抄録
Effects of heating on the action of some food preservatives and antibiotics to bacterial spores were stuied by determining changes in minimal inhibitory concentration (MIC) and in heat resistance of B. subtilis Marburg strain and other species of bacilli.
Results obtained may be summarized as follows:
1. MIC values of B. subtilis spores for various food preservatives and some antibiotics were determined under the following 4 treating conditions; viz., (1), the test drug and spores were heated together in the phosphate buffer of pH 7.0 at 85°C for 30 minutes, (2), the heated spores at 85°C for 30 minutes were inoculated into media containing a binary dilution series of each test drug, (3), unheated spores were inoculated into media containing a binary dilution series of heated test drug at 85°C for 30 minutes, and (4), unheated control, both spores and test drug. Consequently, no marked difference in MIC value for each drug was noted among those values obtained by different treating conditions, except chlortetracycline (CTC) and oxytetracycline (OTC) both of which are known to be easily destructed by heating (Table 1).
2. As to the effect of heating temperature of spores of B. subtilis, no appreciable difference in MIC for nitrofurazone (NFS) or tylosin (TI) was observed by heating at 60°, 70°, 80° or 90°C for 30 minutes (Table 2).
3. Judging from the germination pattern figured in terms of optical density, no detectable combined effect of heating with the action of each drug was noted under the similar condition mentioned above (Fig. 1).
4. Effect of NFS or Tl on the heat sensitivity of spores of bacilli in Sörensen phosphate buffer solution of different pHs was examined by measuring surviving spore numbers after being heated at different temperatures.
Heating at 85°C for 30 minutes at pH 7.0, the presence of each test drug did not change the rate of survivals of B. subtilis spores, while heating at 95°C, a marked decrease in the number of surviving spores was noted. This tendency was more conspicuous at pH 6.0 that at pH 7.0 (Figs. 2-4).
As to the spores of B. megaterium having rather weak heat resistance, NFS showed an apparent combined effect with heating at 85°C for 30 minutes at pH 7.0, whereas Tl did not enhance the effect of heating or decrease in the heat sensitivity of spores of the test organisms even at a higher concentration of it (Fig. 5).
