far exceeded the activity of pipemidic acid and nalidixic acid. The activity of ofloxacin was two to eight times less than that of ciprofloxacin. Ofloxacin was more active against Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Acinetobacter spp., Legionella spp., and Bacteroides fragilis, than norfloxacin, enoxacin, pipemidic acid and nalidixic acid, and the activity of ofloxacin was comparable to that of ciprofloxacin. Ofloxacin was two to seven times more effective than norfloxacin in systemic infections in mice with S. aureus, Escherichia coli, Serratia marcescens and P. aeruginosa. Ofloxacin strongly inhibited DNA supercoiling activity of DNA gyrase purified from E. coli KL-16. There is a parallel relationship between antibacterial activity of ofloxacin and its inhibitory action against DNA gyrases from ofloxacin-susceptible and ofloxacin-resistant clinical isolates of E. coli. These results indicate that the high bactericidal action of ofloxacin and the related new quinolone agents can be explained by their potent inhibitory activities against DNA gyrase in bacterial cells.