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Title: VALIDATION OF THE USDA/ARS PACKAGE RINSE METHOD FOR RECOVERY OF LISTERIA MONOCYTOGENES FROM NATURALLY-CONTAMINATED, COMMERCIALLY-PREPARED FRANKFURTERS

Author
item Wallace, Frederick
item Call, Jeffrey
item Luchansky, John

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2003
Publication Date: 10/1/2003
Citation: WALLACE, F.M., CALL, J.E., LUCHANSKY, J.B. 2003. VALIDATION OF THE USDA/ARS PACKAGE RINSE METHOD FOR RECOVERY OF LISTERIA MONOCYTOGENES FROM NATURALLY-CONTAMINATED, COMMERCIALLY-PREPARED FRANKFURTERS. JOURNAL OF FOOD PROTECTION. 66.1920-1923.

Interpretive Summary: The USDA-ARS package rinse method is a recently-developed technique for the detection of the food borne bacterial pathogen Listeria monocytogenes from ready-to-eat (RTE) meat products. It was found to be much more sensitive than the method currently used by the USDA Food Safety Inspection Service, the USDA-FSIS product composite method, when evaluated with packages of frankfurters that were contaminated in a testing laboratory. Because of concerns that the method would not prove to be as effective in the detection of Listeria in naturally-contaiminated packages, we initiated a study to validate this method using frankfurters from a batch known to be contaminated with L. monocytogenes at a package frequency rate of approximately 16%. In the first part of this study, a direct head-to-head comparison of these 2 techniques was conducted using the same 100 packages for both methods. Four times more positive packages were detected with the USDA-ARS package rinse method than were detected with the USDA-FSIS product composite enrichment method. In the second part of this study, four methods of sampling were used to investigate in more depth the possible sampling methods upon which a routine testing program could be built: i) the fluid exudate was removed and the pathogen was tested for; ii) a 25-g sample consisting of 5-7 sections of frankfurter was removed and processed as in the currently mandated USDA-FSIS product composite enrichment method; iii) the USDA-ARS package rinse method was performed on the remaining material; and iv) the remainder of the frankfurters was tested for the pathogen. As in the first part of this study, the USDA-ARS package rinse method proved statistically more effective than the other techniques studied. This research thus provides further evidence that changes in L. monocytogenes screening methods will result in more effective detection of contaminated RTE meat products and improved food safety.

Technical Abstract: To validate the utility of the USDA-ARS package rinse method for the recovery of Listeria monocytogenes, 100 packages of naturally-contaminated, commercially-prepared frankfurters were examined using this method and the currently used USDA-FSIS product composite enrichment method on the same packages. This lot of frankfurters was previously shown to have contamination with L. monocytogenes at a frequency of approximately 16%. The USDA-ARS package rinse method (28 of 100 packages tested positive) was significantly (p<0.01) more effective than the USDA-FSIS product composite method (7 of 100 packages tested positive) for recovering the pathogen from each of the same 100 vacuum-sealed packages. In related experiments, a different 100 packages of frankfurters from the same batch of naturally-contaminated, commercially-prepared frankfurters were examined as follows: i) the package exudative fluid was removed and tested using the standard USDA-FSIS product composite enrichment method; ii) next, approximately 5-7 portions of frankfurter were removed to obtain a 25-g composite and processed in accordance with the USDA-FSIS product composite enrichment method; iii)the USDA-ARS package rinse method was performed on the remaining material; and iv) the remainder of the frankfurters was enriched. While no method yielded a positive result for every package which was positive by any of the four methods, the USDA-ARS package rinse method was better (p<0.05) than enriching the fluid exudate and the standard USDA-FSIS product composite enrichment method at detecting L. monocytogenes. These studies demonstrate the superiority of the USDA-ARS package rinse method and make a compelling case for its adoption for routine screening of ready-to-eat products.