Synergistic activities of combinations of beta-lactams, fosfomycin, and tobramycin against Pseudomonas aeruginosa

Abstract

The effects of antibiotic combinations against Pseudomonas aeruginosa infections frequently found in hospitalized patients were investigated. By means of an agar plate dilution checkerboard method, combinations of piperacillin-fosfomycin, cefoperazone-fosfomycin, and cefsulodin-fosfomycin were synergistic against 80.0, 85.0, and 82.6% of the strains tested. The mean fractional inhibitory concentration indices of piperacillin-fosfomycin, cefoperazone-fosfomycin, and cefsulodin-fosfomycin were 0.48, 0.42, and 0.46, respectively. The synergistic activities of these combinations were enhanced by the addition of a small amount of tobramycin, 0.25 micrograms/ml.