A COMPARISON OF IMMUNOMAGNETIC AND SURFACE-ADHESION IMMUNOFLUORESCENTTECHNIQUES FOR THE RAPID DETECTION OF LISTERIA-MONOCYTOGENES AND LISTERIA-INNOCUA IN MEAT

An immunomagnetic immunofluorescent method was investigated for the ra pid detection of Listeria monocytogenes and Listeria innouca. This tec hnique involved enrichment of the suspect sample at 30 degrees C overn ight. Listeria monocytogenes cells were isolated from the enriched sam ple using immunomagnetic separation and Listeria were subsequently vis ualized using an immunofluorescent microscopy technique. This techniqu e was used in the detection of Listeria cells from pure culture, inocu lated beef mince samples and naturally contaminated retail beef mince samples, A detection level of approximately 1 x 10(3) cfu ml(-1) was a chieved. When compared with traditional detection methods no false neg atives or positives were recorded for L. monocytogenes or L. innocua. The immunomagnetic immunofluorescent technique had a detection level s imilar to a previously described surface adhesion immunofluorescent te chnique. Isolation of the Listeria cells by surface adhesion involved dipping a membrane attached to a microscope slide into the enriched sa mple for 10 min. This was quicker and simpler to perform than the immu nomagnetic separation technique which took 2 h to carry out.