Comparisons of selected methods with the Fung-Yu tube procedure for determining Listeria monocytogenes and other Listeria spp. in meats

The ability of the motility enrichment Fung-Yu tube procedure with Oxyrase enzyme to detect the presence of Listeria monocytogenes inoculated into ground beef samples was compared to the USDA-FSIS method. Three strains of L. monocytogenes (LM 101M, LM 103M, and Scott A) were inoculated separately into sterilized ground beef or culture broth. The inoculum levels used were as low as 1 to 1000 Listeria cells per g of meat or per ml of broth. The Fung-Yu tube procedure produced results as sensitive as the USDA procedures and provided a shorter detection time of 26-48 h. A total of 215 retail-level meat and poultry products were analyzed comparatively by the Fung-Yu tube and the GENETRAK DNA hybridization methods for Listeria detection. Six Listeria spp. ( L. denitrificans , L. grayi , L. innocua , L. ivanovii , L. monocytogenes , and L. murrayi ) were identified among the isolates. All 48 presumptively positive samples determined by the Fung-Yu tube method were further confirmed to harbor Listeria by biochemical tests. Eleven samples were missed by the GENETRAK procedure, probably because of the enrichment procedure. L. monocytogenes was isolated from ground beef, pork sausage, smokie links, and cheese hot dogs. Among cooked samples examined, only cheese hot dogs and macaroni and cheese loaf showed substantial incidence of Listeria contamination.