Susceptibility of 324 Nonfermentative Gram-Negative Rods to 6 Cephalosporins and Azthreonam

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Abstract
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 spp., 1st and 2nd generation cephalosporins were minimally active against nonfermenters tested. Cefsulodin and azthreonam were mainly active against Pseudomonas aeruginosa. 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 P. maltophilia and P. fluorescens/P. putida and was also the most active against P. cepacia. Acinetobacter 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.