Rapid Detection of Listeria monocytogenes in Ground Turkey Meats by Immunomagnetic Separation (IMS) and Real Time- Polymerase Chain Reaction (RT-PCR)

An immunomagnetic separation (IMS) and real-time polymerase chain reaction (RT-PCR) method was used to detect Listeria monocytogenes (Lm) in ground turkey meats. The IMS beads coated with monoclonal anti-Lm antibodies were used for bacterial separation. The primers and probes targeting the hemolysin O (hyl A) gene were used in the RT-PCR. The following five sets of samples containing Lm at dilutions of (10 0 ,10 1 , 10 2 , 10 3 , 10 4 CFU) were tested by RT-PCR: 1) bacterial suspension without food sample and not subjected to IMS, 2) bacterial suspension without food sample but subjected to IMS, 3) bacterial sample with food sample but not subjected to IMS, and 4) bacterial suspension with food sample and subjected to IMS. In the RT-PCR, all samples that were spiked with 10 CFU and higher, showed positive signals. A drop in RT-PCR sensitivity varying from 5.0% to 9.3% was observed when the bacterial suspension was subjected to IMS. With respect to food samples spiked with Lm, the drop in sensitivity ranged from 11.1% to 14.0% as compared to samples containing the bacterial suspension alone. A total of 60 ground turkey meat samples were then studied without culture enrichment. This study suggests that combining IMS with RT-PCR significantly reduced the detection time of Lm to approximately 4 hours in ground turkey meats.