Enzyme-linked immunosorbent assay for general and specific detection of Listeria spp. and monocytogenes in dairy products

Bacteria of the genus Listeria are widely distributed in the environment and they frequently contaminate food. Among all species in the genus Listeria, only L. monocytogenes has been implicated in serious human illness. The other Listeria spp. are considered to be avirulent to man but they may cause a variety of disease symptoms or even death in animal. These bacteria are well equipped to survive food processing technologies. For example, they tolerate high concentrations of salt and relatively low pHs, and worst of all, they are able to multiply at refrigeration temperatures. This makes Listeria microorganisms a serious threat to food safety and ranks them among the microorganisms that most concern the food industry. The foods most frequently implicated are raw milk, soft cheeses (particularly those made from unpasteurized milk), ice cream, raw vegetables, fermented raw-meat sausages, raw and cooked poultry and raw and smoked fish. Food producers and distributors as well as public health authorities have great interest in timely detection of Listeria contamination. We present here a rapid antibody-based screening assay for the detection of both Listeria spp. and Listeria monocytogenes in dairy samples (milk, cheeses, ice-cream…). A detection system consists of an initial selective enrichment step, where both artificially contaminated samples and real dairy samples were cultivated, followed by direct sandwich format of ELISA using two different polyclonal antibodies; one specific for Listeria spp., and the other specific for L. monocytogenes.