A comparison of immunomagnetic and surface adhesion immunofluorescent techniques for the rapid detection of Listeria monocytogenes and Listeria innocua in meat.

An immunomagnetic immunofluorescent method was investigated for the rapid detection of Listeria monocytogenes and Listeria innouca. This technique involved enrichment of the suspect sample at 30 degrees C overnight. Listeria monocytogenes cells were isolated from the enriched sample using immunomagnetic separation and Listeria were subsequently visualized using an immunofluorescent microscopy technique. This technique was used in the detection of Listeria cells from pure culture, inoculated beef mince samples and naturally contaminated retail beef mince samples. A detection level of approximately 1 x 10(3) cfu ml-1 was achieved. When compared with traditional detection methods no false negatives or positives were recorded for L. monocytogenes or L. innocua. The immunomagnetic immunofluorescent technique had a detection level similar to a previously described surface adhesion immunofluorescent technique. Isolation of the Listeria cells by surface adhesion involved dipping a membrane attached to a microscope slide into the enriched sample for 10 min. This was quicker and simpler to perform than the immunomagnetic separation technique which took 2 h to carry out.