Purpose: The aim of this work is to model Bacillus weihenstephanensis KBAB4 (B. cereus group) and Bacillus licheniformis AD978 behavior during sporulation, spores germination and growth after a heat-treatment, using one single set of parameters: Tmin, Topt, Tmax and pHmin, pHopt, pHmax.
Methods: Effects of temperature and pH on growth of vegetative cells, their ability to produce spores and the spores’ germination and activity recovery capacity after a heat-treatment have been quantified. For every phenomenon, the effect of temperature was quantified from 4°C to 40°C for B. weihenstephanensis and from 15°C to 60°C for B. licheniformis and the pH was studied from 4.5 to 9.5 for both strains. For the sporulation and the spores recovery, heat-resistances at 85°C, 90°C, 95°C for B. weihenstephanensis and 95°C, 100°C, 105°C for B. licheniformis, were estimated using a Bigelow-like model.
Results: Optimal growth temperature was around 31.9°C for B. weihenstephanensis and at 49.0°C for B. licheniformis and optimal pH was between 7.5 and 8.0 for both strains. Sporulation and recovery conditions range are circumscribed in growth conditions field (temperature and pH). Models for each phenomenon have been developed, based on modular mathematical approach, and only one set of values (minimal, optimal and maximal growth temperature and pH) with biological significance are integrated as parameters.
Significance: These models can be easily used to identify process conditions yielding microbial hazard related to spore contamination and predict spore forming bacterial behavior using physiological parameters, largely available in literature.