Effects of the Components in Growing Media on the Radioresistance of Bacterial Spores

Abstract

The radioresistances of 16 species and 39 strains of bacilli spores grown on tryptone glucose extract agar, glucose nutrient agar and yeast extract nutrient agar, were illustrated in Fig. 2 by the dose to give the 10^-4 survival which was obtained from the dose-survival curves (Fig. 1). In some cases, varied radioresistance of the spores of same strain grown in different growing media were observed.
Significance of the concentration level of metals in the growing media on the spore production and on the radioresistanceof the spores were investigated using Bacillus megaterium IMF 1166. A little, spore crop was observed on the media without addition of manganese (Table 2). Variationsin radioresistance of the spores were also observed in theconcentration levels of manganese and calcium added to thegrowing media (Fig. 3 and 4).
Effects of combination of .growing media components, beef extract, yeast extract, peptone and glucose on the radioresistance of spores were examined using Bacillus cereus IMF 1029. Variations in radioresistances of the spores harvestedfrom media having different components were observed in thecomparison of D¹⁰ values (Fig. 5). Different radioresistanceof the spores grown on the potato, milk and beef agar were demonstrated (Fig. 6).
From these observations, it is suggested that the sporulating media compositions must be standardized in the determination of radioresistance of the spores. A significance of the results obtained in practical food irradiationwas discussed.