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Strategies to Detect and Mitigate Listeria in Artisan Cheese Facilities


This project will provide continued research for small-scale cheese makers with the specific goal of assisting cheese makers producing high-risk, washed rind cheeses in managing microbiological risks through research to define best microbiological risk management practices which will be applied to develop written, preventive control plans for cheese making facilities. These written plans will help small scale artisan cheese makers meet requirements of the Food Safety Modernization Act. We will assess survival of Listeria monocytogenes during 60 days of aging of washed rind cheeses. Control of L. monocytogenes will be explored through use of bacteriopahges and competitive cultures, along with brush decontamination strategies. <P>Our objectives are as follows: 1. Assess fate of L. monocytogenes in washed rind cheeses aged for 60 days. Assess the efficacy of anti-listerial products in mitigating Listeria contamination of washed rind cheeses. 2. Compare the efficacy of intervention procedures (sanitizers versus heat treatment) for decontamination of materials used for "smear" or "wash" application during cheese making. 3. Identify sources and niches of Listeria contamination in farmstead cheese facilities producing high risk, washed-rind cheeses. Compare use of novel and traditional testing systems which encompass microbiological monitoring of quality and safety of milk, cheese and environment. 4. Develop Risk Reduction Protocols to control Listeria contamination in farmstead cheese facilities producing high risk cheeses. Conduct a longitudinal study to assess efficacy of the risk reduction protocols.

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Non-Technical Summary:<br/>
Consumer interest in artisan and farmstead cheeses is driving explosive growth of on-farm cheese operations throughout the United States. As many of these enterprises are small to very small establishments, there is a need for focus on assuring the microbiological safety of cheeses produced on farm. During 2010, the U.S. Food and Drug Administration intensified its scrutiny of U.S. cheese makers. In particular, increased regulatory attention was focused on small scale artisan cheese makers and those producing cheeses from raw milk. Smaller operations are considered high risk due to lack of resources, capital and technical expertise to implement effective control programs. With 38 artisan cheese producers, Vermont boasts the highest number of artisan cheese makers per capita in the United States. In order to allow this industry to grow and prosper, it is essential that the safety of artisan cheeses be assured.
Objective 1: We will obtain unripened raw milk wash rind cheeses post-brining from producers. Cheese type 1 will be a semi-soft washed rind cheese, while cheese type 2 will be a soft washed rind cheese. Cheeses will be inoculated with a six strain cocktail of L. monocytogenes and subjected to treatments which will include: inoculated soft cheese control; inoculated soft cheese with protective cultures; inoculated soft cheese with bacteriophage; inoculated soft cheese with both antilisterial products; inoculated semi-soft cheese control; inoculated semi-soft cheese cheese with protective cultures; inoculated semi soft-cheese with bacteriophage; and inoculated semi-soft cheese with both antilisterial products. At prescribed intervals (days 4,7,14,21,28,35,42,49,56,63 and 70) cheeses will be analyzed for presence of L. monocytogenes. We will also evaluate survival of Listeria in smear solutions with and without anti-listerial products. The general linear models procedure (GLM) will be used to determine the effect of cheese type and anti-listerial application on the rate of change in mean log cfu/g as well as the effect of time on changes in both pH and mean log cfu/g.
Objective 2: Four commercially available smear application devices (small sponges, small plastic brushes, and two traditional cheese brushes will be inoculated with Listeria cultures. Tools will then be subjected to treatment with disinfectant treatments (sanitizers versus boiling)to evaluate efficacy as determined by measurement of Listeria survival/destruction.
Objective 3: Environmental sampling for presence of Listeria will be conducted on nine on-farm artisan cheese processing facilities producing high-risk washed rind cheeses. Sites will be selected based on results obtained in previous sampling events. Samples will be analyzed for presence of Listeria using methods prescribed by the FDA, as well as modifications thereof. Isolates will be characterized using the automated Riboprinter Microbial Characterization System.
Objective 4: Risk Reduction protocols will be developed for nine cheese producers. Using a HACCP approach, critical control points in the cheese making process will be identified. Environmental sampling of the facility will be conducted and samples subjected to analysis for presence of Listeria. Finding will be shared with cheese makers, along with recommendations for elimination of niches of contamination. Following implementation of recommendations, comprehensive microbiological analysis will be performed. Date will be compared to determine if changes have resulted in improved process control and improvements in cheese quality.

Donnelly, Catherine
University of Vermont
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