食品防腐剤に関する研究-IV : Pseudomonas fluorescensの抗生物質(CTC)に対する耐性獲得について

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Acquisition of resistance against chlortetracycline (CTC) by Pseudomonas fluorescens, which is closely associated with putrefaction of fish and shellfish, was studied. The results may be summarized as follows: 1. Three starins of P8. fluorescens were exposed to CTC of either a constant dose at the maximal tolerance level (M. T. L.) of each strain or 0.1 ppm, or an increasing dose at M. T. L. at each stage. After 60 successive subculturings in nutrient broth (Difco) containing a constant dose of CTC, the organisms acquired 4 to 16-fold higher resistance at the M. T. L. and 2 to 8-fold at 0.1 ppm, while the corresponding values obtained at the increasing dose were 16 to 64-fold that of the original culture (Figs. 1 and 2). The resistance acquired in vitro seemed to be comparatively stable since 25 successive subculturings of the in vitro resistant organisms in plain nutrient broth held almost the same level of their resistance. 2. A complete cross-resistance against CTC and oxytetracycline was observed. A slight cross-resistance against chloramphenycol was recorded with the CTC-resistant organisms, while that against streptomycine was not appreciable (Table 1). 3. No marked difference in the biochemical characters, especially those relating to putrefaction, was observed between the resistant and sensitive strains (Fig. 3). 4. The distribution curve of resistance of individual cells of a sensitive strain obtained by plotting the numbers of the colonies counted in agar plates added with various levels of CTC appears to be a S shape (Fig. 4), which indicates heterologous sensitivity to CTC by individual cells. While, the curves for the resistant descendants are composed of two linear lines crossing at nearly right angle, which means the majority of the individuals has the same level of resistance. Neither the sensitive nor resistant strain showed CTC-dependence because the largest number of colonies was counted in the plates without CTC.
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食品防腐剤に関する研究-IV : Pseudomonas fluorescensの抗生物質(CTC)に対する耐性獲得について

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