Immunomagnetic separation of Listeria monocytogenes for flow cytometric determination of Viable cells in liquid

A procedure was developed for rapid detection of Listeria monocytogenes in enrichment broth after 24 h incubation. The technique comprised immunomagnetic separation, by use of paramagnetic labelling with iron particles (size 50 nm) and separation on a high gradient column followed by vital staining and flow cytometry. With this method L. monocytogenes could be separated and detected down to approximately 3X10(4) cells per mi of enrichment broth. Working with different concentrations of L. monocytogenes in the range of 10(4) to 10(7) cells/ml, the bacteria were separated at a recovery rate up to 95%. Using mixed cultures of L. monocytogenes and serologically related species including Lactococcus lactis, the non-Listeria could either be eliminated by the immunomagnetic separation, or be distinguished from L. monocytogenes by the flow cytometric profile. (C) 1997 Elsevier Science B.V.