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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: PREVALENCE, LEVELS, AND TYPES OF LISTERIA MONOCYTOGENES IN HIGHER RISK FOODS

Location: Food Safety and Intervention Technologies

2012 Annual Report


1a.Objectives (from AD-416):
Quantify the occurrence of L. monocytogenes in ready-to-eat meat, cheese, and deli-salads obtained from retail establishments.

a) Screen foods for the presence/absence of the pathogen; b) Determine levels of the pathogen in positive samples; c) Subtype multiple isolates from each positive sample.


1b.Approach (from AD-416):
Work with FDA and USDA/FSIS and attendant industry partners to collect/purchase targeted food samples from retail establishments from multiple retail establishments from within four FoodNet States over an 12 to 18-month period. Test samples for presence/absence of the pathogen. Determine levels of the pathogen in each positive sample by direct plating, enrichment, and/or most probable number analyses. Retain multiple isolates from each positive sample for subsequent molecular subtyping.


3.Progress Report:

Over the past decade, the Federal government has focused significant resources on reducing foodborne illness from ready-to-eat (RTE) foods. However, despite these efforts, foodborne illness caused by Listeria monocytogenes (Lm) and associated with RTE foods continues. The Food and Drug Administration (FDA), the USDA, Food Safety and Inspection Service (FSIS), and the USDA, Agricultural Research Service (ARS) have an interest in obtaining more current information on the association of Lm (i.e., rates, amounts, and subtypes) with RTE foods to evaluate the relative public health risk. This information is essential for both Agencies to effectively allocate resources to mitigate public health risks associated with Lm. While there is more current data for Lm in retail deli meats, corresponding data for other RTE foods (e.g., cheese, milk, raw fruits and vegetables, and deli salads) have not been comprehensively estimated since a survey conducted about ten years ago by the National Food Processors Association (NFPA). Thus, FDA provided funding to the United States Department of Agriculture, ARS, to partially support a study on the analysis of food samples collected at retail to determine the prevalence, levels, and subtypes of Lm associated with RTE foods. In Phase I of this FDA/ARS Interagency agreement, we purchased 7944 samples of food from retail establishments in FoodNet sites in California, Maryland, Georgia, and Connecticut between December 2012 and February 2012. Food categories sampled included: smoked seafood (748), seafood salad (738), low acid cut fruits (1362), soft cheese (2029), deli salads (non-meat; 1349), raw milk (326), and sandwiches (1392). Samples were analyzed using the FDA-BAM method, which included screening (25 gram or ml per each sample) and enumeration of positive samples by the MPN method and direct plating. The observed prevalence ranged from ca. 0% to 1.0% for seven product categories. For the 39 samples testing positive during screening, Lm levels ranged from ca. less than 0.3 cells/g estimated statistically to 251 cells/g. This is the most comprehensive survey of Lm in retail RTE foods in the past decade. Our findings provide data to assess changes in Lm prevalence and levels in RTE foods and will be used to update the 2003 Interagency Lm risk assessment. The study also underscores the importance of continued research to develop and validate interventions to ensure a wholesome food supply.


Last Modified: 9/10/2014
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