Growth/no growth interfaces of Bacillus cereus, Staphylococcus aureus and Salmonella enteritidis in model systems based on water activity, pH, temperature and ethanol concentration

This study focuses its attention on the boundary between the growth and no growth of three strains of Salmonella enteritidis, Bacillus cereus and Staphylococcus aureus in the presence of growth controlling factors such as temperature, pH, water activity (A(w)) and ethanol concentration. Preliminarly, the minimal values of pH, A(w) and temperature, and the maximum ethanol concentrations allowing the growth of the considered micro-organisms were determined. The calculation of these values enabled the use of logistic model to evaluate the growth/no growth boundary for the bacteria in relation to the considered independent variables. The location of the growth/no-growth boundaries for S. enteritidis and Staph. aureus were strongly affected at the same ethanol concentration, by temperature, pH and A(w). Among the considered species, Staph. aureus was endowed with the highest sensitivity to low pH values while B. cereus's growth/no growth interface, was quite unaffected by the combination of the stresses, when the physico-chemical conditions were above the minimum for growth. The effects of temperature, A(w) and ethanol on the limitation of growth of the considered species were not merely additive. It was possible to identify the combinations of such factors preventing the growth of Salmonella enteritidis, Staph. aureus and B. cereus. (C) 2001 Academic Press.