After an cultivation of drug-resistant E. coli on the synthetic medium which containes the drug, the content of the drug in the filtrate of the culture medium was determined chemically, and it was found that three kinds of antibiotics such as dihydrostreptomycin, chloramphenicol and tetracycline were decomposed by microorganisms strongly.
The decomposition reaction of the drug is simultaneously an inactivation which was considered to be intracellular. However, sulfisomidine was found to be remained almost undecomposed by microorganisms. As to the three kinds of antibiotics, an ability of drug decomposition by microorganisms is considered to be one of the possible factors in the drug-resistant mechanism of E. coli. However, another mechanism should be considered in the case of sulfa-drugs.