In-vitro activity of ciprofloxacin and other beta-lactam antibiotics against gentamicin- and carbenicillin-resistant isolates of Pseudomonas aeruginosa.

The susceptibilities of gentamicin- and carbenicillin-resistant clinical isolates of Pseudomonas aeruginosa to newer beta-lactams, netilmicin and ciprofloxacin were studied by a broth microdilution technique. Imipenem, aztreonam and ceftazidime were active against most of the P. aeruginosa strains with minimum inhibitory concentration (MIC) for 90% of the isolates at clinically achievable levels. Piperacillin, azlocillin, cefotaxime, ceftriaxone, cefsulodin, cefoperazone and netilmicin showed poor activity against these organisms, ciprofloxacin exhibited poor activity, inhibiting only 30% of these strains.