Survival in foods of Staphylococcus aureus grown under optimal and stressed conditions and the effect of some food preservatives

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Abstract
Staphylococcus aureus was grown in a rich peptone medium which became alkaline with continued incubation. Cells were grown at 37 °C and in the same medium containing 1 M NaCl at 46 °C, a temperature at which this organism can grow only when protected by NaCl. Cells of these cultures are hereafter called 37 °C-cells and 46 °C-cells, respectively. The 37 °C-cells harvested when the pH was 7.1 to 7.7 had decimal reduction times (D60-value) of 1.8 to 3.1 min in 50 mM pH 7.2 Tris buffer. The D60 value of 46 °C-cells tested in the same way, harvested from cultures at pH 6.6 to 7.6, ranged from 5.3 to a maximum of 12.8 min. In milk, green beans, peas, or beef slurry, the D60- value of 46 °C-cells was about four times higher than that of 37 °C-cells. Length of survival after freeze-drying in skim-milk powder exposed to air was longest for the cells with the highest D-value. In freeze-dried peas and media acidified with acetic and lactic acids, 46 °C-cells survived longer than 37 °C-cells. However, the sensitivity of the two kinds of cells to potassium sorbate, sodium benzoate, and sodium propionate was essentially the same, but the 46 °C-cells were more resistant to butylated hydroxyanisole and sodium nitrite.

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