Inactivation of Bacillusglobigii by chlorination: A hierarchical Bayesian model

Recent events in which spores of Bacillus anthracis have been used as a bioterrorist weapon have prompted interest in determining the resistance of this organism to commonly used disinfectants, such as chlorine and ozone. This work was undertaken to study the effect of temperature over the range of 5°C to 30°C for pH levels of 7 or 8, on the inactivation kinetics of the spores of Bacillus globigii and to evaluate whether these spores could serve as a surrogate for the spores of B. anthracis in chlorine inactivation studies in water. The delayed Chick-Watson model, i.e. a lag phase followed by pseudo-first order rate of inactivation, was found to adequately describe the inactivation kinetics of B. globigii. Markov Chain Monte Carlo (MCMC) simulation method was used to estimate the length of the lag phase and the post-lag phase rate constant. As expected, the length of the lag phase decreased with increasing temperature and the post-lag phase rate constant increased with increasing temperature. A hierarchical Bayesian modelling approach was used to model the kinetic parameters of the inactivation model as functions of temperature. The MCMC simulation method was used to estimate the minimum CT requirement (with safety factor) for 99% inactivation of B. globigii.