IMMUNOMAGNETIC SEPARATION OF LISTERIA-MONOCYTOGENES FOR FLOW CYTOMETRIC DETERMINATION OF VIABLE CELLS IN LIQUID

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