An autocatalytic model for bacterial spore germination.

The sigmoidal response observed in kinetic studies of germinating bacterial spores, using nephelometric techniques and phase contrast microscope photometry, is analysed by postulating an autocatalytic process. A scheme A to B to C, where B catalyses the degradation of A, is applied to describe the response accurately by three rate constants. The autocatalytic model is compared with previous proposals for quantifying germination studies and for interpreting the effect of different experimental conditions on initiation of germination. Its effectiveness is demonstrated by quantifying published results for a germinating single spore determined by phase contrast microscopy, and nephelometric results for spore suspensions, including the effect of temperature on the rate of initiation of germination. Although developed for quantitative analysis of spore germination, the model is applicable to other autocatalytic phenomena. To assist the experimentalist, a simple accurate method for deriving the three constants specifying the sigmoidal characteristic is described.