Listeria monocytogenes prevalence and serotype diversity in various foods

The aim of the current study was to estimate the prevalence and serotype diversity of Listeria monocytogenes in various foods of Estonian origin such as meat, milk, fish, pastry, crop, culinary, fruit and vegetable with special reference to ready-to-eat (RTE) foods. In 2008-2010, a total of 554 (2.6%) of 21,574 food samples were positive for L. monocytogenes in Estonia. L. monocytogenes contamination was significantly (P < 0.001) higher in raw meat and raw meat products (18.7%), raw mixed salads (18.5%) and in raw milk (18.1%) compare to raw fish products (8.8%). Among RTE fish products, cold-smoked fish products were most frequently contaminated with L. monocytogenes (32.9%). Generally, the counts of L. monocytogenes in tested products remained under 10 colony forming units (CFU) per gram of product. Only 2.9% and 0.8% of the RTE fish products contained L. monocytogenes in range of 100-1000 CFU/g and >1000 CFU/g at the end of shelf life. The majority of tested isolates (73.6%) belonged to serotype 1/2a, followed by 1/2b (7.4%), 1/2c (7.4%), 4b (7.7%) and 4d (3.5%). Our findings showed that the prevalence of L. monocytogenes in various RTE food categories, in spite of higher prevalence among raw products, was generally low in Estonia.

► A total of 554 (2.6%) of 21,574 food samples were positive for Listeria monocytogenes in Estonia. ► Most often contaminated products were raw meat (18.7%), mixed salads (18.5%) and raw milk (18.1%). ► Among RTE fish products, cold-smoked fish products were most frequently contaminated. ► Generally, the counts of L. monocytogenes in tested products remained under 10 CFU/g. ► The majority of tested isolates (73.6%) belonged to serotype 1/2a.