The interaction of antibiotics to bacteria seen frequently in clinical infections was studied by a tube method or viable count.
The combination of carbenicillin and gentamicin showed synergy to all of the to strains of Pseudomonas aeruginosa, examined but carbenicillin inhibited the antibacterial activity of gentamicin by incubation of mixture of the two drugs for 9 hours at 37°C. This inhibitory effect was observed in combinations of sulbenicillin to gentamicin, carbenicillin to kanamycin, aminodeoxykanamycin sulfate and 3´, 4´-dideoxykanamyin B, ampicillin to kanamycin and cloxacillin to kanamycin.
The combination of gentamicin and clindamycin showed synergy to all of 15 strains of Staphylococcus aureus tested but indifferent to each of 15 strains of Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa though synergy to some strains was seen at extremely high concentration of clindamycin. Antagonism was not observed. Incubation of mixture of these two drugs didn´t show any change of ´their antibacterial activities.
The combination of ampicillin, chlorampenicol and trimethoprim-sulfamethoxazole to Salmonella typhi showed synergy or indifference but antagonism was seen in, the ´higher concentrations of ampicillin(2.5-12.5 ug/ml) and chloramphenicol.
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