The isolation and detection of Listeria from artificially contaminated food by use of immunomagnetic separation and cultivation procedures

Food contaminated with Listeria monocytogenes is considered to be the main source of infections in humans. Listeriae are relatively tolerant to environmental factors such as low pH and high concentration of NaCl and are psychrotrophic, which gives them competitive advantage over the accompanying microflora. Rapid isolation and confirmation methods for L. monocytogenes in foods are urgently needed. The purpose of the present study was to determine the specificity and sensitivity of immunomagnetic separation technique (IMS) with para-magnetic particles targeting Listeria by anti-Listeria antibodies (Dynabeads®-Listeria), IMS was used for testing samples of raw milk, liver paste and PBS, artificially contaminated with Listeria or with a mixed population of Listeria and other species of food-borne pathogens; Enterococcus faecalis or Escherichia coli, The recovery of heat-injured Listeria by IMS was also investigated. It was shown that IMS allows detection of target bacteria with a sensitivity of CFU/25 g. Using immunocapture technique, the shortening of selective Listeria enrichment time was possible despite of a rich background bacterial flora. For heat-injured Listeria, IMS allows recovery of cells repaired during pre-enrichment step, which in other isolation procedures are not able to grow or grow poorly.