Abstract
Soil extract was prepared from soil collected in various locations, and the thermal resistance of genus Bacillus spores sporulated on nutrient agar containing the soil extract samples was determined. Upon addition of soil extract to the sporulation medium, the decimal reduction time (D values) of spores was larger than that of the control in all cases. Soil samples were classified into four categories (from fields, mountains, seashore and river), and it was found that soil from fields enhanced the D value of spores most effectively. The D values of spores sporulated on medium containing soil extract treated with ion exchange resin were slightly decreased. The effects of divalent cations were investigated. Manganese concentration in the sporulatiog medium was correlated with the D values of B. coagulans spores.
