Sporulation environment of emetic toxin-producingBacillus cereusstrains determines spore size, heat resistance and germination capacity

Abstract

Heat resistance, germination and outgrowth capacity of Bacillus cereus spores in processed foods are major factors in causing the emetic type of gastrointestinal disease. In this study, we aim to identify the impact of different sporulation conditions on spore properties of emetic toxin-producing B. cereus strains. Spore properties of eight different emetic toxin-producing strains were tested, with spores produced in five different sporulation conditions: aerated liquid cultures, air-liquid biofilms, 1.5% agar plates, 0.75% agar plates and swarming colonies. Model food studies revealed spores from emetic toxin-producing strains to germinate efficiently on meat broth- and milk-based agar plates, whereas germination on rice-based agar plates was far less efficient. Notably, spores of all strains germinated efficiently when 0.1% meat broth was added to the rice plates. Analysis of spores derived from different environments revealed large diversity and showed biofilm spores for the strains tested to be the largest in size, the most heat resistant and with the lowest germination capacity. Sporulation in complex conditions such as biofilms and surface swarming colonies increases heat resistance and dormancy of spores. The results obtained imply the importance of sporulation conditions on spore properties of emetic toxin-producing B. cereus strains, as occur for instance in food processing.