Determination of the synergy of antibiotic combinations by an overlay inoculum susceptibility disc method.

A method involving an overlay inoculum agar and antibiotic susceptibility discs in the determination of synergy of gentamicin and disc antibiotics against clinical isolates of Pseudomonas aeruginosa has been described. Gentamicin combinations with carbenicillin showed synergism against all test isolates. Combinations containing fosfomycin had indifferent effects.

The combined activity of ampicillin with streptomycin or chloramphenicol against Pseudomonas aeruginosa.

The bacteriostatic and bactericidal activity of ampicillin when combined at ten different ratios with either streptomycin or chloramphenicol against Pseudomonas aeruginosa has been investigated. Synergistic bacteriostatic effect was obtained with all ampicillin/streptomycin combinations and 9 ratios of ampicillin/chloramphenicol combinations. The highest synergistic value was obtained by the ratios containing 98% of ampicillin and 2% of either streptomycin or chloramphenicol.