In-vitro susceptibility of Pseudomonas aeruginosa to old and new beta-lactam antibiotics and aminoglycosides.

In-vitro, activities of gentamicin, tobramycin, netilmicin, amikacin, cefsulodin, latamoxef (moxalactam), carbenicillin, ticarcillin and piperacillin were compared against 147 randomly selected strains of Pseudomonas aeruginosa. Tobramycin was the most active aminoglycoside (MIC 90:4 mg/l), complete cross resistance with gentamicin (MIC 90:8 mg/l) was observed. Amikacin was the best alternative aminoglycoside (MIC 90:12 mg/l) Netilmicin showed only moderate activity (MIC 90:16 mg/l). Cefsulodin was the most active beta-lactam antibiotic (MIC 90:8 mg/l) but significant cross-resistance was observed with ticarcillin (MIC 90:32 mg/l) and piperacillin (MIC 90:12 micrograms/ml). Carbenicillin was two dilutions less active than ticarcillin, latamoxef showed a good activity (MIC 90:64 mg/l). Having the highest ratio between serum achievable concentration and MIC 90, piperacillin could be the best alternative drug to the aminoglycosides, of the tested antibiotics.