Combination effect of piperacillin with four aminoglycosides on nonfermenting gram-negative bacteria.

The in vitro efficacy of piperacillin in combination with gentamicin, tobramycin, amikacin and netilmicin against 57 nonfermenting gram-negative bacterial strains was compared by use of the checkerboard agar dilution technique. On average 34% of all nonfermenting strains were inhibited by additive, 13% by synergistic piperacillin-amino-glycoside combinations. Great variation occurred between the different bacterial species. Piperacillin-aminoglycoside combinations were most active on Pseudomonas aeruginosa and least potent on Pseudomonas cepacia. Piperacillin was highly active against P. aeruginosa, P. cepacia, Pseudomonas fluorescens-putida and Acinetobacter species.