Time-to-turbidity model for non-proteolytic 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°C), pH values, (5–7), NaCl additions (0–4%) and total spores (101−105). 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 (τ) for those tubes that showed growth. The 95% confidence interval (CI95%) for τ was also determined. The τ decreased with increasing temperature and pH, but NaCl levels below 3% had little effect. Decreasing the number of spores in a sample increased both τ and the confidence intervals about τ, reflecting the increasing uncertainty about the estimation of growth times for low spore numbers.