Germination-induced bioluminescence, a route to determine the inhibitory effect of a combination preservation treatment on bacterial spores

In this work, we have used spores of Bacillus subtilis that specifically induce bioluminescence upon initiation of germination as a rapid, real-time monitor of the effects of preservative treatments on germination. Using this tool, we have demonstrated that the combination of mild acidity (pH 5.5 to 5.0), lactic acid (0.5%), and a pasteurization step (90 degrees C for 5 min) results in enhanced inhibition of spore germination compared with the effects of the individual treatments alone. Inhibition by the combination treatment occurred as a result of both direct but reversible inhibition, entirely dependent on the physical presence of the preservative factors, and permanent, nonreversible damage to the L-alanine germination apparatus of the spore. However, we were able to restore germination of the preservative-damaged spores unable to germinate on L alanine by supplementing the medium with the nonnutrient germinant calcium dipicolinic acid. The demonstration that simple combinations of preservative factors inhibit spore germination indicates that food preservation systems providing ambient stability could be designed which do not adhere to the strict limits set by commonly accepted processes and which are based on precise understanding of their inhibitory action.