Comparison between the in-vitro activity of new agents on Pseudomonas aeruginosa isolates from cystic fibrosis patients and other chronic infections.

The in-vitro activities of the newer antipseudomonal agents cefsulodin, ceftazidime, U-63196, aztreonam and piperacillin were compared, together with azlocillin, carbenicillin, ticarcillin and tobramycin against 98 strains of Pseudomonas aeruginosa. On all of the 43 isolates from cystic fibrosis patients and the 55 strains from other chronically infected patients, ceftazidime (MIC90: 5.0 and 2.8 mg/l respectively) and cefsulodin (MIC90: 8.2 and 3.1 mg/l) were the most active cephalosporins, and U-63196 the least active (MIC90: 40.1 and 46.1 mg/l). A high incidence of resistance (23 of 55 strains) to tobramycin was found only in the non-cystic fibrosis isolates. The activity of the other agents was comparable in the cystic fibrosis and non-cystic fibrosis isolates. MIC90 for aztreonam were 15.8 and 13.6 mg/l. Piperacillin was the most active penicillin in both populations (MIC90: 25.8 and 21.8 mg/l). Cross resistance was demonstrated in both populations for the penicillin compounds.