Comparative in vitro antibacterial activity of aztreonam against clinical isolates of gram-negative bacteria

The in vitro antibacterial activity of aztreonam was compared with that of cefoperazone, cefotaxime, ceftazidime, gentamicin, latamoxef, and ticarcillin against 140 clinical isolates of gram-negative bacteria. The activity of aztreonam against Enterobacteriaceae is similar to that of cefotaxime and ceftazidime but greater than that of gentamicin, latamoxef, and ticarcillin. The 90% minimum inhibitory concentration (MIC90) of most of these isolates ranges between 0.8 and 1.6 micrograms/ml. The activity of aztreonam against Pseudomonas aeruginosa is similar to that of cefotaxime and cefoperazone, more active than that of latamoxef, and less active than that of ceftazidime. The minimum bactericidal concentration of aztreonam is equal to or twice the MIC for most strains tested. Time-kill studies of selected strains demonstrated rapid killing when they were exposed to 2-4 times the MIC of aztreonam. The selective spectrum of action of aztreonam makes this drug a useful agent in the therapy of a variety of gram-negative infections.