Heat resistance in different heating media of Listeria monocytogenes ATCC 15313 grown at different temperatures

This paper examines the influence of growth temperature on thermal resistance of Listeria monocytogenes A TCC 15313. Regardless of the incubation temperature the heat resistance of Listeria monocytogenes increased during incubation until the stationary phase of growth was reached. The maximum heat resistance of cells grown at 4C, 20C or 37C was attained after 14 days, 36 h and 18 h of incubation, respectively. After longer incubation times the heat resistance of cells grown at 4C and 20C did not change but that of cells grown at 37C decreased. The maximum heat resistance was usually greater at higher incubation temperatures. However, the magnitude of these differences depended on the pH and composition of heating media. By raising the incubation temperature from 4C to 37C, the D-62 value in pH 7 citrate-phosphate buffer increased from 0.13 to 0.34 min. However, when skimmed milk was used as menstruum this difference was not observed. Cells grown at 37C attained maximum heat resistance at pH 7 but those grown at 4C, at pH 6. The magnitude of the effect of the incubation temperature on heat resistance was constant at all heating temperatures tested (z = 6 +/- 0.8C). The higher heat resistance of cells grown at higher temperatures was not due to a greater capacity of heat damage repair.