In vitro activity of a combination of colimycin and tetracycline againstPseudomonas aeruginosa andEscherichia coli

Summary Thein vitro activity of a combination of colimycin and tetracycline againstPseudomonas aeruginosa andEscherichia coli was studied with the aid of tube dilution tests,Elek andHilson's modification of the replica technique, and growth inhibition curves. The interaction between the two antibiotics was as a rule of an additive nature, but a slight synergism was observed in some instances. The values of the minimum inhibitory concentrations did not seem to influence the nature of the interaction. A considerable synergism observed in all tube dilution tests withE. coli strains is attributed partly to addition and partly to suppression of the growth of more colimycin-resistant bacteria by the tetracycline. Possiblein vivo applications of this antibiotic combination are briefly discussed.