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T10-01 Comparative Evaluation of an Enrichment Media with a Time-release Selective Agent Tablet for Recovering Nitrite-stressed Listeria monocytogenes

Wednesday, July 25, 2012: 8:30 AM
Ballroom E (Rhode Island Convention Center)
Esmond Nyarko, University of Vermont, Burlington, VA
Catherine Donnelly, University of Vermont, Burlington, VT
Bob Koeritzer, 3M Food Safety, Saint Paul, MN
Patrick Mach, 3M, St. Paul, MN
Wensheng Xia, 3M Food Safety, St Paul, MN
Dennis D'Amico, University of Vermont, Burlington, VT
Recorded Presentation
Introduction:   Listeria monocytogenes is a foodborne pathogen that is estimated to cause about 2,500 cases of listeriosis with 500 deaths annually in the United States. The pathogen is often present in a stressed state because of ecological pressure. Isolation from food or environmental sources using traditional enrichment procedures involves manual addition of selective agents during incubation which may cause contamination of media or gradient distribution of selective agents because of inadequate mixing.

Purpose:   The purpose of this study was to evaluate a Listeriarecovery media with a novel proprietary technology developed by 3M™ that incorporates the selective agents into a time-delayed release tablet to overcome these shortcomings.

Methods: Approximately 10 nitrite-stressed (99% injury) cells of L. monocytogenes (strain FSL-R2-499) were added to 225 ml each of the following enrichment media: modified Listeria recovery broth (mLRB) with core tablets added at time 0 (mC-0) or 6 h (mC-6) after inoculation; mLRB with selective agents manually added at time 0 (mA-0) or 6 hours (mA-6); mLRB with the time-delayed release tablet (mD-6); complete mLRB (mC); UVM; Fraser and Buffered Listeria enrichment broth (BLEB) as well as mLRB non-selective and Trypticase soy broth controls. The study was repeated for non-stressed cells as an additional control. Counts of L. monocytogenes were determined at 16-26, 40 and 48 h of incubation.

Results:   mC-6, mA-6 and mD-6 exhibited similar growth kinetics reaching approximately 4 to 9 log CFU/ml between 16 to 24 h. These levels were slightly higher than mA-0, mC-0, mC, UVM, Fraser and BLEB. mLRB control showed the highest recovery capacity for the pathogen. All the mLRB media showed the highest growth reaching 10 log CFU/ml after 48 h of incubation.

Significance:   The time-delayed release tablet would save time, prevent contamination and enable rapid detection of the pathogen at 24 h. Delayed-time release could be indispensable in media for other pathogens requiring addition of selective agents during incubation.

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