Rapid Detection of Listeria monocytogenes in Food and Food Animals

The objective of this study was to streamline the detection and identification of Listeria monocytogenes (LM) in livestock and foods. Hog tonsil scrapings, hog tissues collected at necropsy, ground pork, and turkey washes were inoculated into UVM-1 (10% w/v) and after incubation (3 days) transferred to UVM-2. After 2 days, samples were plated to Palcam agar and incubated (48 h, 37 o C). Characteristic LM colonies were verified with the multiplex Polymerase chain reaction assay, which targets the 16S rRNA gene of Listeria and the hlyA gene unique to the species monocytogenes. To determine when LM achieved detectable levels during enrichment, template DNA was extracted directly from UVM-2 and Palcam agar and screened by multiplex PCR. When screened directly from UVM-2 by PCR, 34% (65 of 190) of ground pork samples and 19% (11 of 60) of turkey washes were positive for LM. In contrast, by multiplex PCR screening of colonies from Palcam agar 39% (75 of 190) of ground pork and 29% (18 of 60) of turkey wash samples were positive. Future studies will focus on improved recovery from UVM-2 with immunomagnetic beads. LM positive isolates (n=33) of ground pork were serotyped and assigned to type 4 (72%) and type 1 (14%). Forteen percent of isolates were neither serotype 1 nor 4. For live hogs, out of 150 samples each of carcasses, tonsils, and ileocecal lymph nodes tested, LM was detected once from tonsils and nodes by multiplex PCR. In contrast, LM was found on ~30% of ground pork produced from that same day from packing plant