Detection of Listeria monocytogenes in ground turkey and turkey frankfurters using ELISA, DNAH, and USDA protocols prior to, and following, exposure to ultracold temperatures.

Abstract

Listeria nlOnocytogenes is one of the most prevalent food-borne pathogens. Listeria has lead to several deaths, and has been determined to be the cause of several recent food recalls, including Ball Park, Bil Mar, Mr. Turkey and Sara Lee Deli Meats. What makes Listeria important to the food industry, the USDA, and alert consumers, is that Listeria can proliferate well within a wide range of temperatures, from I to 45 degrees Celsius. Despite its importance, little information is known about how well Listeria can survive under extended periods of time in ultracold environments, such as a freezer. Eighty-one ground turkey and eighty-one turkey frankfurter samples were obtained from a local grocer and tested for the presence of Listeria monocytogenes, using three diagnostic tests. A total of 150 samples were artificially inoculated with a standard inoculum of I X 106 cells per milliliter per 100 grams of sample. The remaining twelve samples were used as negative controls. The samples were then exposed to ultracold -70 lr.... C for two, four, and six months. At the end of each time period, samples were removed from the freezer and diagnostic tests were performed. Enzyme-linked immunosorbent assay (ELISA), DNA hybridization assay (DNAH), and a modified USDA culture-based method of isolation (USDA protocol) were used as diagnostic tests. Revived cells were then injected into mice, intraperitoneally (IP), at a standard inoculum to determine if virulence was retained. A few of the initial samples from the grocer tested positive for the presence of Listeria by at least one diagnostic test. All three diagnostic tests identified the presence of Listeria within both substrates throughout all three experimental time periods. Additionally, virulence was retained throughout all time periods.