Effect of sporulation and recovery medium on the heat resistance and amount of injury of spores from spoilage bacilli

Aims: To assess the influence of sporulation media on heat resistance, and the use of stress recovery media to measure preservation injury of spores of five representative spoilage bacilli. Methods and Results: Bacillus spores prepared on nutrient agar supplemented with Ca2+, Mg2+, Mn2+, Fe2+ and K+ were more heat-resistant than spores obtained from nutrient agar with Mn2+. This increased heat resistance correlated with a decrease in the protoplast water content as determined by buoyant density sedimentation. The degree of preservation injury severity could be assessed on media containing NaCl at moderate pH and organic acids at acid pH. Ca-DPA, K+ or proline were added to the recovery media to demonstrate that heat probably caused injury to both spore germination and the outgrowth system. Significance and Impact of the Study: The metal content of sporulation media can strongly effect the validity of preservation resistance studies. The distinctive recovery media developed here can be relevant for assessing and comparing new preservation technologies.