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Control Strategies for Listeria Monocytogenes in Food Processing Environments


The goal of this project is to integrate research, extension, and teaching efforts to develop, evaluate and deliver science-based outreach programs for improved control strategies in the food industry for the foodborne pathogen Listeria monocytogenes. L. monocytogenes causes an estimated 2,500 annual disease cases and 500 deaths in the US. This organism is commonly found in many environments and most contamination of cooked ready-to-eat (RTE) foods appears to originate from the food processing plant environment. Our specific hypothesis is that improved environmental control strategies and sanitation procedures will significantly reduce L. monocytogenes contamination of RTE food products. We will use the RTE seafood industry as model system to (i) develop science-based intervention and control strategies for L. monocytogenes using molecular subtyping and detection methods to accurately track the sources and spread of environmental contamination and to (ii) develop formal training programs to communicate, implement, and monitor appropriate control strategies. One additional goal of this project is to improve access to molecular subtyping ("DNA fingerprinting") methods for the food industry and to communicate the utility of these techniques for tracking, monitoring and controlling foodborne pathogens. <P>

Specifically, we will accomplish the following objectives: <OL> <LI> Track sources and spread of L. monocytogenes in 10 RTE seafood plants using molecular subtyping methods. <LI> Develop environmental Listeria control strategies and monitor their effects on contamination patterns and frequencies using molecular detection and subtyping methods. <LI> Develop outreach and training programs to communicate and broadly implement recommended Listeria control strategies.

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NON-TECHNICAL SUMMARY: L. monocytogenes causes an estimated 2,500 annual human disease cases and 500 deaths in the US. This organism is commonly found in many environments and most contamination of cooked ready-to-eat foods appears to originate from the food processing plant environment. This project will determine the most likely sources of L. monocytogenes contamination in food processing plants and develop and communicate control strategies to industry.


APPROACH: We have assembled a uniquely qualified consortium under the leadership of research, teaching and extension faculty at Cornell University and New York Sea Grant to integrate research, teaching and extension in the performance of this project. The research and extension components of the project will be coordinated by a team of experienced individuals from several states and national organizations who have extensive experience in food safety programs and the seafood industry, including PIs Martin Wiedmann (Cornell University) and Ken Gall (New York Sea Grant Extension Program and Cornell University) and Co-PIs George Flick (Virginia Polytechnic Institute and State University), Tom Rippen (University of Maryland Sea Grant Extension Program), Doris Hicks (University of Delaware Sea Grant College Program), Mike Moody (Louisiana Sea Grant Extension Program), the National Fisheries Institute and the National Food Processors Association. All of these individuals or groups have been actively involved in seafood safety extension and outreach programs, the National Seafood HACCP Alliance, and have developed and conducted HACCP and Sanitation training programs. We will specifically apply the following approaches: 1. Select RTE seafood plants in Louisiana, Maryland, Virginia, New York and other states to collect environmental and finished product samples for L. monocytogenes testing. Use molecular subtyping methods to characterize L. monocytogenes isolates and analyze molecular subtypes to determine contamination patterns 2. Assemble a Environmental Listeria Control Team comprised of experts from academia and industry to review results and develop recommendations for Listeria control measure in the participant plants, including specific sanitation protocols. Implement control measures and monitor their effectiveness. 3. Develop extension publications on Listeria control measures based on the results of this study and organize Listeria control workshops to broadly communicate Listeria control strategies.


PROGRESS: 2000/09 TO 2003/09 <BR>
The goal of this project was to integrate research, outreach, and teaching efforts to develop, evaluate and deliver science-based control programs for L. monocytogenes in the food industry. We selected 10 seafood processing plants (4 smoked fish plants, 4 crab plants, 2 crawfish plants) in various US states to participate in this study. All 10 plants were observed over an initial year or harvest season to determine Listeria contamination patterns. For each plant, 12-14 environmental, 6 raw material, and 6 finished product samples were collected 8-12 times throughout the processing season. L. monocytogenes raw material contamination rates varied from 0-10 pct for smoked fish and from 0-4.2 pct for crawfish. Only 3 out of 312 finished product samples were positive for L. monocytogenes. The incidence of L. monocytogenes in environmental samples varied from 0-30 pct, with drains (0-57 pct) and employee contact surfaces (gloves, aprons, and door handles) showed the highest contamination rates (0-21 pct). L. monocytogenes subtype analysis allowed us to define persistent contamination with specific L. monocytogenes in three processing plants. Based on these initial results, plant-specific Listeria control strategies and employee training programs were developed and implemented. Listeria spp. prevalence in raw crawfish varied significantly from one season to another. However, the increased contamination prevalence for raw materials observed in the year after implementation of interventions strategies only resulted in a limited Listeria prevalence increase for the processing plant environment with extremely low levels of finished product contamination. Heat treatment of raw materials combined with Listeria control strategies to prevent cross contamination appear to be effective in achieving low levels of finished product contamination, even with Listeria spp. prevalences for raw crawfish of greather than 50 pct. Data for the smoked fish plants showed significant reductions in the prevalence of environmental Listeria spp. contamination for non-food contact surfaces and overall core environmental samples. Listeria prevalence in environmental samples remained similar in floor drains before and after intervention strategies (49.6 and 54.2 pct, respectively). While there was an initial correlation between prevalence of L. monocytogenes in the environment and prevalence in finished products, after implementation of intervention strategies environmental prevalence of L. monocytogenes had reduced predictability for finished product contamination. Molecular subtyping showed that specific L. monocytogenes ribotypes persisted in 3 processing plants. A few persistent subtypes were responsible for finished product contamination events. Ribotype data also indicated that incoming raw material was only rarely a direct source of finished product contamination. While our data indicated that employee training in combination with targeted, plant-specific Listeria intervention strategies can reduce cross contamination and Listeria spp. and L. monocytogenes prevalence in the plant environment, elimination of persistent L. monocytogenes strains remains a challenge.

IMPACT: 2000/09 TO 2003/09<BR>

The intervention strategies developed this project will provide science-based materials and training programs, which can be used by the food industry to better control Listeria monocytogenes contamination in the processing environment and of finished products. Intense employee training and improved control strategies can lead to a lower number of contaminated food products and thus to a reduction of foodborne Listeria monocytogenes infections.

Gall, Kenneth; Wiedmann, Martin
Cornell University
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