食品防腐剤に関する研究-VIII : タイロシンに対するBacillusそのほかの菌の耐性獲得について

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Tylosin****, a new antibiotic isolated from Streptomyces fradiae, has been reported to have a marked antibacterial action against Gram-positive bacteria. The purpose of this work is to elucidate the in vitro acquisition of resistance against tylosin by 3 species of Bacillus (B. subtilis, B. circulans and B. coagulans), and 1 strain of Staphylococcus aureus. Results obtained may be summarized as follows: 1. The test organisms were exposed to tylosin either a constant dose at 0.1 ppm, or an increasing dose at the maximum tolerance level (M. T. L.) of test organisms at each stage of subculturing. After 50 transfers in the Difco nutrient broth containing a constant dose of tylosin, the organisms acquired 2 to 8-fold higher resistance, while the corresponding values obtained with the increasing dose at M. T. L. were 32 to 128-fold that of the original culture (Fig. 1 and 2). 2. The resistance acquired in vitro by a strain of Staphylococcus seemed to be fairly unstable since 25 transfers of the resistant organisms in the plain nutrient broth markedly decreased in its resistance. To the contrary, resistance acquired by Bacilli seemed to be stable since they kept almost the same level of resistance even after 25 transfers in the plain broth (Fig. 2). 3. There was complete cross-resistance between tylosin and desmycosin, a degradation product of tylosin which has almost the same antibacterial action of tylosin, and mutual but partial cross-resistance between tylosin and erythromycin. No cross-resistance was observed between tylosin and the following drugs; streptomycin, chloramphenicol, chlortetracycline, penicillin, and nitrofurazone. 4. No marked difference was noted in the distribution pattern of resistance in individual cells between the sensitive strain and the corresponding laboratory induced strain which were determined by plotting the numbers of colonies counted in agar plates added with various level of tylosin (Fig. 3).
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食品防腐剤に関する研究-VIII : タイロシンに対するBacillusそのほかの菌の耐性獲得について

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