Effects of temperatures above the maximum for germination on the endospore of Bacillus cereus

Abstract

Knaysi, Georges (Cornell University, Ithaca, N.Y.). Effects of temperatures above the maximum for germination on the endospore of Bacillus cereus. J. Bacteriol. 87:1129-1136. 1964.-This is chiefly a study of heat activation and of the instability observed in spores of Bacillus cereus exposed to high temperatures. Temperatures up to 80 C for periods up to 6 hr were used. The spores were in colonies grown on collodion films, and were observed with the phase microscope, in dark contrast, for any evidence of change in their optical properties, the structure of their spodograms, and any other evidence of germination or growth. Exposure of the endospores to 80 C for 4 hr or more, whether in distilled water or in glucose broth, entirely eliminated stage II (i.e. the germcell stage, when the germinating spore begins to grow), and also tended to render the spores unstable and to produce uniformly dark spodograms. This instability involves some destructive processes and is not equivalent to normal entry into stage I (the initial stage). True heat-activation seemed to take place at a stage prior to the one which yielded uniformly dark spodograms. It was shown to consist of two factors: accumulation of germination-promoting components of the medium and activation of some spore components involved in germination. Activation of the medium components by preheating did not stimulate the spores of the strain employed. Unstable or activated spores can not be instantaneously stabilized, deactivated, or their changes arrested by exposure to acid buffers. It is concluded that the optimal temperature for activation, without danger of injury to the spore, in a given strain, is just above the maximum for stage I in that strain.