THERMAL-RESISTANCE OF YERSINIA-ENTEROCOLITICA AND LISTERIA-MONOCYTOGENES IN MEAT AND POTATO SUBSTRATES

The heat resistance of a wild type and nalidrxic acid resistant strain of Yersinia enterocolitica and Listeria monocytogenes, was measured i n meat (minced beef and minced beef homogenate) and potato substrates over the temperature range 50-60C. Comparisons of hear resistance were determined using D-values calculated using a linear survival model. T he results showed that the wild-type strain of Y. enterocolitica was m ore heat resistant than the mutant (P<0.05). Under mast conditions, th e use of a nonselective/overlay recovery medium resulted in higher D-v alues compared to a selective recovery medium (P<0.05). Analysis of th e data using a nonlinear survival model (D-1 and D-2-values) suggested the presence of heat resistant subpopulations and was particularly ev ident for the mutant strain, and in potatoes compared to minced beef.