Abstract
Many workers studied about the synergism and antagonism that will occur among many antibiotics, but the results differ each other according to the strains of bacteria, drug concentration and the other conditions of experiment.
The authors investigated the combined action of penicillin and aureomycin on staphylococci, and the following results were obtained.
1. Staphylococci became highly resistant to penicillin by continued passages in penicillin-containing media, but these bacteria obtained the slight increase in resistance to aureomycin by continued passages in aureomycin-containing media.
2. The increase in penicillin resistance of staphylococci was inhibited almost completely by continued passages in penicillin media containing either 1/3 or 1/6 dose of minimum inhibitory dose of aureomycin, and the aureomycin resistance of staphylococci was also highly inhibited by continued passages in aureomycin media containing either 1/3 or 1/6 dose of minimum inhibitory dose of penicillin.
3. The effects of combined action of penicillin an aureomycin on staphylococci were synergistic in most cases and slightly antagonistic or indifferent in few cases, when the doses of one drug added to another were varied in quantity from 1/3 to 1/6 dose of minimum inhibitory doses.
4. The toxicity of antibiotic-treated staphylococci to mice was weaker than those of original strains.
