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 (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 ( P max) and the mean time of growth (τ) for those tubes that showed growth. The 95% confidence interval (CI 95%) 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.