TwelveListeria monocytogenesstrains representing seven serovars were heat‐treated in physiological saline by a glass capillary tube method. Five strains were treated at 58°, 60° and 62°C, three at 60°, 62° and 64°C and four at 60°C. Heat‐treated bacteria were recovered on blood agar in two ways: (1) incubation at 37°C for 7 d; and (2) preincubation at 4°C for 5 d, followed by incubation at 37°C for 7 d. D andzvalues were determined. Better average recovery and higherDvalues were obtained when the preincubation procedure was used. The final evaluations of the heat resistance properties of the strains were therefore based on values for preincubated samples.Dvalues recorded at 58°, 60°, 62° and 64°C for preincubated samples were 1.7–3.4, 0.72–3.1, 0.30–1.3 and 0.33–0.68 min, respectively.zvalues determined were 5.2–6.9°C.Dvalues were compared statistically. Significant differences in heat resistance were noted both between serovars and between strains b
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