Gamma Irradiation of Bacillus subtilis Spores in the Presence of Sugars

SUMMARY: Spores of Bacillus subtilis were gamma-irradiated (60Co source) and viable counts performed by surface spread and tube dilution methods. Surface spread counts were greater than tube dilution counts by factors varying from 1·57 to 3·90 (aqueous suspensions) and 2·36 to 6·10 (freeze-dried). In 8 cases out of 10 there was no significant difference in the regression coefficients of log % survivors against radiation dose for the two counting methods under identical conditions of irradiation. Freeze-drying from 5 % (w/v) aqueous solutions of glucose, lactose or fructose had a significant protective effect on the radiation resistance of the spores. Freeze-drying from aqueous suspension, or from 5 % maltose had no effect on the resistance.