Susceptibility of 324 isolates of nonfermentative gram-negative bacteria to cephalothin, cefamandole, cefoxitin, ceftriaxone, ceftazidime, cefsulodin, and azthreonam was determined by agar dilution and disc diffusion techniques. With the exception of Moraxella species, first- and second-generation cephalosporins were minimally active against nonfermenters tested. Cefsulodin and azthreonam were mainly active against Pseudomonas aeruginosa. In contrast, ceftazidime and ceftriaxone exhibited wider activity spectra. Cefsulodin and ceftazidime were the most active against P. aeruginosa, followed by azthreonam and ceftriaxone. Ceftazidime was the only drug with significant activity against Pseudomonas maltophilia and Pseudomonas fluorescens/ Pseudomonas putida, and was also the most active against Pseudomonas cepacia. Acine-tobacter calcoaceticus and Alcaligenes strains were most sensitive to ceftazidime, followed by ceftriaxone and azthreonam. Ceftriaxone was the most active against moraxellas, followed by cefamandole/cefoxitin, ceftazidime, cephalothin, cefsulodin, and azthreonam. Ceftazidime was the most active against uncommonly isolated nonfermenters. Results observed in this study reflect a potential use for ceftazidime in therapy of infections caused by most gram-negative nonfermenters; therapy with cefsulodin and azthreonam in nonfermenter infections should be restricted to those caused by P. aeruginosa, and that with ceftriaxone reserved for non-P. aeruginosa infections.

Susceptibility of 341 isolates of non-fermentative gram-negative bacteria to carbenicillin, piperacillin, cefoperazone, moxalactam, cefotaxime, ceftizoxime, and N-formimidoyl thienamycin was determined by the agar dilution and disc diffusion methods. Piperacillin was the most active agent against Pseudomonas aeruginosa, thienamycin the most active against Pseudomonas fluorescens and Pseudomonas putida, and moxalactam the most active against Pseudomonas maltophilia. Piperacillin and thienamycin were the most active agents against the other Pseudomonas species studied. Thienamycin proved to have excellent activity against Acinetobacter calcoaceticus--90% of strains were inhibited by less than or equal to 1 microgram/ml. The two most active drugs against Alcaligenes species were piperacillin and thienamycin, both of which inhibited 90% of isolates at a concentration of 2 micrograms/ml. All drugs were active against Moraxella species. The broad sensitivity spectrum of piperacillin, thienamycin, and the third-generation cephalosporins against non-fermentative gram-negative bacteria indicates their potential use in infections caused by these organisms.

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