Modelling the inactivation, survival and growth of Salmonella enterica under osmotic stress considering inoculum phase and serotype

Abstract

Aims: This study evaluated the behaviour of the Salmonella enterica serotypes in osmotically stressful BHI broth (0.940 ≤ a w ≤ 0.960), assessing inoculum from two stages of the bacterial life cycle (exponential and stationary) and two temperatures (25°C and 35°C).Methods and Results: Four S. enterica serotypes (Typhimurium, Enteritidis, Heidelberg and Minnesota) were grown in stressful BHI at 25°C. A mathematical model was proposed for describing the total microbial count as the sum of two subpopulations, inactivating and surviving-then-growing. When submitted to a w of 0.950 and 0.960, all strains showed a decreased count, followed by a period of unchanged count and then exponential growth (Phoenix Phenomenon). Strains inoculated at a w = 0.940 and 0.945 showed inactivation kinetics only. Cells cultivated at 25°C and inoculated from the exponential phase were the most reactive to the osmotic stress, showing a higher initial population reduction and shorter adaptation period. The proposed model described the inactivation data and the Phoenix Phenomenon accurately. Conclusions:The results quantified the complex response of S. enterica to the osmotic environment in detail, depending on the inoculum characteristic and serotype evaluated.Significance and impact of study: Quantifying these differences is truly relevant to food safety and improves risk analysis.