[Synergistic activity between ticarcillin, azlocillin, cefsulodin, ceftazidime and tobramycin or amikacin against Pseudomonas aeruginosa (author's transl)].

Activity of azlocillin, cefsulodin, ceftazidime, ticarcillin in combination with amikacin or tobramycin was investigated against 17 Pseudomonas aeruginosa isolates. Synergistic activity was evaluated by the microtiter checkerboard technique. The bactericidal effect of the antibiotic combination was determined by subculturing onto agar and into broth. Synergistic activities of cefsulodin and ticarcillin combined with amikacin or tobramycin were similar in the inhibitory as well as in the bactericidal tests. Synergistic effects of the combination of ceftazidime and amikacin or tobramycin were moderate or indifferent in the inhibitory and bactericidal tests. The combination of azlocillin and amikacin or tobramycin produced synergistic effects greater in bactericidal tests than in inhibitory tests. The bactericidal synergistic activities of the combinations of azlocillin, cefsulodin, ticarcillin were similar. There was no difference between amikacin and tobramycin combined with a beta-lactamine. Antagonism was not observed. A synergistic effect of the combinations was observed against 4 isolates resistant to tobramycin and/or ticarcillin. However the result of the interaction seemed to depend upon the level of resistance to the antibiotic : if the MIC or the MBC of either antibiotic in the test combination was very high, synergy could not be achieved.