Morphological Changes Induced by Wet-heat in Bacillus cereus Endospores

Seven Bacillus cereus food isolates were subjected to microscopic investigation by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) before and after wet-heat treatment at 100°C for 30 min using a heating device designed for rapid development of heat . Endospores suspensions were also autoclaved four times for 15 min each. Scanning electron microscopy showed complete destruction of exosporia in the majority of the strains studied while slight damages in endospore coats were observed. TEM showed destructive thermal treatment changes in cores and slight changes in cortices. Conventional autoclaving preserved endospores intact-structures. The clear morphological damage of the cores and the relatively slight damage to the cortex and coats support previous views suggesting that core contents might play more role/s in endospore resistance than expected. Hydrophobicity of endospores due to heat denatured proteinus exosporium of Bacillus cereus has been suggested as one of endospore wet-heat resistance factors.