2013 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.
Listeria monocytogenes (Lm) is a facultative intracellular bacterium that is the causative agent of listeriosis. It is one of the most virulent foodborne pathogens, with 20 to 30 percent of clinical infections resulting in death, and is one of the top five leading causes of death among foodborne pathogens. 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. To assist in accomplishing these objectives, the USDA, ARS has entered into a Specific Cooperative Agreement (SCA) with Drexel University. In Phase I of this SCA, we purchased 7,917 samples of food from retail establishments in FoodNet sites in California, Maryland, Georgia, and Connecticut between December 2010 and February 2012. Food categories sampled included: smoked seafood (745), seafood salad (738), low acid cut fruits (1,351), soft cheese (2,028), deli salads (non-meat; 1,347), raw milk (317), and sandwiches (1,391). In Phase II of this SCA, we purchased 9,000 additional samples from retail between March 2012 and March 2013. In this phase, food categories sampled included: low acid cut fruits (700), deli salads (non-meat; 1,100), raw milk (200), sandwiches (1,010), cut vegetables (raw; 2,000), sprouts (3,000), eggs (700), artisanal cheese (2,600), and fresh crabmeat and sushi (700). 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. For Phase I, the observed prevalence ranged from ca. 0% to 1.2% for seven product categories. For the 40 samples testing positive during screening, Lm levels ranged from ca. <0.3 cells/g as estimated statistically to 2.4 log CFU/g. For phase II, the data on prevalence and levels of Lm in the additional 9,000 FDA-regulated RTE foods is currently being analyzed. 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.