Resistance to Fluoroquinolones in Pseudomonas aeruginosa and Klebsiella pneumoniae

The fluoroquinolone sensitivity of Pseudomonas aeruginosa and Klebsiella pneumoniae was studied by determinations of Minimum Inhibitory Concentrations (MICs) of norfloxacin and ciprofloxacin in consecutive clinical isolates. In P. aeruginosa, resistance or reduced susceptibility (MIC > or = 8 mg/l for norfloxacin and > or = 2 mg/l for ciprofloxacin) was found in 17% (9/54) of the isolates. Reduced susceptibility (MIC > or = 2 mg/l for norfloxacin) was found in 12% (10/84) of K. pneumoniae isolates. P. aeruginosa strains isolated in 1991 had reduced susceptibility to both norfloxacin and ciprofloxacin significantly more often than isolates from 1984-85 (p = 0.02). 10/84 K. pneumoniae strains from 1991 had reduced susceptibility to norfloxacin, compared with 1/34 from 1984-85. This difference was not statistically significant (p = 0.11).