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P2-139 Evaluation of the Growth Potential of Listeria monocytogenes in Milkshakes Prepared with Contaminated Ice Cream Linked to a Listeriosis Outbreak and Stored at Room Temperature

Tuesday, August 2, 2016
America's Center - St. Louis
Ishani Sheth, U.S. Food and Drug Administration-CFSAN, College Park, MD
Minji Hur, U.S. Food and Drug Administration-CFSAN, College Park, MD
Anna Laasri, U.S. Food and Drug Administration-CFSAN, College Park, MD
Emma Allard, U.S. Food and Drug Administration-CFSAN, College Park, MD
Anna Wooten, U.S. Food and Drug Administration-CFSAN, College Park, MD
Thomas Hammack, U.S. Food and Drug Administration-CFSAN, College Park, MD
Dumitru Macarisin, U.S. Food and Drug Administration-CFSAN, College Park, MD
Yi Chen, U.S. Food and Drug Administration-CFSAN, College Park, MD
Introduction: A multistate listeriosis outbreak linked to contaminated ice cream products caused 4 illnesses, including 3 deaths of highly immunocompromised patients in a Kansas hospital. These patients consumed milkshakes prepared from the contaminated ice cream products. Previous enumeration work showed that L. monocytogenes was detected in 99.4% of the ice cream and 92.3% of the products were contaminated at a level below 20 MPN/g.

Purpose: We evaluated the growth potential of L. monocytogenes in milkshakes prepared with the contaminated ice cream products and stored at room temperature. This would help estimate the level of L. monocytogenes consumed by patients if these milkshakes were temperature abused in the hospital.

Methods: Three different flavors of milkshakes, vanilla, chocolate and strawberry, were prepared according to the receipt from the Kansas hospital and stored at room temperature (68°F and 73°F) for up to 15 hours. Milkshake samples were taken hourly and L. monocytogenes was enumerated by direct plating onto Rapid L. mono agars.

Results: The cell counts, used to construct growth curves of L. monocytogenes in these milkshake samples, demonstrated that the lag phase was 6.5 hours for milkshakes of all three flavors stored at both 68°F and 73°F. The generation time of L. monocytogenes in the exponential phase was 1 hour and 40 min in milkshakes stored at both 68 and 73°F. The results show that even if milkshakes were temperature abused at room temperature in the hospital, L. monocytogenes might not grow to much higher levels than the initial level.

Significance: The data provided valuable information towards the improved assessment of risk for listeriosis in highly susceptible populations and a better understanding of L. monocytogenes growth in ice cream left at room temperature.

Back to: Poster Session 2 – Low-water Activity, Laboratory and Detection Methods, Epidemiology, Produce, Pre-harvest, Dairy and Beverages, Food Defense, General Microbiology
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