Growth Limits and Their Uses to Predict the Cycle of Life of Sporeforming Bacteria

Spore-forming bacteria are responsible of food poisoning (37% in France, 2014) and involved in the spoilage of various processed foods. Bacterial spores are commonly found in the environment, making bacterial spores the natural contaminant of raw materials. The spore properties (heat resistance, germination ability) are impacted by the environment of their formation. During food processing, spores can encounter favourable conditions and then germinate. The new vegetative cell can grow, producing spoilage or toxic enzymes making food unfit for human consumption. Predictive microbiology has proved its efficiency to predict bacterial growth in foods with the growth limits (or cardinal values) according to the environmental factors like pH, temperature or water activity. In this talk, we propose to go further by showing that the growth limits of spore-forming bacteria can also be used to predict the different steps of their cycle of life: growth, sporulation, resistance, germination, and outgrowth. For example, it was shown that the temperature boundaries of Bacillus licheniformis and Bacillus weihenstephanensis were similar for growth, recovery after a heat treatment and sporulation. The heat resistance of their spores was also tightly linked to the sporulation conditions for temperature and pH. Another striking example concerns the behaviour of the thermophilic bacteria Geobacillus stearothermophilus (ie its growth, sporulation and recovery after a heat treatment) that could be explained by the growth limits for pH and temperature only.