Evaluation of the Assurance GDS™ for E. coli O157:H7 Method and Assurance GDS for Shigatoxin Genes Method in Selected Foods: Collaborative Study

Abstract

A multilaboratory collaborative study was conducted to compare the Assurance GDS™ for E. coli O157:H7 method and the reference culture methods for the detection of E. coli O157:H7 in orange juice, raw ground beef, and fresh lettuce. A separate companion assay, the Assurance GDS for Shigatoxin Genes method was also evaluated with the same test portions. Fifteen laboratories participated in the study. A Chi square analysis of each of the 3 food types at the high, low, and uninoculated control levels was performed. For all foods, the Assurance GDS for E. coli O157:H7 method and the Assurance GDS for Shigatoxin Genes method were equivalent to or better than the reference methods.

The physiologic state of Escherichia coli O157:H7 does not affect its detection in two commercial real-time PCR-based tests

“…The sample size of 65 g each was chosen for ease of use and because this is a common size used in the commercial setting for finished ground beef testing. Both experiments detected 100% of the spiked samples as positive for E. coli O157:H7 (Table 2) with GDS Ò or BAX Ò -RT systems, which is similar as other studies that reported detection rates near 100% by these two systems but using a smaller sample size (25 g per sample) and inoculations of 1e5 and 10e50 CFU per sample (Feldsine et al, 2005;Lionberg et al, 2003). Enumeration by PetriFilm AC plates showed exponential bacterial growth from each inoculation after the 8-h enrichment period.…”

“…Since meat products are highly perishable, rapid, accurate, and reliable methods that can detect the presence of E. coli O157:H7 at low levels are critical for meat safety control in the industry. To date, testing methods in a variety of formats for E. coli O157:H7 analysis in food products have been developed and evaluated (Ahmed et al, 2009;Arthur et al, 2005;Feldsine et al, 2005;Fratamico and Bagi, 2007). Among these, the real-time quantitative PCR (RT qPCR) has become one of the most commonly used methods for pathogen nucleic acid detection and quantification.…”