The Viability of Heat-activatable Spores in Nutrient and Nonnutrient Substrates as Influenced by Prestorage or Poststorage Heating and Other Factors

Abstract

Washed spores of heat-activatable and non-heat-activatable aerobic, mesophilic and thermophilc species were heated at sublethal temps, in distilled water, 1% glucose soln. and in milk and their viability detd. (by the plate method) initially and after different periods of storage at different temps. and in mediums differing in pH. Ten cultures embracing 3 spp. were studied. When activated and stored in nutritionally incomplete substrates (distd. water or glucose soln.), spores died rapidly or underwent deactivation with retention of viability; when activation was conducted in a nutritionally complete medium (milk) with storage at subminimum growth temps., the spores died more slowly and there was little evidence of deactivation. Unheated, activatable or nonactivatable spores underwent little or no change in viability over long periods; in glucose soln. the rate of deterioration was measurably increased. The reaction associated with the rapid death of heat-activated spores had a temp. optimum ranging, with the organisms studied, from 30 to 47 [degree]C; depending upon the organism and the pH of the substrate.