タイロシンの安定性および抗菌力に及ぼす金属イオンの影響-I

Cylinder-plate法で測定した場合

抄録

Present studies aimed to disclose the effect of pH value of test solution on the heat: stability of tylosin, and that of various metal ions added to test solutions of varying pHs on the heat stability and antimicrobial activity of tylosin. In the present paper, determination of tylosin activity was carried out by the cylinder-plate assay technique with Sarcina lutea, and a modified streptomycin assay agar of pH 8.5.
Results obtained may be summarized as follows:
1. No appreciable change in the antibacterial activity was observed in the test solution of SÖRENSEN phosphate buffer of pH 6.0, 7.0 or 8.0, as well as of Difco nutrient broth of same pHs on heating at 100°C for 1 hour (Table 1).
2. Tylosin was heated at 100°C for 30 minutes in distilled water, and in SÖRENSEN phosphate buffer solution or Difco nutrient broth of pH 6.0, 7.0 or 8.0 in the presence of metal ions listed in Table 2.
No appreciable decrease in the activity was noted at pH 7.0 and 8.0 in spite of the presence of metal ions, while a marked change was noted in aqueous solution containing each 300 ppm of Al⁺⁺⁺, Fe⁺⁺⁺ or Sn⁺⁺, and similar change was seen with Al⁺⁺⁺ and Fe⁺⁺⁺ in the phosphate buffer of pH 6.0 and nutrient broth as well.
The presence of such metal ions as Al⁺⁺⁺, Fe⁺⁺⁺ or Sn⁺⁺ in test solution resulted in increment of activity as expressed in tylosin equivalent value, although we have expected a reduction in antibacterial activity (Table 3).
3. Below pH 5 at elevated temperature, tylosin has been reported to convert into desmycosin (tylosin B), although antibacterial activity is still retained. However, the activity of desmycosin when measured by the cylinder-plate assay method showed 3 times as much as that of the same concentration of tylosin (see Fig. 1).
This discrepancy might be indicating the necessity of use of an appropriate method other than the cylinder-plate assay technique in order to evaluate precisely the phenomena mentioned above.