[Antibiotic activity and synergism of ceftazidime and netilmicin against gram-negative pathogenic bacteria]

The in vitro activity of ceftazidime and netilmicin against gram-negative bacteria often causing hospital infections was evaluated and furthermore synergistic effects of these antibiotics were studied. Ceftazidime was as active as netilmicin against Enterobacteriaceae, e.g. Enterobacter, Klebsiella, Morganella inhibiting 90% of these strains at concentrations from 0.5 to 4 micrograms/ml. Ceftazidime was the most effective agent against Pseudomonas aeruginosa, being even more active than cefsulodin, with a mean minimal inhibitory concentration (MIC) of 4.57 micrograms/ml (median 2.0 micrograms/ml), also inhibiting cefoperazone- and cefsulodin-resistant Pseudomonas. There was at most a two-fold difference in either MIC or minimal bactericidal concentration (MBC). In all genera tested an increase of the inoculum size from 10(4) to 5 X 10(6) colony forming units had minimal effects upon the MIC or MBC of ceftazidime and there was no decrease of the MIC in the presence of clavulanic acid or sulbactam. When ceftazidime and netilmicin were combined synergism was observed against all strains tested.