Prevalence and Genetic Diversity of Listeria monocytogenes in Vacuum-Packaged Ready-to-Eat Meat Products at Retail Markets in Latvia

Nine groups of different retail ready-to-eat vacuum-packaged meat products from 10 Baltic meat processing plants were analyzed for presence and numbers of Listeria monocytogenes at the end of shelf life. A total of 38 (18%) of 211 samples tested positive for L. monocytogenes serotype 1/2a (88%) or 1/2c (12%). The prevalence of L. monocytogenes in cold-smoked, sliced, vacuum-packaged beef and pork products (42%) was significantly higher than in cooked, sliced, vacuum-packaged meat products (0.8%) (P < 0.001). Enumeration of L. monocytogenes showed that 84% of the positive samples contained <100 CFU/g upon expiry of product shelf life. The numbers of L. monocytogenes exceeded 100 CFU/g only in cold-smoked, sliced, vacuum-packaged beef products. Identical pulsed-field gel electrophoresis types were recovered from different production lots of cold-smoked vacuum-packaged beef and pork products produced by the same meat processing plant, demonstrating L. monocytogenes contamination as a recurrent problem within one meat processing plant.