Modeling the effects of osmotic stress on Staphylococcus aureus.

摘要

Staphylococcus aureus is one of the leading causes of foodborne illness and is ranked as one of the most prevalent causes of gastroenteritis worldwide. S. aureus has the ability to grow over a much wider range of relative humidities (RH) than any other food-associated bacterial pathogen.; For the past several decades in the food science literature, the term ‘water activity’ has been widely used to predict microbial growth. In recent years, increasing evidence based on glass transition theory has shown that molecular mobility may be an attribute that deserves further attention.; Experiments were designed to produce S. aureus growth boundary models as tools for risk assessment. Additionally, the concepts of molecular mobility and the effect of various physical properties of humectants on S. aureus growth were investigated. Growth boundary models were developed and differences were observed in the growth/no growth boundary when different humectants were used to achieve the desired RH values.; The International Commission on Microbiological Specifications for Foods (ICMSF) has recently proposed a scheme for the management of microbial hazards for foods. This work illustrates the application of the ICMSF model via the analysis of the microbiological hazard S. aureus in cream-filled baked goods. Formulations of cream fillings are considered in the development of product criteria intended to prevent growth, utilizing the growth boundary models to make shelf life determinations.; Experiments were conducted to determine if excessive osmotic stress causes cell death by overwhelming the cell's ability to retain osmoprotectants, which requires energy in the form of ATP. Additionally, five humectants were used so that an understanding of the effects of their characteristics on microbial osmoregulation and cell survival could be understood. The results from this study indicate cell inactivation was not due to a lack of ATP being available for metabolic processes. Despite the fact that the same RH was achieved, the rates of cell death varied greatly and the sensitivities of the populations to osmotic stress were quite different, depending on which of the humectants was used. This suggests that the mechanism of inactivation may be different for glass forming solutes as compared to ionic solutes.