Cefoperazone against carbenicillin-resistant isolates of Pseudomonas aeruginosa: comparison with other newer cephalosporins and N-formimidoyl thienamycin.

The in-vitro activities of cefoperazone, cefotaxime, ceftriaxone, latamoxef (moxalactam), ceftazidime and N-formimidoyl-thienamycin (N-f-thienamycin) were compared against clinical isolates of Pseudomonas aeruginosa that were resistant to carbenicillin and gentamicin, or against those which were susceptible. N-f-thienamycin and ceftazidime were more active than cefotaxime, ceftriaxone and latamoxef only against carbenicillin-susceptible isolates: isolates resistant to carbenicillin exhibited markedly increased resistance to cefoperazone, but not to N-f-thienamycin or ceftazidime. A partial cross-resistance was observed between carbenicillin and cefoperazone. This was due to the presence in these Pseudomonas isolates of a plasmid-mediated beta-lactamase which was active against carbenicillin and cefoperazone but not against cefotaxime, ceftriazone and latamoxef.