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. A synergistic and an indifferent combined bactericidal effect was obtained with ampicillin/streptomycin and ampicillin/chloramphenicol combinations respectively. The mechanism of such synergism is briefly discussed.