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P1-35 Validation of a Commercial Real-time PCR Assay for Screening Salmonella in Foods

Monday, July 23, 2012
Exhibit Hall (Rhode Island Convention Center)
Morgan Wallace, DuPont Qualicon, Wilmington, DE
Bridget Andaloro, DuPont, Wilmington, DE
Dawn Fallon, DuPont, Wilmington, DE
Stephen Varkey, DuPont, Wilmington, DE
Daniel DeMarco, DuPont, Wilmington, DE
Andrew Farnum, DuPont Qualicon, Wilmington, DE
Monica Tadler, DuPont, Wilmington, DE
Steven Hoelzer, DuPont, Wilmington, DE
Julie Kraynak, DuPont Qualicon, Wilmington, DE
Eugene Davis, DuPont, Wilmington, DE
Jeffrey Rohrbeck, DuPont, Wilmington, DE
George Tice, DuPont, Wilmington, DE
Introduction: Salmonella is found in many food and environmental sources and can cause serious illness. Since its isolation is long and difficult when in the presence of competing flora, non-culture, rapid detection methods are needed for this organism. To improve assay performance, a real-time version of the BAX® System Salmonella assay was designed, which reduces instrument processing time to approximately one hour.

Purpose: This study evaluated the effectiveness of the test kit for screening Salmonellafrom ground beef, lettuce, chicken, cream cheese, dry pet food, and stainless steel environmental surfaces.

Methods: Artificially contaminated foods and environmental surfaces were tested and results compared with the appropriate Health Canada, USDA or FDA reference culture method(s).  Samples were inoculated with Salmonella at levels expected to yield fractional positive results based on preparatory studies. All sample types were enriched in the appropriate reference method primary enrichment (LB or BPW). Corresponding replicates were also enriched in an alternative media (BAX®System MP media or TSB with novobiocin) where appropriate to improve method performance. For ground beef testing, the reference method was tested on 25 g analytical portions while the alternative method was tested on 375 g portions (25 g spiked sample combined with 350 g of unspiked material) to reflect industry testing norms. Secondary enrichment and culture confirmation from all enrichments was conducted using the appropriate reference method(s).

Results: Testing included 240 spiked and 60 unspiked samples. For ground beef, lettuce, chicken, and cream cheese, 29/100 spiked reference method enrichments were culture positive while 28/100 spiked test method samples were positive by PCR from the alternative enrichments. For pet food and environmental testing, LB and BPW enrichments were found to be equivalent when testing by culture and by the BAX®System method, with 5/20 spiked pet food samples and 13/20 spiked environmental samples being PCR positive for each enrichment method. All PCR-positive samples culture confirmed and all PCR-negative samples were negative by culture. Statistical analysis revealed no significant difference in the alternative PCR and reference culture methods.

Significance: This study indicates that PCR detection of Salmonella using the BAX® System real-time assay is rapid and sensitive. Test kit results demonstrate no significant difference when compared with the reference culture methods.

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