Detection of Listeria monocytogenes in vacuum-packed meat products using real-time PCR, immunoassay and culturing

During the past ten years, several Listeria (L.) monocytogenes outbreaks with febrile gastroenteritis as the predominant clinical manifestation affecting healthy adults have been reported. The main transmission route to humans is believed to be through consumption of contaminated food, especially ready-to-eat (RTE) foods. Rapid and specific detection of L. monocytogenes in food is critical for ensuring the safety of consumers. The aim of this work was to study the occurrence of L. monocytogenes in vacuum-packed meat products using real-time PCR, immunoassay and culturing. In total, 50 vacuum-packed meat products collected 2007 were studied using real-time PCR (iQ-Check (TM) real-time PCR kit), immunoassay (VIDAS LMO2 test) and culturing (L 00.00-22:1998, Official Collection of Examination Methods according to 64 LFGB). Thirty-two of 50 (64%) vacuum-packed meat products were L. monocytogenes positive by real-time PCR. The occurrence was especially high in heat-treated sausages (80%). Only two products (two bacons) were VIDAS and culture positive. Additionally, L. monocytogenes was isolated from one heat-treated sausage, which was VIDAS negative. All VIDAS and culture-positive samples were also PCR positive. In two (12%) out of 17 vacuum-packed RTE products, the number of L. monocytogenes was over 100 cfu/g demonstrating that the shelf life assigned to some vacuum-packed products is not appropriate. Real-time PCR based on iQ-Check (TM) real-time PCR kit was shown to be very sensitive to detect L. monocytogenes in foods and thus a useful tool for screening.