Factors influencing the survival and growth of Listeria monocytogenes on the surface of Canadian retail wieners

A study of survival and growth of Listeria monocytogenes on Canadian retail wieners was undertaken to assess the potential hazard of this product. All-beef, poultry or beef/pork wieners from a total of six processing plants were surface-inoculated with a three-strain cocktail of L. monocytogenes, and stored under vacuum at 5 degrees C for up to 28 days. Of a total of 61 samples tested, 40 (65.6%) supported growth of the pathogen. A model was derived for 35 samples with stepwise multiple regression analysis, which used initial pH (PHO), initial lactic acid bacteria counts (LAB0), and LAB after 14 days (LAB14) to explain 48.1% of the variation in the L. monocytogenes counts after 14 days. The observed times to 1-log increase in counts for 25 samples in which growth occurred were compared to times predicted by the U.S. Dept. of Agriculture (USDA) Pathogen Modelling Program. The latter model, based on storage temperature, and initial pH, nitrite and salt concentrations, explained only 12.4% of the variation in the observed times. Scanning electron microscopy showed that the wiener surface was composed of a dense layer of coagulated protein. This may alter the ability of L. monocytogenes to develop relative to growth conditions in the meat formulation. These results suggest that retail wieners may support growth of L. monocytogenes, which could present a health hazard to target groups of consumers if subjected to post-processing contamination. They also suggest that further work is needed to derive adequate models to allow an accurate prediction of the growth of L. monocytogenes on ready-to-eat meat products