Comparative in vitro activity of norfloxacin and seven other antimicrobial agents against clinical isolates from urinary tract infections.

The in vitro activity of norfloxacin, a new quinolone derivative, was tested against 469 clinical isolates derived mainly from urinary samples from outpatients. It inhibited all Escherichia coli, Klebsiella oxytoca and Proteus strains at a concentration of 0.25 micrograms/ml, and all Pseudomonas aeruginosa, Enterobacter, Klebsiella pneumoniae, Staphylococcus and Enterococcus strains at a concentration of 8 micrograms/ml or less. Norfloxacin proved to be more effective than nalidixic acid, trimethoprim, mecillinam and nitrofurantoin against all gram-negative rods tested.