Detection of Listeria monocytogenes in Ready-to-Eat Meat Products

Problem statement: The objective of this study was to develop a rapid and sensitive method for the detection of Listeria monocytogenes and to screen large number of ready-to-eat (RTE) meat samples. Approach: A total of 250 fresh RTE meat samples of different varieties (chicken, turkey, beef, pork and cold cuts) were purchased from local grocery stores. Results: From the 250 total samples, 50 samples were randomly selected and subjected to DNA extraction, and immunomagnetic Separation (IMS) followed by RT-PCR analysis using primers against L. monocytogenes specific gene (hlyA). Five RTE samples negative by culture and by RT-PCR were spiked with L. monocytogenes (ATCC-19111) and used as positive controls. While all positive samples were detected as positive, all 50 samples were negative with both methods i.e., IMS followed by hlyA gene-based RT-PCR assay and the standard culture methods. Following this, all the 250 samples were tested by standard culture method as well as the IMS+RT-PCR assay. Five samples (2.0%) were presumptively diagnosed as positive for Listeria on Oxford agar. All the five confirmed to be positive for L. monocytogenes by IMS+RT-PCR assay. Conclusion/Recommendations: The IMS + RT-PCR procedure was considerably more rapid and required only 28 h compared to 96-120 h for the conventional culture method. This method would be useful as the criteria for addressing the costly meat recalls and reducing outbreaks.