Time-to-turbidity model for non-protective type B Clostridium botulinum.

A model to predict the time for growth to turbidity from spores of non-proteolytic type B strains of Clostridium botulinum was developed in broth media with varying temperatures (4-28 degrees C), pH values (5-7), NaCl additions (0-4%) and total spores (10(1)-10(5)). The model estimates the probability that a sample will have growth on a given day for up to 90 days of storage. The parameters of the model include the probability of growth after 90 days (Pmax) and the mean time of growth (tau) for those that showed growth. The 95% confidence interval (CI95%) for tau was also determined. The tau decreased with increasing temperature and pH, but NaCl levels below 3% had little effect. Decreasing the number of spores in a sample increased both tau and the confidence intervals about tau, reflecting the increasing uncertainty about the estimation of growth times for low spore numbers.