[Comparative in vitro activity of 5 beta-lactams (cefoperazone, cefsulodin, ceftazidime, azthreonam, N-formimidoyl-thienamycin) on 90 strains of Pseudomonas aeruginosa with various levels of resistance to ticarcillin].

Five beta-lactams with anti-pseudomonal activity were tested against P. aeruginosa strains resistant to various concentrations of ticarcillin (from 256 to 8192 mg/l). MIC geometric means found for the totality of strains were as follows: 1.52 mg/l for ceftazidime; 1.80 mg/l for N-f-thienamycin; 4.79 mg/l for azthreonam; 17.3 mg/l for cefsulodin; 50.9 mg/l for cefoperazone. Activities of ceftazidime, N-f-thienamycin and azthreonam were not related to the level of ticarcillin resistance. Cefoperazone and, to a lesser degree, cefsulodin showed cross resistance with ticarcillin: these drugs were not active when ticarcillin MICs reached 512 mg/l and 4 096 mg/l respectively.