The accelerating effect of sublethal heat on spore germination in mesophilic aerobic bacteria

Abstract

The washed spores of 9 mesophilic aerobic spp. were suspended in distilled water, buffer solns., glucose broth, or evaporated milk and heated at 65[degree] to 95[degree] C for various periods, following which the spores were incubated for 3 hrs. at 37[degree] C in glucose broth or evaporated milk. The suspns. were then heated at 85[degree] C for 10 min. and subcultured on glucose agar plates. Reversion from the heat-stable to the heat-labile condition was regarded as evidence of spore germination. Preincubation heat at 75[degree] to 95[degree] C for 10 min. usually accelerated germination. The effect of preheating upon spore germination is influenced by the nature of the medium in which the spores are heated. With some spp., preheating may accelerate or retard germination, depending on the nature of the preheated medium. Preincubation heat accelerated spore germination in 7 out of 9 cultures heated and incubated in glucose broth; 5 out of 8 cultures heated in dist. water and incubated in glucose broth; and in 9 cultures (no exceptions) heated and incubated in evaporated milk. The opt. pH for acceleration of germination apparently differs with the species. The stimulating effect of preincubation heat upon spores persists for some time after treatment. Three hrs. of incubation preceded by mild heating was approx. equivalent to 24 hrs. of incubation without preheating. Although only a small propor. of spores is affected by preheating, these potentially dormant forms are of primary economic significance, since delayed germination and high heat-resistance are intimately associated.