Presence of Listeria monocytogenes in prepared foods. Analysis of influencing factors

Although food-borne outbreaks of listeriosis are uncommon, they remain a major public health problem. We assessed the prevalence of L. monocytogenes in prepared foods and the influence of different factors (including type of food or presence of accompanying bacteria). Results showed that accompanying bacteria cause interference in the sensitivity of the detection method, being half Fraser the enrichment medium of choice. In 2760 samples, the global prevalence of L. monocytogenes was 1.4%. In ready-to-eat foods, the highest prevalence (23.3%) was found in products containing fermented or cured ingredients and the prevalence was also higher in foods with high counts of aerobic bacteria and lactose positive Enterobacteriaceae, two indicators of process hygiene. We also found that foods stored <0ºC had a higher prevalence (4.1%) of L. monocytogenes. In prepared foods, factors favouring the presence of L. monocytogenes could be some components of ready-to-eat foods, temperatures <0ºC and presence of accompanying bacteria