Evaluation of immunomagnetic separation in combination with ALOA Listeria chromogenic agar for the isolation and identification of Listeria monocytogenes in ready-to-eat foods

A study was conducted to evaluate the performance of the ALOA (chromogenic media) in combination with immunomagnetic separation (IMS) for the detection of Listeria monocytogenes in ready-to-eat food products. IMS-ALOA method was found to be equivalent to Health Canada's reference culture method as well as comparable to BAX-PCR method in terms of the sensitivity of the methods for the detection of L. monocytogenes in ready-to-eat foods such as turkey roast, beef roast, mixed vegetable salads, potato and egg salad, soft cheese and smoked salmon. The IMS-ALOA method gave 100% sensitivity in the inclusivity tests with 42 pure L. monocytogenes strains. Exclusivity testing with five other species of Listeria genus and 29 pure non-L. monocytogenes strains from 21 different genera showed 97% specificity. The method was able to detect L. monocytogenes at levels near or below 1 cfu/25 g regulatory limit in ready-to-eat food matrices after 24 h enrichment, with a turnaround time of 3 days compared to 7-8 days for culture method. IMS-ALOA method is a valuable alternate test method for the screening of L. monocytogenes in a variety of foods especially ready-to-eat foods.